In get_file_mime_type:


        result = gfile_get_mime_type (file, fast_file_type);
...
        if (result == NULL) {
                char *value;
                value = g_content_type_guess (path, NULL, 0, NULL);
                result = get_static_string (value);
                g_free (value);
        }

g_content_type_guess does not return a mime_type - you need g_content_type_get_mime_type for that. Plus, this should be in gfile_get_mime_type, not the get_file_mime_type wrapper.

Extra wrinkle - some functions return const char*, some return char*.

- Mike