NAME

bson_reference - Index

LIBBSON

A Cross Platform BSON Library for C

Introduction

libbson builds, parses, and iterates BSON documents, the native data format of MongoDB. It also converts BSON to and from JSON, and provides a platform compatibility layer for the MongoDB C Driver.

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

#include <stdio.h>
#include <bson/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 import libbson's CMake target and link to libbson (as a shared library):

CMakeLists.txt

# Specify the minimum version you require.
find_package (bson-1.0 1.7 REQUIRED)
# The "hello_bson.c" sample program is shared among four tests.
add_executable (hello_bson ../../hello_bson.c)
target_link_libraries (hello_bson PRIVATE mongo::bson_shared)

You can also use libbson as a static library instead: Use the mongo::bson_static CMake target:

# Specify the minimum version you require.
find_package (bson-1.0 1.7 REQUIRED)
# The "hello_bson.c" sample program is shared among four tests.
add_executable (hello_bson ../../hello_bson.c)
target_link_libraries (hello_bson PRIVATE mongo::bson_static)

pkg-config

If you're not using CMake, use pkg-config on the command line to set header and library paths:

gcc -o hello_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/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" } ] } }

BSON_ERROR_JSON	BSON_JSON_ERROR_READ_CORRUPT_JS BSON_JSON_ERROR_READ_INVALID_PARAM BSON_JSON_ERROR_READ_CB_FAILURE	bson_json_reader_t tried to parse invalid MongoDB 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.