implement fixes based on skosito's remarks

controllers/invoicestream.ctrl.go

@@ -33,28 +33,13 @@ func (controller *InvoiceStreamController) StreamInvoices(c echo.Context) error
 		return err
 	}
 	invoiceChan := make(chan models.Invoice)
-	subId := controller.svc.InvoicePubSub.Subscribe(userId, invoiceChan)
-	upgrader := websocket.Upgrader{}
-	upgrader.CheckOrigin = func(r *http.Request) bool { return true }
 	ticker := time.NewTicker(30 * time.Second)
-	ws, err := upgrader.Upgrade(c.Response(), c.Request(), nil)
+	ws, done, err := createWebsocketUpgrader(c)
 	if err != nil {
-		controller.svc.InvoicePubSub.Unsubscribe(subId, userId)
 		return err
 	}
-	defer ws.Close()
-
-	//start listening for close messages
-	done := make(chan struct{})
-	go func() {
-		defer close(done)
-		for {
-			_, _, err := ws.ReadMessage()
-			if err != nil {
-				return
-			}
-		}
-	}()
+	//start subscription
+	subId := controller.svc.InvoicePubSub.Subscribe(userId, invoiceChan)
 
 	//start with keepalive message
 	err = ws.WriteJSON(&InvoiceEventWrapper{Type: "keepalive"})
@@ -94,5 +79,30 @@ SocketLoop:
 			}
 		}
 	}
-	return controller.svc.InvoicePubSub.Unsubscribe(subId, userId)
+	controller.svc.InvoicePubSub.Unsubscribe(subId, userId)
+	return nil
+}
+
+//open the websocket and start listening for close messages in a goroutine
+func createWebsocketUpgrader(c echo.Context) (conn *websocket.Conn, done chan struct{}, err error) {
+	upgrader := websocket.Upgrader{}
+	upgrader.CheckOrigin = func(r *http.Request) bool { return true }
+	ws, err := upgrader.Upgrade(c.Response(), c.Request(), nil)
+	if err != nil {
+		return nil, nil, err
+	}
+	defer ws.Close()
+
+	//start listening for close messages
+	done = make(chan struct{})
+	go func() {
+		defer close(done)
+		for {
+			_, _, err := ws.ReadMessage()
+			if err != nil {
+				return
+			}
+		}
+	}()
+	return ws, done, nil
 }

lib/service/pubsub.go

@@ -29,18 +29,27 @@ func (ps *Pubsub) Subscribe(topic int64, ch chan models.Invoice) (subId string)
 	return subId
 }
 
-func (ps *Pubsub) Unsubscribe(id string, topic int64) error {
+func (ps *Pubsub) Unsubscribe(id string, topic int64) {
 	ps.mu.Lock()
 	defer ps.mu.Unlock()
+	if ps.subs[topic] == nil {
+		return
+	}
+	if ps.subs[topic][id] == nil {
+		return
+	}
 	close(ps.subs[topic][id])
 	delete(ps.subs[topic], id)
-	return nil
 }
 
 func (ps *Pubsub) Publish(topic int64, msg models.Invoice) {
 	ps.mu.RLock()
 	defer ps.mu.RUnlock()
 
+	if ps.subs[topic] == nil {
+		return
+	}
+
 	for _, ch := range ps.subs[topic] {
 		ch <- msg
 	}