[gnome-software] Use If-Modified-Since to avoid downloading duplicate screenshots

[Joaquim Manuel Pereira Rocha <jrocha src gnome org>]

commit f9022897bdd64b2b334938473445771210620cb4
Author: Richard Hughes <richard hughsie com>
Date:   Wed Nov 9 10:54:02 2016 +0000

    Use If-Modified-Since to avoid downloading duplicate screenshots
    
    Inspired by a patch from Joaquim Rocha <jrocha endlessm com>, many thanks.

 src/gs-screenshot-image.c |   35 +++++++++++++++++++++++++++++++++++
 1 files changed, 35 insertions(+), 0 deletions(-)
---
diff --git a/src/gs-screenshot-image.c b/src/gs-screenshot-image.c
index 8541442..23b7b2d 100644
--- a/src/gs-screenshot-image.c
+++ b/src/gs-screenshot-image.c
@@ -215,6 +215,11 @@ gs_screenshot_image_complete_cb (SoupSession *session,
        if (msg->status_code == SOUP_STATUS_CANCELLED || ssimg->session == NULL)
                return;
 
+       if (msg->status_code == SOUP_STATUS_NOT_MODIFIED) {
+               g_debug ("screenshot has not been modified");
+               as_screenshot_show_image (ssimg);
+               return;
+       }
        if (msg->status_code != SOUP_STATUS_OK) {
                /* TRANSLATORS: this is when we try to download a screenshot and
                 * we get back 404 */
@@ -314,6 +319,29 @@ gs_screenshot_get_cachefn_for_url (const gchar *url)
        return g_strdup_printf ("%s-%s", checksum, basename);
 }
 
+static void
+gs_screenshot_soup_msg_set_modified_request (SoupMessage *msg, GFile *file)
+{
+       GTimeVal time_val;
+       g_autoptr(GDateTime) date_time = NULL;
+       g_autoptr(GFileInfo) info = NULL;
+       g_autofree gchar *mod_date = NULL;
+
+       info = g_file_query_info (file,
+                                 G_FILE_ATTRIBUTE_TIME_MODIFIED,
+                                 G_FILE_QUERY_INFO_NONE,
+                                 NULL,
+                                 NULL);
+       if (info == NULL)
+               return;
+       g_file_info_get_modification_time (info, &time_val);
+       date_time = g_date_time_new_from_timeval_local (&time_val);
+       mod_date = g_date_time_format (date_time, "%a, %d %b %Y %H:%M:%S %Z");
+       soup_message_headers_append (msg->request_headers,
+                                    "If-Modified-Since",
+                                    mod_date);
+}
+
 void
 gs_screenshot_image_load_async (GsScreenshotImage *ssimg,
                                GCancellable *cancellable)
@@ -454,6 +482,13 @@ gs_screenshot_image_load_async (GsScreenshotImage *ssimg,
                return;
        }
 
+       /* not all servers support If-Modified-Since, but worst case we just
+        * re-download the entire file again every 30 days */
+       if (g_file_test (ssimg->filename, G_FILE_TEST_EXISTS)) {
+               g_autoptr(GFile) file = g_file_new_for_path (ssimg->filename);
+               gs_screenshot_soup_msg_set_modified_request (ssimg->message, file);
+       }
+
        /* send async */
        soup_session_queue_message (ssimg->session,
                                    g_object_ref (ssimg->message) /* transfer full */,