table of contents
| BSON_RESERVE_BUFFER(3) | libbson | BSON_RESERVE_BUFFER(3) |
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.
| March 5, 2025 | 1.30.2 |