GH-8785: Propagate WebSocket client connect fail

Fixes #8785

The `ClientWebSocketContainer.start()` delegates to the `IntegrationWebSocketConnectionManager`
which performs an async connection to the server.

* Wait for `connectionLatch` in the `ClientWebSocketContainer.start()`
and check for `this.openConnectionException != null` to re-throw.
Mark `ClientWebSocketContainer` as stopped in that case

**Cherry-pick to `6.1.x` & `6.0.x`**

Author: artembilan

spring-integration-websocket/src/main/java/org/springframework/integration/websocket/ClientWebSocketContainer.java

@@ -192,6 +192,20 @@ public void start() {
 				this.openConnectionException = null;
 				this.connectionLatch = new CountDownLatch(1);
 				this.connectionManager.start();
+
+				try {
+					this.connectionLatch.await(this.connectionTimeout, TimeUnit.SECONDS);
+				}
+				catch (InterruptedException ex) {
+					logger.error("'clientSession' has not been established during 'openConnection'");
+				}
+
+				if (this.openConnectionException != null) {
+					// The next 'this.connectionManager.stop()' call resets 'this.openConnectionException' to null
+					IllegalStateException exceptionToRethrow = new IllegalStateException(this.openConnectionException);
+					this.connectionManager.stop();
+					throw exceptionToRethrow;
+				}
 			}
 		}
 		finally {

spring-integration-websocket/src/test/java/org/springframework/integration/websocket/ClientWebSocketContainerTests.java

@@ -28,6 +28,7 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import jakarta.websocket.DeploymentException;
 import org.apache.tomcat.websocket.Constants;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
@@ -126,10 +127,8 @@ protected CompletableFuture<WebSocketSession> executeInternal(WebSocketHandler w
 
 		failure.set(true);
 
-		container.start();
-
 		assertThatIllegalStateException()
-				.isThrownBy(() -> container.getSession(null))
+				.isThrownBy(container::start)
 				.withCauseInstanceOf(CancellationException.class);
 
 		failure.set(false);
@@ -170,6 +169,20 @@ public void testWebSocketContainerOverflowStrategyPropagation() throws Exception
 				.isEqualTo(ConcurrentWebSocketSessionDecorator.OverflowStrategy.DROP);
 	}
 
+	@Test
+	public void webSocketContainerFailsOnStartForInvalidUrl() {
+		StandardWebSocketClient webSocketClient = new StandardWebSocketClient();
+
+		ClientWebSocketContainer container =
+				new ClientWebSocketContainer(webSocketClient, server.getWsBaseUrl() + "/no_such_endpoint");
+
+		assertThatIllegalStateException()
+				.isThrownBy(container::start)
+				.withCauseExactlyInstanceOf(DeploymentException.class)
+				.withStackTraceContaining(
+						"The HTTP response from the server [404] did not permit the HTTP upgrade to WebSocket");
+	}
+
 	private static class TestWebSocketListener implements WebSocketListener {
 
 		public final CountDownLatch messageLatch = new CountDownLatch(1);