Send hello event containing server version on WebSocket connect (#3936)

webapp/actions/websocket_actions.jsx

@@ -156,6 +156,10 @@ function handleEvent(msg) {
         handleStatusChangedEvent(msg);
         break;
 
+    case SocketEvents.HELLO:
+        handleHelloEvent(msg);
+        break;
+
     default:
     }
 }
@@ -284,3 +288,8 @@ function handleUserTypingEvent(msg) {
 function handleStatusChangedEvent(msg) {
     UserStore.setStatus(msg.user_id, msg.data.status);
 }
+
+function handleHelloEvent(msg) {
+    Client.serverVersion = msg.data.server_version;
+    AsyncClient.checkVersion();
+}

webapp/utils/constants.jsx

@@ -198,7 +198,8 @@ export const Constants = {
         TYPING: 'typing',
         PREFERENCE_CHANGED: 'preference_changed',
         EPHEMERAL_MESSAGE: 'ephemeral_message',
-        STATUS_CHANGED: 'status_change'
+        STATUS_CHANGED: 'status_change',
+        HELLO: 'hello'
     },
 
     UserUpdateEvents: {