[gnome-software] odrs: Use memory mapped I/O when loading individual app rating JSON

[Philip Withnall <pwithnall src gnome org>]

commit a2d0a1ca7715be8f72665ae881a67902e747123c
Author: Philip Withnall <withnall endlessm com>
Date:   Wed Jun 17 20:16:17 2020 +0100

    odrs: Use memory mapped I/O when loading individual app rating JSON
    
    This saves loading the file into a new heap allocation before parsing it
    and freeing the allocation.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 plugins/odrs/gs-plugin-odrs.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)
---
diff --git a/plugins/odrs/gs-plugin-odrs.c b/plugins/odrs/gs-plugin-odrs.c
index 161ceb89..ce529591 100644
--- a/plugins/odrs/gs-plugin-odrs.c
+++ b/plugins/odrs/gs-plugin-odrs.c
@@ -194,7 +194,11 @@ gs_plugin_odrs_load_ratings (GsPlugin *plugin, const gchar *fn, GError **error)
 
        /* parse the data and find the success */
        json_parser = json_parser_new_immutable ();
+#if JSON_CHECK_VERSION(1, 6, 0)
+       if (!json_parser_load_from_mapped_file (json_parser, fn, error)) {
+#else
        if (!json_parser_load_from_file (json_parser, fn, error)) {
+#endif
                gs_utils_error_convert_json_glib (error);
                return FALSE;
        }
@@ -708,13 +712,17 @@ gs_plugin_odrs_fetch_for_app (GsPlugin *plugin, GsApp *app, GError **error)
                return NULL;
        cachefn_file = g_file_new_for_path (cachefn);
        if (gs_utils_get_file_age (cachefn_file) < ODRS_REVIEW_CACHE_AGE_MAX) {
-               g_autofree gchar *json_data = NULL;
-               if (!g_file_get_contents (cachefn, &json_data, NULL, error))
+               g_autoptr(GMappedFile) mapped_file = NULL;
+
+               mapped_file = g_mapped_file_new (cachefn, FALSE, error);
+               if (mapped_file == NULL)
                        return NULL;
+
                g_debug ("got review data for %s from %s",
                         gs_app_get_id (app), cachefn);
                return gs_plugin_odrs_parse_reviews (plugin,
-                                                    json_data, -1,
+                                                    g_mapped_file_get_contents (mapped_file),
+                                                    g_mapped_file_get_length (mapped_file),
                                                     error);
        }