Return an empty stats if "container not found"

If we get "container not found" error from containerd, it's possibly
because that this container has already been stopped. It will be ok to
ignore this error and just return an empty stats.

fix DTS2017062812251
related upstream PR: moby#34004

Signed-off-by: Yuanhong Peng <pengyuanhong@huawei.com>

daemon/daemon_unix.go

@@ -1163,6 +1163,9 @@ func (daemon *Daemon) stats(c *container.Container) (*types.StatsJSON, error) {
 	}
 	stats, err := daemon.containerd.Stats(c.ID)
 	if err != nil {
+		if strings.Contains(err.Error(), "container not found") {
+			return nil, errNotFound{c.ID}
+		}
 		return nil, err
 	}
 	s := &types.StatsJSON{}

daemon/errors.go

@@ -55,3 +55,11 @@ func errExecPaused(id string) error {
 	err := fmt.Errorf("Container %s is paused, unpause the container before exec", id)
 	return errors.NewRequestConflictError(err)
 }
+
+type errNotFound struct {
+	containerID string
+}
+
+func (e errNotFound) Error() string {
+	return fmt.Sprintf("Container %s is not found", e.containerID)
+}

daemon/stats_collector_unix.go

@@ -126,20 +126,21 @@ func (s *statsCollector) run() {
 
 		for _, pair := range pairs {
 			stats, err := s.supervisor.GetContainerStats(pair.container)
-			if err != nil {
-				if _, ok := err.(errNotRunning); !ok {
-					logrus.Errorf("collecting stats for %s: %v", pair.container.ID, err)
-					continue
-				}
 
-				// publish empty stats ID if not running
+			switch err.(type) {
+			case nil:
+				// FIXME: move to containerd
+				stats.CPUStats.SystemUsage = systemUsage
+
+				pair.publisher.Publish(*stats)
+
+			case errNotRunning, errNotFound:
+				// publish empty stats ID if not running or not found
 				pair.publisher.Publish(types.StatsJSON{})
-				continue
-			}
-			// FIXME: move to containerd
-			stats.CPUStats.SystemUsage = systemUsage
 
-			pair.publisher.Publish(*stats)
+			default:
+				logrus.Errorf("collecting stats for %s: %v", pair.container.ID, err)
+			}
 		}
 	}
 }