TCP: Clarify Async Exception Handling

intermediate/tcp-client-server-multiplex/README.md

@@ -26,7 +26,7 @@ on the socket.
 
 This sample now shows how to use the `group-timeout` on the aggregator to release the group under this condition.
 Further, it routes the discarded message to a service activator which return a `MessagingTimeoutException` which
-is routed to the waiting thread.
+is routed to the waiting thread and thrown to the caller.
 
 ````
 gateway -> outbound-channel-adapter
@@ -38,6 +38,12 @@ aggregator(group-timeout discard)->service-activator
 A service activator is used here instead of a transformer because you may wish to take some other action when the
 timeout condition occurs.
 
-Normal gateway processing detects that the payload is an `Exception` and throws it to the caller.
+There are two test cases, one throws an exception; the other returns one as the message payload.
 
-Thus, this shows how to return an exception to a gateway caller, even when the messaging is entirely asynchronous.
+When the payload of the reply messsage is a `Throwable` normal gateway processing detects that and throws it to the
+caller.
+
+Similarly, when the async flow throws an exception, it is wrapped in an `ErrorMessage` and routed to the caller.
+
+Thus, this shows both techniques for returning an exception to a gateway caller, even when the messaging is entirely
+asynchronous.

intermediate/tcp-client-server-multiplex/src/main/java/org/springframework/integration/samples/tcpclientserver/EchoService.java

@@ -31,7 +31,7 @@ public class EchoService {
 		if ("FAIL".equals(input)) {
 			throw new RuntimeException("Failure Demonstration");
 		}
-		else if("TIMEOUT_TEST".equals(input)){
+		else if(input.startsWith("TIMEOUT_TEST")) {
 			Thread.sleep(3000);
 		}
 
@@ -39,7 +39,12 @@ public class EchoService {
 	}
 
 	public MessageTimeoutException noResponse(String input) {
-		return new MessageTimeoutException("No response received for " + input);
+		if ("TIMEOUT_TEST_THROW".equals(input)) {
+			throw new MessageTimeoutException("No response received for " + input);
+		}
+		else {
+			return new MessageTimeoutException("No response received for " + input);
+		}
 	}
 
 }

intermediate/tcp-client-server-multiplex/src/test/java/org/springframework/integration/samples/tcpclientserver/TcpClientServerDemoTest.java

@@ -33,10 +33,10 @@ import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.core.task.SimpleAsyncTaskExecutor;
 import org.springframework.core.task.TaskExecutor;
-import org.springframework.integration.MessageTimeoutException;
 import org.springframework.integration.ip.tcp.connection.AbstractServerConnectionFactory;
 import org.springframework.integration.ip.util.TestingUtilities;
 import org.springframework.integration.samples.tcpclientserver.support.CustomTestContextLoader;
+import org.springframework.messaging.MessagingException;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
@@ -97,12 +97,23 @@ public class TcpClientServerDemoTest {
 	}
 
 	@Test
-	public void testTimeout() {
+	public void testTimeoutThrow() {
 		try {
-			gw.send("TIMEOUT_TEST");
+			gw.send("TIMEOUT_TEST_THROW");
 			fail("expected exception");
 		}
-		catch (MessageTimeoutException e) {
+		catch (MessagingException e) {
+			assertThat(e.getMessage(), containsString("No response received for TIMEOUT_TEST"));
+		}
+	}
+
+	@Test
+	public void testTimeoutReturn() {
+		try {
+			gw.send("TIMEOUT_TEST_RETURN");
+			fail("expected exception");
+		}
+		catch (MessagingException e) {
 			assertThat(e.getMessage(), containsString("No response received for TIMEOUT_TEST"));
 		}
 	}