BSON_VISITOR_T(3)

SYNOPSIS

            #include <bson/bson.h>

            typedef struct {
               /* run before / after descending into a document */
               bool (*visit_before) (const bson_iter_t *iter, const char *key, void *data);
               bool (*visit_after) (const bson_iter_t *iter, const char *key, void *data);
               /* corrupt BSON, or unsupported type and visit_unsupported_type not set */
               void (*visit_corrupt) (const bson_iter_t *iter, void *data);
               /* normal bson field callbacks */
               bool (*visit_double) (const bson_iter_t *iter,
                                     const char *key,
                                     double v_double,
                                     void *data);
               bool (*visit_utf8) (const bson_iter_t *iter,
                                   const char *key,
                                   size_t v_utf8_len,
                                   const char *v_utf8,
                                   void *data);
               bool (*visit_document) (const bson_iter_t *iter,
                                       const char *key,
                                       const bson_t *v_document,
                                       void *data);
               bool (*visit_array) (const bson_iter_t *iter,
                                    const char *key,
                                    const bson_t *v_array,
                                    void *data);
               bool (*visit_binary) (const bson_iter_t *iter,
                                     const char *key,
                                     bson_subtype_t v_subtype,
                                     size_t v_binary_len,
                                     const uint8_t *v_binary,
                                     void *data);
               /* normal field with deprecated "Undefined" BSON type */
               bool (*visit_undefined) (const bson_iter_t *iter,
                                        const char *key,
                                        void *data);
               bool (*visit_oid) (const bson_iter_t *iter,
                                  const char *key,
                                  const bson_oid_t *v_oid,
                                  void *data);
               bool (*visit_bool) (const bson_iter_t *iter,
                                   const char *key,
                                   bool v_bool,
                                   void *data);
               bool (*visit_date_time) (const bson_iter_t *iter,
                                        const char *key,
                                        int64_t msec_since_epoch,
                                        void *data);
               bool (*visit_null) (const bson_iter_t *iter, const char *key, void *data);
               bool (*visit_regex) (const bson_iter_t *iter,
                                    const char *key,
                                    const char *v_regex,
                                    const char *v_options,
                                    void *data);
               bool (*visit_dbpointer) (const bson_iter_t *iter,
                                        const char *key,
                                        size_t v_collection_len,
                                        const char *v_collection,
                                        const bson_oid_t *v_oid,
                                        void *data);
               bool (*visit_code) (const bson_iter_t *iter,
                                   const char *key,
                                   size_t v_code_len,
                                   const char *v_code,
                                   void *data);
               bool (*visit_symbol) (const bson_iter_t *iter,
                                     const char *key,
                                     size_t v_symbol_len,
                                     const char *v_symbol,
                                     void *data);
               bool (*visit_codewscope) (const bson_iter_t *iter,
                                         const char *key,
                                         size_t v_code_len,
                                         const char *v_code,
                                         const bson_t *v_scope,
                                         void *data);
               bool (*visit_int32) (const bson_iter_t *iter,
                                    const char *key,
                                    int32_t v_int32,
                                    void *data);
               bool (*visit_timestamp) (const bson_iter_t *iter,
                                        const char *key,
                                        uint32_t v_timestamp,
                                        uint32_t v_increment,
                                        void *data);
               bool (*visit_int64) (const bson_iter_t *iter,
                                    const char *key,
                                    int64_t v_int64,
                                    void *data);
               bool (*visit_maxkey) (const bson_iter_t *iter, const char *key, void *data);
               bool (*visit_minkey) (const bson_iter_t *iter, const char *key, void *data);
               /* if set, called instead of visit_corrupt when an apparently valid BSON
                * includes an unrecognized field type (reading future version of BSON) */
               void (*visit_unsupported_type) (const bson_iter_t *iter,
                                               const char *key,
                                               uint32_t type_code,
                                               void *data);
               bool (*visit_decimal128) (const bson_iter_t *iter,
                                         const char *key,
                                         const bson_decimal128_t *v_decimal128,
                                         void *data);

               void *padding[7];
            } bson_visitor_t bson_visitor_t;

DESCRIPTION

The bson_visitor_t structure provides a series of callbacks that can be called while iterating a BSON document. This may simplify the conversion of a bson_t to a higher level language structure.

If the optional callback visit_unsupported_type is set, it is called instead of visit_corrupt in the specific case of an unrecognized field type. (Parsing is aborted in either case.) Use this callback to report an error like "unrecognized type" instead of simply "corrupt BSON". This future-proofs code that may use an older version of libbson to parse future BSON formats.

BASIC EXAMPLE

            #include <bson/bson.h>
            #include <stdio.h>

            static bool
            my_visit_before (const bson_iter_t *iter, const char *key, void *data)
            {
               int *count = (int *) data;

               (*count)++;

               /* returning true stops further iteration of the document */

               return false;
            }

            static void
            count_fields (bson_t *doc)
            {
               bson_visitor_t visitor = {0};
               bson_iter_t iter;
               int count = 0;

               visitor.visit_before = my_visit_before;

               if (bson_iter_init (&iter, doc)) {
                  bson_iter_visit_all (&iter, &visitor, &count);
               }

               printf ("Found %d fields.\n", count);
            }

The example below demonstrates how to set your own callbacks to provide information about the location of corrupt or unsupported BSON document entries.

