[gnome-software: 2/6] rpm-ostree: Don’t hang if the daemon crashes

[Philip Withnall <pwithnall src gnome org>]

commit 74587122cb2a265dda5cfe2d96f57ba5fd4c309a
Author: Philip Withnall <pwithnall endlessos org>
Date:   Thu Nov 26 00:08:09 2020 +0000

    rpm-ostree: Don’t hang if the daemon crashes
    
    If the rpm-ostreed daemon crashes during an operation, the rpm-ostree
    plugin will continue to wait to receive a `Finished` signal from it,
    forever.
    
    Prevent that by watching the name owner of the proxy; if it becomes
    unset, the daemon has disappeared for some reason, and the rpm-ostree
    plugin should stop blocking.
    
    Spotted while working on #1091, via code inspection. I haven’t attempted
    to reproduce it in the wild.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>

 plugins/rpm-ostree/gs-plugin-rpm-ostree.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)
---
diff --git a/plugins/rpm-ostree/gs-plugin-rpm-ostree.c b/plugins/rpm-ostree/gs-plugin-rpm-ostree.c
index 2bb8afd0..521136f4 100644
--- a/plugins/rpm-ostree/gs-plugin-rpm-ostree.c
+++ b/plugins/rpm-ostree/gs-plugin-rpm-ostree.c
@@ -325,6 +325,17 @@ on_transaction_progress (GDBusProxy *proxy,
        }
 }
 
+static void
+on_owner_notify (GObject    *obj,
+                 GParamSpec *pspec,
+                 gpointer    user_data)
+{
+       TransactionProgress *tp = user_data;
+
+       /* Wake up the context so it can notice the server has disappeared. */
+       g_main_context_wakeup (tp->context);
+}
+
 static void
 cancelled_handler (GCancellable *cancellable,
                    gpointer user_data)
@@ -344,8 +355,10 @@ gs_rpmostree_transaction_get_response_sync (GsRPMOSTreeSysroot *sysroot_proxy,
        g_autoptr(GDBusConnection) peer_connection = NULL;
        gint cancel_handler;
        gulong signal_handler = 0;
+       gulong notify_handler = 0;
        gboolean success = FALSE;
        gboolean just_started = FALSE;
+       g_autofree gchar *name_owner = NULL;
 
        peer_connection = g_dbus_connection_new_for_address_sync (transaction_address,
                                                                  
G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_CLIENT,
@@ -374,6 +387,10 @@ gs_rpmostree_transaction_get_response_sync (GsRPMOSTreeSysroot *sysroot_proxy,
                                           G_CALLBACK (on_transaction_progress),
                                           tp);
 
+       notify_handler = g_signal_connect (transaction, "notify::g-name-owner",
+                                          G_CALLBACK (on_owner_notify),
+                                          tp);
+
        /* Tell the server we're ready to receive signals. */
        if (!gs_rpmostree_transaction_call_start_sync (transaction,
                                                       &just_started,
@@ -381,8 +398,11 @@ gs_rpmostree_transaction_get_response_sync (GsRPMOSTreeSysroot *sysroot_proxy,
                                                       error))
                goto out;
 
-       /* Process all the signals until we receive the Finished signal. */
-       while (!tp->complete) {
+       /* Process all the signals until we receive the Finished signal or the
+        * daemon disappears (which can happen if it crashes). */
+       while (!tp->complete &&
+              (name_owner = g_dbus_proxy_get_name_owner (G_DBUS_PROXY (transaction))) != NULL) {
+               g_clear_pointer (&name_owner, g_free);
                g_main_context_iteration (tp->context, TRUE);
        }
 
@@ -391,12 +411,17 @@ gs_rpmostree_transaction_get_response_sync (GsRPMOSTreeSysroot *sysroot_proxy,
        if (!g_cancellable_set_error_if_cancelled (cancellable, error)) {
                if (tp->error) {
                        g_propagate_error (error, g_steal_pointer (&tp->error));
+               } else if (!tp->complete && name_owner == NULL) {
+                       g_set_error_literal (error, G_DBUS_ERROR, G_DBUS_ERROR_NO_REPLY,
+                                            "Daemon disappeared");
                } else {
                        success = TRUE;
                }
        }
 
 out:
+       if (notify_handler != 0)
+               g_signal_handler_disconnect (transaction, notify_handler);
        if (signal_handler)
                g_signal_handler_disconnect (transaction, signal_handler);
        if (transaction != NULL)