Provided by: libmongoc-doc_1.24.3-1_all 
NAME
mongoc_guides - 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 (void)
{
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 (void)
{
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 (void)
{
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 (void)
{
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 (void)
{
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 (void)
{
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 (void)
{
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 (void)
{
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.
MANAGE COLLECTION INDEXES
To create indexes on a MongoDB collection, use
mongoc_collection_create_indexes_with_opts():
// `keys` represents an ascending index on field `x`.
bson_t *keys = BCON_NEW ("x", BCON_INT32 (1));
mongoc_index_model_t *im = mongoc_index_model_new (keys, NULL /* opts */);
if (mongoc_collection_create_indexes_with_opts (
coll, &im, 1, NULL /* opts */, NULL /* reply */, &error)) {
printf ("Successfully created index\n");
} else {
bson_destroy (keys);
HANDLE_ERROR ("Failed to create index: %s", error.message);
}
bson_destroy (keys);
To list indexes, use mongoc_collection_find_indexes_with_opts():
mongoc_cursor_t *cursor =
mongoc_collection_find_indexes_with_opts (coll, NULL /* opts */);
printf ("Listing indexes:\n");
const bson_t *got;
while (mongoc_cursor_next (cursor, &got)) {
char *got_str = bson_as_canonical_extended_json (got, NULL);
printf (" %s\n", got_str);
bson_free (got_str);
}
if (mongoc_cursor_error (cursor, &error)) {
mongoc_cursor_destroy (cursor);
HANDLE_ERROR ("Failed to list indexes: %s", error.message);
}
mongoc_cursor_destroy (cursor);
To drop an index, use mongoc_collection_drop_index_with_opts(). The index name may be
obtained from the keys document with mongoc_collection_keys_to_index_string():
bson_t *keys = BCON_NEW ("x", BCON_INT32 (1));
char *index_name = mongoc_collection_keys_to_index_string (keys);
if (mongoc_collection_drop_index_with_opts (
coll, index_name, NULL /* opts */, &error)) {
printf ("Successfully dropped index\n");
} else {
bson_free (index_name);
bson_destroy (keys);
HANDLE_ERROR ("Failed to drop index: %s", error.message);
}
bson_free (index_name);
bson_destroy (keys);
For a full example, see example-manage-collection-indexes.c.
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
The mongo-c-driver repository contains a script lldb_bson.py that can be imported into an
LLDB sessions and allows rich inspection of BSON values.
NOTE:
The lldb_bson.py module requires an LLDB with Python 3.8 or newer.
To activate the script, import it from the LLDB command line:
(lldb) command script import /path/to/mongo-c-driver/lldb_bson.py
Upon success, the message lldb_bson is ready will be printed to the LLDB console.
The import of this script can be made automatic by adding the command to an .lldbinit
file. For example: Create a file ~/.lldbinit containing:
command script import /path/to/mongo-c-driver/lldb_bson.py
The docstring at the top of the lldb_bson.py file contains more information on the
capabilities of the module.
Debug assertions
To enable runtime debug assertions, configure with -DENABLE_DEBUG_ASSERTIONS=ON.
IN-USE ENCRYPTION
In-Use Encryption consists of two features:
Client-Side Field Level Encryption
New in MongoDB 4.2, Client-Side Field Level Encryption (also referred to as CSFLE) allows
administrators and developers to encrypt specific data fields in addition to other MongoDB
encryption features.
With CSFLE, developers can encrypt fields client side without any server-side
configuration or directives. CSFLE 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 dependency for Query Analysis. See In-Use Encryption for more
information.
SEE ALSO:
The MongoDB Manual for Client-Side Field Level Encryption
Automatic Client-Side Field Level Encryption
Automatic encryption is enabled by calling mongoc_client_enable_auto_encryption() on a
mongoc_client_t. The following examples show how to set up automatic encryption using
mongoc_client_encryption_t to create a new encryption data key.
