rewrite ws client to expose a callback instead of a channel

callback gives more power to the publisher. plus it is optional
comparing to a channel, which will block the whole client if you won't
read from it.

rpc/client/httpclient.go

@@ -226,7 +226,9 @@ func (w *WSEvents) Start() (bool, error) {
 	st, err := w.EventSwitch.Start()
 	// if we did start, then OnStart here...
 	if st && err == nil {
-		ws := rpcclient.NewWSClient(w.remote, w.endpoint)
+		ws := rpcclient.NewWSClient(w.remote, w.endpoint, rpcclient.OnReconnect(func() {
+			w.redoSubscriptions()
+		}))
 		_, err = ws.Start()
 		if err == nil {
 			w.ws = ws
@@ -335,8 +337,6 @@ func (w *WSEvents) eventListener() {
 			// before cleaning up the w.ws stuff
 			w.done <- true
 			return
-		case <-w.ws.ReconnectCh:
-			w.redoSubscriptions()
 		}
 	}
 }

rpc/lib/client/ws_client.go

@@ -43,7 +43,9 @@ type WSClient struct {
 	// user facing channels, closed only when the client is being stopped.
 	ResultsCh chan json.RawMessage
 	ErrorsCh  chan error
-	ReconnectCh chan bool
+
+	// Callback, which will be called each time after successful reconnect.
+	onReconnect func()
 
 	// internal channels
 	send            chan types.RPCRequest // user requests
@@ -125,6 +127,14 @@ func PingPeriod(pingPeriod time.Duration) func(*WSClient) {
 	}
 }
 
+// OnReconnect sets the callback, which will be called every time after
+// successful reconnect.
+func OnReconnect(cb func()) func(*WSClient) {
+	return func(c *WSClient) {
+		c.onReconnect = cb
+	}
+}
+
 // String returns WS client full address.
 func (c *WSClient) String() string {
 	return fmt.Sprintf("%s (%s)", c.Address, c.Endpoint)
@@ -140,7 +150,6 @@ func (c *WSClient) OnStart() error {
 
 	c.ResultsCh = make(chan json.RawMessage)
 	c.ErrorsCh = make(chan error)
-	c.ReconnectCh = make(chan bool)
 
 	c.send = make(chan types.RPCRequest)
 	// 1 additional error may come from the read/write
@@ -256,7 +265,9 @@ func (c *WSClient) reconnect() error {
 			c.Logger.Error("failed to redial", "err", err)
 		} else {
 			c.Logger.Info("reconnected")
-			c.ReconnectCh <- true
+			if c.onReconnect != nil {
+				go c.onReconnect()
+			}
 			return nil
 		}
 

rpc/lib/client/ws_client_test.go

@@ -186,8 +186,6 @@ func callWgDoneOnResult(t *testing.T, c *WSClient, wg *sync.WaitGroup) {
 			if err != nil {
 				t.Fatalf("unexpected error: %v", err)
 			}
-		case <-c.ReconnectCh:
-			t.Log("Reconnected")
 		case <-c.Quit:
 			return
 		}