xdsclient: delay resource cache deletion to handle immediate re-subscription of same resource

xds/internal/clients/xdsclient/ads_stream.go

@@ -68,9 +68,10 @@ type dataAndErrTuple struct {
 // occur on the ADS stream. Methods on this interface may be invoked
 // concurrently and implementations need to handle them in a thread-safe manner.
 type adsStreamEventHandler interface {
-	onStreamError(error)                           // Called when the ADS stream breaks.
-	onWatchExpiry(ResourceType, string)            // Called when the watch timer expires for a resource.
-	onResponse(response, func()) ([]string, error) // Called when a response is received on the ADS stream.
+	onStreamError(error)                                       // Called when the ADS stream breaks.
+	onWatchExpiry(ResourceType, string)                        // Called when the watch timer expires for a resource.
+	onResponse(response, func()) ([]string, error)             // Called when a response is received on the ADS stream.
+	onRequiredToRemoveUnsubscribedCacheEntries(typeURL string) // Called when it is needed to remove unsubscribed cache entries.
 }
 
 // state corresponding to a resource type.
@@ -444,6 +445,9 @@ func (s *adsStreamImpl) sendMessageLocked(stream clients.Stream, names []string,
 		}
 	}
 
+	// Call the event handler to remove unsubscribed cache entries.
+	s.eventHandler.onRequiredToRemoveUnsubscribedCacheEntries(url)
+
 	msg, err := proto.Marshal(req)
 	if err != nil {
 		s.logger.Warningf("Failed to marshal DiscoveryRequest: %v", err)
@@ -460,6 +464,7 @@ func (s *adsStreamImpl) sendMessageLocked(stream clients.Stream, names []string,
 	} else if s.logger.V(2) {
 		s.logger.Warningf("ADS request sent for type %q, resources: %v, version: %q, nonce: %q", url, names, version, nonce)
 	}
+
 	return nil
 }
 

xds/internal/clients/xdsclient/authority.go

@@ -655,6 +655,17 @@ func (a *authority) watchResource(rType ResourceType, resourceName string, watch
 			}
 			resources[resourceName] = state
 			xdsChannel.channel.subscribe(rType, resourceName)
+		} else if len(state.watchers) == 0 {
+			if a.logger.V(2) {
+				a.logger.Infof("Re-watch for type %q, resource name %q before unsubscription", rType.TypeName, resourceName)
+			}
+			// Add the active channel to the resource's channel configs if not
+			// already present.
+			state.xdsChannelConfigs[xdsChannel] = true
+			// Ensure the resource is subscribed on the active channel. We do this
+			// even if resource is present in cache as re-watches  might occur
+			// after unsubscribes or channel changes.
+			xdsChannel.channel.subscribe(rType, resourceName)
 		}
 		// Always add the new watcher to the set of watchers.
 		state.watchers[watcher] = true
@@ -720,6 +731,10 @@ func (a *authority) unwatchResource(rType ResourceType, resourceName string, wat
 			// there when the watch was registered.
 			resources := a.resources[rType]
 			state := resources[resourceName]
+			if state == nil {
+				a.logger.Warningf("Attempting to unwatch resource %q of type %q which is not currently watched", resourceName, rType.TypeName)
+				return
+			}
 
 			// Delete this particular watcher from the list of watchers, so that its
 			// callback will not be invoked in the future.
@@ -732,32 +747,16 @@ func (a *authority) unwatchResource(rType ResourceType, resourceName string, wat
 			}
 
 			// There are no more watchers for this resource. Unsubscribe this
-			// resource from all channels where it was subscribed to and delete
-			// the state associated with it.
+			// resource from all channels where it was subscribed to but do not
+			// delete the state associated with it in case the resource is
+			// re-requested later before un-subscription request is completed by
+			// the management server.
 			if a.logger.V(2) {
 				a.logger.Infof("Removing last watch for resource name %q", resourceName)
 			}
 			for xcc := range state.xdsChannelConfigs {
 				xcc.channel.unsubscribe(rType, resourceName)
 			}
-			delete(resources, resourceName)
-
-			// If there are no more watchers for this resource type, delete the
-			// resource type from the top-level map.
-			if len(resources) == 0 {
-				if a.logger.V(2) {
-					a.logger.Infof("Removing last watch for resource type %q", rType.TypeName)
-				}
-				delete(a.resources, rType)
-			}
-			// If there are no more watchers for any resource type, release the
-			// reference to the xdsChannels.
-			if len(a.resources) == 0 {
-				if a.logger.V(2) {
-					a.logger.Infof("Removing last watch for for any resource type, releasing reference to the xdsChannel")
-				}
-				a.closeXDSChannels()
-			}
 		}, func() { close(done) })
 		<-done
 	})
@@ -874,6 +873,41 @@ func (a *authority) close() {
 	}
 }
 
