Provided by: libmongoc-doc_1.22.1-1_all 
NAME
mongoc_reference - Index
LIBMONGOC
A Cross Platform MongoDB Client Library for C
Introduction
The MongoDB C Driver, also known as "libmongoc", is a library for using MongoDB from C
applications, and for writing MongoDB drivers in higher-level languages.
It depends on libbson to generate and parse BSON documents, the native data format of
MongoDB.
Installing the MongoDB C Driver (libmongoc) and BSON library (libbson)
The following guide will step you through the process of downloading, building, and
installing the current release of the MongoDB C Driver (libmongoc) and BSON library
(libbson).
Supported Platforms
The MongoDB C Driver is continuously tested on a variety of platforms including:
• Archlinux
• Debian 9.2, 10.0
• macOS 10.14
• Microsoft Windows Server 2008, 2016
• RHEL 6.2, 7.0, 7.1, 8.2
• Ubuntu 16.04, 18.04
• Clang 3.4, 3.5, 3.7, 3.8, 6.0
• GCC 4.8, 4.9, 5.4, 6.3, 8.2, 8.3
• MinGW-W64
• Visual Studio 2013, 2015, 2017
• x86, x86_64, ARM (aarch64), Power8 (ppc64le), zSeries (s390x)
Install libmongoc with a Package Manager
Several Linux distributions provide packages for libmongoc and its dependencies. One
advantage of installing libmongoc with a package manager is that its dependencies
(including libbson) will be installed automatically. If you choose to install libmongoc
from distribution packages, use the package manager to confirm the version being installed
is sufficient for your needs.
The libmongoc package is available on recent versions of Debian and Ubuntu.
$ apt-get install libmongoc-1.0-0
On Fedora, a mongo-c-driver package is available in the default repositories and can be
installed with:
$ dnf install mongo-c-driver
On recent Red Hat systems, such as CentOS and RHEL 7, a mongo-c-driver package is
available in the EPEL repository. To check which version is available, see
https://packages.fedoraproject.org/pkgs/mongo-c-driver/mongo-c-driver/. The package can be
installed with:
$ yum install mongo-c-driver
On macOS systems with Homebrew, the mongo-c-driver package can be installed with:
$ brew install mongo-c-driver
Install libbson with a Package Manager
The libbson package is available on recent versions of Debian and Ubuntu. If you have
installed libmongoc, then libbson will have already been installed as a dependency. It is
also possible to install libbson without libmongoc.
$ apt-get install libbson-1.0-0
On Fedora, a libbson package is available in the default repositories and can be installed
with:
$ dnf install libbson
On recent Red Hat systems, such as CentOS and RHEL 7, a libbson package is available in
the EPEL repository. To check which version is available, see
https://apps.fedoraproject.org/packages/libbson. The package can be installed with:
$ yum install libbson
Build environment
Build environment on Unix
Prerequisites for libmongoc
OpenSSL is required for authentication or for TLS connections to MongoDB. Kerberos or LDAP
support requires Cyrus SASL.
To install all optional dependencies on RedHat / Fedora:
$ sudo yum install cmake openssl-devel cyrus-sasl-devel
On Debian / Ubuntu:
$ sudo apt-get install cmake libssl-dev libsasl2-dev
On FreeBSD:
$ su -c 'pkg install cmake openssl cyrus-sasl'
Prerequisites for libbson
The only prerequisite for building libbson is cmake. The command lines above can be
adjusted to install only cmake.
Build environment on macOS
Install the XCode Command Line Tools:
$ xcode-select --install
The cmake utility is also required. First install Homebrew according to its instructions,
then:
$ brew install cmake
Build environment on Windows with Visual Studio
Building on Windows requires Windows Vista or newer and Visual Studio 2013 or newer.
Additionally, cmake is required to generate Visual Studio project files. Installation of
these components on Windows is beyond the scope of this document.
Build environment on Windows with MinGW-W64 and MSYS2
Install MSYS2 from msys2.github.io. Choose the x86_64 version, not i686.
Open the MingGW shell with c:\msys64\ming64.exe (not the msys2_shell). Install
dependencies:
$ pacman --noconfirm -Syu
$ pacman --noconfirm -S mingw-w64-x86_64-gcc mingw-w64-x86_64-cmake
$ pacman --noconfirm -S mingw-w64-x86_64-extra-cmake-modules make tar
$ pacman --noconfirm -S mingw64/mingw-w64-x86_64-cyrus-sasl
Configuring the build
Before building libmongoc and/or libbson, it is necessary to configure, or prepare, the
build. The steps to prepare the build depend on how you obtained the source code and the
build platform.
Preparing a build from a release tarball
The most recent release of libmongoc and libbson, both of which are included in
mongo-c-driver, can be downloaded here. The instructions in this document utilize cmake's
out-of-source build feature to keep build artifacts separate from source files. While the
$ prompt is used throughout, the instructions below will work on Linux, macOS, and Windows
(assuming that CMake is in the user's shell path in all cases). See the subsequent
sections for additional platform-specific instructions.
The following snippet will download and extract the driver, and configure it:
$ wget https://github.com/mongodb/mongo-c-driver/releases/download/1.22.1/mongo-c-driver-1.22.1.tar.gz
$ tar xzf mongo-c-driver-1.22.1.tar.gz
$ cd mongo-c-driver-1.22.1
$ mkdir cmake-build
$ cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF ..
The -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF option is recommended, see Initialization and
cleanup. Another useful cmake option is -DCMAKE_BUILD_TYPE=Release for a release optimized
build and -DCMAKE_BUILD_TYPE=Debug for a debug build. For a list of all configure options,
run cmake -L ...
If cmake completed successfully, you will see a considerable amount of output describing
your build configuration. The final line of output should look something like this:
-- Build files have been written to: /home/user/mongo-c-driver-1.22.1/cmake-build
If cmake concludes with anything different, then it is likely an error occurred.
mongo-c-driver contains a copy of libbson, in case your system does not already have
libbson installed. The configuration will detect if libbson is not installed and use the
bundled libbson.
Additionally, it is possible to build only libbson by setting the -DENABLE_MONGOC=OFF
option:
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF -DENABLE_MONGOC=OFF ..
A build configuration description similar to the one above will be displayed, though with
fewer entries. Once the configuration is complete, the selected items can be built and
installed with these commands:
Preparing a build from a git repository clone
Clone the repository and prepare the build on the current branch or a particular release
tag:
$ git clone https://github.com/mongodb/mongo-c-driver.git
$ cd mongo-c-driver
$ git checkout 1.22.1 # To build a particular release
$ python build/calc_release_version.py > VERSION_CURRENT
$ mkdir cmake-build
$ cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF ..
Preparing a build on Windows with Visual Studio
On the Windows platform with Visual Studio, it may be necessary to specify the CMake
generator to use. This is especially important if multiple versions of Visual Studio are
installed on the system or if alternate build tools (e.g., MinGW, MSYS2, Cygwin, etc.) are
present on the system. Specifying the generator will ensure that the build configuration
is known with certainty, rather than relying on the toolchain that CMake happens to find.
Start by generating Visual Studio project files. The following assumes you are compiling
for 64-bit Windows using Visual Studio 2015 Express, which can be freely downloaded from
Microsoft. The sample commands utilize cmake's out-of-source build feature to keep build
artifacts separate from source files.
$ cd mongo-c-driver-1.22.1
$ mkdir cmake-build
$ cd cmake-build
$ cmake -G "Visual Studio 14 2015 Win64" \
"-DCMAKE_INSTALL_PREFIX=C:\mongo-c-driver" \
"-DCMAKE_PREFIX_PATH=C:\mongo-c-driver" \
..
(Run cmake -LH .. for a list of other options.)
To see a complete list of the CMake generators available on your specific system, use a
command like this:
$ cmake --help
Executing a build
Building on Unix, macOS, and Windows (MinGW-W64 and MSYS2)
$ cmake --build .
$ sudo cmake --build . --target install
(Note that the sudo command may not be applicable or available depending on the
configuration of your system.)
In the above commands, the first relies on the default target which builds all configured
components. For fine grained control over what gets built, the following command can be
used (for Ninja and Makefile-based build systems) to list all available targets:
$ cmake --build . help
Building on Windows with Visual Studio
Once the project files are generated, the project can be opened directly in Visual Studio
or compiled from the command line.
Build using the CMake build tool mode:
$ cmake --build . --config RelWithDebInfo
Visual Studio's default build type is Debug, but we recommend a release build with debug
info for production use. Now that libmongoc and libbson are compiled, install them.
Components will be installed to the path specified by CMAKE_INSTALL_PREFIX.
$ cmake --build . --config RelWithDebInfo --target install
You should now see libmongoc and libbson installed in C:\mongo-c-driver
For Visual Studio 2019 (16.4 and newer), this command can be used to list all available
targets:
$ cmake --build . -- /targets
Alternately, you can examine the files matching the glob *.vcxproj in the cmake-build
directory.
To use the driver libraries in your program, see Using libmongoc in a Microsoft Visual
Studio project.
Generating the documentation
Install Sphinx, then:
$ cmake -DENABLE_MAN_PAGES=ON -DENABLE_HTML_DOCS=ON ..
$ cmake --build . --target mongoc-doc
To build only the libbson documentation:
$ cmake -DENABLE_MAN_PAGES=ON -DENABLE_HTML_DOCS=ON ..
$ cmake --build . --target bson-doc
The -DENABLE_MAN_PAGES=ON and -DENABLE_HTML_DOCS=ON can also be added as options to a
normal build from a release tarball or from git so that the documentation is built at the
same time as other components.
Uninstalling the installed components
There are two ways to uninstall the components that have been installed. The first is to
invoke the uninstall program directly. On Linux/Unix:
$ sudo /usr/local/share/mongo-c-driver/uninstall.sh
On Windows:
$ C:\mongo-c-driver\share\mongo-c-driver\uninstall.bat
The second way to uninstall is from within the build directory, assuming that it is in the
exact same state as when the install command was invoked:
$ sudo cmake --build . --target uninstall
The second approach simply invokes the uninstall program referenced in the first approach.
Dealing with Build Failures
If your attempt to build the C driver fails, please see the README for instructions on
requesting assistance.
Additional Options for Integrators
In the event that you are building the BSON library and/or the C driver to embed with
other components and you wish to avoid the potential for collision with components
installed from a standard build or from a distribution package manager, you can make use
of the BSON_OUTPUT_BASENAME and MONGOC_OUTPUT_BASENAME options to cmake.
$ cmake -DBSON_OUTPUT_BASENAME=custom_bson -DMONGOC_OUTPUT_BASENAME=custom_mongoc ..
The above command would produce libraries named libcustom_bson.so and libcustom_mongoc.so
(or with the extension appropriate for the build platform). Those libraries could be
placed in a standard system directory or in an alternate location and could be linked to
by specifying something like -lcustom_mongoc -lcustom_bson on the linker command line
(possibly adjusting the specific flags to those required by your linker).
Tutorial
This guide offers a brief introduction to the MongoDB C Driver.
For more information on the C API, please refer to the API Reference.
Contents
• Tutorial
• Installing
• Starting MongoDB
• Include and link libmongoc in your C program
• Use libmongoc in a Microsoft Visual Studio Project
• Making a Connection
• Creating BSON Documents
• Basic CRUD Operations
• Executing Commands
• Threading
• Next Steps
Installing
For detailed instructions on installing the MongoDB C Driver on a particular platform,
please see the installation guide.
Starting MongoDB
To run the examples in this tutorial, MongoDB must be installed and running on localhost
on the default port, 27017. To check if it is up and running, connect to it with the
MongoDB shell.
$ mongo --host localhost --port 27017
MongoDB shell version: 3.0.6
connecting to: localhost:27017/test
>
Include and link libmongoc in your C program
Include mongoc.h
All libmongoc's functions and types are available in one header file. Simply include
mongoc/mongoc.h:
#include <mongoc/mongoc.h>
CMake
The libmongoc installation includes a CMake config-file package, so you can use CMake's
find_package command to import libmongoc's CMake target and link to libmongoc (as a shared
library):
CMakeLists.txt
# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)
# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_shared)
You can also use libmongoc as a static library instead: Use the mongo::mongoc_static CMake
target:
# Specify the minimum version you require.
find_package (mongoc-1.0 1.7 REQUIRED)
# The "hello_mongoc.c" sample program is shared among four tests.
add_executable (hello_mongoc ../../hello_mongoc.c)
target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_static)
pkg-config
If you're not using CMake, use pkg-config on the command line to set header and library
paths:
gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-1.0)
Or to statically link to libmongoc:
gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-static-1.0)
Specifying header and include paths manually
If you aren't using CMake or pkg-config, paths and libraries can be managed manually.
$ gcc -o hello_mongoc hello_mongoc.c \
-I/usr/local/include/libbson-1.0 -I/usr/local/include/libmongoc-1.0 \
-lmongoc-1.0 -lbson-1.0
$ ./hello_mongoc
{ "ok" : 1.000000 }
For Windows users, the code can be compiled and run with the following commands. (This
assumes that the MongoDB C Driver has been installed to C:\mongo-c-driver; change the
include directory as needed.)
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 hello_mongoc.c
C:\> hello_mongoc
{ "ok" : 1.000000 }
Use libmongoc in a Microsoft Visual Studio Project
See the libmongoc and Visual Studio guide.
Making a Connection
Access MongoDB with a mongoc_client_t. It transparently connects to standalone servers,
replica sets and sharded clusters on demand. To perform operations on a database or
collection, create a mongoc_database_t or mongoc_collection_t struct from the
mongoc_client_t.
At the start of an application, call mongoc_init() before any other libmongoc functions.
At the end, call the appropriate destroy function for each collection, database, or client
handle, in reverse order from how they were constructed. Call mongoc_cleanup() before
exiting.
The example below establishes a connection to a standalone server on localhost, registers
the client application as "connect-example," and performs a simple command.
More information about database operations can be found in the CRUD Operations and
Executing Commands sections. Examples of connecting to replica sets and sharded clusters
can be found on the Advanced Connections page.
hello_mongoc.c
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
const char *uri_string = "mongodb://localhost:27017";
mongoc_uri_t *uri;
mongoc_client_t *client;
mongoc_database_t *database;
mongoc_collection_t *collection;
bson_t *command, reply, *insert;
bson_error_t error;
char *str;
bool retval;
/*
* Required to initialize libmongoc's internals
*/
mongoc_init ();
/*
* Optionally get MongoDB URI from command line
*/
if (argc > 1) {
uri_string = argv[1];
}
/*
* Safely create a MongoDB URI object from the given string
*/
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
/*
* Create a new client instance
*/
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
/*
* Register the application name so we can track it in the profile logs
* on the server. This can also be done from the URI (see other examples).
*/
mongoc_client_set_appname (client, "connect-example");
/*
* Get a handle on the database "db_name" and collection "coll_name"
*/
database = mongoc_client_get_database (client, "db_name");
collection = mongoc_client_get_collection (client, "db_name", "coll_name");
/*
* Do work. This example pings the database, prints the result as JSON and
* performs an insert
*/
command = BCON_NEW ("ping", BCON_INT32 (1));
retval = mongoc_client_command_simple (
client, "admin", command, NULL, &reply, &error);
if (!retval) {
fprintf (stderr, "%s\n", error.message);
return EXIT_FAILURE;
}
str = bson_as_json (&reply, NULL);
printf ("%s\n", str);
insert = BCON_NEW ("hello", BCON_UTF8 ("world"));
if (!mongoc_collection_insert_one (collection, insert, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
}
bson_destroy (insert);
bson_destroy (&reply);
bson_destroy (command);
bson_free (str);
/*
* Release our handles and clean up libmongoc
*/
mongoc_collection_destroy (collection);
mongoc_database_destroy (database);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Creating BSON Documents
Documents are stored in MongoDB's data format, BSON. The C driver uses libbson to create
BSON documents. There are several ways to construct them: appending key-value pairs, using
BCON, or parsing JSON.
Appending BSON
A BSON document, represented as a bson_t in code, can be constructed one field at a time
using libbson's append functions.
For example, to create a document like this:
{
born : ISODate("1906-12-09"),
died : ISODate("1992-01-01"),
name : {
first : "Grace",
last : "Hopper"
},
languages : [ "MATH-MATIC", "FLOW-MATIC", "COBOL" ],
degrees: [ { degree: "BA", school: "Vassar" }, { degree: "PhD", school: "Yale" } ]
}
Use the following code:
#include <bson/bson.h>
int
main (int argc,
char *argv[])
{
struct tm born = { 0 };
struct tm died = { 0 };
const char *lang_names[] = {"MATH-MATIC", "FLOW-MATIC", "COBOL"};
const char *schools[] = {"Vassar", "Yale"};
const char *degrees[] = {"BA", "PhD"};
uint32_t i;
char buf[16];
const char *key;
size_t keylen;
bson_t *document;
bson_t child;
bson_t child2;
char *str;
document = bson_new ();
/*
* Append { "born" : ISODate("1906-12-09") } to the document.
* Passing -1 for the length argument tells libbson to calculate the string length.
*/
born.tm_year = 6; /* years are 1900-based */
born.tm_mon = 11; /* months are 0-based */
born.tm_mday = 9;
bson_append_date_time (document, "born", -1, mktime (&born) * 1000);
/*
* Append { "died" : ISODate("1992-01-01") } to the document.
*/
died.tm_year = 92;
died.tm_mon = 0;
died.tm_mday = 1;
/*
* For convenience, this macro passes length -1 by default.
*/
BSON_APPEND_DATE_TIME (document, "died", mktime (&died) * 1000);
/*
* Append a subdocument.
*/
BSON_APPEND_DOCUMENT_BEGIN (document, "name", &child);
BSON_APPEND_UTF8 (&child, "first", "Grace");
BSON_APPEND_UTF8 (&child, "last", "Hopper");
bson_append_document_end (document, &child);
/*
* Append array of strings. Generate keys "0", "1", "2".
*/
BSON_APPEND_ARRAY_BEGIN (document, "languages", &child);
for (i = 0; i < sizeof lang_names / sizeof (char *); ++i) {
keylen = bson_uint32_to_string (i, &key, buf, sizeof buf);
bson_append_utf8 (&child, key, (int) keylen, lang_names[i], -1);
}
bson_append_array_end (document, &child);
/*
* Array of subdocuments:
* degrees: [ { degree: "BA", school: "Vassar" }, ... ]
*/
BSON_APPEND_ARRAY_BEGIN (document, "degrees", &child);
for (i = 0; i < sizeof degrees / sizeof (char *); ++i) {
keylen = bson_uint32_to_string (i, &key, buf, sizeof buf);
bson_append_document_begin (&child, key, (int) keylen, &child2);
BSON_APPEND_UTF8 (&child2, "degree", degrees[i]);
BSON_APPEND_UTF8 (&child2, "school", schools[i]);
bson_append_document_end (&child, &child2);
}
bson_append_array_end (document, &child);
/*
* Print the document as a JSON string.
*/
str = bson_as_canonical_extended_json (document, NULL);
printf ("%s\n", str);
bson_free (str);
/*
* Clean up allocated bson documents.
*/
bson_destroy (document);
return 0;
}
See the libbson documentation for all of the types that can be appended to a bson_t.
Using BCON
BSON C Object Notation, BCON for short, is an alternative way of constructing BSON
documents in a manner closer to the intended format. It has less type-safety than BSON's
append functions but results in less code.
#include <bson/bson.h>
int
main (int argc,
char *argv[])
{
struct tm born = { 0 };
struct tm died = { 0 };
bson_t *document;
char *str;
born.tm_year = 6;
born.tm_mon = 11;
born.tm_mday = 9;
died.tm_year = 92;
died.tm_mon = 0;
died.tm_mday = 1;
document = BCON_NEW (
"born", BCON_DATE_TIME (mktime (&born) * 1000),
"died", BCON_DATE_TIME (mktime (&died) * 1000),
"name", "{",
"first", BCON_UTF8 ("Grace"),
"last", BCON_UTF8 ("Hopper"),
"}",
"languages", "[",
BCON_UTF8 ("MATH-MATIC"),
BCON_UTF8 ("FLOW-MATIC"),
BCON_UTF8 ("COBOL"),
"]",
"degrees", "[",
"{", "degree", BCON_UTF8 ("BA"), "school", BCON_UTF8 ("Vassar"), "}",
"{", "degree", BCON_UTF8 ("PhD"), "school", BCON_UTF8 ("Yale"), "}",
"]");
/*
* Print the document as a JSON string.
*/
str = bson_as_canonical_extended_json (document, NULL);
printf ("%s\n", str);
bson_free (str);
/*
* Clean up allocated bson documents.
*/
bson_destroy (document);
return 0;
}
Notice that BCON can create arrays, subdocuments and arbitrary fields.
Creating BSON from JSON
For single documents, BSON can be created from JSON strings via bson_new_from_json.
#include <bson/bson.h>
int
main (int argc,
char *argv[])
{
bson_error_t error;
bson_t *bson;
char *string;
const char *json = "{\"name\": {\"first\":\"Grace\", \"last\":\"Hopper\"}}";
bson = bson_new_from_json ((const uint8_t *)json, -1, &error);
if (!bson) {
fprintf (stderr, "%s\n", error.message);
return EXIT_FAILURE;
}
string = bson_as_canonical_extended_json (bson, NULL);
printf ("%s\n", string);
bson_free (string);
return 0;
}
To initialize BSON from a sequence of JSON documents, use bson_json_reader_t.
Basic CRUD Operations
This section demonstrates the basics of using the C Driver to interact with MongoDB.
Inserting a Document
To insert documents into a collection, first obtain a handle to a mongoc_collection_t via
a mongoc_client_t. Then, use mongoc_collection_insert_one() to add BSON documents to the
collection. This example inserts into the database "mydb" and collection "mycoll".
When finished, ensure that allocated structures are freed by using their respective
destroy functions.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc,
char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_oid_t oid;
bson_t *doc;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost:27017/?appname=insert-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
doc = bson_new ();
bson_oid_init (&oid, NULL);
BSON_APPEND_OID (doc, "_id", &oid);
BSON_APPEND_UTF8 (doc, "hello", "world");
if (!mongoc_collection_insert_one (
collection, doc, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o insert insert.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./insert
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 insert.c
C:\> insert
To verify that the insert succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find()
{ "_id" : ObjectId("55ef43766cb5f36a3bae6ee4"), "hello" : "world" }
>
Finding a Document
To query a MongoDB collection with the C driver, use the function
mongoc_collection_find_with_opts(). This returns a cursor to the matching documents. The
following examples iterate through the result cursors and print the matches to stdout as
JSON strings.
Use a document as a query specifier; for example,
{ "color" : "red" }
will match any document with a field named "color" with value "red". An empty document {}
can be used to match all documents.
This first example uses an empty query specifier to find all documents in the database
"mydb" and collection "mycoll".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=find-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To look for a specific document, add a specifier to query. This example adds a call to
BSON_APPEND_UTF8() to look for all documents matching {"hello" : "world"}.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_t *query;
char *str;
mongoc_init ();
client = mongoc_client_new (
"mongodb://localhost:27017/?appname=find-specific-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
query = bson_new ();
BSON_APPEND_UTF8 (query, "hello", "world");
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
Updating a Document
This code snippet gives an example of using mongoc_collection_update_one() to update the
fields of a document.
Using the "mydb" database, the following example inserts an example document into the
"mycoll" collection. Then, using its _id field, the document is updated with different
values and a new field.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_collection_t *collection;
mongoc_client_t *client;
bson_error_t error;
bson_oid_t oid;
bson_t *doc = NULL;
bson_t *update = NULL;
bson_t *query = NULL;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=update-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
bson_oid_init (&oid, NULL);
doc = BCON_NEW ("_id", BCON_OID (&oid), "key", BCON_UTF8 ("old_value"));
if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
goto fail;
}
query = BCON_NEW ("_id", BCON_OID (&oid));
update = BCON_NEW ("$set",
"{",
"key",
BCON_UTF8 ("new_value"),
"updated",
BCON_BOOL (true),
"}");
if (!mongoc_collection_update_one (
collection, query, update, NULL, NULL, &error)) {
fprintf (stderr, "%s\n", error.message);
goto fail;
}
fail:
if (doc)
bson_destroy (doc);
if (query)
bson_destroy (query);
if (update)
bson_destroy (update);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o update update.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./update
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 update.c
C:\> update
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
To verify that the update succeeded, connect with the MongoDB shell.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.find({"updated" : true})
{ "_id" : ObjectId("55ef549236fe322f9490e17b"), "updated" : true, "key" : "new_value" }
>
Deleting a Document
This example illustrates the use of mongoc_collection_delete_one() to delete a document.
The following code inserts a sample document into the database "mydb" and collection
"mycoll". Then, it deletes all documents matching {"hello" : "world"}.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_oid_t oid;
bson_t *doc;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=delete-example");
collection = mongoc_client_get_collection (client, "test", "test");
doc = bson_new ();
bson_oid_init (&oid, NULL);
BSON_APPEND_OID (doc, "_id", &oid);
BSON_APPEND_UTF8 (doc, "hello", "world");
if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
fprintf (stderr, "Insert failed: %s\n", error.message);
}
bson_destroy (doc);
doc = bson_new ();
BSON_APPEND_OID (doc, "_id", &oid);
if (!mongoc_collection_delete_one (
collection, doc, NULL, NULL, &error)) {
fprintf (stderr, "Delete failed: %s\n", error.message);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o delete delete.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./delete
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 delete.c
C:\> delete
Use the MongoDB shell to prove that the documents have been removed successfully.
$ mongo
MongoDB shell version: 3.0.6
connecting to: test
> use mydb
switched to db mydb
> db.mycoll.count({"hello" : "world"})
0
>
Counting Documents
Counting the number of documents in a MongoDB collection is similar to performing a find
operation. This example counts the number of documents matching {"hello" : "world"} in the
database "mydb" and collection "mycoll".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *doc;
int64_t count;
mongoc_init ();
client =
mongoc_client_new ("mongodb://localhost:27017/?appname=count-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
doc = bson_new_from_json (
(const uint8_t *) "{\"hello\" : \"world\"}", -1, &error);
count = mongoc_collection_count (
collection, MONGOC_QUERY_NONE, doc, 0, 0, NULL, &error);
if (count < 0) {
fprintf (stderr, "%s\n", error.message);
} else {
printf ("%" PRId64 "\n", count);
}
bson_destroy (doc);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o count count.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./count
1
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 count.c
C:\> count
1
Executing Commands
The driver provides helper functions for executing MongoDB commands on client, database
and collection structures. These functions return cursors; the _simple variants return
booleans indicating success or failure.
This example executes the collStats command against the collection "mycoll" in database
"mydb".
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
bson_error_t error;
bson_t *command;
bson_t reply;
char *str;
mongoc_init ();
client = mongoc_client_new (
"mongodb://localhost:27017/?appname=executing-example");
collection = mongoc_client_get_collection (client, "mydb", "mycoll");
command = BCON_NEW ("collStats", BCON_UTF8 ("mycoll"));
if (mongoc_collection_command_simple (
collection, command, NULL, &reply, &error)) {
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (stderr, "Failed to run command: %s\n", error.message);
}
bson_destroy (command);
bson_destroy (&reply);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Compile the code and run it:
$ gcc -o executing executing.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./executing
{ "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
"lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
"indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
On Windows:
C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 executing.c
C:\> executing
{ "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
"lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
"indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
Threading
The MongoDB C Driver is thread-unaware in the vast majority of its operations. This means
it is up to the programmer to guarantee thread-safety.
However, mongoc_client_pool_t is thread-safe and is used to fetch a mongoc_client_t in a
thread-safe manner. After retrieving a client from the pool, the client structure should
be considered owned by the calling thread. When the thread is finished, the client should
be placed back into the pool.
example-pool.c
/* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
* libmongoc-1.0) */
/* ./example-pool [CONNECTION_STRING] */
#include <mongoc/mongoc.h>
#include <pthread.h>
#include <stdio.h>
static pthread_mutex_t mutex;
static bool in_shutdown = false;
static void *
worker (void *data)
{
mongoc_client_pool_t *pool = data;
mongoc_client_t *client;
bson_t ping = BSON_INITIALIZER;
bson_error_t error;
bool r;
BSON_APPEND_INT32 (&ping, "ping", 1);
while (true) {
client = mongoc_client_pool_pop (pool);
/* Do something with client. If you are writing an HTTP server, you
* probably only want to hold onto the client for the portion of the
* request performing database queries.
*/
r = mongoc_client_command_simple (
client, "admin", &ping, NULL, NULL, &error);
if (!r) {
fprintf (stderr, "%s\n", error.message);
}
mongoc_client_pool_push (pool, client);
pthread_mutex_lock (&mutex);
if (in_shutdown || !r) {
pthread_mutex_unlock (&mutex);
break;
}
pthread_mutex_unlock (&mutex);
}
bson_destroy (&ping);
return NULL;
}
int
main (int argc, char *argv[])
{
const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_client_pool_t *pool;
pthread_t threads[10];
unsigned i;
void *ret;
pthread_mutex_init (&mutex, NULL);
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
pool = mongoc_client_pool_new (uri);
mongoc_client_pool_set_error_api (pool, 2);
for (i = 0; i < 10; i++) {
pthread_create (&threads[i], NULL, worker, pool);
}
sleep (10);
pthread_mutex_lock (&mutex);
in_shutdown = true;
pthread_mutex_unlock (&mutex);
for (i = 0; i < 10; i++) {
pthread_join (threads[i], &ret);
}
mongoc_client_pool_destroy (pool);
mongoc_uri_destroy (uri);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Next Steps
To find information on advanced topics, browse the rest of the C driver guide or the
official MongoDB documentation.
For help with common issues, consult the Troubleshooting page. To report a bug or request
a new feature, follow these instructions.
Authentication
This guide covers the use of authentication options with the MongoDB C Driver. Ensure that
the MongoDB server is also properly configured for authentication before making a
connection. For more information, see the MongoDB security documentation.
The MongoDB C driver supports several authentication mechanisms through the use of MongoDB
connection URIs.
By default, if a username and password are provided as part of the connection string (and
an optional authentication database), they are used to connect via the default
authentication mechanism of the server.
To select a specific authentication mechanism other than the default, see the list of
supported mechanism below.
mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authSource=mydb");
Currently supported values for the authMechanism connection string option are:
• SCRAM-SHA-1
• MONGODB-CR (deprecated)
• GSSAPI
• PLAIN
• X509
• MONGODB-AWS
Basic Authentication (SCRAM-SHA-256)
MongoDB 4.0 introduces support for authenticating using the SCRAM protocol with the more
secure SHA-256 hash described in RFC 7677. Using this authentication mechanism means that
the password is never actually sent over the wire when authenticating, but rather a
computed proof that the client password is the same as the password the server knows. In
MongoDB 4.0, the C driver can determine the correct default authentication mechanism for
users with stored SCRAM-SHA-1 and SCRAM-SHA-256 credentials:
mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authSource=mydb");
/* the correct authMechanism is negotiated between the driver and server. */
Alternatively, SCRAM-SHA-256 can be explicitly specified as an authMechanism.
mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authMechanism=SCRAM-SHA-256&authSource=mydb");
Passwords for SCRAM-SHA-256 undergo the preprocessing step known as SASLPrep specified in
RFC 4013. SASLPrep will only be performed for passwords containing non-ASCII characters.
SASLPrep requires libicu. If libicu is not available, attempting to authenticate over
SCRAM-SHA-256 with non-ASCII passwords will result in error.
Usernames never undergo SASLPrep.
By default, when building the C driver libicu is linked if available. This can be changed
with the ENABLE_ICU cmake option. To specify an installation path of libicu, specify
ICU_ROOT as a cmake option. See the FindICU documentation for more information.
Basic Authentication (SCRAM-SHA-1)
The default authentication mechanism before MongoDB 4.0 is SCRAM-SHA-1 (RFC 5802). Using
this authentication mechanism means that the password is never actually sent over the wire
when authenticating, but rather a computed proof that the client password is the same as
the password the server knows.
mongoc_client_t *client = mongoc_client_new ("mongodb://user:password@localhost/?authMechanism=SCRAM-SHA-1&authSource=mydb");
NOTE:
SCRAM-SHA-1 authenticates against the admin database by default. If the user is created
in another database, then specifying the authSource is required.
Legacy Authentication (MONGODB-CR)
The MONGODB-CR authMechanism is deprecated and will no longer function in MongoDB 4.0.
Instead, specify no authMechanism and the driver will use an authentication mechanism
compatible with your server.
GSSAPI (Kerberos) Authentication
NOTE:
On UNIX-like environments, Kerberos support requires compiling the driver against
cyrus-sasl.
On Windows, Kerberos support requires compiling the driver against Windows Native SSPI
or cyrus-sasl. The default configuration of the driver will use Windows Native SSPI.
To modify the default configuration, use the cmake option ENABLE_SASL.
GSSAPI (Kerberos) authentication is available in the Enterprise Edition of MongoDB. To
authenticate using GSSAPI, the MongoDB C driver must be installed with SASL support.
