SYNOPSIS
mongoc_gridfs_t * gridfs; bson_t error; gridfs = mongoc_client_get_gridfs (client, "db", "prefix", &error);
DESCRIPTION
mongoc_gridfs 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.
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(7) abstraction, which provides some convenient wrapping for file creation and reading/writing. It can be used without, but its worth looking to see if your problem can fit that model.
THREAD SAFETY
mongoc_gridfs is NOT thread-safe and should only be used from one thread at a time.
LIFECYCLE
Any mongoc_gridfs_file(7)s or mongoc_gridfs_file_list(7)s need to be destroyed before reclaiming the parent gridfs object. It is a programming error to do anything besides destroy() these objects if the parent is gone.
EXAMPLE
The following example demonstrates a trivial gridfs utility capable of reading, writing and listing files in gridfs.
#include <mongoc.h> #include <stdio.h> #include <stdlib.h> #include <fcntl.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; mongoc_stream_t *stream; bson_t query; bson_t child; bson_error_t error; ssize_t r; char buf[4096]; mongoc_iovec_t iov; const char * filename; const char * command; if (argc < 2) { fprintf(stderr, "usage - %s command ...\n", argv[0]); return 1; } mongoc_init(); iov.iov_base = (void *)buf; iov.iov_len = sizeof buf; /* connect to localhost client */ client = mongoc_client_new ("mongodb://127.0.0.1:27017"); assert(client); /* 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 1; } 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; } fwrite(iov.iov_base, r, 1, stdout); } mongoc_stream_destroy (stream); } else if (strcmp(command, "list") == 0) { bson_init (&query); bson_append_document_begin (&query, "$orderby", -1, &child); bson_append_int32 (&child, "filename", -1, 1); bson_append_document_end (&query, &child); bson_append_document_begin (&query, "$query", -1, &child); bson_append_document_end (&query, &child); list = mongoc_gridfs_find (gridfs, &query); bson_destroy (&query); 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 1; } stream = mongoc_stream_file_new_for_path (argv [3], O_RDONLY, 0); assert (stream); opt.filename = filename; file = mongoc_gridfs_create_file_from_stream (gridfs, stream, &opt); assert(file); mongoc_gridfs_file_save(file); mongoc_gridfs_file_destroy(file); } else { fprintf(stderr, "Unknown command"); return 1; } mongoc_gridfs_destroy (gridfs); mongoc_client_destroy (client); return 0; }
SEE ALSO
FUNCTIONS
AUTHORS
This page was written by MongoDB Inc.