MONGOC_GRIDFS_T(3)

hey bestie 💖 welcome to MONGOC_GRIDFS_T(3) — that’s the page, and it lives in the libmongoc manual. Buckle up, because this one is giving “useful but also kind of a lot,” and we’re gonna get through it together 🫶✨

⚠️ WARNING ⚠️

🚨 okay so real talk first: this GridFS implementation does not conform to the MongoDB GridFS specification. For a spec compliant implementation, use mongoc_gridfs_bucket_t. That’s the tea, no cap. 💅

✨ SYNOPSIS ✨

First you gotta pull in the header and meet the typedef, like:

#include <mongoc/mongoc.h>

typedef struct _mongoc_gridfs_t mongoc_gridfs_t;

🦋 DESCRIPTION 🦋

mongoc_gridfs_t provides a MongoDB gridfs implementation. The system as a whole is made up of gridfs objects, which contain gridfs_files and gridfs_file_lists. Essentially: a basic file system API, periodt. 💅

There are extensive caveats about the kind of use cases gridfs is practical for. In particular, any writing after initial file creation is likely to both break any concurrent readers and be quite expensive. That said, this implementation does allow for arbitrary writes to existing gridfs object, just use them with caution. ⚠️

mongoc_gridfs also integrates tightly with the mongoc_stream_t abstraction, which provides some convenient wrapping for file creation and reading/writing. It can be used without, but it’s worth looking to see if your problem can fit that model. Lowkey a vibe check worth doing 🧚

🚨 WARNING: mongoc_gridfs_t does not support read preferences. In a replica set, GridFS queries are always routed to the primary. So yeah — primary only, bestie. 💀

🧵 THREAD SAFETY 🧵

mongoc_gridfs_t is NOT thread-safe and should only be used in the same thread as the owning mongoc_client_t. No sharing, no multitasking chaos, okay? 🙈

🌱 LIFECYCLE 🌱

It is an error to free a mongoc_gridfs_t before freeing all related instances of mongoc_gridfs_file_t and mongoc_gridfs_file_list_t. Clean up your file and file-list babies first, bestie 🫶

🎀 EXAMPLE 🎀

The example file is literally example-gridfs.c, and here’s the whole thing:

#include <mongoc/mongoc.h>

#include <fcntl.h>

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

int
main(int argc, char *argv[])
{
   mongoc_gridfs_t *gridfs;
   mongoc_gridfs_file_t *file;
   mongoc_gridfs_file_list_t *list;
   mongoc_gridfs_file_opt_t opt = {0};
   mongoc_client_t *client;
   const char *uri_string = "mongodb://127.0.0.1:27017/?appname=gridfs-example";
   mongoc_uri_t *uri;
   mongoc_stream_t *stream;
   bson_t filter;
   bson_t opts;
   bson_t child;
   bson_error_t error;
   ssize_t r;
   char buf[4096];
   mongoc_iovec_t iov;
   const char *filename;
   const char *command;
   bson_value_t id;

   if (argc < 2) {
      fprintf(stderr, "usage - %s command ...\n", argv[0]);
      return EXIT_FAILURE;
   }

   mongoc_init();

   iov.iov_base = (void *)buf;
   iov.iov_len = sizeof buf;

   /* connect to localhost client */
   uri = mongoc_uri_new_with_error(uri_string, &error);
   if (!uri) {
      fprintf(stderr,
              "failed to parse URI:\n"
              "error message: %s\n",
              error.message);
      return EXIT_FAILURE;
   }

   client = mongoc_client_new_from_uri(uri);
   assert(client);
   mongoc_client_set_error_api(client, 2);

   /* grab a gridfs handle in test prefixed by fs */
   gridfs = mongoc_client_get_gridfs(client, "test", "fs", &error);
   assert(gridfs);

   command = argv[1];
   filename = argv[2];

   if (strcmp(command, "read") == 0) {
      if (argc != 3) {
         fprintf(stderr, "usage - %s read filename\n", argv[0]);
         return EXIT_FAILURE;
      }
      file = mongoc_gridfs_find_one_by_filename(gridfs, filename, &error);
      assert(file);

      stream = mongoc_stream_gridfs_new(file);
      assert(stream);

      for (;;) {
         r = mongoc_stream_readv(stream, &iov, 1, -1, 0);

         assert(r >= 0);

         if (r == 0) {
            break;
         }

         if (fwrite(iov.iov_base, 1, r, stdout) != (size_t)r) {
            fprintf(stderr, "Failed to write to stdout. Exiting.\n");
            exit(1);
         }
      }

      mongoc_stream_destroy(stream);
      mongoc_gridfs_file_destroy(file);
   } else if (strcmp(command, "list") == 0) {
      bson_init(&filter);

      bson_init(&opts);
      bson_append_document_begin(&opts, "sort", -1, &child);
      BSON_APPEND_INT32(&child, "filename", 1);
      bson_append_document_end(&opts, &child);

      list = mongoc_gridfs_find_with_opts(gridfs, &filter, &opts);

      bson_destroy(&filter);
      bson_destroy(&opts);

      while ((file = mongoc_gridfs_file_list_next(list))) {
         const char *name = mongoc_gridfs_file_get_filename(file);
         printf("%s\n", name ? name : "?");

         mongoc_gridfs_file_destroy(file);
      }

      mongoc_gridfs_file_list_destroy(list);
   } else if (strcmp(command, "write") == 0) {
      if (argc != 4) {
         fprintf(stderr, "usage - %s write filename input_file\n", argv[0]);
         return EXIT_FAILURE;
      }

      stream = mongoc_stream_file_new_for_path(argv[3], O_RDONLY, 0);
      assert(stream);

      opt.filename = filename;

      /* the driver generates a file_id for you */
      file = mongoc_gridfs_create_file_from_stream(gridfs, stream, &opt);
      assert(file);

      id.value_type = BSON_TYPE_INT32;
      id.value.v_int32 = 1;

      /* optional: the following method specifies a file_id of any
         BSON type */
      if (!mongoc_gridfs_file_set_id(file, &id, &error)) {
         fprintf(stderr, "%s\n", error.message);
         return EXIT_FAILURE;
      }

      if (!mongoc_gridfs_file_save(file)) {
         mongoc_gridfs_file_error(file, &error);
         fprintf(stderr, "Could not save: %s\n", error.message);
         return EXIT_FAILURE;
      }

      mongoc_gridfs_file_destroy(file);
   } else {
      fprintf(stderr, "Unknown command");
      return EXIT_FAILURE;
   }

   mongoc_gridfs_destroy(gridfs);
   mongoc_uri_destroy(uri);
   mongoc_client_destroy(client);

   mongoc_cleanup();

   return EXIT_SUCCESS;
}

👀 SEE ALSO 👀

• The MongoDB GridFS specification.
• The spec-compliant mongoc_gridfs_bucket_t.

✍️ AUTHOR ✍️

MongoDB, Inc

©️ COPYRIGHT ©️

2009-present, MongoDB, Inc.

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peace out from libmongoc version 2.5.6, dated Oct 09, 2026 💅✨🌸