On UNIX-like environments, run the kinit command before using the following authentication
methods:
$ kinit mongodbuser@EXAMPLE.COM
mongodbuser@EXAMPLE.COM's Password:
$ klistCredentials cache: FILE:/tmp/krb5cc_1000
Principal: mongodbuser@EXAMPLE.COM
Issued Expires Principal
Feb 9 13:48:51 2013 Feb 9 23:48:51 2013 krbtgt/EXAMPLE.COM@EXAMPLE.COM
Now authenticate using the MongoDB URI. GSSAPI authenticates against the $external virtual
database, so a database does not need to be specified in the URI. Note that the Kerberos
principal must be URL-encoded:
mongoc_client_t *client;
client = mongoc_client_new ("mongodb://mongodbuser%40EXAMPLE.COM@mongo-server.example.com/?authMechanism=GSSAPI");
NOTE:
GSSAPI authenticates against the $external database, so specifying the authSource
database is not required.
The driver supports these GSSAPI properties:
• CANONICALIZE_HOST_NAME: This might be required with Cyrus-SASL when the hosts report
different hostnames than what is used in the Kerberos database. The default is "false".
• SERVICE_NAME: Use a different service name than the default, "mongodb".
Set properties in the URL:
mongoc_client_t *client;
client = mongoc_client_new ("mongodb://mongodbuser%40EXAMPLE.COM@mongo-server.example.com/?authMechanism=GSSAPI&"
"authMechanismProperties=SERVICE_NAME:other,CANONICALIZE_HOST_NAME:true");
If you encounter errors such as Invalid net address, check if the application is behind a
NAT (Network Address Translation) firewall. If so, create a ticket that uses forwardable
and addressless Kerberos tickets. This can be done by passing -f -A to kinit.
$ kinit -f -A mongodbuser@EXAMPLE.COM
SASL Plain Authentication
NOTE:
The MongoDB C Driver must be compiled with SASL support in order to use SASL PLAIN
authentication.
MongoDB Enterprise Edition supports the SASL PLAIN authentication mechanism, initially
intended for delegating authentication to an LDAP server. Using the SASL PLAIN mechanism
is very similar to the challenge response mechanism with usernames and passwords. This
authentication mechanism uses the $external virtual database for LDAP support:
NOTE:
SASL PLAIN is a clear-text authentication mechanism. It is strongly recommended to
connect to MongoDB using TLS with certificate validation when using the PLAIN
mechanism.
mongoc_client_t *client;
client = mongoc_client_new ("mongodb://user:password@example.com/?authMechanism=PLAIN");
PLAIN authenticates against the $external database, so specifying the authSource database
is not required.
X.509 Certificate Authentication
NOTE:
The MongoDB C Driver must be compiled with TLS support for X.509 authentication
support. Once this is done, start a server with the following options:
$ mongod --tlsMode requireTLS --tlsCertificateKeyFile server.pem --tlsCAFile ca.pem
The MONGODB-X509 mechanism authenticates a username derived from the distinguished subject
name of the X.509 certificate presented by the driver during TLS negotiation. This
authentication method requires the use of TLS connections with certificate validation.
mongoc_client_t *client;
mongoc_ssl_opt_t ssl_opts = { 0 };
ssl_opts.pem_file = "mycert.pem";
ssl_opts.pem_pwd = "mycertpassword";
ssl_opts.ca_file = "myca.pem";
ssl_opts.ca_dir = "trust_dir";
ssl_opts.weak_cert_validation = false;
client = mongoc_client_new ("mongodb://x509_derived_username@localhost/?authMechanism=MONGODB-X509");
mongoc_client_set_ssl_opts (client, &ssl_opts);
MONGODB-X509 authenticates against the $external database, so specifying the authSource
database is not required. For more information on the x509_derived_username, see the
MongoDB server x.509 tutorial.
NOTE:
The MongoDB C Driver will attempt to determine the x509 derived username when none is
provided, and as of MongoDB 3.4 providing the username is not required at all.
Authentication via AWS IAM
The MONGODB-AWS mechanism authenticates to MongoDB servers with credentials provided by
AWS Identity and Access Management (IAM).
To authenticate, create a user with an associated Amazon Resource Name (ARN) on the
$external database, and specify the MONGODB-AWS authMechanism in the URI.
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost/?authMechanism=MONGODB-AWS");
Since MONGODB-AWS always authenticates against the $external database, so specifying the
authSource database is not required.
Credentials include the access key id, secret access key, and optional session token. They
may be obtained from the following ways.
AWS credentials via URI
Credentials may be passed directly in the URI as username/password.
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://<access key id>:<secret access key>localhost/?authMechanism=MONGODB-AWS");
This may include a session token passed with authMechanismProperties.
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://<access key id>:<secret access key>localhost/?authMechanism=MONGODB-AWS&authMechanismProperties=AWS_SESSION_TOKEN:<token>");
AWS credentials via environment
If credentials are not passed through the URI, libmongoc will check for the following
environment variables.
• AWS_ACCESS_KEY_ID
• AWS_SECRET_ACCESS_KEY
• AWS_SESSION_TOKEN (optional)
AWS Credentials via ECS
If credentials are not passed in the URI or with environment variables, libmongoc will
check if the environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI is set, and if
so, attempt to retrieve temporary credentials from the ECS task metadata by querying a
link local address.
AWS Credentials via EC2
If credentials are not passed in the URI or with environment variables, and the
environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI is not set, libmongoc will
attempt to retrieve temporary credentials from the EC2 machine metadata by querying link
local addresses.
Basic Troubleshooting
Troubleshooting Checklist
The following is a short list of things to check when you have a problem.
• Did you call mongoc_init() in main()? If not, you will likely see a segfault.
• Have you leaked any clients or cursors as can be found with mongoc-stat <PID>?
• Have packets been delivered to the server? See egress bytes from mongoc-stat <PID>.
• Does valgrind show any leaks? Ensure you call mongoc_cleanup() at the end of your
process to cleanup lingering allocations from the MongoDB C driver.
• If compiling your own copy of MongoDB C Driver, consider using the cmake option
-DENABLE_TRACING=ON to enable function tracing and hex dumps of network packets to
STDERR and STDOUT.
Performance Counters
The MongoDB C driver comes with an optional unique feature to help developers and
sysadmins troubleshoot problems in production. Performance counters are available for
each process using the driver. If available, the counters can be accessed outside of the
application process via a shared memory segment. This means that you can graph statistics
about your application process easily from tools like Munin or Nagios. Your author often
uses watch --interval=0.5 -d mongoc-stat $PID to monitor an application.
Performance counters are only available on Linux platforms and macOS arm64 platforms
supporting shared memory segments. On supported platforms they are enabled by default.
Applications can be built without the counters by specifying the cmake option
-DENABLE_SHM_COUNTERS=OFF. Additionally, if performance counters are already compiled,
they can be disabled at runtime by specifying the environment variable MONGOC_DISABLE_SHM.
Performance counters keep track of the following:
• Active and Disposed Cursors
• Active and Disposed Clients, Client Pools, and Socket Streams.
• Number of operations sent and received, by type.
• Bytes transferred and received.
• Authentication successes and failures.
• Number of wire protocol errors.
To access counters for a given process, simply provide the process id to the mongoc-stat
program installed with the MongoDB C Driver.
$ mongoc-stat 22203
Operations : Egress Total : The number of sent operations. : 13247
Operations : Ingress Total : The number of received operations. : 13246
Operations : Egress Queries : The number of sent Query operations. : 13247
Operations : Ingress Queries : The number of received Query operations. : 0
Operations : Egress GetMore : The number of sent GetMore operations. : 0
Operations : Ingress GetMore : The number of received GetMore operations. : 0
Operations : Egress Insert : The number of sent Insert operations. : 0
Operations : Ingress Insert : The number of received Insert operations. : 0
Operations : Egress Delete : The number of sent Delete operations. : 0
Operations : Ingress Delete : The number of received Delete operations. : 0
Operations : Egress Update : The number of sent Update operations. : 0
Operations : Ingress Update : The number of received Update operations. : 0
Operations : Egress KillCursors : The number of sent KillCursors operations. : 0
Operations : Ingress KillCursors : The number of received KillCursors operations. : 0
Operations : Egress Msg : The number of sent Msg operations. : 0
Operations : Ingress Msg : The number of received Msg operations. : 0
Operations : Egress Reply : The number of sent Reply operations. : 0
Operations : Ingress Reply : The number of received Reply operations. : 13246
Cursors : Active : The number of active cursors. : 1
Cursors : Disposed : The number of disposed cursors. : 13246
Clients : Active : The number of active clients. : 1
Clients : Disposed : The number of disposed clients. : 0
Streams : Active : The number of active streams. : 1
Streams : Disposed : The number of disposed streams. : 0
Streams : Egress Bytes : The number of bytes sent. : 794931
Streams : Ingress Bytes : The number of bytes received. : 589694
Streams : N Socket Timeouts : The number of socket timeouts. : 0
Client Pools : Active : The number of active client pools. : 1
Client Pools : Disposed : The number of disposed client pools. : 0
Protocol : Ingress Errors : The number of protocol errors on ingress. : 0
Auth : Failures : The number of failed authentication requests. : 0
Auth : Success : The number of successful authentication requests. : 0
Submitting a Bug Report
Think you've found a bug? Want to see a new feature in the MongoDB C driver? Please open a
case in our issue management tool, JIRA:
• Create an account and login.
• Navigate to the CDRIVER project.
• Click Create Issue - Please provide as much information as possible about the issue type
and how to reproduce it.
Bug reports in JIRA for all driver projects (i.e. CDRIVER, CSHARP, JAVA) and the Core
Server (i.e. SERVER) project are public.
Guides
Configuring TLS
Configuration with URI options
Enable TLS by including tls=true in the URI.
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);
mongoc_client_t *client = mongoc_client_new_from_uri (uri);
The following URI options may be used to further configure TLS:
┌────────────────────────────────────────────────┬──────────────────────────────────────┬────────────────────────────────────────┐
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
└────────────────────────────────────────────────┴──────────────────────────────────────┴────────────────────────────────────────┘
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
└────────────────────────────────────────────────┴──────────────────────────────────────┴────────────────────────────────────────┘
Configuration with mongoc_ssl_opt_t
Alternatively, the mongoc_ssl_opt_t struct may be used to configure TLS with
mongoc_client_set_ssl_opts() or mongoc_client_pool_set_ssl_opts(). Most of the
configurable options can be set using the Connection String URI.
┌───────────────────────┬─────────────────────────────────┐
│mongoc_ssl_opt_t key │ URI key │
├───────────────────────┼─────────────────────────────────┤
│pem_file │ tlsClientCertificateKeyFile │
├───────────────────────┼─────────────────────────────────┤
│pem_pwd │ tlsClientCertificateKeyPassword │
├───────────────────────┼─────────────────────────────────┤
│ca_file │ tlsCAFile │
├───────────────────────┼─────────────────────────────────┤
│weak_cert_validation │ tlsAllowInvalidCertificates │
├───────────────────────┼─────────────────────────────────┤
│allow_invalid_hostname │ tlsAllowInvalidHostnames │
└───────────────────────┴─────────────────────────────────┘
The only exclusions are crl_file and ca_dir. Those may only be set with mongoc_ssl_opt_t.
Client Authentication
When MongoDB is started with TLS enabled, it will by default require the client to provide
a client certificate issued by a certificate authority specified by --tlsCAFile, or an
authority trusted by the native certificate store in use on the server.
To provide the client certificate, set the tlsCertificateKeyFile in the URI to a PEM
armored certificate file.
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/");
mongoc_uri_set_option_as_bool (uri, MONGOC_URI_TLS, true);
mongoc_uri_set_option_as_utf8 (uri, MONGOC_URI_TLSCERTIFICATEKEYFILE, "/path/to/client-certificate.pem");
mongoc_client_t *client = mongoc_client_new_from_uri (uri);
Server Certificate Verification
The MongoDB C Driver will automatically verify the validity of the server certificate,
such as issued by configured Certificate Authority, hostname validation, and expiration.
To overwrite this behavior, it is possible to disable hostname validation, OCSP endpoint
revocation checking, revocation checking entirely, and allow invalid certificates.
This behavior is controlled using the tlsAllowInvalidHostnames,
tlsDisableOCSPEndpointCheck, tlsDisableCertificateRevocationCheck, and
tlsAllowInvalidCertificates options respectively. By default, all are set to false.
It is not recommended to change these defaults as it exposes the client to Man In The
Middle attacks (when tlsAllowInvalidHostnames is set), invalid certificates (when
tlsAllowInvalidCertificates is set), or potentially revoked certificates (when
tlsDisableOCSPEndpointCheck or tlsDisableCertificateRevocationCheck are set).
Supported Libraries
By default, libmongoc will attempt to find a supported TLS library and enable TLS support.
This is controlled by the cmake flag ENABLE_SSL, which is set to AUTO by default. Valid
values are:
• AUTO the default behavior. Link to the system's native TLS library, or attempt to find
OpenSSL.
• DARWIN link to Secure Transport, the native TLS library on macOS.
• WINDOWS link to Secure Channel, the native TLS library on Windows.
• OPENSSL link to OpenSSL (libssl). An optional install path may be specified with
OPENSSL_ROOT.
• LIBRESSL link to LibreSSL's libtls. (LibreSSL's compatible libssl may be linked to by
setting OPENSSL).
• OFF disable TLS support.
OpenSSL
The MongoDB C Driver uses OpenSSL, if available, on Linux and Unix platforms (besides
macOS). Industry best practices and some regulations require the use of TLS 1.1 or newer,
which requires at least OpenSSL 1.0.1. Check your OpenSSL version like so:
$ openssl version
Ensure your system's OpenSSL is a recent version (at least 1.0.1), or install a recent
version in a non-system path and build against it with:
cmake -DOPENSSL_ROOT_DIR=/absolute/path/to/openssl
When compiled against OpenSSL, the driver will attempt to load the system default
certificate store, as configured by the distribution. That can be overridden by setting
the tlsCAFile URI option or with the fields ca_file and ca_dir in the mongoc_ssl_opt_t.
The Online Certificate Status Protocol (OCSP) (see RFC 6960) is fully supported when using
OpenSSL 1.0.1+ with the following notes:
• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server's
certificate, the certificate is considered revoked (even if the certificate has a valid
stapled OCSP response)
LibreSSL / libtls
The MongoDB C Driver supports LibreSSL through the use of OpenSSL compatibility checks
when configured to compile against openssl. It also supports the new libtls library when
configured to build against libressl.
When compiled against the Windows native libraries, the crl_file option of a
mongoc_ssl_opt_t is not supported, and will issue an error if used.
Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no
effect.
The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with
the following notes:
• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a
Must-Staple certificate is presented with no stapled response (unless the client
receives a revoked response from an OCSP responder).
• Connection will continue if a Must-Staple certificate is presented without a stapled
response and the OCSP responder is down.
Native TLS Support on Windows (Secure Channel)
The MongoDB C Driver supports the Windows native TLS library (Secure Channel, or
SChannel), and its native crypto library (Cryptography API: Next Generation, or CNG).
When compiled against the Windows native libraries, the ca_dir option of a
mongoc_ssl_opt_t is not supported, and will issue an error if used.
Encrypted PEM files (e.g., setting tlsCertificateKeyPassword) are also not supported, and
will result in error when attempting to load them.
When tlsCAFile is set, the driver will only allow server certificates issued by the
authority (or authorities) provided. When no tlsCAFile is set, the driver will look up the
Certificate Authority using the System Local Machine Root certificate store to confirm the
provided certificate.
When crl_file is set with mongoc_ssl_opt_t, the driver will import the revocation list to
the System Local Machine Root certificate store.
Setting tlsDisableOCSPEndpointCheck has no effect.
The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with
the following notes:
• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a
Must-Staple certificate is presented with no stapled response (unless the client
receives a revoked response from an OCSP responder).
• When a crl_file is set with mongoc_ssl_opt_t, and the crl_file revokes the server's
certificate, the OCSP response takes precedence. E.g. if the server presents a
certificate with a valid stapled OCSP response, the certificate is considered valid even
if the crl_file marks it as revoked.
• Connection will continue if a Must-Staple certificate is presented without a stapled
response and the OCSP responder is down.
Native TLS Support on macOS / Darwin (Secure Transport)
The MongoDB C Driver supports the Darwin (OS X, macOS, iOS, etc.) native TLS library
(Secure Transport), and its native crypto library (Common Crypto, or CC).
When compiled against Secure Transport, the ca_dir and crl_file options of a
mongoc_ssl_opt_t are not supported. An error is issued if either are used.
When tlsCAFile is set, the driver will only allow server certificates issued by the
authority (or authorities) provided. When no tlsCAFile is set, the driver will use the
Certificate Authorities in the currently unlocked keychains.
Setting tlsDisableOCSPEndpointCheck and tlsDisableCertificateRevocationCheck has no
effect.
The Online Certificate Status Protocol (OCSP) (see RFC 6960) is partially supported with
the following notes.
• The Must-Staple extension (see RFC 7633) is ignored. Connection may continue if a
Must-Staple certificate is presented with no stapled response (unless the client
receives a revoked response from an OCSP responder).
• Connection will continue if a Must-Staple certificate is presented without a stapled
response and the OCSP responder is down.
Common Tasks
Drivers for some other languages provide helper functions to perform certain common tasks.
In the C Driver we must explicitly build commands to send to the server.
Setup
First we'll write some code to insert sample data:
doc-common-insert.c
/* Don't try to compile this file on its own. It's meant to be #included
by example code */
/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
enum N { ndocs = 4 };
bson_t *docs[ndocs];
bson_error_t error;
int i = 0;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
docs[2] = BCON_NEW (
"x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");
for (i = 0; i < ndocs; i++) {
mongoc_bulk_operation_insert (bulk, docs[i]);
bson_destroy (docs[i]);
docs[i] = NULL;
}
ret = mongoc_bulk_operation_execute (bulk, NULL, &error);
if (!ret) {
fprintf (stderr, "Error inserting data: %s\n", error.message);
}
mongoc_bulk_operation_destroy (bulk);
return ret;
}
/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
char *str;
BSON_ASSERT (reply);
str = bson_as_canonical_extended_json (reply, NULL);
printf ("%s\n", str);
bson_free (str);
}
explain Command
This is how to use the explain command in MongoDB 3.2+:
explain.c
bool
explain (mongoc_collection_t *collection)
{
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
command = BCON_NEW ("explain",
"{",
"find",
BCON_UTF8 (COLLECTION_NAME),
"filter",
"{",
"x",
BCON_INT32 (1),
"}",
"}");
res = mongoc_collection_command_simple (
collection, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with explain: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply */
print_res (&reply);
cleanup:
bson_destroy (&reply);
bson_destroy (command);
return res;
}
Running the Examples
common-operations.c
/*
* Copyright 2016 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <mongoc/mongoc.h>
#include <stdio.h>
const char *COLLECTION_NAME = "things";
#include "../doc-common-insert.c"
#include "explain.c"
int
main (int argc, char *argv[])
{
mongoc_database_t *database = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
mongoc_uri_t *uri = NULL;
bson_error_t error;
char *host_and_port;
int res = 0;
if (argc < 2 || argc > 3) {
fprintf (stderr,
"usage: %s MONGOD-1-CONNECTION-STRING "
"[MONGOD-2-HOST-NAME:MONGOD-2-PORT]\n",
argv[0]);
fprintf (stderr,
"MONGOD-1-CONNECTION-STRING can be "
"of the following forms:\n");
fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
fprintf (stderr,
"mongodb://user:pass@localhost:27017\t"
"local machine on port 27017, and authenticate with username "
"user and password pass\n");
return EXIT_FAILURE;
}
mongoc_init ();
if (strncmp (argv[1], "mongodb://", 10) == 0) {
host_and_port = bson_strdup (argv[1]);
} else {
host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
}
uri = mongoc_uri_new_with_error (host_and_port, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
host_and_port,
error.message);
res = EXIT_FAILURE;
goto cleanup;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
res = EXIT_FAILURE;
goto cleanup;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "test");
collection = mongoc_database_get_collection (database, COLLECTION_NAME);
printf ("Inserting data\n");
if (!insert_data (collection)) {
res = EXIT_FAILURE;
goto cleanup;
}
printf ("explain\n");
if (!explain (collection)) {
res = EXIT_FAILURE;
goto cleanup;
}
cleanup:
if (collection) {
mongoc_collection_destroy (collection);
}
if (database) {
mongoc_database_destroy (database);
}
if (client) {
mongoc_client_destroy (client);
}
if (uri) {
mongoc_uri_destroy (uri);
}
bson_free (host_and_port);
mongoc_cleanup ();
return res;
}
First launch two separate instances of mongod (must be done from separate shells):
$ mongod
$ mkdir /tmp/db2
$ mongod --dbpath /tmp/db2 --port 27018 # second instance
Now compile and run the example program:
$ cd examples/common_operations/$ gcc -Wall -o example common-operations.c $(pkg-config --cflags --libs libmongoc-1.0)$ ./example localhost:27017 localhost:27018
Inserting data
explain
{
"executionStats" : {
"allPlansExecution" : [],
"executionStages" : {
"advanced" : 19,
"direction" : "forward" ,
"docsExamined" : 76,
"executionTimeMillisEstimate" : 0,
"filter" : {
"x" : {
"$eq" : 1
}
},
"invalidates" : 0,
"isEOF" : 1,
"nReturned" : 19,
"needTime" : 58,
"needYield" : 0,
"restoreState" : 0,
"saveState" : 0,
"stage" : "COLLSCAN" ,
"works" : 78
},
"executionSuccess" : true,
"executionTimeMillis" : 0,
"nReturned" : 19,
"totalDocsExamined" : 76,
"totalKeysExamined" : 0
},
"ok" : 1,
"queryPlanner" : {
"indexFilterSet" : false,
"namespace" : "test.things",
"parsedQuery" : {
"x" : {
"$eq" : 1
}
},
"plannerVersion" : 1,
"rejectedPlans" : [],
"winningPlan" : {
"direction" : "forward" ,
"filter" : {
"x" : {
"$eq" : 1
}
},
"stage" : "COLLSCAN"
}
},
"serverInfo" : {
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25" ,
"host" : "MacBook-Pro-57.local",
"port" : 27017,
"version" : "3.2.6"
}
}
Advanced Connections
The following guide contains information specific to certain types of MongoDB
configurations.
For an example of connecting to a simple standalone server, see the Tutorial. To establish
a connection with authentication options enabled, see the Authentication page.
Connecting to a Replica Set
Connecting to a replica set is much like connecting to a standalone MongoDB server. Simply
specify the replica set name using the ?replicaSet=myreplset URI option.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_init ();
/* Create our MongoDB Client */
client = mongoc_client_new (
"mongodb://host01:27017,host02:27017,host03:27017/?replicaSet=myreplset");
/* Do some work */
/* TODO */
/* Clean up */
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
TIP:
Multiple hostnames can be specified in the MongoDB connection string URI, with a comma
separating hosts in the seed list.
It is recommended to use a seed list of members of the replica set to allow the driver
to connect to any node.
Connecting to a Sharded Cluster
To connect to a sharded cluster, specify the mongos nodes the client should connect to.
The C Driver will automatically detect that it has connected to a mongos sharding server.
If more than one hostname is specified, a seed list will be created to attempt failover
between the mongos instances.
WARNING:
Specifying the replicaSet parameter when connecting to a mongos sharding server is
invalid.
#include <bson/bson.h>
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_init ();
/* Create our MongoDB Client */
client = mongoc_client_new ("mongodb://myshard01:27017/");
/* Do something with client ... */
/* Free the client */
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Connecting to an IPv6 Address
The MongoDB C Driver will automatically resolve IPv6 addresses from host names. However,
to specify an IPv6 address directly, wrap the address in [].
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://[::1]:27017");
Connecting with IPv4 and IPv6
If connecting to a hostname that has both IPv4 and IPv6 DNS records, the behavior follows
RFC-6555. A connection to the IPv6 address is attempted first. If IPv6 fails, then a
connection is attempted to the IPv4 address. If the connection attempt to IPv6 does not
complete within 250ms, then IPv4 is tried in parallel. Whichever succeeds connection first
cancels the other. The successful DNS result is cached for 10 minutes.
As a consequence, attempts to connect to a mongod only listening on IPv4 may be delayed if
there are both A (IPv4) and AAAA (IPv6) DNS records associated with the host.
To avoid a delay, configure hostnames to match the MongoDB configuration. That is, only
create an A record if the mongod is only listening on IPv4.
Connecting to a UNIX Domain Socket
On UNIX-like systems, the C Driver can connect directly to a MongoDB server using a UNIX
domain socket. Pass the URL-encoded path to the socket, which must be suffixed with .sock.
For example, to connect to a domain socket at /tmp/mongodb-27017.sock:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://%2Ftmp%2Fmongodb-27017.sock");
Include username and password like so:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://user:pass@%2Ftmp%2Fmongodb-27017.sock");
Connecting to a server over TLS
These are instructions for configuring TLS/SSL connections.
To run a server locally (on port 27017, for example):
$ mongod --port 27017 --tlsMode requireTLS --tlsCertificateKeyFile server.pem --tlsCAFile ca.pem
Add /?tls=true to the end of a client URI.
mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?tls=true");
MongoDB requires client certificates by default, unless the
--tlsAllowConnectionsWithoutCertificates is provided. The C Driver can be configured to
present a client certificate using the URI option tlsCertificateKeyFile, which may be
referenced through the constant MONGOC_URI_TLSCERTIFICATEKEYFILE.
mongoc_client_t *client = NULL;
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://localhost:27017/?tls=true");
mongoc_uri_set_option_as_utf8 (uri, MONGOC_URI_TLSCERTIFICATEKEYFILE, "client.pem");
client = mongoc_client_new_from_uri (uri);
The client certificate provided by tlsCertificateKeyFile must be issued by one of the
server trusted Certificate Authorities listed in --tlsCAFile, or issued by a CA in the
native certificate store on the server when omitted.
See Configuring TLS for more information on the various TLS related options.
Compressing data to and from MongoDB
MongoDB 3.4 added Snappy compression support, zlib compression in 3.6, and zstd
compression in 4.2. To enable compression support the client must be configured with
which compressors to use:
mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?compressors=snappy,zlib,zstd");
The compressors option specifies the priority order of compressors the client wants to
use. Messages are compressed if the client and server share any compressors in common.
Note that the compressor used by the server might not be the same compressor as the client
used. For example, if the client uses the connection string compressors=zlib,snappy the
client will use zlib compression to send data (if possible), but the server might still
reply using snappy, depending on how the server was configured.
The driver must be built with zlib and/or snappy and/or zstd support to enable compression
support, any unknown (or not compiled in) compressor value will be ignored. Note: to build
with zstd requires cmake 3.12 or higher.
Additional Connection Options
The full list of connection options can be found in the mongoc_uri_t docs.
Certain socket/connection related options are not configurable:
┌──────────────┬──────────────────────────┬────────────────────────┐
│Option │ Description │ Value │
├──────────────┼──────────────────────────┼────────────────────────┤
│SO_KEEPALIVE │ TCP Keep Alive │ Enabled │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPIDLE │ How long a connection │ 120 seconds │
│ │ needs to remain idle │ │
│ │ before TCP starts │ │
│ │ sending keepalive probes │ │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPINTVL │ The time in seconds │ 10 seconds │
│ │ between TCP probes │ │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPCNT │ How many probes to send, │ 9 probes │
│ │ without acknowledgement, │ │
│ │ before dropping the │ │
│ │ connection │ │
└──────────────┴──────────────────────────┴────────────────────────┘
│TCP_NODELAY │ Send packets as soon as │ Enabled (no buffering) │
│ │ possible or buffer small │ │
│ │ packets (Nagle │ │
│ │ algorithm) │ │
└──────────────┴──────────────────────────┴────────────────────────┘
Connection Pooling
The MongoDB C driver has two connection modes: single-threaded and pooled. Single-threaded
mode is optimized for embedding the driver within languages like PHP. Multi-threaded
programs should use pooled mode: this mode minimizes the total connection count, and in
pooled mode background threads monitor the MongoDB server topology, so the program need
not block to scan it.
Single Mode
In single mode, your program creates a mongoc_client_t directly:
mongoc_client_t *client = mongoc_client_new (
"mongodb://hostA,hostB/?replicaSet=my_rs");
The client connects on demand when your program first uses it for a MongoDB operation.
Using a non-blocking socket per server, it begins a check on each server concurrently, and
uses the asynchronous poll or select function to receive events from the sockets, until
all have responded or timed out. Put another way, in single-threaded mode the C Driver
fans out to begin all checks concurrently, then fans in once all checks have completed or
timed out. Once the scan completes, the client executes your program's operation and
returns.
In single mode, the client re-scans the server topology roughly once per minute. If more
than a minute has elapsed since the previous scan, the next operation on the client will
block while the client completes its scan. This interval is configurable with
heartbeatFrequencyMS in the connection string. (See mongoc_uri_t.)
A single client opens one connection per server in your topology: these connections are
used both for scanning the topology and performing normal operations.
Pooled Mode
To activate pooled mode, create a mongoc_client_pool_t:
mongoc_uri_t *uri = mongoc_uri_new (
"mongodb://hostA,hostB/?replicaSet=my_rs");
mongoc_client_pool_t *pool = mongoc_client_pool_new (uri);
When your program first calls mongoc_client_pool_pop(), the pool launches monitoring
threads in the background. Monitoring threads independently connect to all servers in the
connection string. As monitoring threads receive hello responses from the servers, they
update the shared view of the server topology. Additional monitoring threads and
connections are created as new servers are discovered. Monitoring threads are terminated
when servers are removed from the shared view of the server topology.
Each thread that executes MongoDB operations must check out a client from the pool:
mongoc_client_t *client = mongoc_client_pool_pop (pool);
/* use the client for operations ... */
mongoc_client_pool_push (pool, client);
The mongoc_client_t object is not thread-safe, only the mongoc_client_pool_t is.
When the driver is in pooled mode, your program's operations are unblocked as soon as
monitoring discovers a usable server. For example, if a thread in your program is waiting
to execute an "insert" on the primary, it is unblocked as soon as the primary is
discovered, rather than waiting for all secondaries to be checked as well.
The pool opens one connection per server for monitoring, and each client opens its own
connection to each server it uses for application operations. Background monitoring
threads re-scan servers independently roughly every 10 seconds. This interval is
configurable with heartbeatFrequencyMS in the connection string. (See mongoc_uri_t.)
The connection string can also specify waitQueueTimeoutMS to limit the time that
mongoc_client_pool_pop() will wait for a client from the pool. (See mongoc_uri_t.) If
waitQueueTimeoutMS is specified, then it is necessary to confirm that a client was
actually returned:
mongoc_uri_t *uri = mongoc_uri_new (
"mongodb://hostA,hostB/?replicaSet=my_rs&waitQueueTimeoutMS=1000");
mongoc_client_pool_t *pool = mongoc_client_pool_new (uri);
mongoc_client_t *client = mongoc_client_pool_pop (pool);
if (client) {
/* use the client for operations ... */
mongoc_client_pool_push (pool, client);
} else {
/* take appropriate action for a timeout */
}
See Connection Pool Options to configure pool size and behavior, and see
mongoc_client_pool_t for an extended example of a multi-threaded program that uses the
driver in pooled mode.
Cursors
Handling Cursor Failures
Cursors exist on a MongoDB server. However, the mongoc_cursor_t structure gives the local
process a handle to the cursor. It is possible for errors to occur on the server while
iterating a cursor on the client. Even a network partition may occur. This means that
applications should be robust in handling cursor failures.
While iterating cursors, you should check to see if an error has occurred. See the
following example for how to robustly check for errors.
static void
print_all_documents (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
char *str;
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Failed to iterate all documents: %s\n", error.message);
}
mongoc_cursor_destroy (cursor);
}
Destroying Server-Side Cursors
The MongoDB C driver will automatically destroy a server-side cursor when
mongoc_cursor_destroy() is called. Failure to call this function when done with a cursor
will leak memory client side as well as consume extra memory server side. If the cursor
was configured to never timeout, it will become a memory leak on the server.
Tailable Cursors
Tailable cursors are cursors that remain open even after they've returned a final result.
This way, if more documents are added to a collection (i.e., to the cursor's result set),
then you can continue to call mongoc_cursor_next() to retrieve those additional results.
Here's a complete test case that demonstrates the use of tailable cursors.
NOTE:
Tailable cursors are for capped collections only.
