Add FinalizerFunc to NATS transport (#790) (#790)

Author: Kirill Parasotchenko

transport/nats/subscriber.go

@@ -18,6 +18,7 @@ type Subscriber struct {
 	before       []RequestFunc
 	after        []SubscriberResponseFunc
 	errorEncoder ErrorEncoder
+	finalizer    []SubscriberFinalizerFunc
 	logger       log.Logger
 }
 
@@ -73,12 +74,26 @@ func SubscriberErrorLogger(logger log.Logger) SubscriberOption {
 	return func(s *Subscriber) { s.logger = logger }
 }
 
+// SubscriberFinalizer is executed at the end of every request from a publisher through NATS.
+// By default, no finalizer is registered.
+func SubscriberFinalizer(f ...SubscriberFinalizerFunc) SubscriberOption {
+	return func(s *Subscriber) { s.finalizer = f }
+}
+
 // ServeMsg provides nats.MsgHandler.
 func (s Subscriber) ServeMsg(nc *nats.Conn) func(msg *nats.Msg) {
 	return func(msg *nats.Msg) {
 		ctx, cancel := context.WithCancel(context.Background())
 		defer cancel()
 
+		if len(s.finalizer) > 0 {
+			defer func() {
+				for _, f := range s.finalizer {
+					f(ctx, msg)
+				}
+			}()
+		}
+
 		for _, f := range s.before {
 			ctx = f(ctx, msg)
 		}
@@ -125,6 +140,11 @@ func (s Subscriber) ServeMsg(nc *nats.Conn) func(msg *nats.Msg) {
 // types.
 type ErrorEncoder func(ctx context.Context, err error, reply string, nc *nats.Conn)
 
+// ServerFinalizerFunc can be used to perform work at the end of an request
+// from a publisher, after the response has been written to the publisher. The principal
+// intended use is for request logging.
+type SubscriberFinalizerFunc func(ctx context.Context, msg *nats.Msg)
+
 // NopRequestDecoder is a DecodeRequestFunc that can be used for requests that do not
 // need to be decoded, and simply returns nil, nil.
 func NopRequestDecoder(_ context.Context, _ *nats.Msg) (interface{}, error) {

transport/nats/subscriber_test.go

@@ -289,6 +289,57 @@ func TestMultipleSubscriberAfter(t *testing.T) {
 	wg.Wait()
 }
 
+func TestSubscriberFinalizerFunc(t *testing.T) {
+	nc := newNatsConn(t)
+	defer nc.Close()
+
+	var (
+		response = struct{ Body string }{"go eat a fly ugly\n"}
+		wg       sync.WaitGroup
+		done     = make(chan struct{})
+	)
+	handler := natstransport.NewSubscriber(
+		endpoint.Nop,
+		func(context.Context, *nats.Msg) (interface{}, error) {
+			return struct{}{}, nil
+		},
+		func(_ context.Context, reply string, nc *nats.Conn, _ interface{}) error {
+			b, err := json.Marshal(response)
+			if err != nil {
+				return err
+			}
+
+			return nc.Publish(reply, b)
+		},
+		natstransport.SubscriberFinalizer(func(ctx context.Context, _ *nats.Msg) {
+			close(done)
+		}),
+	)
+
+	sub, err := nc.QueueSubscribe("natstransport.test", "natstransport", handler.ServeMsg(nc))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer sub.Unsubscribe()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		_, err := nc.Request("natstransport.test", []byte("test data"), 2*time.Second)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("timeout waiting for finalizer")
+	}
+
+	wg.Wait()
+}
+
 func TestEncodeJSONResponse(t *testing.T) {
 	nc := newNatsConn(t)
 	defer nc.Close()