Provided by: libbson-doc_1.9.2-1_all 
NAME
bson_tutorial - Tutorial
USING LIBBSON IN YOUR C PROGRAM
Include bson.h
All libbson's functions and types are available in one header file. Simply include bson.h:
hello_bson.c.INDENT 0.0
#include <stdio.h>
#include <bson.h>
int
main (int argc, const char **argv)
{
bson_t *b;
char *j;
b = BCON_NEW ("hello", BCON_UTF8 ("bson!"));
j = bson_as_canonical_extended_json (b, NULL);
printf ("%s\n", j);
bson_free (j);
bson_destroy (b);
return 0;
}
CMake
The libbson installation includes a CMake config-file package, so you can use CMake's find_package
command to find libbson's header and library paths and link to libbson: CMakeLists.txt.INDENT 0.0
# Specify the minimum version you require.
find_package (libbson-1.0 1.7 REQUIRED)
message ("-- libbson found version \"${BSON_VERSION}\"")
message ("-- libbson include path \"${BSON_INCLUDE_DIRS}\"")
message ("-- libbson libraries \"${BSON_LIBRARIES}\"")
# The "hello_bson.c" sample program is shared among four tests.
add_executable (hello_bson ../../hello_bson.c)
target_include_directories (hello_bson PRIVATE ${BSON_INCLUDE_DIRS})
target_link_libraries (hello_bson PRIVATE ${BSON_LIBRARIES})
target_compile_definitions (hello_bson PRIVATE ${BSON_DEFINITIONS})
libbson-static-1.0 config-file package and (on Unix) link to pthread:
# Specify the minimum version you require.
find_package (libbson-static-1.0 1.7 REQUIRED)
message ("-- libbson-static found version \"${BSON_STATIC_VERSION}\"")
message ("-- libbson-static include path \"${BSON_STATIC_INCLUDE_DIRS}\"")
message ("-- libbson-static libraries \"${BSON_STATIC_LIBRARIES}\"")
# The "hello_bson.c" sample program is shared among four tests.
add_executable (hello_bson ../../hello_bson.c)
target_include_directories (hello_bson PRIVATE ${BSON_STATIC_INCLUDE_DIRS})
target_link_libraries (hello_bson PRIVATE ${BSON_STATIC_LIBRARIES})
target_compile_definitions (hello_bson PRIVATE ${BSON_STATIC_DEFINITIONS})
pkg-config
If you're not using CMake, use pkg-config on the command line to set header and library paths:
gcc -o hello_bson hello_bson.c $(pkg-config --libs --cflags libbson-1.0)
Or to statically link to libbson:
gcc -o hello_bson hello_bson.c $(pkg-config --libs --cflags libbson-static-1.0)
CREATING A BSON DOCUMENT
The bson_t structure
BSON documents are created using the bson_t structure. This structure encapsulates the necessary logic
for encoding using the BSON Specification. At the core, bson_t is a buffer manager and set of encoding
routines.
TIP:
BSON documents can live on the stack or the heap based on the performance needs or preference of the
consumer.
Let's start by creating a new BSON document on the stack. Whenever using libbson, make sure you #include
<bson.h>.
bson_t b;
bson_init (&b);
This creates an empty document. In JSON, this would be the same as {}.
We can now proceed to adding items to the BSON document. A variety of functions prefixed with
bson_append_ can be used based on the type of field you want to append. Let's append a UTF-8 encoded
string.
bson_append_utf8 (&b, "key", -1, "value", -1);
Notice the two -1 parameters. The first indicates that the length of key in bytes should be determined
with strlen(). Alternatively, we could have passed the number 3. The same goes for the second -1, but for
value.
Libbson provides macros to make this less tedious when using string literals. The following two appends
are identical.
bson_append_utf8 (&b, "key", -1, "value", -1);
BSON_APPEND_UTF8 (&b, "key", "value");
Now let's take a look at an example that adds a few different field types to a BSON document.
bson_t b = BSON_INITIALIZER;
BSON_APPEND_INT32 (&b, "a", 1);
BSON_APPEND_UTF8 (&b, "hello", "world");
BSON_APPEND_BOOL (&b, "bool", true);
Notice that we omitted the call to bson_init(). By specifying BSON_INITIALIZER we can remove the need to
initialize the structure to a base state.
