1BSON_RESERVE_BUFFER(3)              libbson             BSON_RESERVE_BUFFER(3)
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SYNOPSIS

6          uint8_t *
7          bson_reserve_buffer (bson_t *bson, uint32_t size);
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PARAMETERS

10       • bson: An initialized bson_t.
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12       • size: The length in bytes of the new buffer.
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DESCRIPTION

15       Grow the internal buffer of bson to size and set the document length to
16       size. Useful for eliminating copies when  reading  BSON  bytes  from  a
17       stream.
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19       First,  initialize  bson with bson_init() or bson_new(), then call this
20       function. After it returns, the length of bson is set to size  but  its
21       contents  are  uninitialized  memory: you must fill the contents with a
22       BSON document of the correct length before any other operations.
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24       The document must be freed with bson_destroy().
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RETURNS

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

31       Use bson_reserve_buffer to write a function that takes a bson_t pointer
32       and reads a file into it directly:
33
34          #include <stdio.h>
35          #include <bson/bson.h>
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37          bool
38          read_into (bson_t *bson, FILE *fp)
39          {
40             uint8_t *buffer;
41             long size;
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43             if (fseek (fp, 0L, SEEK_END) < 0) {
44                perror ("Couldn't get file size");
45                return 1;
46             }
47
48             size = ftell (fp);
49             if (size == EOF) {
50                perror ("Couldn't get file size");
51                return 1;
52             }
53
54             if (size > INT32_MAX) {
55                fprintf (stderr, "File too large\n");
56                return 1;
57             }
58
59             /* reserve buffer space - bson is temporarily invalid */
60             buffer = bson_reserve_buffer (bson, (uint32_t) size);
61             if (!buffer) {
62                fprintf (stderr, "Couldn't reserve %ld bytes", size);
63                return false;
64             }
65
66             /* read file directly into the buffer */
67             rewind (fp);
68             if (fread ((void *) buffer, 1, (size_t) size, fp) < (size_t) size) {
69                perror ("Couldn't read file");
70                return false;
71             }
72
73             return true;
74          }
75
76          int
77          main ()
78          {
79             FILE *fp;
80             char *json;
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82             /* stack-allocated, initialized bson_t */
83             bson_t bson = BSON_INITIALIZER;
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85             if (!(fp = fopen ("document.bson", "rb"))) {
86                perror ("Couldn't read file");
87                return 1;
88             }
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90             read_into (&bson, fp);
91             fclose (fp);
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93             json = bson_as_canonical_extended_json (&bson, NULL);
94             printf ("%s\n", json);
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96             bson_free (json);
97             bson_destroy (&bson);
98
99             return 0;
100          }
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AUTHOR

103       MongoDB, Inc
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106       2017-present, MongoDB, Inc
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1111.25.1                           Nov 08, 2023           BSON_RESERVE_BUFFER(3)
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