An example to tail the oplog from a replica set.
mongoc-tail.c
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#ifdef _WIN32
#define sleep(_n) Sleep ((_n) *1000)
#endif
static void
print_bson (const bson_t *b)
{
char *str;
str = bson_as_canonical_extended_json (b, NULL);
fprintf (stdout, "%s\n", str);
bson_free (str);
}
static mongoc_cursor_t *
query_collection (mongoc_collection_t *collection, uint32_t last_time)
{
mongoc_cursor_t *cursor;
bson_t query;
bson_t gt;
bson_t opts;
BSON_ASSERT (collection);
bson_init (&query);
BSON_APPEND_DOCUMENT_BEGIN (&query, "ts", >);
BSON_APPEND_TIMESTAMP (>, "$gt", last_time, 0);
bson_append_document_end (&query, >);
bson_init (&opts);
BSON_APPEND_BOOL (&opts, "tailable", true);
BSON_APPEND_BOOL (&opts, "awaitData", true);
cursor = mongoc_collection_find_with_opts (collection, &query, &opts, NULL);
bson_destroy (&query);
bson_destroy (&opts);
return cursor;
}
static void
tail_collection (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
uint32_t last_time;
const bson_t *doc;
bson_error_t error;
bson_iter_t iter;
BSON_ASSERT (collection);
last_time = (uint32_t) time (NULL);
while (true) {
cursor = query_collection (collection, last_time);
while (!mongoc_cursor_error (cursor, &error) &&
mongoc_cursor_more (cursor)) {
if (mongoc_cursor_next (cursor, &doc)) {
if (bson_iter_init_find (&iter, doc, "ts") &&
BSON_ITER_HOLDS_TIMESTAMP (&iter)) {
bson_iter_timestamp (&iter, &last_time, NULL);
}
print_bson (doc);
}
}
if (mongoc_cursor_error (cursor, &error)) {
if (error.domain == MONGOC_ERROR_SERVER) {
fprintf (stderr, "%s\n", error.message);
exit (1);
}
}
mongoc_cursor_destroy (cursor);
sleep (1);
}
}
int
main (int argc, char *argv[])
{
mongoc_collection_t *collection;
mongoc_client_t *client;
mongoc_uri_t *uri;
bson_error_t error;
if (argc != 2) {
fprintf (stderr, "usage: %s MONGO_URI\n", argv[0]);
return EXIT_FAILURE;
}
mongoc_init ();
uri = mongoc_uri_new_with_error (argv[1], &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
argv[1],
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "local", "oplog.rs");
tail_collection (collection);
mongoc_collection_destroy (collection);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
return EXIT_SUCCESS;
}
Let's compile and run this example against a replica set to see updates as they are made.
$ gcc -Wall -o mongoc-tail mongoc-tail.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./mongoc-tail mongodb://example.com/?replicaSet=myReplSet
{
"h" : -8458503739429355503,
"ns" : "test.test",
"o" : {
"_id" : {
"$oid" : "5372ab0a25164be923d10d50"
}
},
"op" : "i",
"ts" : {
"$timestamp" : {
"i" : 1,
"t" : 1400023818
}
},
"v" : 2
}
The line of output is a sample from performing db.test.insert({}) from the mongo shell on
the replica set.
SEE ALSO:
mongoc_cursor_set_max_await_time_ms().
Bulk Write Operations
This tutorial explains how to take advantage of MongoDB C driver bulk write operation
features. Executing write operations in batches reduces the number of network round trips,
increasing write throughput.
Bulk Insert
First we need to fetch a bulk operation handle from the mongoc_collection_t.
mongoc_bulk_operation_t *bulk =
mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
We can now start inserting documents to the bulk operation. These will be buffered until
we execute the operation.
The bulk operation will coalesce insertions as a single batch for each consecutive call to
mongoc_bulk_operation_insert(). This creates a pipelined effect when possible.
To execute the bulk operation and receive the result we call
mongoc_bulk_operation_execute().
bulk1.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk1 (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
int i;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
for (i = 0; i < 10000; i++) {
doc = BCON_NEW ("i", BCON_INT32 (i));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
}
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
fprintf (stderr, "Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk1-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk1 (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Example reply document:
{"nInserted" : 10000,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : []
"writeConcernErrors" : [] }
Mixed Bulk Write Operations
MongoDB C driver also supports executing mixed bulk write operations. A batch of insert,
update, and remove operations can be executed together using the bulk write operations
API.
Ordered Bulk Write Operations
Ordered bulk write operations are batched and sent to the server in the order provided for
serial execution. The reply document describes the type and count of operations performed.
bulk2.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk2 (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *query;
bson_t *doc;
bson_t *opts;
bson_t reply;
char *str;
bool ret;
int i;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Remove everything */
query = bson_new ();
mongoc_bulk_operation_remove (bulk, query);
bson_destroy (query);
/* Add a few documents */
for (i = 1; i < 4; i++) {
doc = BCON_NEW ("_id", BCON_INT32 (i));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
}
/* {_id: 1} => {$set: {foo: "bar"}} */
query = BCON_NEW ("_id", BCON_INT32 (1));
doc = BCON_NEW ("$set", "{", "foo", BCON_UTF8 ("bar"), "}");
mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, NULL, &error);
bson_destroy (query);
bson_destroy (doc);
/* {_id: 4} => {'$inc': {'j': 1}} (upsert) */
opts = BCON_NEW ("upsert", BCON_BOOL (true));
query = BCON_NEW ("_id", BCON_INT32 (4));
doc = BCON_NEW ("$inc", "{", "j", BCON_INT32 (1), "}");
mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, opts, &error);
bson_destroy (query);
bson_destroy (doc);
bson_destroy (opts);
/* replace {j:1} with {j:2} */
query = BCON_NEW ("j", BCON_INT32 (1));
doc = BCON_NEW ("j", BCON_INT32 (2));
mongoc_bulk_operation_replace_one_with_opts (bulk, query, doc, NULL, &error);
bson_destroy (query);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk2-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk2 (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Example reply document:
{ "nInserted" : 3,
"nMatched" : 2,
"nModified" : 2,
"nRemoved" : 10000,
"nUpserted" : 1,
"upserted" : [{"index" : 5, "_id" : 4}],
"writeErrors" : []
"writeConcernErrors" : [] }
The index field in the upserted array is the 0-based index of the upsert operation; in
this example, the sixth operation of the overall bulk operation was an upsert, so its
index is 5.
Unordered Bulk Write Operations
Unordered bulk write operations are batched and sent to the server in arbitrary order
where they may be executed in parallel. Any errors that occur are reported after all
operations are attempted.
In the next example the first and third operations fail due to the unique constraint on
_id. Since we are doing unordered execution the second and fourth operations succeed.
bulk3.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk3 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *query;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
/* false indicates unordered */
BSON_APPEND_BOOL (&opts, "ordered", false);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
bson_destroy (&opts);
/* Add a document */
doc = BCON_NEW ("_id", BCON_INT32 (1));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* remove {_id: 2} */
query = BCON_NEW ("_id", BCON_INT32 (2));
mongoc_bulk_operation_remove_one (bulk, query);
bson_destroy (query);
/* insert {_id: 3} */
doc = BCON_NEW ("_id", BCON_INT32 (3));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* replace {_id:4} {'i': 1} */
query = BCON_NEW ("_id", BCON_INT32 (4));
doc = BCON_NEW ("i", BCON_INT32 (1));
mongoc_bulk_operation_replace_one (bulk, query, doc, false);
bson_destroy (query);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk3-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk3 (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Example reply document:
{ "nInserted" : 0,
"nMatched" : 1,
"nModified" : 1,
"nRemoved" : 1,
"nUpserted" : 0,
"writeErrors" : [
{ "index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }" },
{ "index" : 2,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 3 }" } ],
"writeConcernErrors" : [] }
Error: E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }
The bson_error_t domain is MONGOC_ERROR_COMMAND and its code is 11000.
Bulk Operation Bypassing Document Validation
This feature is only available when using MongoDB 3.2 and later.
By default bulk operations are validated against the schema, if any is defined. In certain
cases however it may be necessary to bypass the document validation.
bulk5.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk5_fail (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (31));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (32));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* The above documents do not comply to the schema validation rules
* we created previously, so this will result in an error */
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
static void
bulk5_success (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Allow this document to bypass document validation.
* NOTE: When authentication is enabled, the authenticated user must have
* either the "dbadmin" or "restore" roles to bypass document validation */
mongoc_bulk_operation_set_bypass_document_validation (bulk, true);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (31));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (32));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
bson_t *options;
bson_error_t error;
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_database_t *database;
const char *uri_string = "mongodb://localhost/?appname=bulk5-example";
mongoc_uri_t *uri;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "testasdf");
/* Create schema validator */
options = BCON_NEW (
"validator", "{", "number", "{", "$gte", BCON_INT32 (5), "}", "}");
collection =
mongoc_database_create_collection (database, "collname", options, &error);
if (collection) {
bulk5_fail (collection);
bulk5_success (collection);
mongoc_collection_destroy (collection);
} else {
fprintf (stderr, "Couldn't create collection: '%s'\n", error.message);
}
bson_free (options);
mongoc_uri_destroy (uri);
mongoc_database_destroy (database);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Running the above example will result in:
{ "nInserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [
{ "index" : 0,
"code" : 121,
"errmsg" : "Document failed validation" } ] }
Error: Document failed validation
{ "nInserted" : 2,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [] }
The bson_error_t domain is MONGOC_ERROR_COMMAND.
Bulk Operation Write Concerns
By default bulk operations are executed with the write_concern of the collection they are
executed against. A custom write concern can be passed to the
mongoc_collection_create_bulk_operation_with_opts() method. Write concern errors (e.g.
wtimeout) will be reported after all operations are attempted, regardless of execution
order.
bulk4.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk4 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_write_concern_t *wc;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_w (wc, 4);
mongoc_write_concern_set_wtimeout_int64 (wc, 100); /* milliseconds */
mongoc_write_concern_append (wc, &opts);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (10));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (11));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
mongoc_write_concern_destroy (wc);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk4-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk4 (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Example reply document and error message:
{ "nInserted" : 2,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [],
"writeConcernErrors" : [
{ "code" : 64,
"errmsg" : "waiting for replication timed out" }
] }
Error: waiting for replication timed out
The bson_error_t domain is MONGOC_ERROR_WRITE_CONCERN if there are write concern errors
and no write errors. Write errors indicate failed operations, so they take precedence over
write concern errors, which mean merely that the write concern is not satisfied yet.
Setting Collation Order
This feature is only available when using MongoDB 3.4 and later.
bulk-collation.c
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk_collation (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_t *opts;
bson_t *doc;
bson_t *selector;
bson_t *update;
bson_error_t error;
bson_t reply;
char *str;
uint32_t ret;
/* insert {_id: "one"} and {_id: "One"} */
bulk = mongoc_collection_create_bulk_operation_with_opts (
collection, NULL);
doc = BCON_NEW ("_id", BCON_UTF8 ("one"));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_UTF8 ("One"));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* "One" normally sorts before "one"; make "one" come first */
opts = BCON_NEW ("collation",
"{",
"locale",
BCON_UTF8 ("en_US"),
"caseFirst",
BCON_UTF8 ("lower"),
"}");
/* set x=1 on the document with _id "One", which now sorts after "one" */
update = BCON_NEW ("$set", "{", "x", BCON_INT64 (1), "}");
selector = BCON_NEW ("_id", "{", "$gt", BCON_UTF8 ("one"), "}");
mongoc_bulk_operation_update_one_with_opts (
bulk, selector, update, opts, &error);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (selector);
bson_destroy (opts);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk-collation";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "db", "collection");
bulk_collation (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Running the above example will result in:
{ "nInserted" : 2,
"nMatched" : 1,
"nModified" : 1,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [ ]
}
Unacknowledged Bulk Writes
Set "w" to zero for an unacknowledged write. The driver sends unacknowledged writes using
the legacy opcodes OP_INSERT, OP_UPDATE, and OP_DELETE.
bulk6.c
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
bulk6 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_write_concern_t *wc;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t *selector;
bson_t reply;
char *str;
bool ret;
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_w (wc, 0);
mongoc_write_concern_append (wc, &opts);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
doc = BCON_NEW ("_id", BCON_INT32 (10));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
selector = BCON_NEW ("_id", BCON_INT32 (11));
mongoc_bulk_operation_remove_one (bulk, selector);
bson_destroy (selector);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
mongoc_write_concern_destroy (wc);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string = "mongodb://localhost/?appname=bulk6-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk6 (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
The reply document is empty:
{ }
Further Reading
See the Driver Bulk API Spec, which describes bulk write operations for all MongoDB
drivers.
Aggregation Framework Examples
This document provides a number of practical examples that display the capabilities of the
aggregation framework.
The Aggregations using the Zip Codes Data Set examples uses a publicly available data set
of all zipcodes and populations in the United States. These data are available at:
zips.json.
Requirements
Let's check if everything is installed.
Use the following command to load zips.json data set into mongod instance:
$ mongoimport --drop -d test -c zipcodes zips.json
Let's use the MongoDB shell to verify that everything was imported successfully.
$ mongo test
connecting to: test
> db.zipcodes.count()
29467
> db.zipcodes.findOne()
{
"_id" : "35004",
"city" : "ACMAR",
"loc" : [
-86.51557,
33.584132
],
"pop" : 6055,
"state" : "AL"
}
Aggregations using the Zip Codes Data Set
Each document in this collection has the following form:
{
"_id" : "35004",
"city" : "Acmar",
"state" : "AL",
"pop" : 6055,
"loc" : [-86.51557, 33.584132]
}
In these documents:
• The _id field holds the zipcode as a string.
• The city field holds the city name.
• The state field holds the two letter state abbreviation.
• The pop field holds the population.
• The loc field holds the location as a [latitude, longitude] array.
States with Populations Over 10 Million
To get all states with a population greater than 10 million, use the following aggregation
pipeline:
aggregation1.c
#include <mongoc/mongoc.h>
#include <stdio.h>
static void
print_pipeline (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
bson_error_t error;
const bson_t *doc;
bson_t *pipeline;
char *str;
pipeline = BCON_NEW ("pipeline",
"[",
"{",
"$group",
"{",
"_id",
"$state",
"total_pop",
"{",
"$sum",
"$pop",
"}",
"}",
"}",
"{",
"$match",
"{",
"total_pop",
"{",
"$gte",
BCON_INT32 (10000000),
"}",
"}",
"}",
"]");
cursor = mongoc_collection_aggregate (
collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Cursor Failure: %s\n", error.message);
}
mongoc_cursor_destroy (cursor);
bson_destroy (pipeline);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
const char *uri_string =
"mongodb://localhost:27017/?appname=aggregation-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "zipcodes");
print_pipeline (collection);
mongoc_uri_destroy (uri);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
You should see a result like the following:
{ "_id" : "PA", "total_pop" : 11881643 }
{ "_id" : "OH", "total_pop" : 10847115 }
{ "_id" : "NY", "total_pop" : 17990455 }
{ "_id" : "FL", "total_pop" : 12937284 }
{ "_id" : "TX", "total_pop" : 16986510 }
{ "_id" : "IL", "total_pop" : 11430472 }
{ "_id" : "CA", "total_pop" : 29760021 }
The above aggregation pipeline is build from two pipeline operators: $group and $match.
The $group pipeline operator requires _id field where we specify grouping; remaining
fields specify how to generate composite value and must use one of the group aggregation
functions: $addToSet, $first, $last, $max, $min, $avg, $push, $sum. The $match pipeline
operator syntax is the same as the read operation query syntax.
The $group process reads all documents and for each state it creates a separate document,
for example:
{ "_id" : "WA", "total_pop" : 4866692 }
The total_pop field uses the $sum aggregation function to sum the values of all pop fields
in the source documents.
Documents created by $group are piped to the $match pipeline operator. It returns the
documents with the value of total_pop field greater than or equal to 10 million.
Average City Population by State
To get the first three states with the greatest average population per city, use the
following aggregation:
pipeline = BCON_NEW ("pipeline", "[",
"{", "$group", "{", "_id", "{", "state", "$state", "city", "$city", "}", "pop", "{", "$sum", "$pop", "}", "}", "}",
"{", "$group", "{", "_id", "$_id.state", "avg_city_pop", "{", "$avg", "$pop", "}", "}", "}",
"{", "$sort", "{", "avg_city_pop", BCON_INT32 (-1), "}", "}",
"{", "$limit", BCON_INT32 (3) "}",
"]");
This aggregate pipeline produces:
{ "_id" : "DC", "avg_city_pop" : 303450.0 }
{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }
{ "_id" : "CA", "avg_city_pop" : 27735.341099720412 }
The above aggregation pipeline is build from three pipeline operators: $group, $sort and
$limit.
The first $group operator creates the following documents:
{ "_id" : { "state" : "WY", "city" : "Smoot" }, "pop" : 414 }
Note, that the $group operator can't use nested documents except the _id field.
The second $group uses these documents to create the following documents:
{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }
These documents are sorted by the avg_city_pop field in descending order. Finally, the
$limit pipeline operator returns the first 3 documents from the sorted set.
distinct and mapReduce
This document provides some practical, simple, examples to demonstrate the distinct and
mapReduce commands.
Setup
First we'll write some code to insert sample data:
doc-common-insert.c
/* Don't try to compile this file on its own. It's meant to be #included
by example code */
/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
enum N { ndocs = 4 };
bson_t *docs[ndocs];
bson_error_t error;
int i = 0;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
docs[2] = BCON_NEW (
"x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");
for (i = 0; i < ndocs; i++) {
mongoc_bulk_operation_insert (bulk, docs[i]);
bson_destroy (docs[i]);
docs[i] = NULL;
}
ret = mongoc_bulk_operation_execute (bulk, NULL, &error);
if (!ret) {
fprintf (stderr, "Error inserting data: %s\n", error.message);
}
mongoc_bulk_operation_destroy (bulk);
return ret;
}
/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
char *str;
BSON_ASSERT (reply);
str = bson_as_canonical_extended_json (reply, NULL);
printf ("%s\n", str);
bson_free (str);
}
distinct command
This is how to use the distinct command to get the distinct values of x which are greater
than 1:
distinct.c
bool
distinct (mongoc_database_t *database)
{
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
bson_iter_t iter;
bson_iter_t array_iter;
double val;
command = BCON_NEW ("distinct",
BCON_UTF8 (COLLECTION_NAME),
"key",
BCON_UTF8 ("x"),
"query",
"{",
"x",
"{",
"$gt",
BCON_DOUBLE (1.0),
"}",
"}");
res =
mongoc_database_command_simple (database, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with distinct: %s\n", error.message);
goto cleanup;
}
/* Do something with reply (in this case iterate through the values) */
if (!(bson_iter_init_find (&iter, &reply, "values") &&
BSON_ITER_HOLDS_ARRAY (&iter) &&
bson_iter_recurse (&iter, &array_iter))) {
fprintf (stderr, "Couldn't extract \"values\" field from response\n");
goto cleanup;
}
while (bson_iter_next (&array_iter)) {
if (BSON_ITER_HOLDS_DOUBLE (&array_iter)) {
val = bson_iter_double (&array_iter);
printf ("Next double: %f\n", val);
}
}
cleanup:
/* cleanup */
bson_destroy (command);
bson_destroy (&reply);
return res;
}
mapReduce - basic example
A simple example using the map reduce framework. It simply adds up the number of
occurrences of each "tag".
First define the map and reduce functions:
constants.c
const char *const COLLECTION_NAME = "things";
/* Our map function just emits a single (key, 1) pair for each tag
in the array: */
const char *const MAPPER = "function () {"
"this.tags.forEach(function(z) {"
"emit(z, 1);"
"});"
"}";
/* The reduce function sums over all of the emitted values for a
given key: */
const char *const REDUCER = "function (key, values) {"
"var total = 0;"
"for (var i = 0; i < values.length; i++) {"
"total += values[i];"
"}"
"return total;"
"}";
/* Note We can't just return values.length as the reduce function
might be called iteratively on the results of other reduce
steps. */
Run the mapReduce command. Use the generic command helpers (e.g.
mongoc_database_command_simple()). Do not the read command helpers (e.g.
mongoc_database_read_command_with_opts()) because they are considered retryable read
operations. If retryable reads are enabled, those operations will retry once on a
retryable error, giving undesirable behavior for mapReduce.
map-reduce-basic.c
bool
map_reduce_basic (mongoc_database_t *database)
{
bson_t reply;
bson_t *command;
bool res;
bson_error_t error;
mongoc_cursor_t *cursor;
const bson_t *doc;
bool query_done = false;
const char *out_collection_name = "outCollection";
mongoc_collection_t *out_collection;
/* Empty find query */
bson_t find_query = BSON_INITIALIZER;
/* Construct the mapReduce command */
/* Other arguments can also be specified here, like "query" or
"limit" and so on */
command = BCON_NEW ("mapReduce",
BCON_UTF8 (COLLECTION_NAME),
"map",
BCON_CODE (MAPPER),
"reduce",
BCON_CODE (REDUCER),
"out",
BCON_UTF8 (out_collection_name));
res =
mongoc_database_command_simple (database, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "MapReduce failed: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply (it doesn't contain the mapReduce results) */
print_res (&reply);
/* Now we'll query outCollection to see what the results are */
out_collection =
mongoc_database_get_collection (database, out_collection_name);
cursor = mongoc_collection_find_with_opts (
out_collection, &find_query, NULL, NULL);
query_done = true;
/* Do something with the results */
while (mongoc_cursor_next (cursor, &doc)) {
print_res (doc);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "ERROR: %s\n", error.message);
res = false;
goto cleanup;
}
cleanup:
/* cleanup */
if (query_done) {
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (out_collection);
}
bson_destroy (&reply);
bson_destroy (command);
return res;
}
mapReduce - more complicated example
You must have replica set running for this.
In this example we contact a secondary in the replica set and do an "inline" map reduce,
so the results are returned immediately:
map-reduce-advanced.c
bool
map_reduce_advanced (mongoc_database_t *database)
{
bson_t *command;
bson_error_t error;
bool res = true;
mongoc_cursor_t *cursor;
mongoc_read_prefs_t *read_pref;
const bson_t *doc;
/* Construct the mapReduce command */
/* Other arguments can also be specified here, like "query" or "limit"
and so on */
/* Read the results inline from a secondary replica */
command = BCON_NEW ("mapReduce",
BCON_UTF8 (COLLECTION_NAME),
"map",
BCON_CODE (MAPPER),
"reduce",
BCON_CODE (REDUCER),
"out",
"{",
"inline",
"1",
"}");
read_pref = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
cursor = mongoc_database_command (
database, MONGOC_QUERY_NONE, 0, 0, 0, command, NULL, read_pref);
/* Do something with the results */
while (mongoc_cursor_next (cursor, &doc)) {
print_res (doc);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "ERROR: %s\n", error.message);
res = false;
}
mongoc_cursor_destroy (cursor);
mongoc_read_prefs_destroy (read_pref);
bson_destroy (command);
return res;
}
Running the Examples
Here's how to run the example code
basic-aggregation.c
/*
* Copyright 2016 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <mongoc/mongoc.h>
#include <stdio.h>
#include "constants.c"
#include "../doc-common-insert.c"
#include "distinct.c"
#include "map-reduce-basic.c"
#include "map-reduce-advanced.c"
int
main (int argc, char *argv[])
{
mongoc_database_t *database = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
mongoc_uri_t *uri = NULL;
bson_error_t error;
char *host_and_port = NULL;
int exit_code = EXIT_FAILURE;
if (argc != 2) {
fprintf (stderr, "usage: %s CONNECTION-STRING\n", argv[0]);
fprintf (stderr,
"the connection string can be of the following forms:\n");
fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
fprintf (stderr,
"mongodb://user:pass@localhost:27017\t"
"local machine on port 27017, and authenticate with username "
"user and password pass\n");
return exit_code;
}
mongoc_init ();
if (strncmp (argv[1], "mongodb://", 10) == 0) {
host_and_port = bson_strdup (argv[1]);
} else {
host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
}
uri = mongoc_uri_new_with_error (host_and_port, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
host_and_port,
error.message);
goto cleanup;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
goto cleanup;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "test");
collection = mongoc_database_get_collection (database, COLLECTION_NAME);
printf ("Inserting data\n");
if (!insert_data (collection)) {
goto cleanup;
}
printf ("distinct\n");
if (!distinct (database)) {
goto cleanup;
}
printf ("map reduce\n");
if (!map_reduce_basic (database)) {
goto cleanup;
}
printf ("more complicated map reduce\n");
if (!map_reduce_advanced (database)) {
goto cleanup;
}
exit_code = EXIT_SUCCESS;
cleanup:
if (collection) {
mongoc_collection_destroy (collection);
}
if (database) {
mongoc_database_destroy (database);
}
if (client) {
mongoc_client_destroy (client);
}
if (uri) {
mongoc_uri_destroy (uri);
}
if (host_and_port) {
bson_free (host_and_port);
}
mongoc_cleanup ();
return exit_code;
}
If you want to try the advanced map reduce example with a secondary, start a replica set
(instructions for how to do this can be found here).
Otherwise, just start an instance of MongoDB:
$ mongod
Now compile and run the example program:
$ cd examples/basic_aggregation/
$ gcc -Wall -o agg-example basic-aggregation.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./agg-example localhost
Inserting data
distinct
Next double: 2.000000
Next double: 3.000000
map reduce
{ "result" : "outCollection", "timeMillis" : 155, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }
{ "_id" : "cat", "value" : 63 }
{ "_id" : "dog", "value" : 42 }
{ "_id" : "mouse", "value" : 21 }
more complicated map reduce
{ "results" : [ { "_id" : "cat", "value" : 63 }, { "_id" : "dog", "value" : 42 }, { "_id" : "mouse", "value" : 21 } ], "timeMillis" : 14, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }
Using libmongoc in a Microsoft Visual Studio project
Download and install libmongoc on your system, then open Visual Studio, select
"File→New→Project...", and create a new Win32 Console Application. [image]
Remember to switch the platform from 32-bit to 64-bit: [image]
Right-click on your console application in the Solution Explorer and select "Properties".
Choose to edit properties for "All Configurations", expand the "C/C++" options and choose
"General". Add to the "Additional Include Directories" these paths:
C:\mongo-c-driver\include\libbson-1.0
C:\mongo-c-driver\include\libmongoc-1.0
[image]
(If you chose a different CMAKE_INSTALL_PREFIX when you ran CMake, your include paths will
be different.)
Also in the Properties dialog, expand the "Linker" options and choose "Input", and add to
the "Additional Dependencies" these libraries:
C:\mongo-c-driver\lib\bson-1.0.lib
C:\mongo-c-driver\lib\mongoc-1.0.lib
[image]
Adding these libraries as dependencies provides linker symbols to build your application,
but to actually run it, libbson's and libmongoc's DLLs must be in your executable path.
Select "Debugging" in the Properties dialog, and set the "Environment" option to:
PATH=c:/mongo-c-driver/bin
[image]
Finally, include "mongoc/mongoc.h" in your project's "stdafx.h":
#include <mongoc/mongoc.h>
Static linking
Following the instructions above, you have dynamically linked your application to the
libbson and libmongoc DLLs. This is usually the right choice. If you want to link
statically instead, update your "Additional Dependencies" list by removing bson-1.0.lib
and mongoc-1.0.lib and replacing them with these libraries:
C:\mongo-c-driver\lib\bson-static-1.0.lib
C:\mongo-c-driver\lib\mongoc-static-1.0.lib
ws2_32.lib
Secur32.lib
Crypt32.lib
BCrypt.lib
[image]
(To explain the purpose of each library: bson-static-1.0.lib and mongoc-static-1.0.lib are
static archives of the driver code. The socket library ws2_32 is required by libbson,
which uses the socket routine gethostname to help guarantee ObjectId uniqueness. The
BCrypt library is used by libmongoc for TLS connections to MongoDB, and Secur32 and
Crypt32 are required for enterprise authentication methods like Kerberos.)
Finally, define two preprocessor symbols before including mongoc/mongoc.h in your
stdafx.h:
#define BSON_STATIC
#define MONGOC_STATIC
#include <mongoc/mongoc.h>
Making these changes to your project is only required for static linking; for most people,
the dynamic-linking instructions above are preferred.
Next Steps
Now you can build and debug applications in Visual Studio that use libbson and libmongoc.
Proceed to Making a Connection in the tutorial to learn how connect to MongoDB and perform
operations.
Creating Indexes
To create indexes on a MongoDB collection, execute the createIndexes command with a
command function like mongoc_database_write_command_with_opts() or
mongoc_collection_write_command_with_opts(). See the MongoDB Manual entry for the
createIndexes command for details.
WARNING:
The commitQuorum option to the createIndexes command is only supported in MongoDB 4.4+
servers, but it is not validated in the command functions. Do not pass commitQuorum if
connected to server versions less than 4.4. Using the commitQuorum option on server
versions less than 4.4 may have adverse effects on index builds.
Example
example-create-indexes.c
/* gcc example-create-indexes.c -o example-create-indexes $(pkg-config --cflags
* --libs libmongoc-1.0) */
/* ./example-create-indexes [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
const char *uri_string =
"mongodb://127.0.0.1/?appname=create-indexes-example";
mongoc_uri_t *uri;
mongoc_database_t *db;
const char *collection_name = "test";
bson_t keys;
char *index_name;
bson_t *create_indexes;
bson_t reply;
char *reply_str;
bson_error_t error;
bool r;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
if (argc > 2) {
collection_name = argv[2];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
db = mongoc_client_get_database (client, "test");
/* ascending index on field "x" */
bson_init (&keys);
BSON_APPEND_INT32 (&keys, "x", 1);
index_name = mongoc_collection_keys_to_index_string (&keys);
create_indexes = BCON_NEW ("createIndexes",
BCON_UTF8 (collection_name),
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (&keys),
"name",
BCON_UTF8 (index_name),
"}",
"]");
r = mongoc_database_write_command_with_opts (
db, create_indexes, NULL /* opts */, &reply, &error);
reply_str = bson_as_json (&reply, NULL);
printf ("%s\n", reply_str);
if (!r) {
fprintf (stderr, "Error in createIndexes: %s\n", error.message);
}
bson_free (index_name);
bson_free (reply_str);
bson_destroy (&reply);
bson_destroy (create_indexes);
mongoc_database_destroy (db);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return r ? EXIT_SUCCESS : EXIT_FAILURE;
}
Aids for Debugging
GDB
This repository contains a .gdbinit file that contains helper functions to aid debugging
of data structures. GDB will load this file automatically if you have added the directory
which contains the .gdbinit file to GDB's auto-load safe-path, and you start GDB from the
directory which holds the .gdbinit file.
You can see the safe-path with show auto-load safe-path on a GDB prompt. You can configure
it by setting it in ~/.gdbinit with:
add-auto-load-safe-path /path/to/mongo-c-driver
If you haven't added the path to your auto-load safe-path, or start GDB in another
directory, load the file with:
source path/to/mongo-c-driver/.gdbinit
The .gdbinit file defines the printbson function, which shows the contents of a bson_t *
variable. If you have a local bson_t, then you must prefix the variable with a &.
An example GDB session looks like:
(gdb) printbson bson
ALLOC [0x555556cd7310 + 0] (len=475)
{
'bool' : true,
'int32' : NumberInt("42"),
'int64' : NumberLong("3000000042"),
'string' : "Stŕìñg",
'objectId' : ObjectID("5A1442F3122D331C3C6757E1"),
'utcDateTime' : UTCDateTime(1511277299031),
'arrayOfInts' : [
'0' : NumberInt("1"),
'1' : NumberInt("2")
],
'embeddedDocument' : {
'arrayOfStrings' : [
'0' : "one",
'1' : "two"
],
'double' : 2.718280,
'notherDoc' : {
'true' : NumberInt("1"),
'false' : false
}
},
'binary' : Binary("02", "3031343532333637"),
'regex' : Regex("@[a-z]+@", "im"),
'null' : null,
'js' : JavaScript("print foo"),
'jsws' : JavaScript("print foo") with scope: {
'f' : NumberInt("42"),
'a' : [
'0' : 3.141593,
'1' : 2.718282
]
},
'timestamp' : Timestamp(4294967295, 4294967295),
'double' : 3.141593
}
LLDB
This repository also includes a script that customizes LLDB's standard print command to
print a bson_t or bson_t * as JSON:
(lldb) print b
(bson_t) $0 = {"x": 1, "y": 2}
The custom bson command provides more options:
(lldb) bson --verbose b
len=19
flags=INLINE|STATIC
{
"x": 1,
"y": 2
}
(lldb) bson --raw b
'\x13\x00\x00\x00\x10x\x00\x01\x00\x00\x00\x10y\x00\x02\x00\x00\x00\x00'
Type help bson for a list of options.
The script requires a build of libbson with debug symbols, and an installation of PyMongo.
Install PyMongo with:
python -m pip install pymongo
If you see "No module named pip" then you must install pip, then run the previous command
again.
Create a file ~/.lldbinit containing:
command script import /path/to/mongo-c-driver/lldb_bson.py
If you see "bson command installed by lldb_bson" at the beginning of your LLDB session,
you've installed the script correctly.
Debug assertions
To enable runtime debug assertions, configure with -DENABLE_DEBUG_ASSERTIONS=ON.
Using Client-Side Field Level Encryption
New in MongoDB 4.2, Client-Side Field Level Encryption (also referred to as Client-Side
Encryption) allows administrators and developers to encrypt specific data fields in
addition to other MongoDB encryption features.
With Client-Side Encryption, developers can encrypt fields client side without any
server-side configuration or directives. Client-Side Encryption supports workloads where
applications must guarantee that unauthorized parties, including server administrators,
cannot read the encrypted data.
Automatic encryption, where sensitive fields in commands are encrypted automatically,
requires an Enterprise-only process to do query analysis.
Installation
libmongocrypt
There is a separate library, libmongocrypt, that must be installed prior to configuring
libmongoc to enable Client-Side Encryption.
libmongocrypt depends on libbson. To build libmongoc with Client-Side Encryption support
you must:
1. Install libbson
2. Build and install libmongocrypt
3. Build libmongoc
To install libbson, follow the instructions to install with a package manager: Install
libbson with a Package Manager or build from source with cmake (disable building libmongoc
with -DENABLE_MONGOC=OFF):
$ cd mongo-c-driver
$ mkdir cmake-build && cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF -DENABLE_MONGOC=OFF ..
$ cmake --build . --target install
To build and install libmongocrypt, clone the repository and configure as follows:
$ cd libmongocrypt
$ mkdir cmake-build && cd cmake-build
$ cmake -DENABLE_SHARED_BSON=ON ..
