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 func- tion. 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 ver- ified 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. 1.30.8 Aug 27, 2026 BSON_RESERVE_BUFFER(3)
SYNOPSIS | PARAMETERS | DESCRIPTION | RETURNS | EXAMPLE | AUTHOR | COPYRIGHT
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