fix: resume client to server communication after web socket reconnection

flow-client/src/main/java/com/vaadin/client/communication/AtmospherePushConnection.java

@@ -686,6 +686,7 @@ protected final native AtmosphereConfiguration createConfig()
             fallbackTransport: 'long-polling',
             contentType: 'application/json; charset=UTF-8',
             reconnectInterval: 5000,
+            maxWebsocketErrorRetries: 12,
             timeout: -1,
             maxReconnectOnClose: 10000000,
             trackMessageLength: true,

flow-client/src/main/java/com/vaadin/client/communication/DefaultConnectionStateHandler.java

@@ -458,6 +458,18 @@ public void pushOk(PushConnection pushConnection) {
         debug("pushOk()");
         if (isReconnecting()) {
             resolveTemporaryError(Type.PUSH);
+            if (registry.getRequestResponseTracker().hasActiveRequest()) {
+                debug("pushOk() Reset active request state when reconnecting PUSH because of a network error.");
+                endRequest();
+                // for bidirectional transport, the pending message is not sent
+                // as reconnection payload, so immediately push the pending
+                // changes on reconnect
+                if (pushConnection.isBidirectional()) {
+                    Console.debug(
+                            "Flush pending messages after PUSH reconnection.");
+                    registry.getMessageSender().sendInvocationsToServer();
+                }
+            }
         }
     }
 

flow-client/src/main/java/com/vaadin/client/communication/MessageSender.java

@@ -64,6 +64,8 @@ public enum ResynchronizationState {
 
     private ResynchronizationState resynchronizationState = ResynchronizationState.NOT_ACTIVE;
 
+    private JsonObject pushPendingMessage;
+
     /**
      * Creates a new instance connected to the given registry.
      *
@@ -104,6 +106,17 @@ public void sendInvocationsToServer() {
      *
      */
     private void doSendInvocationsToServer() {
+        // If there's a stored message, resend it and postpone processing the
+        // rest of the queued messages to prevent resynchronization issues.
+        if (pushPendingMessage != null) {
+            Console.log("Sending pending push message "
+                    + pushPendingMessage.toJson());
+            JsonObject payload = pushPendingMessage;
+            pushPendingMessage = null;
+            registry.getRequestResponseTracker().startRequest();
+            send(payload);
+            return;
+        }
 
         ServerRpcQueue serverRpcQueue = registry.getServerRpcQueue();
         if (serverRpcQueue.isEmpty()
@@ -181,6 +194,13 @@ private JsonObject preparePayload(final JsonArray reqInvocations,
      */
     public void send(final JsonObject payload) {
         if (push != null && push.isBidirectional()) {
+            // When using bidirectional transport, the payload is not resent
+            // to the server during reconnection attempts.
+            // Keep a copy of the message, so that it could be resent to the
+            // server after a reconnection.
+            // Reference will be cleaned up once the server confirms it has
+            // seen this message
+            pushPendingMessage = payload;
             push.push(payload);
         } else {
             registry.getXhrConnection().send(payload);
@@ -260,7 +280,14 @@ public void resynchronize() {
      */
     public void setClientToServerMessageId(int nextExpectedId, boolean force) {
         if (nextExpectedId == clientToServerMessageId) {
-            // No op as everything matches they way it should
+            // Everything matches they way it should
+            // Remove potential pending PUSH message if it has already been seen
+            // by the server.
+            if (pushPendingMessage != null
+                    && (int) pushPendingMessage.getNumber(
+                            ApplicationConstants.CLIENT_TO_SERVER_ID) < nextExpectedId) {
+                pushPendingMessage = null;
+            }
             return;
         }
         if (force) {