$ cmake --build . --target install
Then, you should be able to build libmongoc with Client-Side Encryption.
$ cd mongo-c-driver
$ mkdir cmake-build && cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF -DENABLE_MONGOC=ON -DENABLE_CLIENT_SIDE_ENCRYPTION=ON ..
$ cmake --build . --target install
mongocryptd
The mongocryptd binary is required for automatic Client-Side Encryption and is included as
a component in the MongoDB Enterprise Server package. For detailed installation
instructions see the MongoDB documentation on mongocryptd.
mongocryptd performs the following:
• Parses the automatic encryption rules specified to the database connection. If the JSON
schema contains invalid automatic encryption syntax or any document validation syntax,
mongocryptd returns an error.
• Uses the specified automatic encryption rules to mark fields in read and write
operations for encryption.
• Rejects read/write operations that may return unexpected or incorrect results when
applied to an encrypted field. For supported and unsupported operations, see Read/Write
Support with Automatic Field Level Encryption.
A mongoc_client_t configured with auto encryption will automatically spawn the mongocryptd
process from the application's PATH. Applications can control the spawning behavior as
part of the automatic encryption options. For example, to set a custom path to the
mongocryptd process, set the mongocryptdSpawnPath with
mongoc_auto_encryption_opts_set_extra().
bson_t *extra = BCON_NEW ("mongocryptdSpawnPath", "/path/to/mongocryptd");
mongoc_auto_encryption_opts_set_extra (opts, extra);
To control the logging output of mongocryptd pass mongocryptdSpawnArgs to
mongoc_auto_encryption_opts_set_extra():
bson_t *extra = BCON_NEW ("mongocryptdSpawnArgs",
"[", "--logpath=/path/to/mongocryptd.log", "--logappend", "]");
mongoc_auto_encryption_opts_set_extra (opts, extra);
If your application wishes to manage the mongocryptd process manually, it is possible to
disable spawning mongocryptd:
bson_t *extra = BCON_NEW ("mongocryptdBypassSpawn",
BCON_BOOL(true), "mongocryptdURI", "mongodb://localhost:27020");
mongoc_auto_encryption_opts_set_extra (opts, extra);
mongocryptd is only responsible for supporting automatic Client-Side Encryption in the
driver and does not itself perform any encryption or decryption.
Automatic Client-Side Field Level Encryption
Automatic Client-Side Encryption is enabled by calling
mongoc_client_enable_auto_encryption() on a mongoc_client_t. The following examples show
how to set up automatic client-side field level encryption using
mongoc_client_encryption_t to create a new encryption data key.
NOTE:
Automatic client-side field level encryption requires MongoDB 4.2 enterprise or a
MongoDB 4.2 Atlas cluster. The community version of the server supports automatic
decryption as well as Explicit Encryption.
Providing Local Automatic Encryption Rules
The following example shows how to specify automatic encryption rules using a schema map
set with mongoc_auto_encryption_opts_set_schema_map(). The automatic encryption rules are
expressed using a strict subset of the JSON Schema syntax.
Supplying a schema map provides more security than relying on JSON Schemas obtained from
the server. It protects against a malicious server advertising a false JSON Schema, which
could trick the client into sending unencrypted data that should be encrypted.
JSON Schemas supplied in the schema map only apply to configuring automatic client-side
field level encryption. Other validation rules in the JSON schema will not be enforced by
the driver and will result in an error:
client-side-encryption-schema-map.c
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include "client-side-encryption-helpers.h"
/* Helper method to create a new data key in the key vault, a schema to use that
* key, and writes the schema to a file for later use. */
static bool
create_schema_file (bson_t *kms_providers,
const char *keyvault_db,
const char *keyvault_coll,
mongoc_client_t *keyvault_client,
bson_error_t *error)
{
mongoc_client_encryption_t *client_encryption = NULL;
mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
bson_value_t datakey_id = {0};
char *keyaltnames[] = {"mongoc_encryption_example_1"};
bson_t *schema = NULL;
char *schema_string = NULL;
size_t schema_string_len;
FILE *outfile = NULL;
bool ret = false;
client_encryption_opts = mongoc_client_encryption_opts_new ();
mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
kms_providers);
mongoc_client_encryption_opts_set_keyvault_namespace (
client_encryption_opts, keyvault_db, keyvault_coll);
mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
keyvault_client);
client_encryption =
mongoc_client_encryption_new (client_encryption_opts, error);
if (!client_encryption) {
goto fail;
}
/* Create a new data key and json schema for the encryptedField.
* https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
*/
datakey_opts = mongoc_client_encryption_datakey_opts_new ();
mongoc_client_encryption_datakey_opts_set_keyaltnames (
datakey_opts, keyaltnames, 1);
if (!mongoc_client_encryption_create_datakey (
client_encryption, "local", datakey_opts, &datakey_id, error)) {
goto fail;
}
/* Create a schema describing that "encryptedField" is a string encrypted
* with the newly created data key using deterministic encryption. */
schema = BCON_NEW ("properties",
"{",
"encryptedField",
"{",
"encrypt",
"{",
"keyId",
"[",
BCON_BIN (datakey_id.value.v_binary.subtype,
datakey_id.value.v_binary.data,
datakey_id.value.v_binary.data_len),
"]",
"bsonType",
"string",
"algorithm",
MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC,
"}",
"}",
"}",
"bsonType",
"object");
/* Use canonical JSON so that other drivers and tools will be
* able to parse the MongoDB extended JSON file. */
schema_string = bson_as_canonical_extended_json (schema, &schema_string_len);
outfile = fopen ("jsonSchema.json", "w");
if (0 == fwrite (schema_string, sizeof (char), schema_string_len, outfile)) {
fprintf (stderr, "failed to write to file\n");
goto fail;
}
ret = true;
fail:
mongoc_client_encryption_destroy (client_encryption);
mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
mongoc_client_encryption_opts_destroy (client_encryption_opts);
bson_free (schema_string);
bson_destroy (schema);
bson_value_destroy (&datakey_id);
if (outfile) {
fclose (outfile);
}
return true;
}
/* This example demonstrates how to use automatic encryption with a client-side
* schema map using the enterprise version of MongoDB */
int
main (int argc, char **argv)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"
int exit_status = EXIT_FAILURE;
bool ret;
uint8_t *local_masterkey = NULL;
uint32_t local_masterkey_len;
bson_t *kms_providers = NULL;
bson_error_t error = {0};
bson_t *index_keys = NULL;
char *index_name = NULL;
bson_t *create_index_cmd = NULL;
bson_json_reader_t *reader = NULL;
bson_t schema = BSON_INITIALIZER;
bson_t *schema_map = NULL;
/* The MongoClient used to access the key vault (keyvault_namespace). */
mongoc_client_t *keyvault_client = NULL;
mongoc_collection_t *keyvault_coll = NULL;
mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *coll = NULL;
bson_t *to_insert = NULL;
mongoc_client_t *unencrypted_client = NULL;
mongoc_collection_t *unencrypted_coll = NULL;
mongoc_init ();
/* Configure the master key. This must be the same master key that was used
* to create the encryption key. */
local_masterkey =
hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
if (!local_masterkey || local_masterkey_len != 96) {
fprintf (stderr,
"Specify LOCAL_MASTERKEY environment variable as a "
"secure random 96 byte hex value.\n");
goto fail;
}
kms_providers = BCON_NEW ("local",
"{",
"key",
BCON_BIN (0, local_masterkey, local_masterkey_len),
"}");
/* Set up the key vault for this example. */
keyvault_client = mongoc_client_new (
"mongodb://localhost/?appname=client-side-encryption-keyvault");
keyvault_coll = mongoc_client_get_collection (
keyvault_client, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_collection_drop (keyvault_coll, NULL);
/* Create a unique index to ensure that two data keys cannot share the same
* keyAltName. This is recommended practice for the key vault. */
index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
index_name = mongoc_collection_keys_to_index_string (index_keys);
create_index_cmd = BCON_NEW ("createIndexes",
KEYVAULT_COLL,
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (index_keys),
"name",
index_name,
"unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}",
"}",
"]");
ret = mongoc_client_command_simple (keyvault_client,
KEYVAULT_DB,
create_index_cmd,
NULL /* read prefs */,
NULL /* reply */,
&error);
if (!ret) {
goto fail;
}
/* Create a new data key and a schema using it for encryption. Save the
* schema to the file jsonSchema.json */
ret = create_schema_file (
kms_providers, KEYVAULT_DB, KEYVAULT_COLL, keyvault_client, &error);
if (!ret) {
goto fail;
}
/* Load the JSON Schema and construct the local schema_map option. */
reader = bson_json_reader_new_from_file ("jsonSchema.json", &error);
if (!reader) {
goto fail;
}
bson_json_reader_read (reader, &schema, &error);
/* Construct the schema map, mapping the namespace of the collection to the
* schema describing encryption. */
schema_map =
BCON_NEW (ENCRYPTED_DB "." ENCRYPTED_COLL, BCON_DOCUMENT (&schema));
auto_encryption_opts = mongoc_auto_encryption_opts_new ();
mongoc_auto_encryption_opts_set_keyvault_client (auto_encryption_opts,
keyvault_client);
mongoc_auto_encryption_opts_set_keyvault_namespace (
auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
kms_providers);
mongoc_auto_encryption_opts_set_schema_map (auto_encryption_opts,
schema_map);
client =
mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
/* Enable automatic encryption. It will determine that encryption is
* necessary from the schema map instead of relying on the server to provide
* a schema. */
ret = mongoc_client_enable_auto_encryption (
client, auto_encryption_opts, &error);
if (!ret) {
goto fail;
}
coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);
/* Clear old data */
mongoc_collection_drop (coll, NULL);
to_insert = BCON_NEW ("encryptedField", "123456789");
ret = mongoc_collection_insert_one (
coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
if (!ret) {
goto fail;
}
printf ("decrypted document: ");
if (!print_one_document (coll, &error)) {
goto fail;
}
printf ("\n");
unencrypted_client = mongoc_client_new (
"mongodb://localhost/?appname=client-side-encryption-unencrypted");
unencrypted_coll = mongoc_client_get_collection (
unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);
printf ("encrypted document: ");
if (!print_one_document (unencrypted_coll, &error)) {
goto fail;
}
printf ("\n");
exit_status = EXIT_SUCCESS;
fail:
if (error.code) {
fprintf (stderr, "error: %s\n", error.message);
}
bson_free (local_masterkey);
bson_destroy (kms_providers);
mongoc_collection_destroy (keyvault_coll);
bson_destroy (index_keys);
bson_free (index_name);
bson_destroy (create_index_cmd);
bson_json_reader_destroy (reader);
mongoc_auto_encryption_opts_destroy (auto_encryption_opts);
mongoc_collection_destroy (coll);
mongoc_client_destroy (client);
bson_destroy (to_insert);
mongoc_collection_destroy (unencrypted_coll);
mongoc_client_destroy (unencrypted_client);
mongoc_client_destroy (keyvault_client);
bson_destroy (&schema);
bson_destroy (schema_map);
mongoc_cleanup ();
return exit_status;
}
Server-Side Field Level Encryption Enforcement
The MongoDB 4.2 server supports using schema validation to enforce encryption of specific
fields in a collection. This schema validation will prevent an application from inserting
unencrypted values for any fields marked with the "encrypt" JSON schema keyword.
The following example shows how to set up automatic client-side field level encryption
using mongoc_client_encryption_t to create a new encryption data key and create a
collection with the Automatic Encryption JSON Schema Syntax:
client-side-encryption-server-schema.c
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include "client-side-encryption-helpers.h"
/* Helper method to create and return a JSON schema to use for encryption.
The caller will use the returned schema for server-side encryption validation.
*/
static bson_t *
create_schema (bson_t *kms_providers,
const char *keyvault_db,
const char *keyvault_coll,
mongoc_client_t *keyvault_client,
bson_error_t *error)
{
mongoc_client_encryption_t *client_encryption = NULL;
mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
bson_value_t datakey_id = {0};
char *keyaltnames[] = {"mongoc_encryption_example_2"};
bson_t *schema = NULL;
client_encryption_opts = mongoc_client_encryption_opts_new ();
mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
kms_providers);
mongoc_client_encryption_opts_set_keyvault_namespace (
client_encryption_opts, keyvault_db, keyvault_coll);
mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
keyvault_client);
client_encryption =
mongoc_client_encryption_new (client_encryption_opts, error);
if (!client_encryption) {
goto fail;
}
/* Create a new data key and json schema for the encryptedField.
* https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
*/
datakey_opts = mongoc_client_encryption_datakey_opts_new ();
mongoc_client_encryption_datakey_opts_set_keyaltnames (
datakey_opts, keyaltnames, 1);
if (!mongoc_client_encryption_create_datakey (
client_encryption, "local", datakey_opts, &datakey_id, error)) {
goto fail;
}
/* Create a schema describing that "encryptedField" is a string encrypted
* with the newly created data key using deterministic encryption. */
schema = BCON_NEW ("properties",
"{",
"encryptedField",
"{",
"encrypt",
"{",
"keyId",
"[",
BCON_BIN (datakey_id.value.v_binary.subtype,
datakey_id.value.v_binary.data,
datakey_id.value.v_binary.data_len),
"]",
"bsonType",
"string",
"algorithm",
MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC,
"}",
"}",
"}",
"bsonType",
"object");
fail:
mongoc_client_encryption_destroy (client_encryption);
mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
mongoc_client_encryption_opts_destroy (client_encryption_opts);
bson_value_destroy (&datakey_id);
return schema;
}
/* This example demonstrates how to use automatic encryption with a server-side
* schema using the enterprise version of MongoDB */
int
main (int argc, char **argv)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"
int exit_status = EXIT_FAILURE;
bool ret;
uint8_t *local_masterkey = NULL;
uint32_t local_masterkey_len;
bson_t *kms_providers = NULL;
bson_error_t error = {0};
bson_t *index_keys = NULL;
char *index_name = NULL;
bson_t *create_index_cmd = NULL;
bson_json_reader_t *reader = NULL;
bson_t *schema = NULL;
/* The MongoClient used to access the key vault (keyvault_namespace). */
mongoc_client_t *keyvault_client = NULL;
mongoc_collection_t *keyvault_coll = NULL;
mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *coll = NULL;
bson_t *to_insert = NULL;
mongoc_client_t *unencrypted_client = NULL;
mongoc_collection_t *unencrypted_coll = NULL;
bson_t *create_cmd = NULL;
bson_t *create_cmd_opts = NULL;
mongoc_write_concern_t *wc = NULL;
mongoc_init ();
/* Configure the master key. This must be the same master key that was used
* to create
* the encryption key. */
local_masterkey =
hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
if (!local_masterkey || local_masterkey_len != 96) {
fprintf (stderr,
"Specify LOCAL_MASTERKEY environment variable as a "
"secure random 96 byte hex value.\n");
goto fail;
}
kms_providers = BCON_NEW ("local",
"{",
"key",
BCON_BIN (0, local_masterkey, local_masterkey_len),
"}");
/* Set up the key vault for this example. */
keyvault_client = mongoc_client_new (
"mongodb://localhost/?appname=client-side-encryption-keyvault");
keyvault_coll = mongoc_client_get_collection (
keyvault_client, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_collection_drop (keyvault_coll, NULL);
/* Create a unique index to ensure that two data keys cannot share the same
* keyAltName. This is recommended practice for the key vault. */
index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
index_name = mongoc_collection_keys_to_index_string (index_keys);
create_index_cmd = BCON_NEW ("createIndexes",
KEYVAULT_COLL,
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (index_keys),
"name",
index_name,
"unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}",
"}",
"]");
ret = mongoc_client_command_simple (keyvault_client,
KEYVAULT_DB,
create_index_cmd,
NULL /* read prefs */,
NULL /* reply */,
&error);
if (!ret) {
goto fail;
}
auto_encryption_opts = mongoc_auto_encryption_opts_new ();
mongoc_auto_encryption_opts_set_keyvault_client (auto_encryption_opts,
keyvault_client);
mongoc_auto_encryption_opts_set_keyvault_namespace (
auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
kms_providers);
schema = create_schema (
kms_providers, KEYVAULT_DB, KEYVAULT_COLL, keyvault_client, &error);
if (!schema) {
goto fail;
}
client =
mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
ret = mongoc_client_enable_auto_encryption (
client, auto_encryption_opts, &error);
if (!ret) {
goto fail;
}
coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);
/* Clear old data */
mongoc_collection_drop (coll, NULL);
/* Create the collection with the encryption JSON Schema. */
create_cmd = BCON_NEW ("create",
ENCRYPTED_COLL,
"validator",
"{",
"$jsonSchema",
BCON_DOCUMENT (schema),
"}");
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_wmajority (wc, 0);
create_cmd_opts = bson_new ();
mongoc_write_concern_append (wc, create_cmd_opts);
ret = mongoc_client_command_with_opts (client,
ENCRYPTED_DB,
create_cmd,
NULL /* read prefs */,
create_cmd_opts,
NULL /* reply */,
&error);
if (!ret) {
goto fail;
}
to_insert = BCON_NEW ("encryptedField", "123456789");
ret = mongoc_collection_insert_one (
coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
if (!ret) {
goto fail;
}
printf ("decrypted document: ");
if (!print_one_document (coll, &error)) {
goto fail;
}
printf ("\n");
unencrypted_client = mongoc_client_new (
"mongodb://localhost/?appname=client-side-encryption-unencrypted");
unencrypted_coll = mongoc_client_get_collection (
unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);
printf ("encrypted document: ");
if (!print_one_document (unencrypted_coll, &error)) {
goto fail;
}
printf ("\n");
/* Expect a server-side error if inserting with the unencrypted collection.
*/
ret = mongoc_collection_insert_one (
unencrypted_coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
if (!ret) {
printf ("insert with unencrypted collection failed: %s\n", error.message);
memset (&error, 0, sizeof (error));
}
exit_status = EXIT_SUCCESS;
fail:
if (error.code) {
fprintf (stderr, "error: %s\n", error.message);
}
bson_free (local_masterkey);
bson_destroy (kms_providers);
mongoc_collection_destroy (keyvault_coll);
bson_destroy (index_keys);
bson_free (index_name);
bson_destroy (create_index_cmd);
bson_json_reader_destroy (reader);
mongoc_auto_encryption_opts_destroy (auto_encryption_opts);
mongoc_collection_destroy (coll);
mongoc_client_destroy (client);
bson_destroy (to_insert);
mongoc_collection_destroy (unencrypted_coll);
mongoc_client_destroy (unencrypted_client);
mongoc_client_destroy (keyvault_client);
bson_destroy (schema);
bson_destroy (create_cmd);
bson_destroy (create_cmd_opts);
mongoc_write_concern_destroy (wc);
mongoc_cleanup ();
return exit_status;
}
Explicit Encryption
Explicit encryption is a MongoDB community feature and does not use the mongocryptd
process. Explicit encryption is provided by the mongoc_client_encryption_t class, for
example:
client-side-encryption-explicit.c
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include "client-side-encryption-helpers.h"
/* This example demonstrates how to use explicit encryption and decryption using
* the community version of MongoDB */
int
main (int argc, char **argv)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"
int exit_status = EXIT_FAILURE;
bool ret;
uint8_t *local_masterkey = NULL;
uint32_t local_masterkey_len;
bson_t *kms_providers = NULL;
bson_error_t error = {0};
bson_t *index_keys = NULL;
char *index_name = NULL;
bson_t *create_index_cmd = NULL;
bson_t *schema = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *coll = NULL;
mongoc_collection_t *keyvault_coll = NULL;
bson_t *to_insert = NULL;
bson_t *create_cmd = NULL;
bson_t *create_cmd_opts = NULL;
mongoc_write_concern_t *wc = NULL;
mongoc_client_encryption_t *client_encryption = NULL;
mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
char *keyaltnames[] = {"mongoc_encryption_example_3"};
bson_value_t datakey_id = {0};
bson_value_t encrypted_field = {0};
bson_value_t to_encrypt = {0};
mongoc_client_encryption_encrypt_opts_t *encrypt_opts = NULL;
bson_value_t decrypted = {0};
mongoc_init ();
/* Configure the master key. This must be the same master key that was used
* to create the encryption key. */
local_masterkey =
hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
if (!local_masterkey || local_masterkey_len != 96) {
fprintf (stderr,
"Specify LOCAL_MASTERKEY environment variable as a "
"secure random 96 byte hex value.\n");
goto fail;
}
kms_providers = BCON_NEW ("local",
"{",
"key",
BCON_BIN (0, local_masterkey, local_masterkey_len),
"}");
/* The mongoc_client_t used to read/write application data. */
client =
mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);
/* Clear old data */
mongoc_collection_drop (coll, NULL);
/* Set up the key vault for this example. */
keyvault_coll =
mongoc_client_get_collection (client, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_collection_drop (keyvault_coll, NULL);
/* Create a unique index to ensure that two data keys cannot share the same
* keyAltName. This is recommended practice for the key vault. */
index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
index_name = mongoc_collection_keys_to_index_string (index_keys);
create_index_cmd = BCON_NEW ("createIndexes",
KEYVAULT_COLL,
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (index_keys),
"name",
index_name,
"unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}",
"}",
"]");
ret = mongoc_client_command_simple (client,
KEYVAULT_DB,
create_index_cmd,
NULL /* read prefs */,
NULL /* reply */,
&error);
if (!ret) {
goto fail;
}
client_encryption_opts = mongoc_client_encryption_opts_new ();
mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
kms_providers);
mongoc_client_encryption_opts_set_keyvault_namespace (
client_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
/* Set a mongoc_client_t to use for reading/writing to the key vault. This
* can be the same mongoc_client_t used by the main application. */
mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
client);
client_encryption =
mongoc_client_encryption_new (client_encryption_opts, &error);
if (!client_encryption) {
goto fail;
}
/* Create a new data key for the encryptedField.
* https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
*/
datakey_opts = mongoc_client_encryption_datakey_opts_new ();
mongoc_client_encryption_datakey_opts_set_keyaltnames (
datakey_opts, keyaltnames, 1);
if (!mongoc_client_encryption_create_datakey (
client_encryption, "local", datakey_opts, &datakey_id, &error)) {
goto fail;
}
/* Explicitly encrypt a field */
encrypt_opts = mongoc_client_encryption_encrypt_opts_new ();
mongoc_client_encryption_encrypt_opts_set_algorithm (
encrypt_opts, MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC);
mongoc_client_encryption_encrypt_opts_set_keyid (encrypt_opts, &datakey_id);
to_encrypt.value_type = BSON_TYPE_UTF8;
to_encrypt.value.v_utf8.str = "123456789";
to_encrypt.value.v_utf8.len = strlen (to_encrypt.value.v_utf8.str);
ret = mongoc_client_encryption_encrypt (
client_encryption, &to_encrypt, encrypt_opts, &encrypted_field, &error);
if (!ret) {
goto fail;
}
to_insert = bson_new ();
BSON_APPEND_VALUE (to_insert, "encryptedField", &encrypted_field);
ret = mongoc_collection_insert_one (
coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
if (!ret) {
goto fail;
}
printf ("encrypted document: ");
if (!print_one_document (coll, &error)) {
goto fail;
}
printf ("\n");
/* Explicitly decrypt a field */
ret = mongoc_client_encryption_decrypt (
client_encryption, &encrypted_field, &decrypted, &error);
if (!ret) {
goto fail;
}
printf ("decrypted value: %s\n", decrypted.value.v_utf8.str);
exit_status = EXIT_SUCCESS;
fail:
if (error.code) {
fprintf (stderr, "error: %s\n", error.message);
}
bson_free (local_masterkey);
bson_destroy (kms_providers);
mongoc_collection_destroy (keyvault_coll);
bson_destroy (index_keys);
bson_free (index_name);
bson_destroy (create_index_cmd);
mongoc_collection_destroy (coll);
mongoc_client_destroy (client);
bson_destroy (to_insert);
bson_destroy (schema);
bson_destroy (create_cmd);
bson_destroy (create_cmd_opts);
mongoc_write_concern_destroy (wc);
mongoc_client_encryption_destroy (client_encryption);
mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
mongoc_client_encryption_opts_destroy (client_encryption_opts);
bson_value_destroy (&encrypted_field);
mongoc_client_encryption_encrypt_opts_destroy (encrypt_opts);
bson_value_destroy (&decrypted);
bson_value_destroy (&datakey_id);
mongoc_cleanup ();
return exit_status;
}
Explicit Encryption with Automatic Decryption
Although automatic encryption requires MongoDB 4.2 enterprise or a MongoDB 4.2 Atlas
cluster, automatic decryption is supported for all users. To configure automatic
decryption without automatic encryption set bypass_auto_encryption=True in
mongoc_auto_encryption_opts_t:
client-side-encryption-auto-decryption.c
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include "client-side-encryption-helpers.h"
/* This example demonstrates how to set up automatic decryption without
* automatic encryption using the community version of MongoDB */
int
main (int argc, char **argv)
{
/* The collection used to store the encryption data keys. */
#define KEYVAULT_DB "encryption"
#define KEYVAULT_COLL "__libmongocTestKeyVault"
/* The collection used to store the encrypted documents in this example. */
#define ENCRYPTED_DB "test"
#define ENCRYPTED_COLL "coll"
int exit_status = EXIT_FAILURE;
bool ret;
uint8_t *local_masterkey = NULL;
uint32_t local_masterkey_len;
bson_t *kms_providers = NULL;
bson_error_t error = {0};
bson_t *index_keys = NULL;
char *index_name = NULL;
bson_t *create_index_cmd = NULL;
bson_t *schema = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *coll = NULL;
mongoc_collection_t *keyvault_coll = NULL;
bson_t *to_insert = NULL;
bson_t *create_cmd = NULL;
bson_t *create_cmd_opts = NULL;
mongoc_write_concern_t *wc = NULL;
mongoc_client_encryption_t *client_encryption = NULL;
mongoc_client_encryption_opts_t *client_encryption_opts = NULL;
mongoc_client_encryption_datakey_opts_t *datakey_opts = NULL;
char *keyaltnames[] = {"mongoc_encryption_example_4"};
bson_value_t datakey_id = {0};
bson_value_t encrypted_field = {0};
bson_value_t to_encrypt = {0};
mongoc_client_encryption_encrypt_opts_t *encrypt_opts = NULL;
bson_value_t decrypted = {0};
mongoc_auto_encryption_opts_t *auto_encryption_opts = NULL;
mongoc_client_t *unencrypted_client = NULL;
mongoc_collection_t *unencrypted_coll = NULL;
mongoc_init ();
/* Configure the master key. This must be the same master key that was used
* to create the encryption key. */
local_masterkey =
hex_to_bin (getenv ("LOCAL_MASTERKEY"), &local_masterkey_len);
if (!local_masterkey || local_masterkey_len != 96) {
fprintf (stderr,
"Specify LOCAL_MASTERKEY environment variable as a "
"secure random 96 byte hex value.\n");
goto fail;
}
kms_providers = BCON_NEW ("local",
"{",
"key",
BCON_BIN (0, local_masterkey, local_masterkey_len),
"}");
client =
mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
auto_encryption_opts = mongoc_auto_encryption_opts_new ();
mongoc_auto_encryption_opts_set_keyvault_namespace (
auto_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_auto_encryption_opts_set_kms_providers (auto_encryption_opts,
kms_providers);
/* Setting bypass_auto_encryption to true disables automatic encryption but
* keeps the automatic decryption behavior. bypass_auto_encryption will also
* disable spawning mongocryptd */
mongoc_auto_encryption_opts_set_bypass_auto_encryption (auto_encryption_opts,
true);
/* Once bypass_auto_encryption is set, community users can enable auto
* encryption on the client. This will, in fact, only perform automatic
* decryption. */
ret = mongoc_client_enable_auto_encryption (
client, auto_encryption_opts, &error);
if (!ret) {
goto fail;
}
/* Now that automatic decryption is on, we can test it by inserting a
* document with an explicitly encrypted value into the collection. When we
* look up the document later, it should be automatically decrypted for us.
*/
coll = mongoc_client_get_collection (client, ENCRYPTED_DB, ENCRYPTED_COLL);
/* Clear old data */
mongoc_collection_drop (coll, NULL);
/* Set up the key vault for this example. */
keyvault_coll =
mongoc_client_get_collection (client, KEYVAULT_DB, KEYVAULT_COLL);
mongoc_collection_drop (keyvault_coll, NULL);
/* Create a unique index to ensure that two data keys cannot share the same
* keyAltName. This is recommended practice for the key vault. */
index_keys = BCON_NEW ("keyAltNames", BCON_INT32 (1));
index_name = mongoc_collection_keys_to_index_string (index_keys);
create_index_cmd = BCON_NEW ("createIndexes",
KEYVAULT_COLL,
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (index_keys),
"name",
index_name,
"unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}",
"}",
"]");
ret = mongoc_client_command_simple (client,
KEYVAULT_DB,
create_index_cmd,
NULL /* read prefs */,
NULL /* reply */,
&error);
if (!ret) {
goto fail;
}
client_encryption_opts = mongoc_client_encryption_opts_new ();
mongoc_client_encryption_opts_set_kms_providers (client_encryption_opts,
kms_providers);
mongoc_client_encryption_opts_set_keyvault_namespace (
client_encryption_opts, KEYVAULT_DB, KEYVAULT_COLL);
/* The key vault client is used for reading to/from the key vault. This can
* be the same mongoc_client_t used by the application. */
mongoc_client_encryption_opts_set_keyvault_client (client_encryption_opts,
client);
client_encryption =
mongoc_client_encryption_new (client_encryption_opts, &error);
if (!client_encryption) {
goto fail;
}
/* Create a new data key for the encryptedField.
* https://dochub.mongodb.org/core/client-side-field-level-encryption-automatic-encryption-rules
*/
datakey_opts = mongoc_client_encryption_datakey_opts_new ();
mongoc_client_encryption_datakey_opts_set_keyaltnames (
datakey_opts, keyaltnames, 1);
ret = mongoc_client_encryption_create_datakey (
client_encryption, "local", datakey_opts, &datakey_id, &error);
if (!ret) {
goto fail;
}
/* Explicitly encrypt a field. */
encrypt_opts = mongoc_client_encryption_encrypt_opts_new ();
mongoc_client_encryption_encrypt_opts_set_algorithm (
encrypt_opts, MONGOC_AEAD_AES_256_CBC_HMAC_SHA_512_DETERMINISTIC);
mongoc_client_encryption_encrypt_opts_set_keyaltname (
encrypt_opts, "mongoc_encryption_example_4");
to_encrypt.value_type = BSON_TYPE_UTF8;
to_encrypt.value.v_utf8.str = "123456789";
to_encrypt.value.v_utf8.len = strlen (to_encrypt.value.v_utf8.str);
ret = mongoc_client_encryption_encrypt (
client_encryption, &to_encrypt, encrypt_opts, &encrypted_field, &error);
if (!ret) {
goto fail;
}
to_insert = bson_new ();
BSON_APPEND_VALUE (to_insert, "encryptedField", &encrypted_field);
ret = mongoc_collection_insert_one (
coll, to_insert, NULL /* opts */, NULL /* reply */, &error);
if (!ret) {
goto fail;
}
/* When we retrieve the document, any encrypted fields will get automatically
* decrypted by the driver. */
printf ("decrypted document: ");
if (!print_one_document (coll, &error)) {
goto fail;
}
printf ("\n");
unencrypted_client =
mongoc_client_new ("mongodb://localhost/?appname=client-side-encryption");
unencrypted_coll = mongoc_client_get_collection (
unencrypted_client, ENCRYPTED_DB, ENCRYPTED_COLL);
printf ("encrypted document: ");
if (!print_one_document (unencrypted_coll, &error)) {
goto fail;
}
printf ("\n");
exit_status = EXIT_SUCCESS;
fail:
if (error.code) {
fprintf (stderr, "error: %s\n", error.message);
}
bson_free (local_masterkey);
bson_destroy (kms_providers);
mongoc_collection_destroy (keyvault_coll);
bson_destroy (index_keys);
bson_free (index_name);
bson_destroy (create_index_cmd);
mongoc_collection_destroy (coll);
mongoc_client_destroy (client);
bson_destroy (to_insert);
bson_destroy (schema);
bson_destroy (create_cmd);
bson_destroy (create_cmd_opts);
mongoc_write_concern_destroy (wc);
mongoc_client_encryption_destroy (client_encryption);
mongoc_client_encryption_datakey_opts_destroy (datakey_opts);
mongoc_client_encryption_opts_destroy (client_encryption_opts);
bson_value_destroy (&encrypted_field);
mongoc_client_encryption_encrypt_opts_destroy (encrypt_opts);
bson_value_destroy (&decrypted);
bson_value_destroy (&datakey_id);
mongoc_collection_destroy (unencrypted_coll);
mongoc_client_destroy (unencrypted_client);
mongoc_auto_encryption_opts_destroy (auto_encryption_opts);
mongoc_cleanup ();
return exit_status;
}
API Reference
Initialization and cleanup
Synopsis
Initialize the MongoDB C Driver by calling mongoc_init() exactly once at the beginning of
your program. It is responsible for initializing global state such as process counters,
SSL, and threading primitives.
Exception to this is mongoc_log_set_handler(), which should be called before mongoc_init()
or some log traces would not use your log handling function. See Custom Log Handlers for a
detailed example.
