@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -306,6 +306,12 @@ protected void handleMessageInternal(Message<?> message) {
 		else if (SimpMessageType.CONNECT.equals(messageType)) {
 			logMessage(message);
 			if (sessionId != null) {
+				if (this.sessions.get(sessionId) != null) {
+					if (logger.isWarnEnabled()) {
+						logger.warn("Ignoring CONNECT in session " + sessionId + ". Already connected.");
+					}
+					return;
+				}
 				long[] heartbeatIn = SimpMessageHeaderAccessor.getHeartbeat(headers);
 				long[] heartbeatOut = getHeartbeatValue();
 				Principal user = SimpMessageHeaderAccessor.getUser(headers);
 
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -532,6 +532,12 @@ else if (accessor instanceof SimpMessageHeaderAccessor) {
 		}
 
 		if (StompCommand.CONNECT.equals(command) || StompCommand.STOMP.equals(command)) {
+			if (this.connectionHandlers.get(sessionId) != null) {
+				if (logger.isWarnEnabled()) {
+					logger.warn("Ignoring CONNECT in session " + sessionId + ". Already connected.");
+				}
+				return;
+			}
 			if (logger.isDebugEnabled()) {
 				logger.debug(stompAccessor.getShortLogMessage(EMPTY_PAYLOAD));
 			}
 
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -223,6 +223,30 @@ void systemSubscription() {
 		assertThat(captor.getValue()).isSameAs(message);
 	}
 
+	@Test
+	void alreadyConnected() {
+
+		this.brokerRelay.start();
+
+		Message<byte[]> connect = connectMessage("sess1", "joe");
+		this.brokerRelay.handleMessage(connect);
+
+		assertThat(this.tcpClient.getSentMessages().size()).isEqualTo(2);
+
+		StompHeaderAccessor headers1 = this.tcpClient.getSentHeaders(0);
+		assertThat(headers1.getCommand()).isEqualTo(StompCommand.CONNECT);
+		assertThat(headers1.getSessionId()).isEqualTo(StompBrokerRelayMessageHandler.SYSTEM_SESSION_ID);
+
+		StompHeaderAccessor headers2 = this.tcpClient.getSentHeaders(1);
+		assertThat(headers2.getCommand()).isEqualTo(StompCommand.CONNECT);
+		assertThat(headers2.getSessionId()).isEqualTo("sess1");
+
+		this.brokerRelay.handleMessage(connect);
+
+		assertThat(this.tcpClient.getSentMessages().size()).isEqualTo(2);
+		assertThat(this.outboundChannel.getMessages()).isEmpty();
+	}
+
 	private Message<byte[]> connectMessage(String sessionId, String user) {
 		StompHeaderAccessor headers = StompHeaderAccessor.create(StompCommand.CONNECT);
 		headers.setSessionId(sessionId);
Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,5 @@`
`1`	`1`	`/*`
`2`		`- * Copyright 2002-2019 the original author or authors.`
	`2`	`+ * Copyright 2002-2022 the original author or authors.`
`3`	`3`	`*`
`4`	`4`	`* Licensed under the Apache License, Version 2.0 (the "License");`
`5`	`5`	`* you may not use this file except in compliance with the License.`
`@@ -532,6 +532,12 @@ else if (accessor instanceof SimpMessageHeaderAccessor) {`
`532`	`532`	`}`
`533`	`533`
`534`	`534`	`if (StompCommand.CONNECT.equals(command) \|\| StompCommand.STOMP.equals(command)) {`
	`535`	`+ if (this.connectionHandlers.get(sessionId) != null) {`
	`536`	`+ if (logger.isWarnEnabled()) {`
	`537`	`+ logger.warn("Ignoring CONNECT in session " + sessionId + ". Already connected.");`
	`538`	`+ }`
	`539`	`+ return;`
	`540`	`+ }`
`535`	`541`	`if (logger.isDebugEnabled()) {`
`536`	`542`	`logger.debug(stompAccessor.getShortLogMessage(EMPTY_PAYLOAD));`
`537`	`543`	`}`