fix subscription hanging on error and add a stop subscription option …

…inside the callback (shurcooL#39)

* fix the deadlock issue that the subscription client can't receive error events from the channel.
* close the connection when there is no running subscription
* add a particular error that stops the subscription inside the callback

README.md

@@ -28,6 +28,7 @@ For more information, see package [`github.com/shurcooL/githubv4`](https://githu
 		- [Subscription](#subscription)
 			- [Usage](#usage-1)
 			- [Subscribe](#subscribe)
+			- [Stop the subscription](#stop-the-subscription)
 			- [Authentication](#authentication-1)
 			- [Options](#options)
 			- [Events](#events)
@@ -490,13 +491,30 @@ subscriptionId, err := client.Subscribe(&query, nil, func(dataValue *json.RawMes
 	fmt.Println(query.Me.Name)
 
 	// Output: Luke Skywalker
+	return nil
+})
+
+if err != nil {
+	// Handle error.
+}
+```
+
+#### Stop the subscription
+
+You can programmatically stop the subscription while the client is running by using the `Unsubscribe` method, or returning a special error to stop it in the callback.
+
+```Go
+subscriptionId, err := client.Subscribe(&query, nil, func(dataValue *json.RawMessage, errValue error) error {
+	// ...
+	// return this error to stop the subscription in the callback
+	return graphql.ErrSubscriptionStopped
 })
 
 if err != nil {
 	// Handle error.
 }
 
-// you can unsubscribe the subscription while the client is running
+// unsubscribe the subscription while the client is running with the subscription ID
 client.Unsubscribe(subscriptionId)
 ```
 
@@ -537,7 +555,7 @@ client.
 // OnConnected event is triggered when the websocket connected to GraphQL server sucessfully
 client.OnConnected(fn func())
 
-// OnDisconnected event is triggered when the websocket server was stil down after retry timeout
+// OnDisconnected event is triggered when the websocket client was disconnected
 client.OnDisconnected(fn func())
 
 // OnConnected event is triggered when there is any connection error. This is bottom exception handler level

example/subscription/client.go

@@ -46,7 +46,7 @@ func startSubscription() error {
 		} `graphql:"helloSaid"`
 	}
 
-	_, err := client.Subscribe(sub, nil, func(data *json.RawMessage, err error) error {
+	subId, err := client.Subscribe(sub, nil, func(data *json.RawMessage, err error) error {
 
 		if err != nil {
 			log.Println(err)
@@ -64,15 +64,22 @@ func startSubscription() error {
 		panic(err)
 	}
 
+	// automatically unsubscribe after 10 seconds
+	go func() {
+		time.Sleep(10 * time.Second)
+		client.Unsubscribe(subId)
+	}()
+
 	return client.Run()
 }
 
 // send hello mutations to the graphql server, so the subscription client can receive messages
 func startSendHello() {
 
 	client := graphql.NewClient(getServerEndpoint(), &http.Client{Transport: http.DefaultTransport})
-
-	for i := 0; i < 120; i++ {
+	// stop until the subscription client is connected
+	time.Sleep(time.Second)
+	for i := 0; i < 10; i++ {
 		/*
 			mutation ($msg: String!) {
 				sayHello(msg: $msg) {

example/subscription/main.go

@@ -7,6 +7,6 @@ package main
 
 func main() {
 	go startServer()
-	go startSubscription()
-	startSendHello()
+	go startSendHello()
+	startSubscription()
 }