1BSON_GUIDES(3)                      libbson                     BSON_GUIDES(3)
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NAME

6       bson_guides - Guides
7

STREAMING BSON

9       bson_reader_t provides a streaming reader which can be initialized with
10       a filedescriptor or memory region. bson_writer_t provides  a  streaming
11       writer  which  can be initialized with a memory region. (Streaming BSON
12       to a file descriptor is not yet supported.)
13
14   Reading from a BSON Stream
15       bson_reader_t provides a convenient API to read sequential  BSON  docu‐
16       ments  from  a file-descriptor or memory buffer. The bson_reader_read()
17       function will read forward in the underlying stream and return a bson_t
18       that can be inspected and iterated upon.
19
20          #include <stdio.h>
21          #include <bson/bson.h>
22
23          int
24          main (int argc, char *argv[])
25          {
26             bson_reader_t *reader;
27             const bson_t *doc;
28             bson_error_t error;
29             bool eof;
30
31             reader = bson_reader_new_from_file ("mycollection.bson", &error);
32
33             if (!reader) {
34                fprintf (stderr, "Failed to open file.\n");
35                return 1;
36             }
37
38             while ((doc = bson_reader_read (reader, &eof))) {
39                char *str = bson_as_canonical_extended_json (doc, NULL);
40                printf ("%s\n", str);
41                bson_free (str);
42             }
43
44             if (!eof) {
45                fprintf (stderr,
46                         "corrupted bson document found at %u\n",
47                         (unsigned) bson_reader_tell (reader));
48             }
49
50             bson_reader_destroy (reader);
51
52             return 0;
53          }
54
55       See    bson_reader_new_from_fd(),    bson_reader_new_from_file(),   and
56       bson_reader_new_from_data() for more information.
57
58   Writing a sequence of BSON Documents
59       bson_writer_t provides a convenient API to write  a  sequence  of  BSON
60       documents  to  a  memory  buffer  that  can  grow  with  realloc(). The
61       bson_writer_begin() and bson_writer_end() functions will manage the un‐
62       derlying buffer while building the sequence of documents.
63
64       This  could  also  be  useful  if you want to write to a network packet
65       while serializing the documents from a higher level language,  (but  do
66       so just after the packets header).
67
68          #include <stdio.h>
69          #include <bson/bson.h>
70          #include <assert.h>
71
72          int
73          main (int argc, char *argv[])
74          {
75             bson_writer_t *writer;
76             bson_t *doc;
77             uint8_t *buf = NULL;
78             size_t buflen = 0;
79             bool r;
80             int i;
81
82             writer = bson_writer_new (&buf, &buflen, 0, bson_realloc_ctx, NULL);
83
84             for (i = 0; i < 10000; i++) {
85                r = bson_writer_begin (writer, &doc);
86                assert (r);
87
88                r = BSON_APPEND_INT32 (doc, "i", i);
89                assert (r);
90
91                bson_writer_end (writer);
92             }
93
94             bson_free (buf);
95
96             return 0;
97          }
98
99       See bson_writer_new() for more information.
100