Sub-Documents and Sub-Arrays
To simplify the creation of sub-documents and arrays, bson_append_document_begin() and
bson_append_array_begin() exist. These can be used to build a sub-document using the parent documents
memory region as the destination buffer.
bson_t parent;
bson_t child;
char *str;
bson_init (&parent);
bson_append_document_begin (&parent, "foo", 3, &child);
bson_append_int32 (&child, "baz", 3, 1);
bson_append_document_end (&parent, &child);
str = bson_as_canonical_extended_json (&parent, NULL);
printf ("%s\n", str);
bson_free (str);
bson_destroy (&parent);
{ "foo" : { "baz" : 1 } }
Simplified BSON C Object Notation
Creating BSON documents by hand can be tedious and time consuming. BCON, or BSON C Object Notation, was
added to allow for the creation of BSON documents in a format that looks closer to the destination
format.
The following example shows the use of BCON. Notice that values for fields are wrapped in the BCON_*
macros. These are required for the variadic processor to determine the parameter type.
bson_t *doc;
doc = BCON_NEW ("foo",
"{",
"int",
BCON_INT32 (1),
"array",
"[",
BCON_INT32 (100),
"{",
"sub",
BCON_UTF8 ("value"),
"}",
"]",
"}");
Creates the following document
{ "foo" : { "int" : 1, "array" : [ 100, { "sub" : "value" } ] } }
HANDLING ERRORS
Description
Many libbson functions report errors by returning NULL or -1 and filling out a bson_error_t structure
with an error domain, error code, and message.
• error.domain names the subsystem that generated the error.
• error.code is a domain-specific error type.
• error.message describes the error.
Some error codes overlap with others; always check both the domain and code to determine the type of
error.
┌──────────────────┬────────────────────────────────────┬────────────────────────────────┐
│BSON_ERROR_JSON │ BSON_JSON_ERROR_READ_CORRUPT_JS │ bson_json_reader_t tried to │
│ │ BSON_JSON_ERROR_READ_INVALID_PARAM │ parse invalid MongoDB │
│ │ BSON_JSON_ERROR_READ_CB_FAILURE │ Extended JSON. Tried to │
│ │ │ parse a valid JSON document │
│ │ │ that is invalid as │
│ │ │ MongoDBExtended JSON. An │
│ │ │ internal callback failure │
│ │ │ during JSON parsing. │
├──────────────────┼────────────────────────────────────┼────────────────────────────────┤
│BSON_ERROR_READER │ BSON_ERROR_READER_BADFD │ bson_json_reader_new_from_file │
│ │ │ could not open the file. │
└──────────────────┴────────────────────────────────────┴────────────────────────────────┘
OBJECTIDS
Libbson provides a simple way to generate ObjectIDs. It can be used in a single-threaded or
multi-threaded manner depending on your requirements.
The bson_oid_t structure represents an ObjectID in MongoDB. It is a 96-bit identifier that includes
various information about the system generating the OID.
Composition
• 4 bytes : The UNIX timestamp in big-endian format.
• 3 bytes : The first 3 bytes of MD5(hostname).
• 2 bytes : The pid_t of the current process. Alternatively the task-id if configured.
• 3 bytes : A 24-bit monotonic counter incrementing from rand() in big-endian.
Sorting ObjectIDs
The typical way to sort in C is using qsort(). Therefore, Libbson provides a qsort() compatible callback
function named bson_oid_compare(). It returns less than 1, greater than 1, or 0 depending on the equality
of two bson_oid_t structures.
Comparing Object IDs
If you simply want to compare two bson_oid_t structures for equality, use bson_oid_equal().
Generating
To generate a bson_oid_t, you may use the following.
bson_oid_t oid;
bson_oid_init (&oid, NULL);
Parsing ObjectID Strings
You can also parse a string containing a bson_oid_t. The input string MUST be 24 characters or more in
length.
bson_oid_t oid;
bson_oid_init_from_string (&oid, "123456789012345678901234");
If you need to parse may bson_oid_t in a tight loop and can guarantee the data is safe, you might
consider using the inline variant. It will be inlined into your code and reduce the need for a foreign
function call.
bson_oid_t oid;
bson_oid_init_from_string_unsafe (&oid, "123456789012345678901234");
Hashing ObjectIDs
If you need to store items in a hashtable, you may want to use the bson_oid_t as the key. Libbson
provides a hash function for just this purpose. It is based on DJB hash.
unsigned hash;
hash = bson_oid_hash (oid);
Fetching ObjectID Creation Time
You can easily fetch the time that a bson_oid_t was generated using bson_oid_get_time_t().
time_t t;
t = bson_oid_get_time_t (oid);
printf ("The OID was generated at %u\n", (unsigned) t);
PARSING AND ITERATING BSON DOCUMENTS
Parsing
BSON documents are lazily parsed as necessary. To begin parsing a BSON document, use one of the provided
Libbson functions to create a new bson_t from existing data such as bson_new_from_data(). This will make
a copy of the data so that additional mutations may occur to the BSON document.