Call mongoc_cleanup() exactly once at the end of your program to release all memory and
other resources allocated by the driver. You must not call any other MongoDB C Driver
functions after mongoc_cleanup(). Note that mongoc_init() does not reinitialize the driver
after mongoc_cleanup().
Deprecated feature: automatic initialization and cleanup
On some platforms the driver can automatically call mongoc_init() before main, and call
mongoc_cleanup() as the process exits. This is problematic in situations where related
libraries also execute cleanup code on shutdown, and it creates inconsistent rules across
platforms. Therefore the automatic initialization and cleanup feature is deprecated, and
will be dropped in version 2.0. Meanwhile, for backward compatibility, the feature is
enabled by default on platforms where it is available.
For portable, future-proof code, always call mongoc_init() and mongoc_cleanup() yourself,
and configure the driver like:
cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF
Logging
MongoDB C driver Logging Abstraction
Synopsis
typedef enum {
MONGOC_LOG_LEVEL_ERROR,
MONGOC_LOG_LEVEL_CRITICAL,
MONGOC_LOG_LEVEL_WARNING,
MONGOC_LOG_LEVEL_MESSAGE,
MONGOC_LOG_LEVEL_INFO,
MONGOC_LOG_LEVEL_DEBUG,
MONGOC_LOG_LEVEL_TRACE,
} mongoc_log_level_t;
#define MONGOC_ERROR(...)
#define MONGOC_CRITICAL(...)
#define MONGOC_WARNING(...)
#define MONGOC_MESSAGE(...)
#define MONGOC_INFO(...)
#define MONGOC_DEBUG(...)
typedef void (*mongoc_log_func_t) (mongoc_log_level_t log_level,
const char *log_domain,
const char *message,
void *user_data);
void
mongoc_log_set_handler (mongoc_log_func_t log_func, void *user_data);
void
mongoc_log (mongoc_log_level_t log_level,
const char *log_domain,
const char *format,
...) BSON_GNUC_PRINTF (3, 4);
const char *
mongoc_log_level_str (mongoc_log_level_t log_level);
void
mongoc_log_default_handler (mongoc_log_level_t log_level,
const char *log_domain,
const char *message,
void *user_data);
void
mongoc_log_trace_enable (void);
void
mongoc_log_trace_disable (void);
The MongoDB C driver comes with an abstraction for logging that you can use in your
application, or integrate with an existing logging system.
Macros
To make logging a little less painful, various helper macros are provided. See the
following example.
#undef MONGOC_LOG_DOMAIN
#define MONGOC_LOG_DOMAIN "my-custom-domain"
MONGOC_WARNING ("An error occurred: %s", strerror (errno));
Custom Log Handlers
The default log handler prints a timestamp and the log message to stdout, or to stderr for
warnings, critical messages, and errors.
You can override the handler with mongoc_log_set_handler(). Your handler function
is called in a mutex for thread safety.
For example, you could register a custom handler to suppress messages at INFO level and
below:
void
my_logger (mongoc_log_level_t log_level,
const char *log_domain,
const char *message,
void *user_data)
{
/* smaller values are more important */
if (log_level < MONGOC_LOG_LEVEL_INFO) {
mongoc_log_default_handler (log_level, log_domain, message, user_data);
}
}
int
main (int argc, char *argv[])
{
mongoc_log_set_handler (my_logger, NULL);
mongoc_init ();
/* ... your code ... */
mongoc_cleanup ();
return 0;
}
Note that in the example above mongoc_log_set_handler() is called before mongoc_init().
Otherwise, some log traces could not be processed by the log handler.
To restore the default handler:
mongoc_log_set_handler (mongoc_log_default_handler, NULL);
Disable logging
To disable all logging, including warnings, critical messages and errors, provide an empty
log handler:
mongoc_log_set_handler (NULL, NULL);
Tracing
If compiling your own copy of the MongoDB C driver, consider configuring with
-DENABLE_TRACING=ON to enable function tracing and hex dumps of network packets to STDERR
and STDOUT during development and debugging.
This is especially useful when debugging what may be going on internally in the driver.
Trace messages can be enabled and disabled by calling mongoc_log_trace_enable() and
mongoc_log_trace_disable()
NOTE:
Compiling the driver with -DENABLE_TRACING=ON will affect its performance. Disabling
tracing with mongoc_log_trace_disable() significantly reduces the overhead, but cannot
remove it completely.
« libmongoc
Error Reporting
Description
Many C Driver functions report errors by returning false or -1 and filling out a
bson_error_t structure with an error domain, error code, and message. Use domain to
determine which subsystem generated the error, and code for the specific error. message is
a human-readable error description.
SEE ALSO:
Handling Errors in libbson.
┌────────────────────────────────────┬──────────────────────────────────────────────┬────────────────────────────────────────────┐
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_CLIENT │ MONGOC_ERROR_CLIENT_TOO_BIG │ You tried to send a │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_AUTHENTICATE │ Wrong credentials, or │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_NO_ACCEPTABLE_PEER │ You tried an TLS │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_IN_EXHAUST │ You began iterating an │
│ │ │ mongoc_client_t. │
└────────────────────────────────────┴──────────────────────────────────────────────┴────────────────────────────────────────────┘
│ │ MONGOC_ERROR_CLIENT_SESSION_FAILURE │ Failure related to │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_INVALID_ENCRYPTION_ARG │ Failure related to │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_INVALID_ENCRYPTION_STATE │ Failure related to │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CLIENT_INVALID_LOAD_BALANCER │ You attempted to connect │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_STREAM │ MONGOC_ERROR_STREAM_NAME_RESOLUTION │ DNS failure. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_STREAM_SOCKET │ Timeout communicating │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_STREAM_CONNECT │ Failed to connect to │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_PROTOCOL │ MONGOC_ERROR_PROTOCOL_INVALID_REPLY │ Corrupt response from │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_PROTOCOL_BAD_WIRE_VERSION │ The server version is │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_CURSOR │ MONGOC_ERROR_CURSOR_INVALID_CURSOR │ You passed bad arguments │
│ │ │ mongoc_collection_find_with_opts(), │
│ │ │ mongoc_cursor_next() on │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_CHANGE_STREAM_NO_RESUME_TOKEN │ A resume token was not returned in │
│ │ │ mongoc_change_stream_next() │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_QUERY │ MONGOC_ERROR_QUERY_FAILURE │ Error API Version 1: Server error │
│ │ │ error message is in message. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SERVER │ MONGOC_ERROR_QUERY_FAILURE │ Error API Version 2: Server error │
│ │ │ error message is in message. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SASL │ A SASL error code. │ man sasl_errors for a list of │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_BSON │ MONGOC_ERROR_BSON_INVALID │ You passed an invalid or oversized │
│ │ │ mongoc_collection_create_index() │
└────────────────────────────────────┴──────────────────────────────────────────────┴────────────────────────────────────────────┘
│MONGOC_ERROR_NAMESPACE │ MONGOC_ERROR_NAMESPACE_INVALID │ You tried to create a collection │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_COMMAND │ MONGOC_ERROR_COMMAND_INVALID_ARG │ Many functions set this error code │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_PROTOCOL_BAD_WIRE_VERSION │ You tried to use a command option │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_DUPLICATE_KEY │ An insert or update failed because │
│ │ │ because of a duplicate _id or other │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_MAX_TIME_MS_EXPIRED │ The operation failed because │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_SERVER_SELECTION_INVALID_ID │ The serverId option for an │
│ │ │ session (denoted by the sessionId │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_COMMAND │ Error code from server. │ Error API Version 1: Server error │
│ │ │ message is in message. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SERVER │ Error code from server. │ Error API Version 2: Server error │
│ │ │ message is in message. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_COLLECTION │ MONGOC_ERROR_COLLECTION_INSERT_FAILED, │ Invalid or empty input to │
│ │ MONGOC_ERROR_COLLECTION_UPDATE_FAILED, │ mongoc_collection_insert_one(), │
│ │ MONGOC_ERROR_COLLECTION_DELETE_FAILED. │ mongoc_collection_insert_bulk(), │
│ │ │ mongoc_collection_update_one(), │
│ │ │ mongoc_collection_update_many(), │
│ │ │ mongoc_collection_replace_one(), │
│ │ │ mongoc_collection_delete_one(), or │
│ │ │ mongoc_collection_delete_many(). │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_COLLECTION │ Error code from server. │ Error API Version 1: Server error │
│ │ │ mongoc_collection_insert_one(), │
│ │ │ mongoc_collection_insert_bulk(), │
│ │ │ mongoc_collection_update_one(), │
│ │ │ mongoc_collection_update_many(), │
│ │ │ mongoc_collection_replace_one(), │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SERVER │ Error code from server. │ Error API Version 2: Server error │
│ │ │ mongoc_collection_insert_one(), │
│ │ │ mongoc_collection_insert_bulk(), │
│ │ │ mongoc_collection_update_one(), │
│ │ │ mongoc_collection_update_many(), │
│ │ │ mongoc_collection_replace_one(), │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_GRIDFS │ MONGOC_ERROR_GRIDFS_CHUNK_MISSING │ The GridFS file is missing a │
│ │ │ document in its chunks collection. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_GRIDFS_CORRUPT │ A data inconsistency was detected │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_GRIDFS_INVALID_FILENAME │ You passed a NULL filename to │
│ │ │ mongoc_gridfs_remove_by_filename(). │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_GRIDFS_PROTOCOL_ERROR │ You called │
│ │ │ mongoc_gridfs_file_set_id() after │
│ │ │ mongoc_gridfs_file_save(), or tried │
└────────────────────────────────────┴──────────────────────────────────────────────┴────────────────────────────────────────────┘
│ │ MONGOC_ERROR_GRIDFS_BUCKET_FILE_NOT_FOUND │ A GridFS file is missing from files │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│ │ MONGOC_ERROR_GRIDFS_BUCKET_STREAM │ An error occurred on a stream │
│ │ │ mongoc_gridfs_bucket_upload_from_stream(). │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SCRAM │ MONGOC_ERROR_SCRAM_PROTOCOL_ERROR │ Failure in SCRAM-SHA-1 authentication. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_SERVER_SELECTION │ MONGOC_ERROR_SERVER_SELECTION_FAILURE │ No replica set member or mongos is │
│ │ │ available, or none matches your read │
│ │ │ preference, or you supplied an invalid │
│ │ │ mongoc_read_prefs_t. │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_WRITE_CONCERN │ Error code from server. │ There was a write concern error or timeout │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_TRANSACTION │ MONGOC_ERROR_TRANSACTION_INVALID │ You attempted to start a transaction when │
├────────────────────────────────────┼──────────────────────────────────────────────┼────────────────────────────────────────────┤
│MONGOC_ERROR_CLIENT_SIDE_ENCRYPTION │ Error code produced by libmongocrypt. │ An error occurred in the library │
└────────────────────────────────────┴──────────────────────────────────────────────┴────────────────────────────────────────────┘
Error Labels
In some cases your application must make decisions based on what category of error the
driver has returned, but these categories do not correspond perfectly to an error domain
or code. In such cases, error labels provide a reliable way to determine how your
application should respond to an error.
Any C Driver function that has a bson_t out-parameter named reply may include error labels
to the reply, in the form of a BSON field named "errorLabels" containing an array of
strings:
{ "errorLabels": [ "TransientTransactionError" ] }
Use mongoc_error_has_label() to test if a reply contains a specific label. See
mongoc_client_session_start_transaction() for example code that demonstrates the use of
error labels in application logic.
The following error labels are currently defined. Future versions of MongoDB may introduce
new labels.
TransientTransactionError
Within a multi-document transaction, certain errors can leave the transaction in an
unknown or aborted state. These include write conflicts, primary stepdowns, and network
errors. In response, the application should abort the transaction and try the same
sequence of operations again in a new transaction.
UnknownTransactionCommitResult
When mongoc_client_session_commit_transaction() encounters a network error or certain
server errors, it is not known whether the transaction was committed. Applications should
attempt to commit the transaction again until: the commit succeeds, the commit fails with
an error not labeled "UnknownTransactionCommitResult", or the application chooses to give
up.
Setting the Error API Version
The driver's error reporting began with a design flaw: when the error domain is
MONGOC_ERROR_COLLECTION, MONGOC_ERROR_QUERY, or MONGOC_ERROR_COMMAND, the error code might
originate from the server or the driver. An application cannot always know where an error
originated, and therefore cannot tell what the code means.
For example, if mongoc_collection_update_one() sets the error's domain to
MONGOC_ERROR_COLLECTION and its code to 24, the application cannot know whether 24 is the
generic driver error code MONGOC_ERROR_COLLECTION_UPDATE_FAILED or the specific server
error code "LockTimeout".
To fix this flaw while preserving backward compatibility, the C Driver 1.4 introduces
"Error API Versions". Version 1, the default Error API Version, maintains the flawed
behavior. Version 2 adds a new error domain, MONGOC_ERROR_SERVER. In Version 2, error
codes originating on the server always have error domain MONGOC_ERROR_SERVER or
MONGOC_ERROR_WRITE_CONCERN. When the driver uses Version 2 the application can always
determine the origin and meaning of error codes. New applications should use Version 2,
and existing applications should be updated to use Version 2 as well.
┌──────────────────────────────────────────────┬────────────────────────────┬────────────────────────────┐
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│mongoc_cursor_error() │ MONGOC_ERROR_QUERY │ MONGOC_ERROR_SERVER │
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│mongoc_client_command_with_opts(), │ MONGOC_ERROR_QUERY │ MONGOC_ERROR_SERVER │
│mongoc_database_command_with_opts(), │ │ │
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│mongoc_collection_count_with_opts() │ MONGOC_ERROR_QUERY │ MONGOC_ERROR_SERVER │
│mongoc_client_get_database_names_with_opts(), │ │ │
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│mongoc_collection_insert_one() │ MONGOC_ERROR_COMMAND │ MONGOC_ERROR_SERVER │
│mongoc_collection_insert_bulk() │ │ │
│mongoc_collection_update_one() │ │ │
│mongoc_collection_update_many() │ │ │
│mongoc_collection_replace_one() │ │ │
│mongoc_collection_delete_one() │ │ │
│mongoc_collection_delete_many() │ │ │
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│mongoc_bulk_operation_execute() │ MONGOC_ERROR_COMMAND │ MONGOC_ERROR_SERVER │
├──────────────────────────────────────────────┼────────────────────────────┼────────────────────────────┤
│Write-concern timeout │ MONGOC_ERROR_WRITE_CONCERN │ MONGOC_ERROR_WRITE_CONCERN │
└──────────────────────────────────────────────┴────────────────────────────┴────────────────────────────┘
The Error API Versions are defined with MONGOC_ERROR_API_VERSION_LEGACY and
MONGOC_ERROR_API_VERSION_2. Set the version with mongoc_client_set_error_api() or
mongoc_client_pool_set_error_api().
SEE ALSO:
MongoDB Server Error Codes
Object Lifecycle
This page documents the order of creation and destruction for libmongoc's main struct
types.
Clients and pools
Call mongoc_init() once, before calling any other libmongoc functions, and call
mongoc_cleanup() once before your program exits.
A program that uses libmongoc from multiple threads should create a mongoc_client_pool_t
with mongoc_client_pool_new(). Each thread acquires a mongoc_client_t from the pool with
mongoc_client_pool_pop() and returns it with mongoc_client_pool_push() when the thread is
finished using it. To destroy the pool, first return all clients, then call
mongoc_client_pool_destroy().
If your program uses libmongoc from only one thread, create a mongoc_client_t directly
with mongoc_client_new() or mongoc_client_new_from_uri(). Destroy it with
mongoc_client_destroy().
Databases, collections, and related objects
You can create a mongoc_database_t or mongoc_collection_t from a mongoc_client_t, and
create a mongoc_cursor_t or mongoc_bulk_operation_t from a mongoc_collection_t.
Each of these objects must be destroyed before the client they were created from, but
their lifetimes are otherwise independent.
GridFS objects
You can create a mongoc_gridfs_t from a mongoc_client_t, create a mongoc_gridfs_file_t or
mongoc_gridfs_file_list_t from a mongoc_gridfs_t, create a mongoc_gridfs_file_t from a
mongoc_gridfs_file_list_t, and create a mongoc_stream_t from a mongoc_gridfs_file_t.
Each of these objects depends on the object it was created from. Always destroy GridFS
objects in the reverse of the order they were created. The sole exception is that a
mongoc_gridfs_file_t need not be destroyed before the mongoc_gridfs_file_list_t it was
created from.
GridFS bucket objects
Create mongoc_gridfs_bucket_t with a mongoc_database_t derived from a mongoc_client_t. The
mongoc_database_t is independent from the mongoc_gridfs_bucket_t. But the mongoc_client_t
must outlive the mongoc_gridfs_bucket_t.
A mongoc_stream_t may be created from the mongoc_gridfs_bucket_t. The
mongoc_gridfs_bucket_t must outlive the mongoc_stream_t.
Sessions
Start a session with mongoc_client_start_session(), use the session for a sequence of
operations and multi-document transactions, then free it with
mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a
session must be destroyed before the session, and a session must be destroyed before the
mongoc_client_t it came from.
By default, sessions are causally consistent. To disable causal consistency, before
starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call
mongoc_session_opts_set_causal_consistency(), then free the struct with
mongoc_session_opts_destroy().
Unacknowledged writes are prohibited with sessions.
A mongoc_client_session_t must be used by only one thread at a time. Due to session
pooling, mongoc_client_start_session() may return a session that has been idle for some
time and is about to be closed after its idle timeout. Use the session within one minute
of acquiring it to refresh the session and avoid a timeout.
Client Side Encryption
When configuring a mongoc_client_t for automatic encryption via
mongoc_client_enable_auto_encryption(), if a separate key vault client is set in the
options (via mongoc_auto_encryption_opts_set_keyvault_client()) the key vault client must
outlive the encrypted client.
When configuring a mongoc_client_pool_t for automatic encryption via
mongoc_client_pool_enable_auto_encryption(), if a separate key vault client pool is set in
the options (via mongoc_auto_encryption_opts_set_keyvault_client_pool()) the key vault
client pool must outlive the encrypted client pool.
When creating a mongoc_client_encryption_t, the configured key vault client (set via
mongoc_client_encryption_opts_set_keyvault_client()) must outlive the
mongoc_client_encryption_t.
GridFS
The C driver includes two APIs for GridFS.
The older API consists of mongoc_gridfs_t and its derivatives. It contains deprecated API,
does not support read preferences, and is not recommended in new applications. It does not
conform to the MongoDB GridFS specification.
The newer API consists of mongoc_gridfs_bucket_t and allows uploading/downloading through
derived mongoc_stream_t objects. It conforms to the MongoDB GridFS specification.
There is not always a straightforward upgrade path from an application built with
mongoc_gridfs_t to mongoc_gridfs_bucket_t (e.g. a mongoc_gridfs_file_t provides functions
to seek but mongoc_stream_t does not). But users are encouraged to upgrade when possible.
mongoc_auto_encryption_opts_t
Options for enabling automatic encryption and decryption for Client-Side Field Level
Encryption.
Synopsis
typedef struct _mongoc_auto_encryption_opts_t mongoc_auto_encryption_opts_t;
SEE ALSO:
The guide for Using Client-Side Field Level Encryption
mongoc_bulk_operation_t
Bulk Write Operations
Synopsis
typedef struct _mongoc_bulk_operation_t mongoc_bulk_operation_t;
The opaque type mongoc_bulk_operation_t provides an abstraction for submitting multiple
write operations as a single batch.
After adding all of the write operations to the mongoc_bulk_operation_t, call
mongoc_bulk_operation_execute() to execute the operation.
WARNING:
It is only valid to call mongoc_bulk_operation_execute() once. The
mongoc_bulk_operation_t must be destroyed afterwards.
SEE ALSO:
Bulk Write Operations
mongoc_change_stream_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_change_stream_t mongoc_change_stream_t;
mongoc_change_stream_t is a handle to a change stream. A collection change stream can be
obtained using mongoc_collection_watch().
It is recommended to use a mongoc_change_stream_t and its functions instead of a raw
aggregation with a $changeStream stage. For more information see the MongoDB Manual Entry
on Change Streams.
Example
example-collection-watch.c
#include <mongoc/mongoc.h>
int
main ()
{
bson_t empty = BSON_INITIALIZER;
const bson_t *doc;
bson_t *to_insert = BCON_NEW ("x", BCON_INT32 (1));
const bson_t *err_doc;
bson_error_t error;
const char *uri_string;
mongoc_uri_t *uri;
mongoc_client_t *client;
mongoc_collection_t *coll;
mongoc_change_stream_t *stream;
mongoc_write_concern_t *wc = mongoc_write_concern_new ();
bson_t opts = BSON_INITIALIZER;
bool r;
mongoc_init ();
uri_string = "mongodb://"
"localhost:27017,localhost:27018,localhost:"
"27019/db?replicaSet=rs0";
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
coll = mongoc_client_get_collection (client, "db", "coll");
stream = mongoc_collection_watch (coll, &empty, NULL);
mongoc_write_concern_set_wmajority (wc, 10000);
mongoc_write_concern_append (wc, &opts);
r = mongoc_collection_insert_one (coll, to_insert, &opts, NULL, &error);
if (!r) {
fprintf (stderr, "Error: %s\n", error.message);
return EXIT_FAILURE;
}
while (mongoc_change_stream_next (stream, &doc)) {
char *as_json = bson_as_relaxed_extended_json (doc, NULL);
fprintf (stderr, "Got document: %s\n", as_json);
bson_free (as_json);
}
if (mongoc_change_stream_error_document (stream, &error, &err_doc)) {
if (!bson_empty (err_doc)) {
fprintf (stderr,
"Server Error: %s\n",
bson_as_relaxed_extended_json (err_doc, NULL));
} else {
fprintf (stderr, "Client Error: %s\n", error.message);
}
return EXIT_FAILURE;
}
bson_destroy (to_insert);
mongoc_write_concern_destroy (wc);
bson_destroy (&opts);
mongoc_change_stream_destroy (stream);
mongoc_collection_destroy (coll);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Starting and Resuming
All watch functions accept several options to indicate where a change stream should start
returning changes from: resumeAfter, startAfter, and startAtOperationTime.
All changes returned by mongoc_change_stream_next() include a resume token in the _id
field. MongoDB 4.2 also includes an additional resume token in each "aggregate" and
"getMore" command response, which points to the end of that response's batch. The current
token is automatically cached by libmongoc. In the event of an error, libmongoc attempts
to recreate the change stream starting where it left off by passing the cached resume
token. libmongoc only attempts to resume once, but client applications can access the
cached resume token with mongoc_change_stream_get_resume_token() and use it for their own
resume logic by passing it as either the resumeAfter or startAfter option.
Additionally, change streams can start returning changes at an operation time by using the
startAtOperationTime field. This can be the timestamp returned in the operationTime field
of a command reply.
resumeAfter, startAfter, and startAtOperationTime are mutually exclusive options. Setting
more than one will result in a server error.
The following example implements custom resuming logic, persisting the resume token in a
file.
example-resume.c
#include <mongoc/mongoc.h>
/* An example implementation of custom resume logic in a change stream.
* example-resume starts a client-wide change stream and persists the resume
* token in a file "resume-token.json". On restart, if "resume-token.json"
* exists, the change stream starts watching after the persisted resume token.
*
* This behavior allows a user to exit example-resume, and restart it later
* without missing any change events.
*/
#include <unistd.h>
static const char *RESUME_TOKEN_PATH = "resume-token.json";
static bool
_save_resume_token (const bson_t *doc)
{
FILE *file_stream;
bson_iter_t iter;
bson_t resume_token_doc;
char *as_json = NULL;
size_t as_json_len;
ssize_t r, n_written;
const bson_value_t *resume_token;
if (!bson_iter_init_find (&iter, doc, "_id")) {
fprintf (stderr, "reply does not contain operationTime.");
return false;
}
resume_token = bson_iter_value (&iter);
/* store the resume token in a document, { resumeAfter: <resume token> }
* which we can later append easily. */
file_stream = fopen (RESUME_TOKEN_PATH, "w+");
if (!file_stream) {
fprintf (stderr, "failed to open %s for writing\n", RESUME_TOKEN_PATH);
return false;
}
bson_init (&resume_token_doc);
BSON_APPEND_VALUE (&resume_token_doc, "resumeAfter", resume_token);
as_json = bson_as_canonical_extended_json (&resume_token_doc, &as_json_len);
bson_destroy (&resume_token_doc);
n_written = 0;
while (n_written < as_json_len) {
r = fwrite ((void *) (as_json + n_written),
sizeof (char),
as_json_len - n_written,
file_stream);
if (r == -1) {
fprintf (stderr, "failed to write to %s\n", RESUME_TOKEN_PATH);
bson_free (as_json);
fclose (file_stream);
return false;
}
n_written += r;
}
bson_free (as_json);
fclose (file_stream);
return true;
}
bool
_load_resume_token (bson_t *opts)
{
bson_error_t error;
bson_json_reader_t *reader;
bson_t doc;
/* if the file does not exist, skip. */
if (-1 == access (RESUME_TOKEN_PATH, R_OK)) {
return true;
}
reader = bson_json_reader_new_from_file (RESUME_TOKEN_PATH, &error);
if (!reader) {
fprintf (stderr,
"failed to open %s for reading: %s\n",
RESUME_TOKEN_PATH,
error.message);
return false;
}
bson_init (&doc);
if (-1 == bson_json_reader_read (reader, &doc, &error)) {
fprintf (stderr, "failed to read doc from %s\n", RESUME_TOKEN_PATH);
bson_destroy (&doc);
bson_json_reader_destroy (reader);
return false;
}
printf ("found cached resume token in %s, resuming change stream.\n",
RESUME_TOKEN_PATH);
bson_concat (opts, &doc);
bson_destroy (&doc);
bson_json_reader_destroy (reader);
return true;
}
int
main ()
{
int exit_code = EXIT_FAILURE;
const char *uri_string;
mongoc_uri_t *uri = NULL;
bson_error_t error;
mongoc_client_t *client = NULL;
bson_t pipeline = BSON_INITIALIZER;
bson_t opts = BSON_INITIALIZER;
mongoc_change_stream_t *stream = NULL;
const bson_t *doc;
const int max_time = 30; /* max amount of time, in seconds, that
mongoc_change_stream_next can block. */
mongoc_init ();
uri_string = "mongodb://localhost:27017/db?replicaSet=rs0";
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
goto cleanup;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
goto cleanup;
}
if (!_load_resume_token (&opts)) {
goto cleanup;
}
BSON_APPEND_INT64 (&opts, "maxAwaitTimeMS", max_time * 1000);
printf ("listening for changes on the client (max %d seconds).\n", max_time);
stream = mongoc_client_watch (client, &pipeline, &opts);
while (mongoc_change_stream_next (stream, &doc)) {
char *as_json;
as_json = bson_as_canonical_extended_json (doc, NULL);
printf ("change received: %s\n", as_json);
bson_free (as_json);
if (!_save_resume_token (doc)) {
goto cleanup;
}
}
exit_code = EXIT_SUCCESS;
cleanup:
mongoc_uri_destroy (uri);
bson_destroy (&pipeline);
bson_destroy (&opts);
mongoc_change_stream_destroy (stream);
mongoc_client_destroy (client);
mongoc_cleanup ();
return exit_code;
}
The following example shows using startAtOperationTime to synchronize a change stream with
another operation.
example-start-at-optime.c
/* An example of starting a change stream with startAtOperationTime. */
#include <mongoc/mongoc.h>
int
main ()
{
int exit_code = EXIT_FAILURE;
const char *uri_string;
mongoc_uri_t *uri = NULL;
bson_error_t error;
mongoc_client_t *client = NULL;
mongoc_collection_t *coll = NULL;
bson_t pipeline = BSON_INITIALIZER;
bson_t opts = BSON_INITIALIZER;
mongoc_change_stream_t *stream = NULL;
bson_iter_t iter;
const bson_t *doc;
bson_value_t cached_operation_time = {0};
int i;
bool r;
mongoc_init ();
uri_string = "mongodb://localhost:27017/db?replicaSet=rs0";
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
goto cleanup;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
goto cleanup;
}
/* insert five documents. */
coll = mongoc_client_get_collection (client, "db", "coll");
for (i = 0; i < 5; i++) {
bson_t reply;
bson_t *insert_cmd = BCON_NEW ("insert",
"coll",
"documents",
"[",
"{",
"x",
BCON_INT64 (i),
"}",
"]");
r = mongoc_collection_write_command_with_opts (
coll, insert_cmd, NULL, &reply, &error);
bson_destroy (insert_cmd);
if (!r) {
bson_destroy (&reply);
fprintf (stderr, "failed to insert: %s\n", error.message);
goto cleanup;
}
if (i == 0) {
/* cache the operation time in the first reply. */
if (bson_iter_init_find (&iter, &reply, "operationTime")) {
bson_value_copy (bson_iter_value (&iter), &cached_operation_time);
} else {
fprintf (stderr, "reply does not contain operationTime.");
bson_destroy (&reply);
goto cleanup;
}
}
bson_destroy (&reply);
}
/* start a change stream at the first returned operationTime. */
BSON_APPEND_VALUE (&opts, "startAtOperationTime", &cached_operation_time);
stream = mongoc_collection_watch (coll, &pipeline, &opts);
/* since the change stream started at the operation time of the first
* insert, the five inserts are returned. */
printf ("listening for changes on db.coll:\n");
while (mongoc_change_stream_next (stream, &doc)) {
char *as_json;
as_json = bson_as_canonical_extended_json (doc, NULL);
printf ("change received: %s\n", as_json);
bson_free (as_json);
}
exit_code = EXIT_SUCCESS;
cleanup:
mongoc_uri_destroy (uri);
bson_destroy (&pipeline);
bson_destroy (&opts);
if (cached_operation_time.value_type) {
bson_value_destroy (&cached_operation_time);
}
mongoc_change_stream_destroy (stream);
mongoc_collection_destroy (coll);
mongoc_client_destroy (client);
mongoc_cleanup ();
return exit_code;
}
mongoc_client_encryption_t
Synopsis
typedef struct _mongoc_client_encryption_t mongoc_client_encryption_t;
mongoc_client_encryption_t provides utility functions for Client-Side Field Level
Encryption. See the guide for Using Client-Side Field Level Encryption.
Thread Safety
mongoc_client_encryption_t is NOT thread-safe and should only be used in the same thread
as the mongoc_client_t that is configured via
mongoc_client_encryption_opts_set_keyvault_client().
Lifecycle
The key vault client, configured via mongoc_client_encryption_opts_set_keyvault_client(),
must outlive the mongoc_client_encryption_t.
SEE ALSO:
mongoc_client_enable_auto_encryption()
mongoc_client_pool_enable_auto_encryption()
The guide for Using Client-Side Field Level Encryption for libmongoc
The MongoDB Manual for Client-Side Field Level Encryption
mongoc_client_encryption_datakey_opts_t
Synopsis
typedef struct _mongoc_client_encryption_datakey_opts_t mongoc_client_encryption_datakey_opts_t;
Used to set options for mongoc_client_encryption_create_datakey().
SEE ALSO:
mongoc_client_encryption_create_datakey()
mongoc_client_encryption_rewrap_many_datakey_result_t
Synopsis
typedef struct _mongoc_client_encryption_rewrap_many_datakey_result_t
mongoc_client_encryption_rewrap_many_datakey_result_t;
Used to access the result of mongoc_client_encryption_rewrap_many_datakey().
SEE ALSO:
mongoc_client_encryption_rewrap_many_datakey()
mongoc_client_encryption_encrypt_opts_t
Synopsis
typedef struct _mongoc_client_encryption_encrypt_opts_t mongoc_client_encryption_encrypt_opts_t;
Used to set options for mongoc_client_encryption_encrypt().
SEE ALSO:
mongoc_client_encryption_encrypt()
mongoc_client_encryption_opts_t
Synopsis
typedef struct _mongoc_client_encryption_opts_t mongoc_client_encryption_opts_t;
Used to set options for mongoc_client_encryption_new().
SEE ALSO:
mongoc_client_encryption_new()
mongoc_client_pool_t
A connection pool for multi-threaded programs. See Connection Pooling.
Synopsis
typedef struct _mongoc_client_pool_t mongoc_client_pool_t
mongoc_client_pool_t is the basis for multi-threading in the MongoDB C driver. Since
mongoc_client_t structures are not thread-safe, this structure is used to retrieve a new
mongoc_client_t for a given thread. This structure is thread-safe, except for its
destructor method, mongoc_client_pool_destroy(), which is not thread-safe and must only be
called from one thread.
Example
example-pool.c
/* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
* libmongoc-1.0) */
/* ./example-pool [CONNECTION_STRING] */
#include <mongoc/mongoc.h>
#include <pthread.h>
#include <stdio.h>
static pthread_mutex_t mutex;
static bool in_shutdown = false;
static void *
worker (void *data)
{
mongoc_client_pool_t *pool = data;
mongoc_client_t *client;
bson_t ping = BSON_INITIALIZER;
bson_error_t error;
bool r;
BSON_APPEND_INT32 (&ping, "ping", 1);
while (true) {
client = mongoc_client_pool_pop (pool);
/* Do something with client. If you are writing an HTTP server, you
* probably only want to hold onto the client for the portion of the
* request performing database queries.
