[gnome-software: 16/20] gs-download-utils: Ensure the ETag remains set if a file is not modified

[Philip Withnall <pwithnall src gnome org>]

commit d9ab60ca587286d550c87c2b9a830ee3357ccafd
Author: Philip Withnall <pwithnall endlessos org>
Date:   Fri Mar 11 13:27:18 2022 +0000

    gs-download-utils: Ensure the ETag remains set if a file is not modified
    
    If there is a cache hit when downloading a file, meaning the local copy
    is up to date with the server’s copy, ensure that the up-to-date ETag is
    returned by `gs_download_stream_finish()`. Previously it was incorrectly
    returning `NULL`.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>

 lib/gs-download-utils.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/lib/gs-download-utils.c b/lib/gs-download-utils.c
index 5808f431e..60bdaf1d4 100644
--- a/lib/gs-download-utils.c
+++ b/lib/gs-download-utils.c
@@ -55,6 +55,7 @@ typedef struct {
        GInputStream *input_stream;  /* (nullable) (owned) */
        GOutputStream *output_stream;  /* (nullable) (owned) */
        gsize buffer_size_bytes;
+       gchar *last_etag;  /* (nullable) (owned) */
        int io_priority;
        GsDownloadProgressCallback progress_callback;  /* (nullable) */
        gpointer progress_user_data;
@@ -85,6 +86,7 @@ download_data_free (DownloadData *data)
        g_clear_object (&data->input_stream);
        g_clear_object (&data->output_stream);
 
+       g_clear_pointer (&data->last_etag, g_free);
        g_clear_object (&data->message);
        g_clear_pointer (&data->uri, g_free);
        g_clear_pointer (&data->new_etag, g_free);
@@ -199,7 +201,11 @@ gs_download_stream_async (SoupSession                *soup_session,
 
        data->message = g_object_ref (msg);
 
-       if (last_etag != NULL && *last_etag != '\0') {
+       if (last_etag != NULL && *last_etag == '\0')
+               last_etag = NULL;
+       data->last_etag = g_strdup (last_etag);
+
+       if (last_etag != NULL) {
 #if SOUP_CHECK_VERSION(3, 0, 0)
                soup_message_headers_append (soup_message_get_request_headers (msg), "If-None-Match", 
last_etag);
 #else
@@ -267,8 +273,11 @@ open_input_stream_cb (GObject      *source_object,
                        /* If the file has not been modified from the ETag we
                         * have, finish the download early. Ensure to close the
                         * output stream so that its existing content is *not*
-                        * overwritten. */
+                        * overwritten.
+                        *
+                        * Preserve the existing ETag. */
                        data->discard_output_stream = TRUE;
+                       data->new_etag = g_strdup (data->last_etag);
                        finish_download (task, NULL);
                        return;
                } else if (status_code != SOUP_STATUS_OK) {