JSON

102       Libbson  provides  routines for converting to and from the JSON format.
103       In particular, it supports the MongoDB extended JSON format.
104
105   Converting BSON to JSON
106       There are often times where you might want to convert a  BSON  document
107       to  JSON. It is convenient for debugging as well as an interchange for‐
108       mat. To help with this, Libbson contains the functions  bson_as_canoni‐
109       cal_extended_json()  and bson_as_relaxed_extended_json(). The canonical
110       format preserves BSON type information for values that may have ambigu‐
111       ous representations in JSON (e.g. numeric types).
112
113          bson_t *b;
114          size_t len;
115          char *str;
116
117          b = BCON_NEW ("a", BCON_INT32 (1));
118
119          str = bson_as_canonical_extended_json (b, &len);
120          printf ("%s\n", str);
121          bson_free (str);
122
123          bson_destroy (b);
124
125          { "a" : { "$numberInt": "1" } }
126
127       The  relaxed  format prefers JSON primitives for numeric values and may
128       be used if type fidelity is not required.
129
130          bson_t *b;
131          size_t len;
132          char *str;
133
134          b = BCON_NEW ("a", BCON_INT32 (1));
135
136          str = bson_as_relaxed_extended_json (b, &len);
137          printf ("%s\n", str);
138          bson_free (str);
139
140          bson_destroy (b);
141
142          { "a" : 1 }
143
144   Converting JSON to BSON
145       Converting back from JSON is also useful  and  common  enough  that  we
146       added bson_init_from_json() and bson_new_from_json().
147
148       The  following  example  creates  a  new  bson_t  from  the JSON string
149       {"a":1}.
150
151          bson_t *b;
152          bson_error_t error;
153
154          b = bson_new_from_json ("{\"a\":1}", -1, &error);
155
156          if (!b) {
157             printf ("Error: %s\n", error.message);
158          } else {
159             bson_destroy (b);
160          }
161
162   Streaming JSON Parsing
163       Libbson provides bson_json_reader_t to allow for parsing a sequence  of
164       JSON documents into BSON. The interface is similar to bson_reader_t but
165       expects the input to be in the MongoDB extended JSON format.
166
167          /*
168           * Copyright 2013 MongoDB, Inc.
169           *
170           * Licensed under the Apache License, Version 2.0 (the "License");
171           * you may not use this file except in compliance with the License.
172           * You may obtain a copy of the License at
173           *
174           *   http://www.apache.org/licenses/LICENSE-2.0
175           *
176           * Unless required by applicable law or agreed to in writing, software
177           * distributed under the License is distributed on an "AS IS" BASIS,
178           * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
179           * See the License for the specific language governing permissions and
180           * limitations under the License.
181           */
182
183
184          /*
185           * This program will print each JSON document contained in the provided files
186           * as a BSON string to STDOUT.
187           */
188
189
190          #include <bson/bson.h>
191          #include <stdlib.h>
192          #include <stdio.h>
193
194
195          int
196          main (int argc, char *argv[])
197          {
198             bson_json_reader_t *reader;
199             bson_error_t error;
200             const char *filename;
201             bson_t doc = BSON_INITIALIZER;
202             int i;
203             int b;
204
205             /*
206              * Print program usage if no arguments are provided.
207              */
208             if (argc == 1) {
209                fprintf (stderr, "usage: %s FILE...\n", argv[0]);
210                return 1;
211             }
212
213             /*
214              * Process command line arguments expecting each to be a filename.
215              */
216             for (i = 1; i < argc; i++) {
217                filename = argv[i];
218
219                /*
220                 * Open the filename provided in command line arguments.
221                 */
222                if (0 == strcmp (filename, "-")) {
223                   reader = bson_json_reader_new_from_fd (STDIN_FILENO, false);
224                } else {
225                   if (!(reader = bson_json_reader_new_from_file (filename, &error))) {
226                      fprintf (
227                         stderr, "Failed to open \"%s\": %s\n", filename, error.message);
228                      continue;
229                   }
230                }
231
232                /*
233                 * Convert each incoming document to BSON and print to stdout.
234                 */
235                while ((b = bson_json_reader_read (reader, &doc, &error))) {
236                   if (b < 0) {
237                      fprintf (stderr, "Error in json parsing:\n%s\n", error.message);
238                      abort ();
239                   }
240
241                   if (fwrite (bson_get_data (&doc), 1, doc.len, stdout) != doc.len) {
242                      fprintf (stderr, "Failed to write to stdout, exiting.\n");
243                      exit (1);
244                   }
245                   bson_reinit (&doc);
246                }
247
248                bson_json_reader_destroy (reader);
249                bson_destroy (&doc);
250             }
251
252             return 0;
253          }
254
255   Examples
256       The following example reads BSON documents from stdin and  prints  them
257       to stdout as JSON.
258
259          /*
260           * Copyright 2013 MongoDB, Inc.
261           *
262           * Licensed under the Apache License, Version 2.0 (the "License");
263           * you may not use this file except in compliance with the License.
264           * You may obtain a copy of the License at
265           *
266           *   http://www.apache.org/licenses/LICENSE-2.0
267           *
268           * Unless required by applicable law or agreed to in writing, software
269           * distributed under the License is distributed on an "AS IS" BASIS,
270           * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
271           * See the License for the specific language governing permissions and
272           * limitations under the License.
273           */
274
275
276          /*
277           * This program will print each BSON document contained in the provided files
278           * as a JSON string to STDOUT.
279           */
280
281
282          #include <bson/bson.h>
283          #include <stdio.h>
284
285
286          int
287          main (int argc, char *argv[])
288          {
289             bson_reader_t *reader;
290             const bson_t *b;
291             bson_error_t error;
292             const char *filename;
293             char *str;
294             int i;
295
296             /*
297              * Print program usage if no arguments are provided.
298              */
299             if (argc == 1) {
300                fprintf (stderr, "usage: %s [FILE | -]...\nUse - for STDIN.\n", argv[0]);
301                return 1;
302             }
303
304             /*
305              * Process command line arguments expecting each to be a filename.
306              */
307             for (i = 1; i < argc; i++) {
308                filename = argv[i];
309
310                if (strcmp (filename, "-") == 0) {
311                   reader = bson_reader_new_from_fd (STDIN_FILENO, false);
312                } else {
313                   if (!(reader = bson_reader_new_from_file (filename, &error))) {
314                      fprintf (
315                         stderr, "Failed to open \"%s\": %s\n", filename, error.message);
316                      continue;
317                   }
318                }
319
320                /*
321                 * Convert each incoming document to JSON and print to stdout.
322                 */
323                while ((b = bson_reader_read (reader, NULL))) {
324                   str = bson_as_canonical_extended_json (b, NULL);
325                   fprintf (stdout, "%s\n", str);
326                   bson_free (str);
327                }
328
329                /*
330                 * Cleanup after our reader, which closes the file descriptor.
331                 */
332                bson_reader_destroy (reader);
333             }
334
335             return 0;
336          }
337

USE VALGRIND TO CHECK FOR BSON DATA LEAKS

339       A  stack-allocated  bson_t  contains  a  small internal buffer; it only
340       heap-allocates additional storage if necessary, depending on  its  data
341       size. Therefore if you forget to call bson_destroy on a stack-allocated
342       bson_t, it might or might not cause a leak that can be detected by val‐
343       grind during testing.
344
345       To  catch  all  potential  BSON  data leaks in your code, configure the
346       BSON_MEMCHECK flag:
347
348          cmake -DCMAKE_C_FLAGS="-DBSON_MEMCHECK -g" .
349
350       With this flag set, every bson_t mallocs at least one  byte.  Run  your
351       program's  unittests with valgrind to verify all bson_t structs are de‐
352       stroyed.
353
354       Set the environment variable MONGOC_TEST_VALGRIND to on  to  skip  tim‐
355       ing-dependent tests known to fail with valgrind.
356

AUTHOR

358       MongoDB, Inc
359
361       2017-present, MongoDB, Inc
362
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3661.17.6                           Jun 03, 2021                   BSON_GUIDES(3)
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