*/
r = mongoc_client_command_simple (
client, "admin", &ping, NULL, NULL, &error);
if (!r) {
fprintf (stderr, "%s\n", error.message);
}
mongoc_client_pool_push (pool, client);
pthread_mutex_lock (&mutex);
if (in_shutdown || !r) {
pthread_mutex_unlock (&mutex);
break;
}
pthread_mutex_unlock (&mutex);
}
bson_destroy (&ping);
return NULL;
}
int
main (int argc, char *argv[])
{
const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
mongoc_uri_t *uri;
bson_error_t error;
mongoc_client_pool_t *pool;
pthread_t threads[10];
unsigned i;
void *ret;
pthread_mutex_init (&mutex, NULL);
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
pool = mongoc_client_pool_new (uri);
mongoc_client_pool_set_error_api (pool, 2);
for (i = 0; i < 10; i++) {
pthread_create (&threads[i], NULL, worker, pool);
}
sleep (10);
pthread_mutex_lock (&mutex);
in_shutdown = true;
pthread_mutex_unlock (&mutex);
for (i = 0; i < 10; i++) {
pthread_join (threads[i], &ret);
}
mongoc_client_pool_destroy (pool);
mongoc_uri_destroy (uri);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
mongoc_client_session_t
Use a session for a sequence of operations, optionally with causal consistency. See the
MongoDB Manual Entry for Causal Consistency.
Synopsis
Start a session with mongoc_client_start_session(), use the session for a sequence of
operations and multi-document transactions, then free it with
mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a
session must be destroyed before the session, and a session must be destroyed before the
mongoc_client_t it came from.
By default, sessions are causally consistent. To disable causal consistency, before
starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call
mongoc_session_opts_set_causal_consistency(), then free the struct with
mongoc_session_opts_destroy().
Unacknowledged writes are prohibited with sessions.
A mongoc_client_session_t must be used by only one thread at a time. Due to session
pooling, mongoc_client_start_session() may return a session that has been idle for some
time and is about to be closed after its idle timeout. Use the session within one minute
of acquiring it to refresh the session and avoid a timeout.
Example
example-session.c
/* gcc example-session.c -o example-session \
* $(pkg-config --cflags --libs libmongoc-1.0) */
/* ./example-session [CONNECTION_STRING] */
#include <stdio.h>
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
int exit_code = EXIT_FAILURE;
mongoc_client_t *client = NULL;
const char *uri_string = "mongodb://127.0.0.1/?appname=session-example";
mongoc_uri_t *uri = NULL;
mongoc_client_session_t *client_session = NULL;
mongoc_collection_t *collection = NULL;
bson_error_t error;
bson_t *selector = NULL;
bson_t *update = NULL;
bson_t *update_opts = NULL;
bson_t *find_opts = NULL;
mongoc_read_prefs_t *secondary = NULL;
mongoc_cursor_t *cursor = NULL;
const bson_t *doc;
char *str;
bool r;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
goto done;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
goto done;
}
mongoc_client_set_error_api (client, 2);
/* pass NULL for options - by default the session is causally consistent */
client_session = mongoc_client_start_session (client, NULL, &error);
if (!client_session) {
fprintf (stderr, "Failed to start session: %s\n", error.message);
goto done;
}
collection = mongoc_client_get_collection (client, "test", "collection");
selector = BCON_NEW ("_id", BCON_INT32 (1));
update = BCON_NEW ("$inc", "{", "x", BCON_INT32 (1), "}");
update_opts = bson_new ();
if (!mongoc_client_session_append (client_session, update_opts, &error)) {
fprintf (stderr, "Could not add session to opts: %s\n", error.message);
goto done;
}
r = mongoc_collection_update_one (
collection, selector, update, update_opts, NULL /* reply */, &error);
if (!r) {
fprintf (stderr, "Update failed: %s\n", error.message);
goto done;
}
bson_destroy (selector);
selector = BCON_NEW ("_id", BCON_INT32 (1));
secondary = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
find_opts = BCON_NEW ("maxTimeMS", BCON_INT32 (2000));
if (!mongoc_client_session_append (client_session, find_opts, &error)) {
fprintf (stderr, "Could not add session to opts: %s\n", error.message);
goto done;
};
/* read from secondary. since we're in a causally consistent session, the
* data is guaranteed to reflect the update we did on the primary. the query
* blocks waiting for the secondary to catch up, if necessary, or times out
* and fails after 2000 ms.
*/
cursor = mongoc_collection_find_with_opts (
collection, selector, find_opts, secondary);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_json (doc, NULL);
fprintf (stdout, "%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Cursor Failure: %s\n", error.message);
goto done;
}
exit_code = EXIT_SUCCESS;
done:
if (find_opts) {
bson_destroy (find_opts);
}
if (update) {
bson_destroy (update);
}
if (selector) {
bson_destroy (selector);
}
if (update_opts) {
bson_destroy (update_opts);
}
if (secondary) {
mongoc_read_prefs_destroy (secondary);
}
/* destroy cursor, collection, session before the client they came from */
if (cursor) {
mongoc_cursor_destroy (cursor);
}
if (collection) {
mongoc_collection_destroy (collection);
}
if (client_session) {
mongoc_client_session_destroy (client_session);
}
if (uri) {
mongoc_uri_destroy (uri);
}
if (client) {
mongoc_client_destroy (client);
}
mongoc_cleanup ();
return exit_code;
}
mongoc_client_session_with_transaction_cb_t
Synopsis
typedef bool (*mongoc_client_session_with_transaction_cb_t) (
mongoc_client_session_t *session,
void *ctx,
bson_t **reply,
bson_error_t *error);
Provide this callback to mongoc_client_session_with_transaction(). The callback should run
a sequence of operations meant to be contained within a transaction. The callback should
not attempt to start or commit transactions.
Parameters
• session: A mongoc_client_session_t.
• ctx: A void* set to the the user-provided ctx passed to
mongoc_client_session_with_transaction().
• reply: An optional location for a bson_t or NULL. The callback should set this if it
runs any operations against the server and receives replies.
• error: A bson_error_t. The callback should set this if it receives any errors while
running operations against the server.
Return
Returns true for success and false on failure. If cb returns false then it should also set
error.
SEE ALSO:
mongoc_client_session_with_transaction()
mongoc_client_t
A single-threaded MongoDB connection. See Connection Pooling.
Synopsis
typedef struct _mongoc_client_t mongoc_client_t;
typedef mongoc_stream_t *(*mongoc_stream_initiator_t) (
const mongoc_uri_t *uri,
const mongoc_host_list_t *host,
void *user_data,
bson_error_t *error);
mongoc_client_t is an opaque type that provides access to a MongoDB server, replica set,
or sharded cluster. It maintains management of underlying sockets and routing to
individual nodes based on mongoc_read_prefs_t or mongoc_write_concern_t.
Streams
The underlying transport for a given client can be customized, wrapped or replaced by any
implementation that fulfills mongoc_stream_t. A custom transport can be set with
mongoc_client_set_stream_initiator().
Thread Safety
mongoc_client_t is NOT thread-safe and should only be used from one thread at a time. When
used in multi-threaded scenarios, it is recommended that you use the thread-safe
mongoc_client_pool_t to retrieve a mongoc_client_t for your thread.
Example
example-client.c
/* gcc example-client.c -o example-client $(pkg-config --cflags --libs
* libmongoc-1.0) */
/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
bson_error_t error;
const bson_t *doc;
const char *collection_name = "test";
bson_t query;
char *str;
const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
mongoc_uri_t *uri;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
if (argc > 2) {
collection_name = argv[2];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
bson_init (&query);
collection = mongoc_client_get_collection (client, "test", collection_name);
cursor = mongoc_collection_find_with_opts (
collection,
&query,
NULL, /* additional options */
NULL); /* read prefs, NULL for default */
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
fprintf (stdout, "%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Cursor Failure: %s\n", error.message);
return EXIT_FAILURE;
}
bson_destroy (&query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
mongoc_collection_t
Synopsis
typedef struct _mongoc_collection_t mongoc_collection_t;
mongoc_collection_t provides access to a MongoDB collection. This handle is useful for
actions for most CRUD operations, I.e. insert, update, delete, find, etc.
Read Preferences and Write Concerns
Read preferences and write concerns are inherited from the parent client. They can be
overridden by set_* commands if so desired.
mongoc_cursor_t
Client-side cursor abstraction
Synopsis
typedef struct _mongoc_cursor_t mongoc_cursor_t;
mongoc_cursor_t provides access to a MongoDB query cursor. It wraps up the wire protocol
negotiation required to initiate a query and retrieve an unknown number of documents.
Common cursor operations include:
• Determine which host we've connected to with mongoc_cursor_get_host().
• Retrieve more records with repeated calls to mongoc_cursor_next().
• Clone a query to repeat execution at a later point with mongoc_cursor_clone().
• Test for errors with mongoc_cursor_error().
Cursors are lazy, meaning that no connection is established and no network traffic occurs
until the first call to mongoc_cursor_next().
Thread Safety
mongoc_cursor_t is NOT thread safe. It may only be used from within the thread in which it
was created.
Example
Query MongoDB and iterate results
/* gcc example-client.c -o example-client $(pkg-config --cflags --libs
* libmongoc-1.0) */
/* ./example-client [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_cursor_t *cursor;
bson_error_t error;
const bson_t *doc;
const char *collection_name = "test";
bson_t query;
char *str;
const char *uri_string = "mongodb://127.0.0.1/?appname=client-example";
mongoc_uri_t *uri;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
if (argc > 2) {
collection_name = argv[2];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
bson_init (&query);
collection = mongoc_client_get_collection (client, "test", collection_name);
cursor = mongoc_collection_find_with_opts (
collection,
&query,
NULL, /* additional options */
NULL); /* read prefs, NULL for default */
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
fprintf (stdout, "%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Cursor Failure: %s\n", error.message);
return EXIT_FAILURE;
}
bson_destroy (&query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
mongoc_database_t
MongoDB Database Abstraction
Synopsis
typedef struct _mongoc_database_t mongoc_database_t;
mongoc_database_t provides access to a MongoDB database. This handle is useful for actions
a particular database object. It is not a container for mongoc_collection_t structures.
Read preferences and write concerns are inherited from the parent client. They can be
overridden with mongoc_database_set_read_prefs() and mongoc_database_set_write_concern().
Examples
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
mongoc_database_t *database;
mongoc_client_t *client;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/");
database = mongoc_client_get_database (client, "test");
mongoc_database_destroy (database);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
mongoc_delete_flags_t
Flags for deletion operations
Synopsis
typedef enum {
MONGOC_DELETE_NONE = 0,
MONGOC_DELETE_SINGLE_REMOVE = 1 << 0,
} mongoc_delete_flags_t;
Deprecated
WARNING:
These flags are deprecated and should not be used in new code.
Please use mongoc_collection_delete_one() or mongoc_collection_delete_many() instead.
mongoc_find_and_modify_opts_t
find_and_modify abstraction
Synopsis
mongoc_find_and_modify_opts_t is a builder interface to construct a find_and_modify
command.
It was created to be able to accommodate new arguments to the MongoDB find_and_modify
command.
As of MongoDB 3.2, the mongoc_write_concern_t specified on the mongoc_collection_t will be
used, if any.
Example
flags.c
void
fam_flags (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t reply;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
bson_t *update;
bool success;
/* Find Zlatan Ibrahimovic, the striker */
BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
BSON_APPEND_UTF8 (&query, "profession", "Football player");
BSON_APPEND_INT32 (&query, "age", 34);
BSON_APPEND_INT32 (
&query, "goals", (16 + 35 + 23 + 57 + 16 + 14 + 28 + 84) + (1 + 6 + 62));
/* Add his football position */
update = BCON_NEW ("$set", "{", "position", BCON_UTF8 ("striker"), "}");
opts = mongoc_find_and_modify_opts_new ();
mongoc_find_and_modify_opts_set_update (opts, update);
/* Create the document if it didn't exist, and return the updated document */
mongoc_find_and_modify_opts_set_flags (
opts, MONGOC_FIND_AND_MODIFY_UPSERT | MONGOC_FIND_AND_MODIFY_RETURN_NEW);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (&query);
mongoc_find_and_modify_opts_destroy (opts);
}
bypass.c
void
fam_bypass (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t reply;
bson_t *update;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
bool success;
/* Find Zlatan Ibrahimovic, the striker */
BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
BSON_APPEND_UTF8 (&query, "profession", "Football player");
/* Bump his age */
update = BCON_NEW ("$inc", "{", "age", BCON_INT32 (1), "}");
opts = mongoc_find_and_modify_opts_new ();
mongoc_find_and_modify_opts_set_update (opts, update);
/* He can still play, even though he is pretty old. */
mongoc_find_and_modify_opts_set_bypass_document_validation (opts, true);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (&query);
mongoc_find_and_modify_opts_destroy (opts);
}
update.c
void
fam_update (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t *update;
bson_t reply;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
bool success;
/* Find Zlatan Ibrahimovic */
BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
/* Make him a book author */
update = BCON_NEW ("$set", "{", "author", BCON_BOOL (true), "}");
opts = mongoc_find_and_modify_opts_new ();
/* Note that the document returned is the _previous_ version of the document
* To fetch the modified new version, use
* mongoc_find_and_modify_opts_set_flags (opts,
* MONGOC_FIND_AND_MODIFY_RETURN_NEW);
*/
mongoc_find_and_modify_opts_set_update (opts, update);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (&query);
mongoc_find_and_modify_opts_destroy (opts);
}
fields.c
void
fam_fields (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t fields = BSON_INITIALIZER;
bson_t *update;
bson_t reply;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
bool success;
/* Find Zlatan Ibrahimovic */
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
/* Return his goal tally */
BSON_APPEND_INT32 (&fields, "goals", 1);
/* Bump his goal tally */
update = BCON_NEW ("$inc", "{", "goals", BCON_INT32 (1), "}");
opts = mongoc_find_and_modify_opts_new ();
mongoc_find_and_modify_opts_set_update (opts, update);
mongoc_find_and_modify_opts_set_fields (opts, &fields);
/* Return the new tally */
mongoc_find_and_modify_opts_set_flags (opts,
MONGOC_FIND_AND_MODIFY_RETURN_NEW);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (&fields);
bson_destroy (&query);
mongoc_find_and_modify_opts_destroy (opts);
}
sort.c
void
fam_sort (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t *update;
bson_t sort = BSON_INITIALIZER;
bson_t reply;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
bool success;
/* Find all users with the lastname Ibrahimovic */
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
/* Sort by age (descending) */
BSON_APPEND_INT32 (&sort, "age", -1);
/* Bump his goal tally */
update = BCON_NEW ("$set", "{", "oldest", BCON_BOOL (true), "}");
opts = mongoc_find_and_modify_opts_new ();
mongoc_find_and_modify_opts_set_update (opts, update);
mongoc_find_and_modify_opts_set_sort (opts, &sort);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (&sort);
bson_destroy (&query);
mongoc_find_and_modify_opts_destroy (opts);
}
opts.c
void
fam_opts (mongoc_collection_t *collection)
{
mongoc_find_and_modify_opts_t *opts;
bson_t reply;
bson_t *update;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
mongoc_write_concern_t *wc;
bson_t extra = BSON_INITIALIZER;
bool success;
/* Find Zlatan Ibrahimovic, the striker */
BSON_APPEND_UTF8 (&query, "firstname", "Zlatan");
BSON_APPEND_UTF8 (&query, "lastname", "Ibrahimovic");
BSON_APPEND_UTF8 (&query, "profession", "Football player");
/* Bump his age */
update = BCON_NEW ("$inc", "{", "age", BCON_INT32 (1), "}");
opts = mongoc_find_and_modify_opts_new ();
mongoc_find_and_modify_opts_set_update (opts, update);
/* Abort if the operation takes too long. */
mongoc_find_and_modify_opts_set_max_time_ms (opts, 100);
/* Set write concern w: 2 */
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_w (wc, 2);
mongoc_write_concern_append (wc, &extra);
/* Some future findAndModify option the driver doesn't support conveniently
*/
BSON_APPEND_INT32 (&extra, "futureOption", 42);
mongoc_find_and_modify_opts_append (opts, &extra);
success = mongoc_collection_find_and_modify_with_opts (
collection, &query, opts, &reply, &error);
if (success) {
char *str;
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
} else {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
}
bson_destroy (&reply);
bson_destroy (&extra);
bson_destroy (update);
bson_destroy (&query);
mongoc_write_concern_destroy (wc);
mongoc_find_and_modify_opts_destroy (opts);
}
fam.c
int
main (void)
{
mongoc_collection_t *collection;
mongoc_database_t *database;
mongoc_client_t *client;
const char *uri_string =
"mongodb://localhost:27017/admin?appname=find-and-modify-opts-example";
mongoc_uri_t *uri;
bson_error_t error;
bson_t *options;
mongoc_init ();
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "databaseName");
options = BCON_NEW ("validator",
"{",
"age",
"{",
"$lte",
BCON_INT32 (34),
"}",
"}",
"validationAction",
BCON_UTF8 ("error"),
"validationLevel",
BCON_UTF8 ("moderate"));
collection = mongoc_database_create_collection (
database, "collectionName", options, &error);
if (!collection) {
fprintf (
stderr, "Got error: \"%s\" on line %d\n", error.message, __LINE__);
return EXIT_FAILURE;
}
fam_flags (collection);
fam_bypass (collection);
fam_update (collection);
fam_fields (collection);
fam_opts (collection);
fam_sort (collection);
mongoc_collection_drop (collection, NULL);
bson_destroy (options);
mongoc_uri_destroy (uri);
mongoc_database_destroy (database);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Outputs:
{
"lastErrorObject": {
"updatedExisting": false,
"n": 1,
"upserted": {
"$oid": "56562a99d13e6d86239c7b00"
}
},
"value": {
"_id": {
"$oid": "56562a99d13e6d86239c7b00"
},
"age": 34,
"firstname": "Zlatan",
"goals": 342,
"lastname": "Ibrahimovic",
"profession": "Football player",
"position": "striker"
},
"ok": 1
}
{
"lastErrorObject": {
"updatedExisting": true,
"n": 1
},
"value": {
"_id": {
"$oid": "56562a99d13e6d86239c7b00"
},
"age": 34,
"firstname": "Zlatan",
"goals": 342,
"lastname": "Ibrahimovic",
"profession": "Football player",
"position": "striker"
},
"ok": 1
}
{
"lastErrorObject": {
"updatedExisting": true,
"n": 1
},
"value": {
"_id": {
"$oid": "56562a99d13e6d86239c7b00"
},
"age": 35,
"firstname": "Zlatan",
"goals": 342,
"lastname": "Ibrahimovic",
"profession": "Football player",
"position": "striker"
},
"ok": 1
}
{
"lastErrorObject": {
"updatedExisting": true,
"n": 1
},
"value": {
"_id": {
"$oid": "56562a99d13e6d86239c7b00"
},
"goals": 343
},
"ok": 1
}
{
"lastErrorObject": {
"updatedExisting": true,
"n": 1
},
"value": {
"_id": {
"$oid": "56562a99d13e6d86239c7b00"
},
"age": 35,
"firstname": "Zlatan",
"goals": 343,
"lastname": "Ibrahimovic",
"profession": "Football player",
"position": "striker",
"author": true
},
"ok": 1
}
mongoc_gridfs_file_list_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_gridfs_file_list_t mongoc_gridfs_file_list_t;
Description
mongoc_gridfs_file_list_t provides a gridfs file list abstraction. It provides iteration
and basic marshalling on top of a regular mongoc_collection_find_with_opts() style query.
In interface, it's styled after mongoc_cursor_t.
Example
mongoc_gridfs_file_list_t *list;
mongoc_gridfs_file_t *file;
list = mongoc_gridfs_find (gridfs, query);
while ((file = mongoc_gridfs_file_list_next (list))) {
do_something (file);
mongoc_gridfs_file_destroy (file);
}
mongoc_gridfs_file_list_destroy (list);
mongoc_gridfs_file_opt_t
Synopsis
typedef struct {
const char *md5;
const char *filename;
const char *content_type;
const bson_t *aliases;
const bson_t *metadata;
uint32_t chunk_size;
} mongoc_gridfs_file_opt_t;
Description
This structure contains options that can be set on a mongoc_gridfs_file_t. It can be used
by various functions when creating a new gridfs file.
mongoc_gridfs_file_t
Synopsis
typedef struct _mongoc_gridfs_file_t mongoc_gridfs_file_t;
Description
This structure provides a MongoDB GridFS file abstraction. It provides several APIs.
• readv, writev, seek, and tell.
• General file metadata such as filename and length.
• GridFS metadata such as md5, filename, content_type, aliases, metadata, chunk_size, and
upload_date.
Thread Safety
This structure is NOT thread-safe and should only be used from one thread at a time.
Related
• mongoc_client_t
• mongoc_gridfs_t
• mongoc_gridfs_file_list_t
• mongoc_gridfs_file_opt_t
mongoc_gridfs_bucket_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_gridfs_bucket_t mongoc_gridfs_bucket_t;
Description
mongoc_gridfs_bucket_t provides a spec-compliant MongoDB GridFS implementation,
superseding mongoc_gridfs_t. See the GridFS MongoDB documentation.
Thread Safety
mongoc_gridfs_bucket_t is NOT thread-safe and should only be used in the same thread as
the owning mongoc_client_t.
Lifecycle
It is an error to free a mongoc_gridfs_bucket_t before freeing all derived instances of
mongoc_stream_t. The owning mongoc_client_t must outlive the mongoc_gridfs_bucket_t.
Example
example-gridfs-bucket.c
#include <stdio.h>
#include <stdlib.h>
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
const char *uri_string =
"mongodb://localhost:27017/?appname=new-gridfs-example";
mongoc_client_t *client;
mongoc_database_t *db;
mongoc_stream_t *file_stream;
mongoc_gridfs_bucket_t *bucket;
mongoc_cursor_t *cursor;
bson_t filter;
bool res;
bson_value_t file_id;
bson_error_t error;
const bson_t *doc;
char *str;
mongoc_init ();
if (argc != 3) {
fprintf (stderr, "usage: %s SOURCE_FILE_PATH FILE_COPY_PATH\n", argv[0]);
return EXIT_FAILURE;
}
/* 1. Make a bucket. */
client = mongoc_client_new (uri_string);
db = mongoc_client_get_database (client, "test");
bucket = mongoc_gridfs_bucket_new (db, NULL, NULL, &error);
if (!bucket) {
printf ("Error creating gridfs bucket: %s\n", error.message);
return EXIT_FAILURE;
}
/* 2. Insert a file. */
file_stream = mongoc_stream_file_new_for_path (argv[1], O_RDONLY, 0);
res = mongoc_gridfs_bucket_upload_from_stream (
bucket, "my-file", file_stream, NULL, &file_id, &error);
if (!res) {
printf ("Error uploading file: %s\n", error.message);
return EXIT_FAILURE;
}
mongoc_stream_close (file_stream);
mongoc_stream_destroy (file_stream);
/* 3. Download the file in GridFS to a local file. */
file_stream = mongoc_stream_file_new_for_path (argv[2], O_CREAT | O_RDWR, 0);
if (!file_stream) {
perror ("Error opening file stream");
return EXIT_FAILURE;
}
res = mongoc_gridfs_bucket_download_to_stream (
bucket, &file_id, file_stream, &error);
if (!res) {
printf ("Error downloading file to stream: %s\n", error.message);
return EXIT_FAILURE;
}
mongoc_stream_close (file_stream);
mongoc_stream_destroy (file_stream);
/* 4. List what files are available in GridFS. */
bson_init (&filter);
cursor = mongoc_gridfs_bucket_find (bucket, &filter, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
/* 5. Delete the file that we added. */
res = mongoc_gridfs_bucket_delete_by_id (bucket, &file_id, &error);
if (!res) {
printf ("Error deleting the file: %s\n", error.message);
return EXIT_FAILURE;
}
/* 6. Cleanup. */
mongoc_stream_close (file_stream);
mongoc_stream_destroy (file_stream);
mongoc_cursor_destroy (cursor);
bson_destroy (&filter);
mongoc_gridfs_bucket_destroy (bucket);
mongoc_database_destroy (db);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
SEE ALSO:
The MongoDB GridFS specification.
The non spec-compliant mongoc_gridfs_t.
mongoc_gridfs_t
WARNING:
This GridFS implementation does not conform to the MongoDB GridFS specification. For a
spec compliant implementation, use mongoc_gridfs_bucket_t.
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_gridfs_t mongoc_gridfs_t;
Description
mongoc_gridfs_t provides a MongoDB gridfs implementation. The system as a whole is made up
of gridfs objects, which contain gridfs_files and gridfs_file_lists. Essentially, a basic
file system API.
There are extensive caveats about the kind of use cases gridfs is practical for. In
particular, any writing after initial file creation is likely to both break any concurrent
readers and be quite expensive. That said, this implementation does allow for arbitrary
writes to existing gridfs object, just use them with caution.
mongoc_gridfs also integrates tightly with the mongoc_stream_t abstraction, which provides
some convenient wrapping for file creation and reading/writing. It can be used without,
but its worth looking to see if your problem can fit that model.
WARNING:
mongoc_gridfs_t does not support read preferences. In a replica set, GridFS queries are
always routed to the primary.
Thread Safety
mongoc_gridfs_t is NOT thread-safe and should only be used in the same thread as the
owning mongoc_client_t.
Lifecycle
It is an error to free a mongoc_gridfs_t before freeing all related instances of
mongoc_gridfs_file_t and mongoc_gridfs_file_list_t.
Example
example-gridfs.c
#include <assert.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
int
main (int argc, char *argv[])
{
mongoc_gridfs_t *gridfs;
mongoc_gridfs_file_t *file;
mongoc_gridfs_file_list_t *list;
mongoc_gridfs_file_opt_t opt = {0};
mongoc_client_t *client;
const char *uri_string = "mongodb://127.0.0.1:27017/?appname=gridfs-example";
mongoc_uri_t *uri;
mongoc_stream_t *stream;
bson_t filter;
bson_t opts;
bson_t child;
bson_error_t error;
ssize_t r;
char buf[4096];
mongoc_iovec_t iov;
const char *filename;
const char *command;
bson_value_t id;
if (argc < 2) {
fprintf (stderr, "usage - %s command ...\n", argv[0]);
return EXIT_FAILURE;
}
mongoc_init ();
iov.iov_base = (void *) buf;
iov.iov_len = sizeof buf;
/* connect to localhost client */
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
assert (client);
mongoc_client_set_error_api (client, 2);
/* grab a gridfs handle in test prefixed by fs */
gridfs = mongoc_client_get_gridfs (client, "test", "fs", &error);
assert (gridfs);
command = argv[1];
filename = argv[2];
if (strcmp (command, "read") == 0) {
if (argc != 3) {
fprintf (stderr, "usage - %s read filename\n", argv[0]);
return EXIT_FAILURE;
}
file = mongoc_gridfs_find_one_by_filename (gridfs, filename, &error);
assert (file);
stream = mongoc_stream_gridfs_new (file);
assert (stream);
for (;;) {
r = mongoc_stream_readv (stream, &iov, 1, -1, 0);
assert (r >= 0);
if (r == 0) {
break;
}
if (fwrite (iov.iov_base, 1, r, stdout) != r) {
MONGOC_ERROR ("Failed to write to stdout. Exiting.\n");
exit (1);
}
}
mongoc_stream_destroy (stream);
mongoc_gridfs_file_destroy (file);
} else if (strcmp (command, "list") == 0) {
bson_init (&filter);
bson_init (&opts);
bson_append_document_begin (&opts, "sort", -1, &child);
BSON_APPEND_INT32 (&child, "filename", 1);
bson_append_document_end (&opts, &child);
list = mongoc_gridfs_find_with_opts (gridfs, &filter, &opts);
bson_destroy (&filter);
bson_destroy (&opts);
while ((file = mongoc_gridfs_file_list_next (list))) {
const char *name = mongoc_gridfs_file_get_filename (file);
printf ("%s\n", name ? name : "?");
mongoc_gridfs_file_destroy (file);
}
mongoc_gridfs_file_list_destroy (list);
} else if (strcmp (command, "write") == 0) {
if (argc != 4) {
fprintf (stderr, "usage - %s write filename input_file\n", argv[0]);
return EXIT_FAILURE;
}
stream = mongoc_stream_file_new_for_path (argv[3], O_RDONLY, 0);
assert (stream);
opt.filename = filename;
/* the driver generates a file_id for you */
file = mongoc_gridfs_create_file_from_stream (gridfs, stream, &opt);
assert (file);
id.value_type = BSON_TYPE_INT32;
id.value.v_int32 = 1;
/* optional: the following method specifies a file_id of any
BSON type */
if (!mongoc_gridfs_file_set_id (file, &id, &error)) {
fprintf (stderr, "%s\n", error.message);
return EXIT_FAILURE;
}
if (!mongoc_gridfs_file_save (file)) {
mongoc_gridfs_file_error (file, &error);
fprintf (stderr, "Could not save: %s\n", error.message);
return EXIT_FAILURE;
}
mongoc_gridfs_file_destroy (file);
} else {
fprintf (stderr, "Unknown command");
return EXIT_FAILURE;
}
mongoc_gridfs_destroy (gridfs);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
SEE ALSO:
The MongoDB GridFS specification.
The spec-compliant mongoc_gridfs_bucket_t.
mongoc_host_list_t
Synopsis
typedef struct {
mongoc_host_list_t *next;
char host[BSON_HOST_NAME_MAX + 1];
char host_and_port[BSON_HOST_NAME_MAX + 7];
uint16_t port;
int family;
void *padding[4];
} mongoc_host_list_t;
Description
The host and port of a MongoDB server. Can be part of a linked list: for example the
return value of mongoc_uri_get_hosts() when multiple hosts are provided in the MongoDB
URI.
SEE ALSO:
mongoc_uri_get_hosts() and mongoc_cursor_get_host().
mongoc_index_opt_geo_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct {
uint8_t twod_sphere_version;
uint8_t twod_bits_precision;
double twod_location_min;
double twod_location_max;
double haystack_bucket_size;
uint8_t *padding[32];
} mongoc_index_opt_geo_t;
Description
This structure contains the options that may be used for tuning a GEO index.
SEE ALSO:
mongoc_index_opt_t
mongoc_index_opt_wt_t
mongoc_index_opt_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct {
bool is_initialized;
bool background;
bool unique;
const char *name;
bool drop_dups;
bool sparse;
int32_t expire_after_seconds;
int32_t v;
const bson_t *weights;
const char *default_language;
const char *language_override;
mongoc_index_opt_geo_t *geo_options;
mongoc_index_opt_storage_t *storage_options;
const bson_t *partial_filter_expression;
const bson_t *collation;
void *padding[4];
} mongoc_index_opt_t;
Deprecated
This structure is deprecated and should not be used in new code. See Creating Indexes.
Description
This structure contains the options that may be used for tuning a specific index.
See the createIndexes documentations in the MongoDB manual for descriptions of individual
options.
NOTE:
dropDups is deprecated as of MongoDB version 3.0.0. This option is silently ignored by
the server and unique index builds using this option will fail if a duplicate value is
detected.
Example
{
bson_t keys;
bson_error_t error;
mongoc_index_opt_t opt;
mongoc_index_opt_geo_t geo_opt;
mongoc_index_opt_init (&opt);
mongoc_index_opt_geo_init (&geo_opt);
bson_init (&keys);
BSON_APPEND_UTF8 (&keys, "location", "2d");
geo_opt.twod_location_min = -123;
geo_opt.twod_location_max = +123;
geo_opt.twod_bits_precision = 30;
opt.geo_options = &geo_opt;
collection = mongoc_client_get_collection (client, "test", "geo_test");
if (mongoc_collection_create_index (collection, &keys, &opt, &error)) {
/* Successfully created the geo index */
}
bson_destroy (&keys);
mongoc_collection_destroy (&collection);
}
SEE ALSO:
mongoc_index_opt_geo_t
mongoc_index_opt_wt_t
mongoc_index_opt_wt_t
Synopsis
#include <mongoc/mongoc.h>
typedef struct {
mongoc_index_opt_storage_t base;
const char *config_str;
void *padding[8];
} mongoc_index_opt_wt_t;
Description
This structure contains the options that may be used for tuning a WiredTiger specific
index.
SEE ALSO:
mongoc_index_opt_t
mongoc_index_opt_geo_t
mongoc_insert_flags_t
Flags for insert operations
Synopsis
typedef enum {
MONGOC_INSERT_NONE = 0,
MONGOC_INSERT_CONTINUE_ON_ERROR = 1 << 0,
} mongoc_insert_flags_t;
#define MONGOC_INSERT_NO_VALIDATE (1U << 31)
Description
These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together.
They may modify how an insert happens on the MongoDB server.
Flag Values
┌────────────────────────────────┬──────────────────────────────────┐
│MONGOC_INSERT_NONE │ Specify no insert flags. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_INSERT_CONTINUE_ON_ERROR │ Continue inserting documents │
│ │ from the insertion set even if │
│ │ one insert fails. │
└────────────────────────────────┴──────────────────────────────────┘
│MONGOC_INSERT_NO_VALIDATE │ Do not validate insertion │
│ │ documents before performing an │
│ │ insert. Validation can be │
│ │ expensive, so this can save some │
│ │ time if you know your documents │
│ │ are already valid. │
└────────────────────────────────┴──────────────────────────────────┘
mongoc_iovec_t
Synopsis
Synopsis
#include <mongoc/mongoc.h>
#ifdef _WIN32
typedef struct {
u_long iov_len;
char *iov_base;
} mongoc_iovec_t;
#else
typedef struct iovec mongoc_iovec_t;
#endif
The mongoc_iovec_t structure is a portability abstraction for consumers of the
mongoc_stream_t interfaces. It allows for scatter/gather I/O through the socket subsystem.
