fixed deadlock in json-rpc mode

* properly unlock mutex to avoid deadlock

see #572

src/api/api.go

@@ -531,10 +531,11 @@ func (a *Api) wsPing(ws *websocket.Conn, stop chan struct{}) {
 			return
 		case <-pingTicker.C:
 			a.wsMutex.Lock()
-			defer a.wsMutex.Unlock()
 			if err := ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
+				a.wsMutex.Unlock()
 				return
 			}
+			a.wsMutex.Unlock()
 		}
 	}
 }

src/client/jsonrpc2.go

@@ -229,14 +229,14 @@ func (r *JsonRpc2Client) GetReceiveChannel() (chan JsonRpc2ReceivedMessage, stri
 	}
 
 	r.receivedMessagesMutex.Lock()
-	defer r.receivedMessagesMutex.Unlock()
 	r.receivedMessagesChannels[channelUuid.String()] = c
+	r.receivedMessagesMutex.Unlock()
 
 	return c, channelUuid.String(), nil
 }
 
 func (r *JsonRpc2Client) RemoveReceiveChannel(channelUuid string) {
 	r.receivedMessagesMutex.Lock()
-	defer r.receivedMessagesMutex.Unlock()
 	delete(r.receivedMessagesChannels, channelUuid)
+	r.receivedMessagesMutex.Unlock()
 }