+// removeUnsubscribedCacheEntries iterates through all resources of the given type and
+// removes the state for resources that have no active watchers. This is called
+// after sending a discovery request to ensure that resources that were
+// unsubscribed (and thus have no watchers) are eventually removed from the
+// authority's cache.
+func (a *authority) removeUnsubscribedCacheEntries(rType ResourceType) {
+	resources := a.resources[rType]
+	if resources == nil {
+		return
+	}
+
+	for name, state := range resources {
+		if len(state.watchers) == 0 {
+			if a.logger.V(2) {
+				a.logger.Infof("Removing resource state for %q of type %q as it has no watchers after an update cycle", name, rType.TypeName)
+			}
+			delete(resources, name)
+		}
+	}
+
+	if len(resources) == 0 {
+		if a.logger.V(2) {
+			a.logger.Infof("Removing resource type %q from cache as it has no more resources", rType.TypeName)
+		}
+		delete(a.resources, rType)
+	}
+
+	if len(a.resources) == 0 {
+		if a.logger.V(2) {
+			a.logger.Infof("Removing last watch for any resource type, releasing reference to the xdsChannels")
+		}
+		a.closeXDSChannels()
+	}
+}
+
 func serviceStatusToProto(serviceStatus xdsresource.ServiceStatus) v3adminpb.ClientResourceStatus {
 	switch serviceStatus {
 	case xdsresource.ServiceStatusUnknown:

xds/internal/clients/xdsclient/channel.go

@@ -59,6 +59,10 @@ type xdsChannelEventHandler interface {
 	// adsResourceDoesNotExist is called when the xdsChannel determines that a
 	// requested ADS resource does not exist.
 	adsResourceDoesNotExist(ResourceType, string)
+
+	// requiredToRemoveUnsubscribedCacheEntries is called when the xdsChannel
+	// needs to remove unsubscribed cache entries.
+	requiredToRemoveUnsubscribedCacheEntries(ResourceType)
 }
 
 // xdsChannelOpts holds the options for creating a new xdsChannel.
@@ -136,8 +140,30 @@ type xdsChannel struct {
 }
 
 func (xc *xdsChannel) close() {
+	if xc.closed.HasFired() {
+		return
+	}
 	xc.closed.Fire()
+
+	// Get the resource types that this specific ADS stream was handling
+	// before stopping it.
+	xc.ads.mu.Lock()
+	typesHandledByStream := make([]ResourceType, 0, len(xc.ads.resourceTypeState))
+	for typ := range xc.ads.resourceTypeState {
+		typesHandledByStream = append(typesHandledByStream, typ)
+	}
+	xc.ads.mu.Unlock()
+
 	xc.ads.Stop()
+
+	// Schedule removeUnsubscribedCacheEntries for the types this stream was handling,
+	// on all authorities that were interested in this channel.
+	if _, ok := xc.eventHandler.(*channelState); ok {
+		for _, typ := range typesHandledByStream {
+			xc.eventHandler.requiredToRemoveUnsubscribedCacheEntries(typ)
+		}
+	}
+
 	xc.transport.Close()
 	xc.logger.Infof("Shutdown")
 }
@@ -228,6 +254,24 @@ func (xc *xdsChannel) onResponse(resp response, onDone func()) ([]string, error)
 	return names, err
 }
 
+func (xc *xdsChannel) onRequiredToRemoveUnsubscribedCacheEntries(typeURL string) {
+	if xc.closed.HasFired() {
+		if xc.logger.V(2) {
+			xc.logger.Infof("Received an update from the ADS stream on closed ADS stream")
+		}
+		return
+	}
+
+	// Lookup the resource parser based on the resource type.
+	rType, ok := xc.clientConfig.ResourceTypes[typeURL]
+	if !ok {
+		logger.Warningf("Resource type URL %q unknown in response from server", typeURL)
+		return
+	}
+
+	xc.eventHandler.requiredToRemoveUnsubscribedCacheEntries(rType)
+}
+
 // decodeResponse decodes the resources in the given ADS response.
 //
 // The opts parameter provides configuration options for decoding the resources.

xds/internal/clients/xdsclient/channel_test.go

@@ -772,3 +772,6 @@ func (ta *testEventHandler) waitForResourceDoesNotExist(ctx context.Context) (Re
 	}
 	return typ, name, nil
 }
+
+func (*testEventHandler) requiredToRemoveUnsubscribedCacheEntries(ResourceType) {
+}

xds/internal/clients/xdsclient/test/ads_stream_ack_nack_test.go

@@ -469,8 +469,10 @@ func (s) TestADS_ACK_NACK_ResourceIsNotRequestedAnymore(t *testing.T) {
 	}
 
 	// Cancel the watch on the listener resource. This should result in the
-	// existing connection to be management server getting closed.
+	// existing connection to be management server getting closed after the
+	// unsubscription discovery request is sent.
 	ldsCancel()
+	// Verify that the connection to the management server is closed.
 	if _, err := streamCloseCh.Receive(ctx); err != nil {
 		t.Fatalf("Timeout when expecting existing connection to be closed: %v", err)
 	}

xds/internal/clients/xdsclient/xdsclient.go

@@ -439,6 +439,21 @@ func (cs *channelState) adsResourceDoesNotExist(typ ResourceType, resourceName s
 	}
 }
 
+func (cs *channelState) requiredToRemoveUnsubscribedCacheEntries(rType ResourceType) {
+	if cs.parent.done.HasFired() {
+		return
+	}
+
+	cs.parent.channelsMu.Lock()
+	defer cs.parent.channelsMu.Unlock()
+
+	for authority := range cs.interestedAuthorities {
+		authority.xdsClientSerializer.TrySchedule(func(context.Context) {
+			authority.removeUnsubscribedCacheEntries(rType)
+		})
+	}
+}
+
 func resourceWatchStateForTesting(c *XDSClient, rType ResourceType, resourceName string) (xdsresource.ResourceWatchState, error) {
 	c.channelsMu.Lock()
 	defer c.channelsMu.Unlock()