WARNING:
When writing portable code, beware of the ordering of iov_len and iov_base as they are
different on various platforms. Therefore, you should not use C initializers for
initialization.
mongoc_matcher_t
Client-side document matching abstraction
Synopsis
typedef struct _mongoc_matcher_t mongoc_matcher_t;
mongoc_matcher_t provides a reduced-interface for client-side matching of BSON documents.
It can perform the basics such as $in, $nin, $eq, $neq, $gt, $gte, $lt, and $lte.
WARNING:
mongoc_matcher_t does not currently support the full spectrum of query operations that
the MongoDB server supports.
Deprecated
WARNING:
mongoc_matcher_t is deprecated and will be removed in version 2.0.
Example
Filter a sequence of BSON documents from STDIN based on a query
#include <bson/bson.h>
#include <mongoc/mongoc.h>
#include <stdio.h>
int
main (int argc, char *argv[])
{
mongoc_matcher_t *matcher;
bson_reader_t *reader;
const bson_t *bson;
bson_t *spec;
char *str;
int fd;
mongoc_init ();
#ifdef _WIN32
fd = fileno (stdin);
#else
fd = STDIN_FILENO;
#endif
reader = bson_reader_new_from_fd (fd, false);
spec = BCON_NEW ("hello", "world");
matcher = mongoc_matcher_new (spec, NULL);
while ((bson = bson_reader_read (reader, NULL))) {
if (mongoc_matcher_match (matcher, bson)) {
str = bson_as_canonical_extended_json (bson, NULL);
printf ("%s\n", str);
bson_free (str);
}
}
bson_reader_destroy (reader);
bson_destroy (spec);
mongoc_cleanup ();
return 0;
}
mongoc_optional_t
A struct to store optional boolean values.
Synopsis
Used to specify optional boolean flags, which may remain unset.
This is used within mongoc_server_api_t to track whether a flag was explicitly set.
mongoc_query_flags_t
Flags for query operations
Synopsis
typedef enum {
MONGOC_QUERY_NONE = 0,
MONGOC_QUERY_TAILABLE_CURSOR = 1 << 1,
MONGOC_QUERY_SECONDARY_OK = 1 << 2,
MONGOC_QUERY_OPLOG_REPLAY = 1 << 3,
MONGOC_QUERY_NO_CURSOR_TIMEOUT = 1 << 4,
MONGOC_QUERY_AWAIT_DATA = 1 << 5,
MONGOC_QUERY_EXHAUST = 1 << 6,
MONGOC_QUERY_PARTIAL = 1 << 7,
} mongoc_query_flags_t;
Description
These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together.
They may modify how a query is performed in the MongoDB server.
Flag Values
┌───────────────────────────────┬──────────────────────────────────┐
│MONGOC_QUERY_NONE │ Specify no query flags. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_TAILABLE_CURSOR │ Cursor will not be closed when │
│ │ the last data is retrieved. You │
│ │ can resume this cursor later. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_SECONDARY_OK │ Allow query of replica set │
│ │ secondaries. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_OPLOG_REPLAY │ Used internally by MongoDB. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_NO_CURSOR_TIMEOUT │ The server normally times out an │
│ │ idle cursor after an inactivity │
│ │ period (10 minutes). This │
│ │ prevents that. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_AWAIT_DATA │ Use with │
│ │ MONGOC_QUERY_TAILABLE_CURSOR. │
│ │ Block rather than returning no │
│ │ data. After a period, time out. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_QUERY_EXHAUST │ Stream the data down full blast │
│ │ in multiple "reply" packets. │
│ │ Faster when you are pulling down │
│ │ a lot of data and you know you │
│ │ want to retrieve it all. Only │
│ │ applies to cursors created from │
│ │ a find operation (i.e. │
│ │ mongoc_collection_find()). │
└───────────────────────────────┴──────────────────────────────────┘
│MONGOC_QUERY_PARTIAL │ Get partial results from mongos │
│ │ if some shards are down (instead │
│ │ of throwing an error). │
└───────────────────────────────┴──────────────────────────────────┘
mongoc_rand
MongoDB Random Number Generator
Synopsis
void
mongoc_rand_add (const void *buf, int num, double entropy);
void
mongoc_rand_seed (const void *buf, int num);
int
mongoc_rand_status (void);
Description
The mongoc_rand family of functions provide access to the low level randomness primitives
used by the MongoDB C Driver. In particular, they control the creation of
cryptographically strong pseudo-random bytes required by some security mechanisms.
While we can usually pull enough entropy from the environment, you may be required to seed
the PRNG manually depending on your OS, hardware and other entropy consumers running on
the same system.
Entropy
mongoc_rand_add and mongoc_rand_seed allow the user to directly provide entropy. They
differ insofar as mongoc_rand_seed requires that each bit provided is fully random.
mongoc_rand_add allows the user to specify the degree of randomness in the provided bytes
as well.
Status
The mongoc_rand_status function allows the user to check the status of the mongoc PRNG.
This can be used to guarantee sufficient entropy at program startup, rather than waiting
for runtime errors to occur.
mongoc_read_concern_t
Read Concern abstraction
Synopsis
New in MongoDB 3.2.
The mongoc_read_concern_t allows clients to choose a level of isolation for their reads.
The default, MONGOC_READ_CONCERN_LEVEL_LOCAL, is right for the great majority of
applications.
You can specify a read concern on connection objects, database objects, or collection
objects.
See readConcern on the MongoDB website for more information.
Read Concern is only sent to MongoDB when it has explicitly been set by
mongoc_read_concern_set_level() to anything other than NULL.
Read Concern Levels
┌───────────────────────────────────────┬──────────────────────────┬───────────────────────┐
│Macro │ Description │ First MongoDB version │
├───────────────────────────────────────┼──────────────────────────┼───────────────────────┤
│MONGOC_READ_CONCERN_LEVEL_LOCAL │ Level "local", the │ 3.2 │
│ │ default. │ │
├───────────────────────────────────────┼──────────────────────────┼───────────────────────┤
│MONGOC_READ_CONCERN_LEVEL_MAJORITY │ Level "majority". │ 3.2 │
├───────────────────────────────────────┼──────────────────────────┼───────────────────────┤
│MONGOC_READ_CONCERN_LEVEL_LINEARIZABLE │ Level "linearizable". │ 3.4 │
├───────────────────────────────────────┼──────────────────────────┼───────────────────────┤
│MONGOC_READ_CONCERN_LEVEL_AVAILABLE │ Level "available". │ 3.6 │
├───────────────────────────────────────┼──────────────────────────┼───────────────────────┤
│MONGOC_READ_CONCERN_LEVEL_SNAPSHOT │ Level "snapshot". │ 4.0 │
└───────────────────────────────────────┴──────────────────────────┴───────────────────────┘
For the sake of compatibility with future versions of MongoDB,
mongoc_read_concern_set_level() allows any string, not just this list of known read
concern levels.
See Read Concern Levels in the MongoDB manual for more information about the individual
read concern levels.
mongoc_read_mode_t
Read Preference Modes
Synopsis
typedef enum {
MONGOC_READ_PRIMARY = (1 << 0),
MONGOC_READ_SECONDARY = (1 << 1),
MONGOC_READ_PRIMARY_PREFERRED = (1 << 2) | MONGOC_READ_PRIMARY,
MONGOC_READ_SECONDARY_PREFERRED = (1 << 2) | MONGOC_READ_SECONDARY,
MONGOC_READ_NEAREST = (1 << 3) | MONGOC_READ_SECONDARY,
} mongoc_read_mode_t;
Description
This enum describes how reads should be dispatched. The default is MONGOC_READ_PRIMARY.
Please see the MongoDB website for a description of Read Preferences.
mongoc_read_prefs_t
A read preference abstraction
Synopsis
mongoc_read_prefs_t provides an abstraction on top of the MongoDB connection read
preferences. It allows for hinting to the driver which nodes in a replica set should be
accessed first and how.
You can specify a read preference mode on connection objects, database objects, collection
objects, or per-operation. Generally, it makes the most sense to stick with the global
default mode, MONGOC_READ_PRIMARY. All of the other modes come with caveats that won't be
covered in great detail here.
Read Modes
┌────────────────────────────────┬──────────────────────────────────┐
│MONGOC_READ_PRIMARY │ Default mode. All operations │
│ │ read from the current replica │
│ │ set primary. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_READ_SECONDARY │ All operations read from among │
│ │ the nearest secondary members of │
│ │ the replica set. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_READ_PRIMARY_PREFERRED │ In most situations, operations │
│ │ read from the primary but if it │
│ │ is unavailable, operations read │
│ │ from secondary members. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_READ_SECONDARY_PREFERRED │ In most situations, operations │
│ │ read from among the nearest │
│ │ secondary members, but if no │
│ │ secondaries are available, │
│ │ operations read from the │
│ │ primary. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_READ_NEAREST │ Operations read from among the │
│ │ nearest members of the replica │
│ │ set, irrespective of the │
│ │ member's type. │
└────────────────────────────────┴──────────────────────────────────┘
Tag Sets
Tag sets allow you to specify custom read preferences and write concerns so that your
application can target operations to specific members.
Custom read preferences and write concerns evaluate tags sets in different ways: read
preferences consider the value of a tag when selecting a member to read from, while write
concerns ignore the value of a tag when selecting a member, except to consider whether or
not the value is unique.
You can specify tag sets with the following read preference modes:
• primaryPreferred
• secondary
• secondaryPreferred
• nearest
Tags are not compatible with MONGOC_READ_PRIMARY and, in general, only apply when
selecting a secondary member of a set for a read operation. However, the nearest read
mode, when combined with a tag set, will select the nearest member that matches the
specified tag set, which may be a primary or secondary.
Tag sets are represented as a comma-separated list of colon-separated key-value pairs when
provided as a connection string, e.g. dc:ny,rack:1.
To specify a list of tag sets, using multiple readPreferenceTags, e.g.
readPreferenceTags=dc:ny,rack:1;readPreferenceTags=dc:ny;readPreferenceTags=
Note the empty value for the last one, which means "match any secondary as a last resort".
Order matters when using multiple readPreferenceTags.
Tag Sets can also be configured using mongoc_read_prefs_set_tags().
All interfaces use the same member selection logic to choose the member to which to direct
read operations, basing the choice on read preference mode and tag sets.
Max Staleness
When connected to replica set running MongoDB 3.4 or later, the driver estimates the
staleness of each secondary based on lastWriteDate values provided in server hello
responses.
Max Staleness is the maximum replication lag in seconds (wall clock time) that a secondary
can suffer and still be eligible for reads. The default is MONGOC_NO_MAX_STALENESS, which
disables staleness checks. Otherwise, it must be a positive integer at least
MONGOC_SMALLEST_MAX_STALENESS_SECONDS (90 seconds).
Max Staleness is also supported by sharded clusters of replica sets if all servers run
MongoDB 3.4 or later.
Hedged Reads
When connecting to a sharded cluster running MongoDB 4.4 or later, reads can be sent in
parallel to the two "best" hosts. Once one result returns, any other outstanding
operations that were part of the hedged read are cancelled.
When the read preference mode is MONGOC_READ_NEAREST and the sharded cluster is running
MongoDB 4.4 or later, hedged reads are enabled by default. Additionally, hedged reads may
be explicitly enabled or disabled by calling mongoc_read_prefs_set_hedge() with a BSON
document, e.g.
{
enabled: true
}
Appropriate values for the enabled key are true or false.
mongoc_remove_flags_t
Flags for deletion operations
Synopsis
typedef enum {
MONGOC_REMOVE_NONE = 0,
MONGOC_REMOVE_SINGLE_REMOVE = 1 << 0,
} mongoc_remove_flags_t;
Description
These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together.
They may change the number of documents that are removed during a remove command.
Flag Values
┌────────────────────────────┬──────────────────────────────────┐
│MONGOC_REMOVE_NONE │ Specify no removal flags. All │
│ │ matching documents will be │
│ │ removed. │
├────────────────────────────┼──────────────────────────────────┤
│MONGOC_REMOVE_SINGLE_REMOVE │ Only remove the first matching │
│ │ document from the selector. │
└────────────────────────────┴──────────────────────────────────┘
mongoc_reply_flags_t
Flags from server replies
Synopsis
typedef enum {
MONGOC_REPLY_NONE = 0,
MONGOC_REPLY_CURSOR_NOT_FOUND = 1 << 0,
MONGOC_REPLY_QUERY_FAILURE = 1 << 1,
MONGOC_REPLY_SHARD_CONFIG_STALE = 1 << 2,
MONGOC_REPLY_AWAIT_CAPABLE = 1 << 3,
} mongoc_reply_flags_t;
Description
These flags correspond to the wire protocol. They may be bitwise or'd together.
Flag Values
┌────────────────────────────────┬──────────────────────────────────┐
│MONGOC_REPLY_NONE │ No flags set. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_REPLY_CURSOR_NOT_FOUND │ No matching cursor was found on │
│ │ the server. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_REPLY_QUERY_FAILURE │ The query failed or was invalid. │
│ │ Error document has been │
│ │ provided. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_REPLY_SHARD_CONFIG_STALE │ Shard config is stale. │
├────────────────────────────────┼──────────────────────────────────┤
│MONGOC_REPLY_AWAIT_CAPABLE │ If the returned cursor is │
│ │ capable of │
│ │ MONGOC_QUERY_AWAIT_DATA. │
└────────────────────────────────┴──────────────────────────────────┘
mongoc_server_api_t
A versioned API to use for connections.
Synopsis
Used to specify which version of the MongoDB server's API to use for driver connections.
The server API type takes a mongoc_server_api_version_t. It can optionally be strict about
the list of allowed commands in that API version, and can also optionally provide errors
for deprecated commands in that API version.
A mongoc_server_api_t can be set on a client, and will then be sent to MongoDB for most
commands run using that client.
mongoc_server_api_version_t
A representation of server API version numbers.
Synopsis
Used to specify which version of the MongoDB server's API to use for driver connections.
Supported API Versions
The driver currently supports the following MongoDB API versions:
┌─────────────────────┬────────────────────────┐
│Enum value │ MongoDB version string │
├─────────────────────┼────────────────────────┤
│MONGOC_SERVER_API_V1 │ "1" │
└─────────────────────┴────────────────────────┘
mongoc_server_description_t
Server description
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_server_description_t mongoc_server_description_t
mongoc_server_description_t holds information about a mongod or mongos the driver is
connected to.
Lifecycle
Clean up a mongoc_server_description_t with mongoc_server_description_destroy() when
necessary.
Applications receive a temporary reference to a mongoc_server_description_t as a parameter
to an SDAM Monitoring callback that must not be destroyed. See Introduction to Application
Performance Monitoring.
SEE ALSO:
mongoc_client_get_server_descriptions().
mongoc_session_opt_t
#include <mongoc/mongoc.h>
typedef struct _mongoc_session_opt_t mongoc_session_opt_t;
Synopsis
Start a session with mongoc_client_start_session(), use the session for a sequence of
operations and multi-document transactions, then free it with
mongoc_client_session_destroy(). Any mongoc_cursor_t or mongoc_change_stream_t using a
session must be destroyed before the session, and a session must be destroyed before the
mongoc_client_t it came from.
By default, sessions are causally consistent. To disable causal consistency, before
starting a session create a mongoc_session_opt_t with mongoc_session_opts_new() and call
mongoc_session_opts_set_causal_consistency(), then free the struct with
mongoc_session_opts_destroy().
Unacknowledged writes are prohibited with sessions.
A mongoc_client_session_t must be used by only one thread at a time. Due to session
pooling, mongoc_client_start_session() may return a session that has been idle for some
time and is about to be closed after its idle timeout. Use the session within one minute
of acquiring it to refresh the session and avoid a timeout.
See the example code for mongoc_session_opts_set_causal_consistency().
mongoc_socket_t
Portable socket abstraction
Synopsis
#include <mongoc/mongoc.h>
typedef struct _mongoc_socket_t mongoc_socket_t
Synopsis
This structure provides a socket abstraction that is friendlier for portability than BSD
sockets directly. Inconsistencies between Linux, various BSDs, Solaris, and Windows are
handled here.
mongoc_ssl_opt_t
Synopsis
typedef struct {
const char *pem_file;
const char *pem_pwd;
const char *ca_file;
const char *ca_dir;
const char *crl_file;
bool weak_cert_validation;
bool allow_invalid_hostname;
void *internal;
void *padding[6];
} mongoc_ssl_opt_t;
Description
This structure is used to set the TLS options for a mongoc_client_t or
mongoc_client_pool_t.
Beginning in version 1.2.0, once a pool or client has any TLS options set, all connections
use TLS, even if ssl=true is omitted from the MongoDB URI. Before, TLS options were
ignored unless tls=true was included in the URI.
As of 1.4.0, the mongoc_client_pool_set_ssl_opts() and mongoc_client_set_ssl_opts() will
not only shallow copy the struct, but will also copy the const char*. It is therefore no
longer needed to make sure the values remain valid after setting them.
SEE ALSO:
Configuring TLS
mongoc_client_set_ssl_opts()
mongoc_client_pool_set_ssl_opts()
mongoc_stream_buffered_t
Synopsis
typedef struct _mongoc_stream_buffered_t mongoc_stream_buffered_t;
Description
mongoc_stream_buffered_t should be considered a subclass of mongoc_stream_t. It performs
buffering on an underlying stream.
SEE ALSO:
mongoc_stream_buffered_new()
mongoc_stream_destroy()
mongoc_stream_file_t
Synopsis
typedef struct _mongoc_stream_file_t mongoc_stream_file_t
mongoc_stream_file_t is a mongoc_stream_t subclass for working with standard UNIX style
file-descriptors.
mongoc_stream_socket_t
Synopsis
typedef struct _mongoc_stream_socket_t mongoc_stream_socket_t
mongoc_stream_socket_t should be considered a subclass of mongoc_stream_t that works upon
socket streams.
mongoc_stream_t
Synopsis
typedef struct _mongoc_stream_t mongoc_stream_t
mongoc_stream_t provides a generic streaming IO abstraction based on a struct of pointers
interface. The idea is to allow wrappers, perhaps other language drivers, to easily shim
their IO system on top of mongoc_stream_t.
The API for the stream abstraction is currently private and non-extensible.
Stream Types
There are a number of built in stream types that come with mongoc. The default
configuration is a buffered unix stream. If TLS is in use, that in turn is wrapped in a
tls stream.
SEE ALSO:
mongoc_stream_buffered_t
mongoc_stream_file_t
mongoc_stream_socket_t
mongoc_stream_tls_t
mongoc_stream_tls_t
Synopsis
typedef struct _mongoc_stream_tls_t mongoc_stream_tls_t
mongoc_stream_tls_t is a mongoc_stream_t subclass for working with TLS streams.
mongoc_topology_description_t
Status of MongoDB Servers
Synopsis
typedef struct _mongoc_topology_description_t mongoc_topology_description_t;
mongoc_topology_description_t is an opaque type representing the driver's knowledge of the
MongoDB server or servers it is connected to. Its API conforms to the SDAM Monitoring
Specification.
Applications receive a temporary reference to a mongoc_topology_description_t as a
parameter to an SDAM Monitoring callback that must not be destroyed. See Introduction to
Application Performance Monitoring.
mongoc_transaction_opt_t
#include <mongoc/mongoc.h>
typedef struct _mongoc_transaction_opt_t mongoc_transaction_opt_t;
Synopsis
Options for starting a multi-document transaction.
When a session is first created with mongoc_client_start_session(), it inherits from the
client the read concern, write concern, and read preference with which to start
transactions. Each of these fields can be overridden independently. Create a
mongoc_transaction_opt_t with mongoc_transaction_opts_new(), and pass a non-NULL option to
any of the mongoc_transaction_opt_t setter functions:
• mongoc_transaction_opts_set_read_concern()
• mongoc_transaction_opts_set_write_concern()
• mongoc_transaction_opts_set_read_prefs()
Pass the resulting transaction options to mongoc_client_session_start_transaction(). Each
field set in the transaction options overrides the inherited client configuration.
Example
example-transaction.c
/* gcc example-transaction.c -o example-transaction \
* $(pkg-config --cflags --libs libmongoc-1.0) */
/* ./example-transaction [CONNECTION_STRING] */
#include <stdio.h>
#include <mongoc/mongoc.h>
int
main (int argc, char *argv[])
{
int exit_code = EXIT_FAILURE;
mongoc_client_t *client = NULL;
mongoc_database_t *database = NULL;
mongoc_collection_t *collection = NULL;
mongoc_client_session_t *session = NULL;
mongoc_session_opt_t *session_opts = NULL;
mongoc_transaction_opt_t *default_txn_opts = NULL;
mongoc_transaction_opt_t *txn_opts = NULL;
mongoc_read_concern_t *read_concern = NULL;
mongoc_write_concern_t *write_concern = NULL;
const char *uri_string = "mongodb://127.0.0.1/?appname=transaction-example";
mongoc_uri_t *uri;
bson_error_t error;
bson_t *doc = NULL;
bson_t *insert_opts = NULL;
int32_t i;
int64_t start;
bson_t reply = BSON_INITIALIZER;
char *reply_json;
bool r;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
MONGOC_ERROR ("failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
goto done;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
goto done;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "example-transaction");
/* inserting into a nonexistent collection normally creates it, but a
* collection can't be created in a transaction; create it now */
collection =
mongoc_database_create_collection (database, "collection", NULL, &error);
if (!collection) {
/* code 48 is NamespaceExists, see error_codes.err in mongodb source */
if (error.code == 48) {
collection = mongoc_database_get_collection (database, "collection");
} else {
MONGOC_ERROR ("Failed to create collection: %s", error.message);
goto done;
}
}
/* a transaction's read preferences, read concern, and write concern can be
* set on the client, on the default transaction options, or when starting
* the transaction. for the sake of this example, set read concern on the
* default transaction options. */
default_txn_opts = mongoc_transaction_opts_new ();
read_concern = mongoc_read_concern_new ();
mongoc_read_concern_set_level (read_concern, "snapshot");
mongoc_transaction_opts_set_read_concern (default_txn_opts, read_concern);
session_opts = mongoc_session_opts_new ();
mongoc_session_opts_set_default_transaction_opts (session_opts,
default_txn_opts);
session = mongoc_client_start_session (client, session_opts, &error);
if (!session) {
MONGOC_ERROR ("Failed to start session: %s", error.message);
goto done;
}
/* in this example, set write concern when starting the transaction */
txn_opts = mongoc_transaction_opts_new ();
write_concern = mongoc_write_concern_new ();
mongoc_write_concern_set_wmajority (write_concern, 1000 /* wtimeout */);
mongoc_transaction_opts_set_write_concern (txn_opts, write_concern);
insert_opts = bson_new ();
if (!mongoc_client_session_append (session, insert_opts, &error)) {
MONGOC_ERROR ("Could not add session to opts: %s", error.message);
goto done;
}
retry_transaction:
r = mongoc_client_session_start_transaction (session, txn_opts, &error);
if (!r) {
MONGOC_ERROR ("Failed to start transaction: %s", error.message);
goto done;
}
/* insert two documents - on error, retry the whole transaction */
for (i = 0; i < 2; i++) {
doc = BCON_NEW ("_id", BCON_INT32 (i));
bson_destroy (&reply);
r = mongoc_collection_insert_one (
collection, doc, insert_opts, &reply, &error);
bson_destroy (doc);
if (!r) {
MONGOC_ERROR ("Insert failed: %s", error.message);
mongoc_client_session_abort_transaction (session, NULL);
/* a network error, primary failover, or other temporary error in a
* transaction includes {"errorLabels": ["TransientTransactionError"]},
* meaning that trying the entire transaction again may succeed
*/
if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
goto retry_transaction;
}
goto done;
}
reply_json = bson_as_json (&reply, NULL);
printf ("%s\n", reply_json);
bson_free (reply_json);
}
/* in case of transient errors, retry for 5 seconds to commit transaction */
start = bson_get_monotonic_time ();
while (bson_get_monotonic_time () - start < 5 * 1000 * 1000) {
bson_destroy (&reply);
r = mongoc_client_session_commit_transaction (session, &reply, &error);
if (r) {
/* success */
break;
} else {
MONGOC_ERROR ("Warning: commit failed: %s", error.message);
if (mongoc_error_has_label (&reply, "TransientTransactionError")) {
goto retry_transaction;
} else if (mongoc_error_has_label (&reply,
"UnknownTransactionCommitResult")) {
/* try again to commit */
continue;
}
/* unrecoverable error trying to commit */
break;
}
}
exit_code = EXIT_SUCCESS;
done:
bson_destroy (&reply);
bson_destroy (insert_opts);
mongoc_write_concern_destroy (write_concern);
mongoc_read_concern_destroy (read_concern);
mongoc_transaction_opts_destroy (txn_opts);
mongoc_transaction_opts_destroy (default_txn_opts);
mongoc_client_session_destroy (session);
mongoc_collection_destroy (collection);
mongoc_database_destroy (database);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
mongoc_cleanup ();
return exit_code;
}
mongoc_transaction_state_t
Constants for transaction states
Synopsis
typedef enum {
MONGOC_TRANSACTION_NONE = 0,
MONGOC_TRANSACTION_STARTING = 1,
MONGOC_TRANSACTION_IN_PROGRESS = 2,
MONGOC_TRANSACTION_COMMITTED = 3,
MONGOC_TRANSACTION_ABORTED = 4,
} mongoc_transaction_state_t;
Description
These constants describe the current transaction state of a session.
Flag Values
┌───────────────────────────────┬──────────────────────────────────┐
│MONGOC_TRANSACTION_NONE │ There is no transaction in │
│ │ progress. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_TRANSACTION_STARTING │ A transaction has been started, │
│ │ but no operation has been sent │
│ │ to the server. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_TRANSACTION_IN_PROGRESS │ A transaction is in progress. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_TRANSACTION_COMMITTED │ The transaction was committed. │
├───────────────────────────────┼──────────────────────────────────┤
│MONGOC_TRANSACTION_ABORTED │ The transaction was aborted. │
└───────────────────────────────┴──────────────────────────────────┘
mongoc_update_flags_t
Flags for update operations
Synopsis
typedef enum {
MONGOC_UPDATE_NONE = 0,
MONGOC_UPDATE_UPSERT = 1 << 0,
MONGOC_UPDATE_MULTI_UPDATE = 1 << 1,
} mongoc_update_flags_t;
#define MONGOC_UPDATE_NO_VALIDATE (1U << 31)
Description
These flags correspond to the MongoDB wire protocol. They may be bitwise or'd together.
The allow for modifying the way an update is performed in the MongoDB server.
Flag Values
┌───────────────────────────┬──────────────────────────────────┐
│MONGOC_UPDATE_NONE │ No update flags set. │
└───────────────────────────┴──────────────────────────────────┘
│MONGOC_UPDATE_UPSERT │ If an upsert should be │
│ │ performed. │
├───────────────────────────┼──────────────────────────────────┤
│MONGOC_UPDATE_MULTI_UPDATE │ If more than a single matching │
│ │ document should be updated. By │
│ │ default only the first document │
│ │ is updated. │
├───────────────────────────┼──────────────────────────────────┤
│MONGOC_UPDATE_NO_VALIDATE │ Do not perform client side BSON │
│ │ validations when performing an │
│ │ update. This is useful if you │
│ │ already know your BSON documents │
│ │ are valid. │
└───────────────────────────┴──────────────────────────────────┘
mongoc_uri_t
Synopsis
typedef struct _mongoc_uri_t mongoc_uri_t;
Description
mongoc_uri_t provides an abstraction on top of the MongoDB connection URI format. It
provides standardized parsing as well as convenience methods for extracting useful
information such as replica hosts or authorization information.
See Connection String URI Reference on the MongoDB website for more information.
Format
mongodb[+srv]:// <1>
[username:password@] <2>
host1 <3>
[:port1] <4>
[,host2[:port2],...[,hostN[:portN]]] <5>
[/[database] <6>
[?options]] <7>
1. "mongodb" is the specifier of the MongoDB protocol. Use "mongodb+srv" with a single
service name in place of "host1" to specify the initial list of servers with an SRV
record.
2. An optional username and password.
3. The only required part of the uri. This specifies either a hostname, IPv4 address,
IPv6 address enclosed in "[" and "]", or UNIX domain socket.
4. An optional port number. Defaults to :27017.
5. Extra optional hosts and ports. You would specify multiple hosts, for example, for
connections to replica sets.
6. The name of the database to authenticate if the connection string includes
authentication credentials. If /database is not specified and the connection string
includes credentials, defaults to the 'admin' database.
7. Connection specific options.
NOTE:
Option names are case-insensitive. Do not repeat the same option (e.g.
"mongodb://localhost/db?opt=value1&OPT=value2") since this may have unexpected results.
The MongoDB C Driver exposes constants for each supported connection option. These
constants make it easier to discover connection options, but their string values can be
used as well.
For example, the following calls are equal.
uri = mongoc_uri_new ("mongodb://localhost/?" MONGOC_URI_APPNAME "=applicationName");
uri = mongoc_uri_new ("mongodb://localhost/?appname=applicationName");
uri = mongoc_uri_new ("mongodb://localhost/?appName=applicationName");
Replica Set Example
To describe a connection to a replica set named 'test' with the following mongod hosts:
• db1.example.com on port 27017
• db2.example.com on port 2500
You would use a connection string that resembles the following.
mongodb://db1.example.com,db2.example.com:2500/?replicaSet=test
SRV Example
If you have configured an SRV record with a name like "_mongodb._tcp.server.example.com"
whose records are a list of one or more MongoDB server hostnames, use a connection string
like this:
uri = mongoc_uri_new ("mongodb+srv://server.example.com/?replicaSet=rs&appName=applicationName");
The driver prefixes the service name with "_mongodb._tcp.", then performs a DNS SRV query
to resolve the service name to one or more hostnames. If this query succeeds, the driver
performs a DNS TXT query on the service name (without the "_mongodb._tcp" prefix) for
additional URI options configured as TXT records.
On Unix, the MongoDB C Driver relies on libresolv to look up SRV and TXT records. If
libresolv is unavailable, then using a "mongodb+srv" URI will cause an error. If your
libresolv lacks res_nsearch then the driver will fall back to res_search, which is not
thread-safe.
IPv4 and IPv6
If connecting to a hostname that has both IPv4 and IPv6 DNS records, the behavior follows
RFC-6555. A connection to the IPv6 address is attempted first. If IPv6 fails, then a
connection is attempted to the IPv4 address. If the connection attempt to IPv6 does not
complete within 250ms, then IPv4 is tried in parallel. Whichever succeeds connection first
cancels the other. The successful DNS result is cached for 10 minutes.
As a consequence, attempts to connect to a mongod only listening on IPv4 may be delayed if
there are both A (IPv4) and AAAA (IPv6) DNS records associated with the host.
To avoid a delay, configure hostnames to match the MongoDB configuration. That is, only
create an A record if the mongod is only listening on IPv4.
Connection Options
┌────────────────────────────────┬──────────────────────┬─────────────────────┬─────────────────────────────────────┐
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
│ │ │ │ mongoc_client_set_ssl_opts() │
│ │ │ │ mongoc_client_pool_set_ssl_opts().) │
└────────────────────────────────┴──────────────────────┴─────────────────────┴─────────────────────────────────────┘
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
├────────────────────────────────┼──────────────────────┼─────────────────────┼─────────────────────────────────────┤
└────────────────────────────────┴──────────────────────┴─────────────────────┴─────────────────────────────────────┘
Setting any of the *timeoutMS options above to 0 will be interpreted as "use the default
value".
Authentication Options
┌───────────────────────────────────┬─────────────────────────┬──────────────────────────┐
│Constant │ Key │ Description │
├───────────────────────────────────┼─────────────────────────┼──────────────────────────┤
│MONGOC_URI_AUTHMECHANISM │ authmechanism │ Specifies the mechanism │
│ │ │ to use when │
│ │ │ authenticating as the │
│ │ │ provided user. See │
│ │ │ Authentication for │
│ │ │ supported values. │
├───────────────────────────────────┼─────────────────────────┼──────────────────────────┤
│MONGOC_URI_AUTHMECHANISMPROPERTIES │ authmechanismproperties │ Certain authentication │
│ │ │ mechanisms have │
│ │ │ additional options that │
│ │ │ can be configured. These │
│ │ │ options should be │
│ │ │ provided as comma │
│ │ │ separated │
│ │ │ option_key:option_value │
│ │ │ pair and provided as │
│ │ │ authMechanismProperties. │
│ │ │ Specifying the same │
│ │ │ option_key multiple │
│ │ │ times has undefined │
│ │ │ behavior. │
├───────────────────────────────────┼─────────────────────────┼──────────────────────────┤
│MONGOC_URI_AUTHSOURCE │ authsource │ The authSource defines │
│ │ │ the database that should │
│ │ │ be used to authenticate │
│ │ │ to. It is unnecessary to │
│ │ │ provide this option the │
│ │ │ database name is the │
│ │ │ same as the database │
│ │ │ used in the URI. │
└───────────────────────────────────┴─────────────────────────┴──────────────────────────┘
Mechanism Properties
┌────────────────────────────────┬──────────────────────┬──────────────────────────┐
│Constant │ Key │ Description │
└────────────────────────────────┴──────────────────────┴──────────────────────────┘
│MONGOC_URI_CANONICALIZEHOSTNAME │ canonicalizehostname │ Use the canonical │
│ │ │ hostname of the service, │
│ │ │ rather than its │
│ │ │ configured alias, when │
│ │ │ authenticating with │
│ │ │ Cyrus-SASL Kerberos. │
├────────────────────────────────┼──────────────────────┼──────────────────────────┤
│MONGOC_URI_GSSAPISERVICENAME │ gssapiservicename │ Use alternative service │
│ │ │ name. The default is │
│ │ │ mongodb. │
└────────────────────────────────┴──────────────────────┴──────────────────────────┘
TLS Options
┌────────────────────────────────────────────────┬──────────────────────────────────────┬────────────────────────────────────────┐
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
├────────────────────────────────────────────────┼──────────────────────────────────────┼────────────────────────────────────────┤
└────────────────────────────────────────────────┴──────────────────────────────────────┴────────────────────────────────────────┘
See Configuring TLS for details about these options and about building libmongoc with TLS
support.
