system-helper: Add CancelPull D-Bus method

If there is a pull failure in a child repo created by GetChildRepoForPull
system helper method, there is no way to go back to the system helper and
notify it to cleanup. Therefore, CancelPull is required on the pull failure
error path, so that the ongoing pull can be cleaned up nicely and prevent
any dangling mounts and subprocesses.

ostreedev/ostree#1723

data/org.freedesktop.Flatpak.xml

@@ -167,6 +167,13 @@
       <arg type='s' name='repo_path' direction='out'/>
     </method>
 
+    <!-- This method cancels an ongoing pull at repo_path. The cancellation triggered
+         by the client helps to cleanup the mount setup -->
+    <method name="CancelPull">
+      <arg type='s' name='installation' direction='in'/>
+      <arg type='s' name='repo_path' direction='in'/>
+    </method>
+
   </interface>
 
 </node>

system-helper/flatpak-system-helper.c

@@ -1812,6 +1812,42 @@ handle_update_summary (FlatpakSystemHelper   *object,
   return TRUE;
 }
 
+static gboolean
+handle_cancel_pull (FlatpakSystemHelper   *object,
+                    GDBusMethodInvocation *invocation,
+                    const gchar           *arg_installation,
+                    const gchar           *arg_repo_path)
+{
+  g_autoptr(OngoingPull) ongoing_pull = NULL;
+  g_autoptr(FlatpakDir) system = NULL;
+  g_autoptr(GError) error = NULL;
+
+  g_debug ("CancelPull %s", arg_installation);
+
+  system = dir_get_system (arg_installation, &error);
+  if (system == NULL)
+    {
+      g_dbus_method_invocation_return_gerror (invocation, error);
+      return TRUE;
+    }
+
+  ongoing_pull = take_ongoing_pull_by_dir (arg_repo_path);
+  if (ongoing_pull != NULL)
+    {
+      ongoing_pull_teardown (ongoing_pull);
+      ongoing_pull_unref (ongoing_pull);
+    }
+  else
+    {
+      /* Should not be reached */
+      g_warning ("Cannot find ongoing pull to cancel at: %s", arg_repo_path);
+    }
+
+  flatpak_system_helper_complete_cancel_pull (object, invocation);
+
+  return TRUE;
+}
+
 static gboolean
 flatpak_authorize_method_handler (GDBusInterfaceSkeleton *interface,
                                   GDBusMethodInvocation  *invocation,
@@ -1941,7 +1977,8 @@ flatpak_authorize_method_handler (GDBusInterfaceSkeleton *interface,
            g_strcmp0 (method_name, "EnsureRepo") == 0 ||
            g_strcmp0 (method_name, "RunTriggers") == 0 ||
            g_strcmp0 (method_name, "UpdateSummary") == 0 ||
-           g_strcmp0 (method_name, "GetChildRepoForPull") == 0)
+           g_strcmp0 (method_name, "GetChildRepoForPull") == 0 ||
+           g_strcmp0 (method_name, "CancelPull") == 0)
     {
       const char *remote;
 
@@ -2013,6 +2050,7 @@ on_bus_acquired (GDBusConnection *connection,
   g_signal_connect (helper, "handle-run-triggers", G_CALLBACK (handle_run_triggers), NULL);
   g_signal_connect (helper, "handle-update-summary", G_CALLBACK (handle_update_summary), NULL);
   g_signal_connect (helper, "handle-get-child-repo-for-pull", G_CALLBACK (handle_get_child_repo_for_pull), NULL);
+  g_signal_connect (helper, "handle-cancel-pull", G_CALLBACK (handle_cancel_pull), NULL);
 
   g_signal_connect (helper, "g-authorize-method",
                     G_CALLBACK (flatpak_authorize_method_handler),