fix: data race in send message

channel.go

@@ -26,7 +26,9 @@ func newChannel(name string) *Channel {
 
 // SendMessage broadcast a message to all clients in a channel.
 func (c *Channel) SendMessage(message *Message) {
+	c.mu.Lock()
 	c.lastEventID = message.id
+	c.mu.Unlock()
 
 	timer := time.NewTimer(sendMessageToClientTimeout)
 	defer timer.Stop()

sse_test.go

@@ -189,3 +189,68 @@ func TestServerDontStartServer(t *testing.T) {
 	// check for number of message received
 	assert.Equal(t, numChannels*numSubscribersEachChannel, countMessageReceived)
 }
+
+func TestMultipleTopics(t *testing.T) {
+	// The usage pattern: Imagine  we have a client which subsribed to multiple topics
+	// inside a connection. It track changes of specific items state by their ID
+	// for example.
+	sendersWg := sync.WaitGroup{}
+	workerWg := sync.WaitGroup{}
+	m := sync.Mutex{}
+	messageCount := 0
+	numMessages := 3
+	topics := []string{"Sunday", "Monday", "Tuesday", "Wednesday", "Thuesday", "Friday", "Saturday"}
+
+	srv := NewServer(&Options{
+		Logger: log.New(os.Stdout, "go-sse: ", log.Ldate|log.Ltime|log.Lshortfile),
+	})
+
+	defer srv.Shutdown()
+
+	name := "CH-0"
+	ch := srv.addChannel(name)
+	fmt.Printf("Channel %s registed\n", name)
+
+	// Create new client
+	c := newClient("", name)
+	// Add client to current channel
+	ch.addClient(c)
+
+	// receive messages
+	workerWg.Add(1)
+	go func() {
+		defer workerWg.Done()
+		// Wait for messages in the channel
+		for msg := range c.send {
+			m.Lock()
+			messageCount++
+			m.Unlock()
+			fmt.Printf("ID: %s - Topic: %s - Message: %s\n", msg.id, msg.event, msg.data)
+		}
+	}()
+
+	for _, day := range topics {
+		sendersWg.Add(1)
+		go func(topic string) {
+			defer sendersWg.Done()
+			for n := 0; n < numMessages; n++ {
+				srv.SendMessage(name, NewMessage(id(), "hello", topic))
+			}
+		}(day)
+	}
+	// Wait senders to complete
+	sendersWg.Wait()
+
+	srv.close()
+	// Wait recipient routine
+	workerWg.Wait()
+
+	if messageCount != len(topics)*numMessages {
+		t.Errorf("Expected %d messages but got %d", 3*numMessages, messageCount)
+	}
+
+}
+
+func id() string {
+	return fmt.Sprintf("%d", time.Now().UTC().Unix()*1000)
+}