Deprecated SSL Options
The following options have been deprecated and may be removed from future releases of
libmongoc.
┌───────────────────────────────────────────┬─────────────────────────────────┬──────────────────────────────────────────┬─────────────────────────────┐
├───────────────────────────────────────────┼─────────────────────────────────┼──────────────────────────────────────────┼─────────────────────────────┤
├───────────────────────────────────────────┼─────────────────────────────────┼──────────────────────────────────────────┼─────────────────────────────┤
├───────────────────────────────────────────┼─────────────────────────────────┼──────────────────────────────────────────┼─────────────────────────────┤
├───────────────────────────────────────────┼─────────────────────────────────┼──────────────────────────────────────────┼─────────────────────────────┤
└───────────────────────────────────────────┴─────────────────────────────────┴──────────────────────────────────────────┴─────────────────────────────┘
├───────────────────────────────────────────┼─────────────────────────────────┼──────────────────────────────────────────┼─────────────────────────────┤
└───────────────────────────────────────────┴─────────────────────────────────┴──────────────────────────────────────────┴─────────────────────────────┘
Server Discovery, Monitoring, and Selection Options
Clients in a mongoc_client_pool_t share a topology scanner that runs on a background
thread. The thread wakes every heartbeatFrequencyMS (default 10 seconds) to scan all
MongoDB servers in parallel. Whenever an application operation requires a server that is
not known--for example, if there is no known primary and your application attempts an
insert--the thread rescans all servers every half-second. In this situation the pooled
client waits up to serverSelectionTimeoutMS (default 30 seconds) for the thread to find a
server suitable for the operation, then returns an error with domain
MONGOC_ERROR_SERVER_SELECTION.
Technically, the total time an operation may wait while a pooled client scans the topology
is controlled both by serverSelectionTimeoutMS and connectTimeoutMS. The longest wait
occurs if the last scan begins just at the end of the selection timeout, and a slow or
down server requires the full connection timeout before the client gives up.
A non-pooled client is single-threaded. Every heartbeatFrequencyMS, it blocks the next
application operation while it does a parallel scan. This scan takes as long as needed to
check the slowest server: roughly connectTimeoutMS. Therefore the default
heartbeatFrequencyMS for single-threaded clients is greater than for pooled clients: 60
seconds.
By default, single-threaded (non-pooled) clients scan only once when an operation requires
a server that is not known. If you attempt an insert and there is no known primary, the
client checks all servers once trying to find it, then succeeds or returns an error with
domain MONGOC_ERROR_SERVER_SELECTION. But if you set serverSelectionTryOnce to "false",
the single-threaded client loops, checking all servers every half-second, until
serverSelectionTimeoutMS.
The total time an operation may wait for a single-threaded client to scan the topology is
determined by connectTimeoutMS in the try-once case, or serverSelectionTimeoutMS and
connectTimeoutMS if serverSelectionTryOnce is set "false".
┌────────────────────────────────────┬──────────────────────────┬──────────────────────────┐
│Constant │ Key │ Description │
├────────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│MONGOC_URI_HEARTBEATFREQUENCYMS │ heartbeatfrequencyms │ The interval between │
│ │ │ server monitoring │
│ │ │ checks. Defaults to │
│ │ │ 10,000ms (10 seconds) in │
│ │ │ pooled (multi-threaded) │
│ │ │ mode, 60,000ms (60 │
│ │ │ seconds) in non-pooled │
│ │ │ mode (single-threaded). │
├────────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│MONGOC_URI_SERVERSELECTIONTIMEOUTMS │ serverselectiontimeoutms │ A timeout in │
│ │ │ milliseconds to block │
│ │ │ for server selection │
│ │ │ before throwing an │
│ │ │ exception. The default │
│ │ │ is 30,0000ms (30 │
│ │ │ seconds). │
└────────────────────────────────────┴──────────────────────────┴──────────────────────────┘
│MONGOC_URI_SERVERSELECTIONTRYONCE │ serverselectiontryonce │ If "true", the driver │
│ │ │ scans the topology │
│ │ │ exactly once after │
│ │ │ server selection fails, │
│ │ │ then either selects a │
│ │ │ server or returns an │
│ │ │ error. If it is false, │
│ │ │ then the driver │
│ │ │ repeatedly searches for │
│ │ │ a suitable server for up │
│ │ │ to │
│ │ │ serverSelectionTimeoutMS │
│ │ │ milliseconds (pausing a │
│ │ │ half second between │
│ │ │ attempts). The default │
│ │ │ for │
│ │ │ serverSelectionTryOnce │
│ │ │ is "false" for pooled │
│ │ │ clients, otherwise │
│ │ │ "true". Pooled clients │
│ │ │ ignore │
│ │ │ serverSelectionTryOnce; │
│ │ │ they signal the thread │
│ │ │ to rescan the topology │
│ │ │ every half-second until │
│ │ │ serverSelectionTimeoutMS │
│ │ │ expires. │
├────────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│MONGOC_URI_SOCKETCHECKINTERVALMS │ socketcheckintervalms │ Only applies to single │
│ │ │ threaded clients. If a │
│ │ │ socket has not been used │
│ │ │ within this time, its │
│ │ │ connection is checked │
│ │ │ with a quick "hello" │
│ │ │ call before it is used │
│ │ │ again. Defaults to │
│ │ │ 5,000ms (5 seconds). │
├────────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│MONGOC_URI_DIRECTCONNECTION │ directconnection │ If "true", the driver │
│ │ │ connects to a single │
│ │ │ server directly and will │
│ │ │ not monitor additional │
│ │ │ servers. If "false", │
│ │ │ the driver connects │
│ │ │ based on the presence │
│ │ │ and value of the │
│ │ │ replicaSet option. │
└────────────────────────────────────┴──────────────────────────┴──────────────────────────┘
Setting any of the *TimeoutMS options above to 0 will be interpreted as "use the default
value".
Connection Pool Options
These options govern the behavior of a mongoc_client_pool_t. They are ignored by a
non-pooled mongoc_client_t.
┌──────────────────────────────┬────────────────────┬──────────────────────────┐
│Constant │ Key │ Description │
├──────────────────────────────┼────────────────────┼──────────────────────────┤
│MONGOC_URI_MAXPOOLSIZE │ maxpoolsize │ The maximum number of │
│ │ │ clients created by a │
│ │ │ mongoc_client_pool_t │
│ │ │ total (both in the pool │
│ │ │ and checked out). The │
│ │ │ default value is 100. │
│ │ │ Once it is reached, │
│ │ │ mongoc_client_pool_pop() │
│ │ │ blocks until another │
│ │ │ thread pushes a client. │
├──────────────────────────────┼────────────────────┼──────────────────────────┤
│MONGOC_URI_MINPOOLSIZE │ minpoolsize │ Deprecated. This │
│ │ │ option's behavior does │
│ │ │ not match its name, and │
│ │ │ its actual behavior will │
│ │ │ likely hurt performance. │
├──────────────────────────────┼────────────────────┼──────────────────────────┤
│MONGOC_URI_MAXIDLETIMEMS │ maxidletimems │ Not implemented. │
├──────────────────────────────┼────────────────────┼──────────────────────────┤
│MONGOC_URI_WAITQUEUEMULTIPLE │ waitqueuemultiple │ Not implemented. │
└──────────────────────────────┴────────────────────┴──────────────────────────┘
│MONGOC_URI_WAITQUEUETIMEOUTMS │ waitqueuetimeoutms │ The maximum time to wait │
│ │ │ for a client to become │
│ │ │ available from the pool. │
└──────────────────────────────┴────────────────────┴──────────────────────────┘
Write Concern Options
┌──────────────────────┬────────────┬──────────────────────────┐
│Constant │ Key │ Description │
└──────────────────────┴────────────┴──────────────────────────┘
MONGOC_URI_W w Determines the write
concern (guarantee).
Valid values:
• 0 = The driver
will not
acknowledge
write
operations but
will pass or
handle any
network and
socket errors
that it
receives to the
client. If you
disable write
concern but
enable the
getLastError
command’s w
option, w
overrides the w
option.
• 1 = Provides
basic
acknowledgement
of write
operations. By
specifying 1,
you require
that a
standalone
mongod
instance, or
the primary for
replica sets,
acknowledge all
write
operations. For
drivers
released after
the default
write concern
change, this is
the default
write concern
setting.
• majority = For
replica sets,
if you specify
the special
majority value
to w option,
write
operations will
only return
successfully
after a
majority of the
configured
replica set
members have
acknowledged
the write
operation.
• n = For replica
sets, if you
specify a
number n
greater than 1,
operations with
this write
concern return
only after n
members of the
set have
acknowledged
the write. If
you set n to a
number that is
greater than
the number of
available set
members or
members that
hold data,
MongoDB will
wait,
potentially
indefinitely,
for these
members to
become
available.
• tags = For
replica sets,
you can specify
a tag set to
require that
all members of
the set that
have these tags
configured
return
confirmation of
the write
operation.
├──────────────────────┼────────────┼──────────────────────────┤
│MONGOC_URI_WTIMEOUTMS │ wtimeoutms │ The time in milliseconds │
│ │ │ to wait for replication │
│ │ │ to succeed, as specified │
│ │ │ in the w option, before │
│ │ │ timing out. When │
│ │ │ wtimeoutMS is 0, write │
│ │ │ operations will never │
│ │ │ time out. │
├──────────────────────┼────────────┼──────────────────────────┤
│MONGOC_URI_JOURNAL │ journal │ Controls whether write │
│ │ │ operations will wait │
│ │ │ until the mongod │
│ │ │ acknowledges the write │
│ │ │ operations and commits │
│ │ │ the data to the on disk │
│ │ │ journal. │
│ │ │ │
│ │ │ • true = Enables │
│ │ │ journal commit │
│ │ │ acknowledgement │
│ │ │ write concern. │
│ │ │ Equivalent to │
│ │ │ specifying the │
│ │ │ getLastError │
│ │ │ command with │
│ │ │ the j option │
│ │ │ enabled. │
│ │ │ │
│ │ │ • false = Does │
│ │ │ not require │
│ │ │ that mongod │
│ │ │ commit write │
│ │ │ operations to │
│ │ │ the journal │
│ │ │ before │
│ │ │ acknowledging │
│ │ │ the write │
│ │ │ operation. This │
│ │ │ is the default │
│ │ │ option for the │
│ │ │ journal │
│ │ │ parameter. │
└──────────────────────┴────────────┴──────────────────────────┘
Read Concern Options
┌────────────────────────────┬──────────────────┬──────────────────────────┐
│Constant │ Key │ Description │
├────────────────────────────┼──────────────────┼──────────────────────────┤
│MONGOC_URI_READCONCERNLEVEL │ readconcernlevel │ The level of isolation │
│ │ │ for read operations. If │
│ │ │ the level is left │
│ │ │ unspecified, the server │
│ │ │ default will be used. │
│ │ │ See readConcern in the │
│ │ │ MongoDB Manual for │
│ │ │ details. │
└────────────────────────────┴──────────────────┴──────────────────────────┘
Read Preference Options
When connected to a replica set, the driver chooses which member to query using the read
preference:
1. Choose members whose type matches "readPreference".
2. From these, if there are any tags sets configured, choose members matching the first
tag set. If there are none, fall back to the next tag set and so on, until some members
are chosen or the tag sets are exhausted.
3. From the chosen servers, distribute queries randomly among the server with the fastest
round-trip times. These include the server with the fastest time and any whose
round-trip time is no more than "localThresholdMS" slower.
┌───────────────────────────────┬─────────────────────┬─────────────────────────────┐
│Constant │ Key │ Description │
└───────────────────────────────┴─────────────────────┴─────────────────────────────┘
│MONGOC_URI_READPREFERENCE │ readpreference │ Specifies the replica │
│ │ │ set read preference for │
│ │ │ this connection. This │
│ │ │ setting overrides any │
│ │ │ secondaryOk value. The │
│ │ │ read preference values │
│ │ │ are the following: │
│ │ │ │
│ │ │ • primary │
│ │ │ (default) │
│ │ │ │
│ │ │ • primaryPreferred │
│ │ │ │
│ │ │ • secondary │
│ │ │ │
│ │ │ • secondaryPreferred │
│ │ │ │
│ │ │ • nearest │
├───────────────────────────────┼─────────────────────┼─────────────────────────────┤
│MONGOC_URI_READPREFERENCETAGS │ readpreferencetags │ A representation of a tag │
│ │ │ set. See also Tag Sets. │
├───────────────────────────────┼─────────────────────┼─────────────────────────────┤
│MONGOC_URI_LOCALTHRESHOLDMS │ localthresholdms │ How far to distribute │
│ │ │ queries, beyond the server │
│ │ │ with the fastest round-trip │
│ │ │ time. By default, only │
│ │ │ servers within 15ms of the │
│ │ │ fastest round-trip time │
│ │ │ receive queries. │
├───────────────────────────────┼─────────────────────┼─────────────────────────────┤
│MONGOC_URI_MAXSTALENESSSECONDS │ maxstalenessseconds │ The maximum replication │
│ │ │ lag, in wall clock time, │
│ │ │ that a secondary can suffer │
│ │ │ and still be eligible. The │
│ │ │ smallest allowed value for │
│ │ │ maxStalenessSeconds is 90 │
│ │ │ seconds. │
└───────────────────────────────┴─────────────────────┴─────────────────────────────┘
NOTE:
When connecting to more than one mongos, libmongoc's localThresholdMS applies only to
the selection of mongos servers. The threshold for selecting among replica set members
in shards is controlled by the mongos's localThreshold command line option.
Legacy Options
For historical reasons, the following options are available. They should however not be
used.
┌────────────────┬──────┬──────────────────────────┐
│Constant │ Key │ Description │
├────────────────┼──────┼──────────────────────────┤
│MONGOC_URI_SAFE │ safe │ {true|false} Same as │
│ │ │ w={1|0} │
└────────────────┴──────┴──────────────────────────┘
Version Checks
Conditional compilation based on mongoc version
Description
The following preprocessor macros can be used to perform various checks based on the
version of the library you are compiling against. This may be useful if you only want to
enable a feature on a certain version of the library.
#include <mongoc/mongoc.h>
#define MONGOC_MAJOR_VERSION (x)
#define MONGOC_MINOR_VERSION (y)
#define MONGOC_MICRO_VERSION (z)
#define MONGOC_VERSION_S "x.y.z"
#define MONGOC_VERSION_HEX ((1 << 24) | (0 << 16) | (0 << 8) | 0)
#define MONGOC_CHECK_VERSION(major, minor, micro)
Only compile a block on MongoDB C Driver 1.1.0 and newer.
#if MONGOC_CHECK_VERSION(1, 1, 0)
static void
do_something (void)
{
}
#endif
mongoc_write_concern_t
Write Concern abstraction
Synopsis
mongoc_write_concern_t tells the driver what level of acknowledgement to await from the
server. The default, MONGOC_WRITE_CONCERN_W_DEFAULT, is right for the great majority of
applications.
You can specify a write concern on connection objects, database objects, collection
objects, or per-operation. Data-modifying operations typically use the write concern of
the object they operate on, and check the server response for a write concern error or
write concern timeout. For example, mongoc_collection_drop_index() uses the collection's
write concern, and a write concern error or timeout in the response is considered a
failure.
Exceptions to this principle are the generic command functions:
• mongoc_client_command()
• mongoc_client_command_simple()
• mongoc_database_command()
• mongoc_database_command_simple()
• mongoc_collection_command()
• mongoc_collection_command_simple()
These generic command functions do not automatically apply a write concern, and they do
not check the server response for a write concern error or write concern timeout.
See Write Concern on the MongoDB website for more information.
Write Concern Levels
Set the write concern level with mongoc_write_concern_set_w().
┌──────────────────────────────────────┬──────────────────────────────────┐
│MONGOC_WRITE_CONCERN_W_DEFAULT │ By default, writes block │
│(1) │ awaiting acknowledgement from │
│ │ MongoDB. Acknowledged write │
│ │ concern allows clients to catch │
│ │ network, duplicate key, and │
│ │ other errors. │
├──────────────────────────────────────┼──────────────────────────────────┤
│MONGOC_WRITE_CONCERN_W_UNACKNOWLEDGED │ With this write concern, MongoDB │
│(0) │ does not acknowledge the receipt │
│ │ of write operation. │
│ │ Unacknowledged is similar to │
│ │ errors ignored; however, mongoc │
│ │ attempts to receive and handle │
│ │ network errors when possible. │
├──────────────────────────────────────┼──────────────────────────────────┤
│MONGOC_WRITE_CONCERN_W_MAJORITY │ Block until a write has been │
│(majority) │ propagated to a majority of the │
│ │ nodes in the replica set. │
├──────────────────────────────────────┼──────────────────────────────────┤
│n │ Block until a write has been │
│ │ propagated to at least n nodes │
│ │ in the replica set. │
└──────────────────────────────────────┴──────────────────────────────────┘
Deprecations
The write concern MONGOC_WRITE_CONCERN_W_ERRORS_IGNORED (value -1) is a deprecated synonym
for MONGOC_WRITE_CONCERN_W_UNACKNOWLEDGED (value 0), and will be removed in the next major
release.
mongoc_write_concern_set_fsync() is deprecated.
Application Performance Monitoring (APM)
The MongoDB C Driver allows you to monitor all the MongoDB operations the driver executes.
This event-notification system conforms to two MongoDB driver specs:
• Command Monitoring: events related to all application operations.
• SDAM Monitoring: events related to the driver's Server Discovery And Monitoring logic.
To receive notifications, create a mongoc_apm_callbacks_t with mongoc_apm_callbacks_new(),
set callbacks on it, then pass it to mongoc_client_set_apm_callbacks() or
mongoc_client_pool_set_apm_callbacks().
Command-Monitoring Example
example-command-monitoring.c
/* gcc example-command-monitoring.c -o example-command-monitoring \
* $(pkg-config --cflags --libs libmongoc-1.0) */
/* ./example-command-monitoring [CONNECTION_STRING] */
#include <mongoc/mongoc.h>
#include <stdio.h>
typedef struct {
int started;
int succeeded;
int failed;
} stats_t;
void
command_started (const mongoc_apm_command_started_t *event)
{
char *s;
s = bson_as_relaxed_extended_json (
mongoc_apm_command_started_get_command (event), NULL);
printf ("Command %s started on %s:\n%s\n\n",
mongoc_apm_command_started_get_command_name (event),
mongoc_apm_command_started_get_host (event)->host,
s);
((stats_t *) mongoc_apm_command_started_get_context (event))->started++;
bson_free (s);
}
void
command_succeeded (const mongoc_apm_command_succeeded_t *event)
{
char *s;
s = bson_as_relaxed_extended_json (
mongoc_apm_command_succeeded_get_reply (event), NULL);
printf ("Command %s succeeded:\n%s\n\n",
mongoc_apm_command_succeeded_get_command_name (event),
s);
((stats_t *) mongoc_apm_command_succeeded_get_context (event))->succeeded++;
bson_free (s);
}
void
command_failed (const mongoc_apm_command_failed_t *event)
{
bson_error_t error;
mongoc_apm_command_failed_get_error (event, &error);
printf ("Command %s failed:\n\"%s\"\n\n",
mongoc_apm_command_failed_get_command_name (event),
error.message);
((stats_t *) mongoc_apm_command_failed_get_context (event))->failed++;
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_apm_callbacks_t *callbacks;
stats_t stats = {0};
mongoc_collection_t *collection;
bson_error_t error;
const char *uri_string =
"mongodb://127.0.0.1/?appname=cmd-monitoring-example";
mongoc_uri_t *uri;
const char *collection_name = "test";
bson_t *docs[2];
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
callbacks = mongoc_apm_callbacks_new ();
mongoc_apm_set_command_started_cb (callbacks, command_started);
mongoc_apm_set_command_succeeded_cb (callbacks, command_succeeded);
mongoc_apm_set_command_failed_cb (callbacks, command_failed);
mongoc_client_set_apm_callbacks (
client, callbacks, (void *) &stats /* context pointer */);
collection = mongoc_client_get_collection (client, "test", collection_name);
mongoc_collection_drop (collection, NULL);
docs[0] = BCON_NEW ("_id", BCON_INT32 (0));
docs[1] = BCON_NEW ("_id", BCON_INT32 (1));
mongoc_collection_insert_many (
collection, (const bson_t **) docs, 2, NULL, NULL, NULL);
/* duplicate key error on the second insert */
mongoc_collection_insert_one (collection, docs[0], NULL, NULL, NULL);
mongoc_collection_destroy (collection);
mongoc_apm_callbacks_destroy (callbacks);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
printf ("started: %d\nsucceeded: %d\nfailed: %d\n",
stats.started,
stats.succeeded,
stats.failed);
bson_destroy (docs[0]);
bson_destroy (docs[1]);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
This example program prints:
Command drop started on 127.0.0.1:
{ "drop" : "test" }
Command drop succeeded:
{ "ns" : "test.test", "nIndexesWas" : 1, "ok" : 1.0 }
Command insert started on 127.0.0.1:
{
"insert" : "test",
"ordered" : true,
"documents" : [
{ "_id" : 0 }, { "_id" : 1 }
]
}
Command insert succeeded:
{ "n" : 2, "ok" : 1.0 }
Command insert started on 127.0.0.1:
{
"insert" : "test",
"ordered" : true,
"documents" : [
{ "_id" : 0 }
]
}
Command insert succeeded:
{
"n" : 0,
"writeErrors" : [
{ "index" : 0, "code" : 11000, "errmsg" : "duplicate key" }
],
"ok" : 1.0
}
started: 3
succeeded: 3
failed: 0
The output has been edited and formatted for clarity. Depending on your server
configuration, messages may include metadata like database name, logical session ids, or
cluster times that are not shown here.
The final "insert" command is considered successful, despite the writeError, because the
server replied to the overall command with "ok": 1.
SDAM Monitoring Example
example-sdam-monitoring.c
/* gcc example-sdam-monitoring.c -o example-sdam-monitoring \
* $(pkg-config --cflags --libs libmongoc-1.0) */
/* ./example-sdam-monitoring [CONNECTION_STRING] */
#include <mongoc/mongoc.h>
#include <stdio.h>
typedef struct {
int server_changed_events;
int server_opening_events;
int server_closed_events;
int topology_changed_events;
int topology_opening_events;
int topology_closed_events;
int heartbeat_started_events;
int heartbeat_succeeded_events;
int heartbeat_failed_events;
} stats_t;
static void
server_changed (const mongoc_apm_server_changed_t *event)
{
stats_t *context;
const mongoc_server_description_t *prev_sd, *new_sd;
context = (stats_t *) mongoc_apm_server_changed_get_context (event);
context->server_changed_events++;
prev_sd = mongoc_apm_server_changed_get_previous_description (event);
new_sd = mongoc_apm_server_changed_get_new_description (event);
printf ("server changed: %s %s -> %s\n",
mongoc_apm_server_changed_get_host (event)->host_and_port,
mongoc_server_description_type (prev_sd),
mongoc_server_description_type (new_sd));
}
static void
server_opening (const mongoc_apm_server_opening_t *event)
{
stats_t *context;
context = (stats_t *) mongoc_apm_server_opening_get_context (event);
context->server_opening_events++;
printf ("server opening: %s\n",
mongoc_apm_server_opening_get_host (event)->host_and_port);
}
static void
server_closed (const mongoc_apm_server_closed_t *event)
{
stats_t *context;
context = (stats_t *) mongoc_apm_server_closed_get_context (event);
context->server_closed_events++;
printf ("server closed: %s\n",
mongoc_apm_server_closed_get_host (event)->host_and_port);
}
static void
topology_changed (const mongoc_apm_topology_changed_t *event)
{
stats_t *context;
const mongoc_topology_description_t *prev_td;
const mongoc_topology_description_t *new_td;
mongoc_server_description_t **prev_sds;
size_t n_prev_sds;
mongoc_server_description_t **new_sds;
size_t n_new_sds;
size_t i;
mongoc_read_prefs_t *prefs;
context = (stats_t *) mongoc_apm_topology_changed_get_context (event);
context->topology_changed_events++;
prev_td = mongoc_apm_topology_changed_get_previous_description (event);
prev_sds = mongoc_topology_description_get_servers (prev_td, &n_prev_sds);
new_td = mongoc_apm_topology_changed_get_new_description (event);
new_sds = mongoc_topology_description_get_servers (new_td, &n_new_sds);
printf ("topology changed: %s -> %s\n",
mongoc_topology_description_type (prev_td),
mongoc_topology_description_type (new_td));
if (n_prev_sds) {
printf (" previous servers:\n");
for (i = 0; i < n_prev_sds; i++) {
printf (" %s %s\n",
mongoc_server_description_type (prev_sds[i]),
mongoc_server_description_host (prev_sds[i])->host_and_port);
}
}
if (n_new_sds) {
printf (" new servers:\n");
for (i = 0; i < n_new_sds; i++) {
printf (" %s %s\n",
mongoc_server_description_type (new_sds[i]),
mongoc_server_description_host (new_sds[i])->host_and_port);
}
}
prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
/* it is safe, and unfortunately necessary, to cast away const here */
if (mongoc_topology_description_has_readable_server (
(mongoc_topology_description_t *) new_td, prefs)) {
printf (" secondary AVAILABLE\n");
} else {
printf (" secondary UNAVAILABLE\n");
}
if (mongoc_topology_description_has_writable_server (
(mongoc_topology_description_t *) new_td)) {
printf (" primary AVAILABLE\n");
} else {
printf (" primary UNAVAILABLE\n");
}
mongoc_read_prefs_destroy (prefs);
mongoc_server_descriptions_destroy_all (prev_sds, n_prev_sds);
mongoc_server_descriptions_destroy_all (new_sds, n_new_sds);
}
static void
topology_opening (const mongoc_apm_topology_opening_t *event)
{
stats_t *context;
context = (stats_t *) mongoc_apm_topology_opening_get_context (event);
context->topology_opening_events++;
printf ("topology opening\n");
}
static void
topology_closed (const mongoc_apm_topology_closed_t *event)
{
stats_t *context;
context = (stats_t *) mongoc_apm_topology_closed_get_context (event);
context->topology_closed_events++;
printf ("topology closed\n");
}
static void
server_heartbeat_started (const mongoc_apm_server_heartbeat_started_t *event)
{
stats_t *context;
context =
(stats_t *) mongoc_apm_server_heartbeat_started_get_context (event);
context->heartbeat_started_events++;
printf ("%s heartbeat started\n",
mongoc_apm_server_heartbeat_started_get_host (event)->host_and_port);
}
static void
server_heartbeat_succeeded (
const mongoc_apm_server_heartbeat_succeeded_t *event)
{
stats_t *context;
char *reply;
context =
(stats_t *) mongoc_apm_server_heartbeat_succeeded_get_context (event);
context->heartbeat_succeeded_events++;
reply = bson_as_canonical_extended_json (
mongoc_apm_server_heartbeat_succeeded_get_reply (event), NULL);
printf (
"%s heartbeat succeeded: %s\n",
mongoc_apm_server_heartbeat_succeeded_get_host (event)->host_and_port,
reply);
bson_free (reply);
}
static void
server_heartbeat_failed (const mongoc_apm_server_heartbeat_failed_t *event)
{
stats_t *context;
bson_error_t error;
context = (stats_t *) mongoc_apm_server_heartbeat_failed_get_context (event);
context->heartbeat_failed_events++;
mongoc_apm_server_heartbeat_failed_get_error (event, &error);
printf ("%s heartbeat failed: %s\n",
mongoc_apm_server_heartbeat_failed_get_host (event)->host_and_port,
error.message);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_apm_callbacks_t *cbs;
stats_t stats = {0};
const char *uri_string =
"mongodb://127.0.0.1/?appname=sdam-monitoring-example";
mongoc_uri_t *uri;
bson_t cmd = BSON_INITIALIZER;
bson_t reply;
bson_error_t error;
mongoc_init ();
if (argc > 1) {
uri_string = argv[1];
}
uri = mongoc_uri_new_with_error (uri_string, &error);
if (!uri) {
fprintf (stderr,
"failed to parse URI: %s\n"
"error message: %s\n",
uri_string,
error.message);
return EXIT_FAILURE;
}
client = mongoc_client_new_from_uri (uri);
if (!client) {
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
cbs = mongoc_apm_callbacks_new ();
mongoc_apm_set_server_changed_cb (cbs, server_changed);
mongoc_apm_set_server_opening_cb (cbs, server_opening);
mongoc_apm_set_server_closed_cb (cbs, server_closed);
mongoc_apm_set_topology_changed_cb (cbs, topology_changed);
mongoc_apm_set_topology_opening_cb (cbs, topology_opening);
mongoc_apm_set_topology_closed_cb (cbs, topology_closed);
mongoc_apm_set_server_heartbeat_started_cb (cbs, server_heartbeat_started);
mongoc_apm_set_server_heartbeat_succeeded_cb (cbs,
server_heartbeat_succeeded);
mongoc_apm_set_server_heartbeat_failed_cb (cbs, server_heartbeat_failed);
mongoc_client_set_apm_callbacks (
client, cbs, (void *) &stats /* context pointer */);
/* the driver connects on demand to perform first operation */
BSON_APPEND_INT32 (&cmd, "buildinfo", 1);
mongoc_client_command_simple (client, "admin", &cmd, NULL, &reply, &error);
mongoc_uri_destroy (uri);
mongoc_client_destroy (client);
printf ("Events:\n"
" server changed: %d\n"
" server opening: %d\n"
" server closed: %d\n"
" topology changed: %d\n"
" topology opening: %d\n"
" topology closed: %d\n"
" heartbeat started: %d\n"
" heartbeat succeeded: %d\n"
" heartbeat failed: %d\n",
stats.server_changed_events,
stats.server_opening_events,
stats.server_closed_events,
stats.topology_changed_events,
stats.topology_opening_events,
stats.topology_closed_events,
stats.heartbeat_started_events,
stats.heartbeat_succeeded_events,
stats.heartbeat_failed_events);
bson_destroy (&cmd);
bson_destroy (&reply);
mongoc_apm_callbacks_destroy (cbs);
mongoc_cleanup ();
return EXIT_SUCCESS;
}
Start a 3-node replica set on localhost with set name "rs" and start the program:
./example-sdam-monitoring "mongodb://localhost:27017,localhost:27018/?replicaSet=rs"
This example program prints something like:
topology opening
topology changed: Unknown -> ReplicaSetNoPrimary
secondary UNAVAILABLE
primary UNAVAILABLE
server opening: localhost:27017
server opening: localhost:27018
localhost:27017 heartbeat started
localhost:27018 heartbeat started
localhost:27017 heartbeat succeeded: { ... reply ... }
server changed: localhost:27017 Unknown -> RSPrimary
server opening: localhost:27019
topology changed: ReplicaSetNoPrimary -> ReplicaSetWithPrimary
new servers:
RSPrimary localhost:27017
secondary UNAVAILABLE
primary AVAILABLE
localhost:27019 heartbeat started
localhost:27018 heartbeat succeeded: { ... reply ... }
server changed: localhost:27018 Unknown -> RSSecondary
topology changed: ReplicaSetWithPrimary -> ReplicaSetWithPrimary
previous servers:
RSPrimary localhost:27017
new servers:
RSPrimary localhost:27017
RSSecondary localhost:27018
secondary AVAILABLE
primary AVAILABLE
localhost:27019 heartbeat succeeded: { ... reply ... }
server changed: localhost:27019 Unknown -> RSSecondary
topology changed: ReplicaSetWithPrimary -> ReplicaSetWithPrimary
previous servers:
RSPrimary localhost:27017
RSSecondary localhost:27018
new servers:
RSPrimary localhost:27017
RSSecondary localhost:27018
RSSecondary localhost:27019
secondary AVAILABLE
primary AVAILABLE
topology closed
Events:
server changed: 3
server opening: 3
server closed: 0
topology changed: 4
topology opening: 1
topology closed: 1
heartbeat started: 3
heartbeat succeeded: 3
heartbeat failed: 0
The driver connects to the mongods on ports 27017 and 27018, which were specified in the
URI, and determines which is primary. It also discovers the third member,
"localhost:27019", and adds it to the topology.
AUTHOR
MongoDB, Inc
COPYRIGHT
2017-present, MongoDB, Inc