NOTE:
Automatic 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 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 ret;
}
/* This example demonstrates how to use automatic encryption with a client-side
* schema map using the enterprise version of MongoDB */
int
main (void)
{
/* 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;
bson_t *index_opts = NULL;
mongoc_index_model_t *index_model = 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");
BSON_ASSERT (keyvault_client);
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_opts = BCON_NEW ("unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}");
index_model = mongoc_index_model_new (index_keys, index_opts);
ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
&index_model,
1,
NULL /* opts */,
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");
BSON_ASSERT (client);
/* 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");
BSON_ASSERT (unencrypted_client);
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);
mongoc_index_model_destroy (index_model);
bson_destroy (index_opts);
bson_destroy (index_keys);
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 encryption using
mongoc_client_encryption_t to create a new encryption data key and create a collection
with the necessary JSON Schema:
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 (void)
{
/* 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;
bson_t *index_opts = NULL;
mongoc_index_model_t *index_model = 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");
BSON_ASSERT (keyvault_client);
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_opts = BCON_NEW ("unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}");
index_model = mongoc_index_model_new (index_keys, index_opts);
ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
&index_model,
1,
NULL /* opts */,
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");
BSON_ASSERT (client);
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");
BSON_ASSERT (unencrypted_client);
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);
mongoc_index_model_destroy (index_model);
bson_destroy (index_opts);
bson_destroy (index_keys);
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 Query Analysis
(mongocryptd or crypt_shared). 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 (void)
{
/* 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;
bson_t *index_opts = NULL;
mongoc_index_model_t *index_model = 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_opts = BCON_NEW ("unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}");
index_model = mongoc_index_model_new (index_keys, index_opts);
ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
&index_model,
1,
NULL /* opts */,
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";
const size_t len = strlen (to_encrypt.value.v_utf8.str);
BSON_ASSERT (bson_in_range_unsigned (uint32_t, len));
to_encrypt.value.v_utf8.len = (uint32_t) len;
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);
mongoc_index_model_destroy (index_model);
bson_destroy (index_opts);
bson_destroy (index_keys);
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 (void)
{
/* 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;
bson_t *index_opts = NULL;
mongoc_index_model_t *index_model = 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_opts = BCON_NEW ("unique",
BCON_BOOL (true),
"partialFilterExpression",
"{",
"keyAltNames",
"{",
"$exists",
BCON_BOOL (true),
"}",
"}");
index_model = mongoc_index_model_new (index_keys, index_opts);
ret = mongoc_collection_create_indexes_with_opts (keyvault_coll,
&index_model,
1,
NULL /* opts */,
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";
const size_t len = strlen (to_encrypt.value.v_utf8.str);
BSON_ASSERT (bson_in_range_unsigned (uint32_t, len));
to_encrypt.value.v_utf8.len = (uint32_t) len;
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);
mongoc_index_model_destroy (index_model);
bson_destroy (index_opts);
bson_destroy (index_keys);
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;
}
Queryable Encryption
Using Queryable Encryption requires MongoDB Server 7.0 or higher.
See the MongoDB Manual for Queryable Encryption for more information about the feature.
API related to the "rangePreview" algorithm is still experimental and subject to breaking
changes!
Queryable Encryption in older MongoDB Server versions
MongoDB Server 6.0 introduced Queryable Encryption as a Public Technical Preview. MongoDB
Server 7.0 includes backwards breaking changes to the Queryable Encryption protocol.
The backwards breaking changes are applied in the client protocol in libmongocrypt 1.8.0.
libmongoc 1.24.0 requires libmongocrypt 1.8.0 or newer. libmongoc 1.24.0 no longer
supports Queryable Encryption in MongoDB Server <7.0. Using Queryable Encryption
libmongoc 1.24.0 and higher requires MongoDB Server >=7.0.
Using Queryable Encryption with libmongocrypt<1.8.0 on a MongoDB Server>=7.0, or using
libmongocrypt>=1.8.0 on a MongoDB Server<6.0 will result in a server error when using the
incompatible protocol.
SEE ALSO:
The MongoDB Manual for Queryable Encryption
Installation
Using In-Use Encryption in the C driver requires the dependency libmongocrypt. See the
MongoDB Manual for libmongocrypt installation instructions.
Once libmongocrypt is installed, configure the C driver with
-DENABLE_CLIENT_SIDE_ENCRYPTION=ON to require In-Use Encryption be enabled.
$ cd mongo-c-driver
$ mkdir cmake-build && cd cmake-build
$ cmake -DENABLE_AUTOMATIC_INIT_AND_CLEANUP=OFF -DENABLE_CLIENT_SIDE_ENCRYPTION=ON ..
$ cmake --build . --target install
API
mongoc_client_encryption_t is used for explicit encryption and key management.
mongoc_client_enable_auto_encryption() and mongoc_client_pool_enable_auto_encryption() is
used to enable automatic encryption.
The Queryable Encryption and CSFLE features share much of the same API with some
exceptions.
• The supported algorithms documented in
mongoc_client_encryption_encrypt_opts_set_algorithm() do not apply to both features.
• mongoc_auto_encryption_opts_set_encrypted_fields_map() only applies to Queryable
Encryption.
• mongoc_auto_encryption_opts_set_schema_map() only applies to CSFLE.
Query Analysis
To support the automatic encryption feature, one of the following dependencies are
required:
• The mongocryptd executable. See the MongoDB Manual documentation: Install and Configure
mongocryptd
• The crypt_shared library. See the MongoDB Manual documentation: Automatic Encryption
Shared Library
A mongoc_client_t or mongoc_client_pool_t configured with auto encryption will
automatically try to load the crypt_shared library. If loading the crypt_shared library
fails, the mongoc_client_t or mongoc_client_pool_t will try to spawn the mongocryptd
process from the application's PATH. To configure use of crypt_shared and mongocryptd see
mongoc_auto_encryption_opts_set_extra().
AUTHOR
MongoDB, Inc
COPYRIGHT
2017-present, MongoDB, Inc