TIP:
If you only want to parse a BSON document and have no need to mutate it, you may use
bson_init_static() to avoid making a copy of the data.
bson_t *b;
b = bson_new_from_data (my_data, my_data_len);
if (!b) {
fprintf (stderr, "The specified length embedded in <my_data> did not match "
"<my_data_len>\n");
return;
}
bson_destroy (b);
Only two checks are performed when creating a new bson_t from an existing buffer. First, the document
must begin with the buffer length, matching what was expected by the caller. Second, the document must
end with the expected trailing \0 byte.
To parse the document further we use a bson_iter_t to iterate the elements within the document. Let's
print all of the field names in the document.
bson_t *b;
bson_iter_t iter;
if ((b = bson_new_from_data (my_data, my_data_len))) {
if (bson_iter_init (&iter, b)) {
while (bson_iter_next (&iter)) {
printf ("Found element key: \"%s\"\n", bson_iter_key (&iter));
}
}
bson_destroy (b);
}
Converting a document to JSON uses a bson_iter_t and bson_visitor_t to iterate all fields of a BSON
document recursively and generate a UTF-8 encoded JSON string.
bson_t *b;
char *json;
if ((b = bson_new_from_data (my_data, my_data_len))) {
if ((json = bson_as_canonical_extended_json (b, NULL))) {
printf ("%s\n", json);
bson_free (json);
}
bson_destroy (b);
}
Recursing into Sub-Documents
Libbson provides convenient sub-iterators to dive down into a sub-document or sub-array. Below is an
example that will dive into a sub-document named "foo" and print it's field names.
bson_iter_t iter;
bson_iter_t *child;
char *json;
if (bson_iter_init_find (&iter, doc, "foo") &&
BSON_ITER_HOLDS_DOCUMENT (&iter) && bson_iter_recurse (&iter, &child)) {
while (bson_iter_next (&child)) {
printf ("Found sub-key of \"foo\" named \"%s\"\n",
bson_iter_key (&child));
}
}
Finding Fields using Dot Notation
Using the bson_iter_recurse() function exemplified above, bson_iter_find_descendant() can find a field
for you using the MongoDB style path notation such as "foo.bar.0.baz".
Let's create a document like {"foo": {"bar": [{"baz: 1}]}} and locate the "baz" field.
bson_t *b;
bson_iter_t iter;
bson_iter_t baz;
b =
BCON_NEW ("foo", "{", "bar", "[", "{", "baz", BCON_INT32 (1), "}", "]", "}");
if (bson_iter_init (&iter, b) &&
bson_iter_find_descendant (&iter, "foo.bar.0.baz", &baz) &&
BSON_ITER_HOLDS_INT32 (&baz)) {
printf ("baz = %d\n", bson_iter_int32 (&baz));
}
bson_destroy (b);
Validating a BSON Document
If all you want to do is validate that a BSON document is valid, you can use bson_validate().
size_t err_offset;
if (!bson_validate (doc, BSON_VALIDATE_NONE, &err_offset)) {
fprintf (stderr,
"The document failed to validate at offset: %u\n",
(unsigned) err_offset);
}
See the bson_validate() documentation for more information and examples.
UTF-8
Encoding
Libbson expects that you are always working with UTF-8 encoded text. Anything else is invalid API use.
If you should need to walk through UTF-8 sequences, you can use the various UTF-8 helper functions
distributed with Libbson.
Validating a UTF-8 Sequence
To validate the string contained in my_string, use the following. You may pass -1 for the string length
if you know the string is NULL-terminated.
if (!bson_utf8_validate (my_string, -1, false)) {
printf ("Validation failed.\n");
}
If my_string has NULL bytes within the string, you must provide the string length. Use the following
format. Notice the true at the end indicating \0 is allowed.
if (!bson_utf8_validate (my_string, my_string_len, true)) {
printf ("Validation failed.\n");
}
For more information see the API reference for bson_utf8_validate().
AUTHOR
MongoDB, Inc
COPYRIGHT
2018, MongoDB, Inc