Add formatting for SockJS GoAway frame

Prevents infinite loop for xhr-polling and xhr-streaming transports.

See gh-28000

Author: Ivan Zbykovskyi

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/handler/AbstractHttpSendingTransportHandler.java

@@ -79,9 +79,11 @@ else if (sockJsSession.isClosed()) {
 			if (logger.isDebugEnabled()) {
 				logger.debug("Connection already closed (but not removed yet) for " + sockJsSession);
 			}
+			SockJsFrameFormat frameFormat = this.getFrameFormat(request);
 			SockJsFrame frame = SockJsFrame.closeFrameGoAway();
+			String formattedFrame = frameFormat.format(frame);
 			try {
-				response.getBody().write(frame.getContentBytes());
+				response.getBody().write(formattedFrame.getBytes(SockJsFrame.CHARSET));
 			}
 			catch (IOException ex) {
 				throw new SockJsException("Failed to send " + frame, sockJsSession.getId(), ex);

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/AbstractHttpSockJsSession.java

@@ -257,7 +257,8 @@ public void handleSuccessiveRequest(ServerHttpRequest request, ServerHttpRespons
 		synchronized (this.responseLock) {
 			try {
 				if (isClosed()) {
-					response.getBody().write(SockJsFrame.closeFrameGoAway().getContentBytes());
+					String formattedFrame = frameFormat.format(SockJsFrame.closeFrameGoAway());
+					response.getBody().write(formattedFrame.getBytes(SockJsFrame.CHARSET));
 					return;
 				}
 				this.response = response;