EXAMPLE CORRUPTION CHECK

            #include <bson/bson.h>
            #include <stdio.h>

            typedef struct {
               ssize_t *err_offset;
            } my_state_t;

            static void
            my_visit_corrupt (const bson_iter_t *iter, void *data)
            {
               *(((my_state_t *) data)->err_offset) = iter->off;
            }

            static void
            my_visit_unsupported_type (const bson_iter_t *iter,
                                       const char *key,
                                       uint32_t type_code,
                                       void *data)
            {
               *(((my_state_t *) data)->err_offset) = iter->off;
            }

            static void
            find_error_location (bson_t *doc)
            {
               bson_visitor_t visitors = {0};
               bson_iter_t iter;
               my_state_t state;
               ssize_t err_offset = -1;

               visitors.visit_corrupt = my_visit_corrupt;
               visitors.visit_unsupported_type = my_visit_unsupported_type;
               /* provide additional visitors as needed based on your requirements */
               state.err_offset = &err_offset;

               if (!bson_iter_init (&iter, doc)) {
                  printf ("Could not initialize iterator!");
                  exit (1);
               }

               if (bson_iter_visit_all (&iter, &visitors, &state) ||
                   err_offset != -1) {
                  printf ("Found error at offset %d.\n", err_offset);
               } else {
                  printf ("BSON document had no errors.\n");
               }
            }

The example below demonstrates how to use a visitor to validate a BSON document's maximum depth.

EXAMPLE CUSTOM VALIDATION

bson-check-depth.c

            /* Reports the maximum nested depth of a BSON document. */
            #include <bson/bson.h>

            #include <assert.h>
            #include <inttypes.h>
            #include <stdio.h>
            #include <stdlib.h>

            typedef struct {
               uint32_t depth;
               uint32_t max_depth;
               bool valid;
            } check_depth_t;

            bool
            _check_depth_document (const bson_iter_t *iter,
                                   const char *key,
                                   const bson_t *v_document,
                                   void *data);

            static const bson_visitor_t check_depth_funcs = {
               NULL,
               NULL,
               NULL,
               NULL,
               NULL,
               _check_depth_document,
               _check_depth_document,
               NULL,
            };

            bool
            _check_depth_document (const bson_iter_t *iter,
                                   const char *key,
                                   const bson_t *v_document,
                                   void *data)
            {
               check_depth_t *state = (check_depth_t *) data;
               bson_iter_t child;

               BSON_UNUSED (iter);
               BSON_UNUSED (key);

               if (!bson_iter_init (&child, v_document)) {
                  fprintf (stderr, "corrupt\n");
                  return true; /* cancel */
               }

               state->depth++;
               if (state->depth > state->max_depth) {
                  state->valid = false;
                  return true; /* cancel */
               }

               bson_iter_visit_all (&child, &check_depth_funcs, state);
               state->depth--;
               return false; /* continue */
            }

            void
            check_depth (const bson_t *bson, uint32_t max_depth)
            {
               bson_iter_t iter;
               check_depth_t state = {0};

               if (!bson_iter_init (&iter, bson)) {
                  fprintf (stderr, "corrupt\n");
               }

               state.valid = true;
               state.max_depth = max_depth;
               _check_depth_document (&iter, NULL, bson, &state);
               if (!state.valid) {
                  printf ("document exceeds maximum depth of %" PRIu32 "\n",
                          state.max_depth);
               } else {
                  char *as_json = bson_as_canonical_extended_json (bson, NULL);
                  printf ("document %s ", as_json);
                  printf ("is valid\n");
                  bson_free (as_json);
               }
            }

            int
            main (int argc, char **argv)
            {
               bson_reader_t *bson_reader;
               const bson_t *bson;
               bool reached_eof;
               bson_error_t error;

               if (argc != 3) {
                  fprintf (stderr, "usage: %s FILE MAX_DEPTH\n", argv[0]);
                  fprintf (stderr, "Checks that the depth of the BSON contained in FILE\n");
                  fprintf (stderr, "does not exceed MAX_DEPTH\n");
               }

               const char *const filename = argv[1];
               const int max_depth = atoi (argv[2]);

               bson_reader = bson_reader_new_from_file (filename, &error);
               if (!bson_reader) {
                  printf ("could not read %s: %s\n", filename, error.message);
                  return 1;
               }

               BSON_ASSERT (bson_in_range_signed (uint32_t, max_depth));

               while ((bson = bson_reader_read (bson_reader, &reached_eof))) {
                  check_depth (bson, (uint32_t) max_depth);
               }

               if (!reached_eof) {
                  printf ("error reading BSON\n");
               }

               bson_reader_destroy (bson_reader);
               return 0;
            }

AUTHOR
MongoDB, Inc

COPYRIGHT
2017-present, MongoDB, Inc