Man page - bson_reserve_buffer(3)

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Manual

BSON_RESERVE_BUFFER

SYNOPSIS
PARAMETERS
DESCRIPTION
RETURNS
EXAMPLE
AUTHOR
COPYRIGHT

SYNOPSIS

uint8_t *
bson_reserve_buffer (bson_t *bson, uint32_t total_size);

PARAMETERS

•

bson : An initialized bson_t .

•

total_size : The length in bytes of the new buffer.

DESCRIPTION

Grow the internal buffer of bson to total_size and set the document length to total_size . Useful for eliminating copies when reading BSON bytes from a stream.

First, initialize bson with bson_init() or bson_new() , then call this function. After it returns, the length of bson is set to total_size but its contents are uninitialized memory: you must fill the contents with a BSON document of the correct length before any other operations.

The document must be freed with bson_destroy() .

Note that, in this usage, the BSON header and footer bytes will not be verified or used by Libbson. The bson_t document length and buffer size limit are both set to total_size regardless of the value encoded in the document header.

RETURNS

A pointer to the internal buffer, which is at least total_size bytes, or NULL if the space could not be allocated.

EXAMPLE

Use bson_reserve_buffer to write a function that takes a bson_t pointer and reads a file into it directly:

#include <stdio.h>
#include <bson/bson.h>

bool
read_into (bson_t *bson, FILE *fp)
{
uint8_t *buffer;
long size;

if (fseek (fp, 0L, SEEK_END) < 0) {
perror ("Couldn't get file size");
return 1;
}

size = ftell (fp);
if (size == EOF) {
perror ("Couldn't get file size");
return 1;
}

if (size > INT32_MAX) {
fprintf (stderr, "File too large\n");
return 1;
}

/* reserve buffer space - bson is temporarily invalid */
buffer = bson_reserve_buffer (bson, (uint32_t) size);
if (!buffer) {
fprintf (stderr, "Couldn't reserve %ld bytes", size);
return false;
}

/* read file directly into the buffer */
rewind (fp);
if (fread ((void *) buffer, 1, (size_t) size, fp) < (size_t) size) {
perror ("Couldn't read file");
return false;
}

return true;
}

int
main ()
{
FILE *fp;
char *json;

/* stack-allocated, initialized bson_t */
bson_t bson = BSON_INITIALIZER;

if (!(fp = fopen ("document.bson", "rb"))) {
perror ("Couldn't read file");
return 1;
}

read_into (&bson, fp);
fclose (fp);

json = bson_as_canonical_extended_json (&bson, NULL);
printf ("%s\n", json);

bson_free (json);
bson_destroy (&bson);

return 0;
}

AUTHOR

MongoDB, Inc

COPYRIGHT

2009-present, MongoDB, Inc.