Fall back to sleeve when "Overlays" not present in features

prog/weaver/main.go

@@ -196,7 +196,9 @@ func main() {
 	if fastDPOverlay != nil {
 		overlays.Add("fastdp", fastDPOverlay)
 	}
-	overlays.Add("sleeve", weave.NewSleeveOverlay(config.Port))
+	sleeve := weave.NewSleeveOverlay(config.Port)
+	overlays.Add("sleeve", sleeve)
+	overlays.SetCompatOverlay(sleeve)
 	config.Overlay = overlays
 
 	if routerName == "" {

router/overlay_switch.go

@@ -13,8 +13,9 @@ import (
 // uses the best one that seems to be working.
 
 type OverlaySwitch struct {
-	overlays     map[string]Overlay
-	overlayNames []string
+	overlays      map[string]Overlay
+	overlayNames  []string
+	compatOverlay Overlay
 }
 
 func NewOverlaySwitch() *OverlaySwitch {
@@ -31,6 +32,10 @@ func (osw *OverlaySwitch) Add(name string, overlay Overlay) {
 	osw.overlayNames = append(osw.overlayNames, name)
 }
 
+func (osw *OverlaySwitch) SetCompatOverlay(overlay Overlay) {
+	osw.compatOverlay = overlay
+}
+
 func (osw *OverlaySwitch) AddFeaturesTo(features map[string]string) {
 	features["Overlays"] = strings.Join(osw.overlayNames, " ")
 }
@@ -159,6 +164,10 @@ type subForwarderEvent struct {
 
 func (osw *OverlaySwitch) MakeForwarder(
 	params ForwarderParams) (OverlayForwarder, error) {
+	if _, present := params.Features["Overlays"]; !present && osw.compatOverlay != nil {
+		return osw.compatOverlay.MakeForwarder(params)
+	}
+
 	overlays, err := osw.commonOverlays(params)
 	if err != nil {
 		return nil, err