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.