Improve handling of connection failures in remote debug tunnel

Previously, if an application had been started without remote
debugging enabled, an attempt to connect to it via
RemoteSpringApplication and the HTTP tunnel would result in the
application being hammered by connection attempts for 30 seconds.

This commit updates the tunnel server to respond with Service
Unavailable (503) when a connection attempt is made and the JVM
does not have remote debugging enabled. When the client receives a
503 response, it now logs a warning message describing the possible
problem before closing the connection.

The client has also been updated to provide improved diagnostics when
a connection to the tunnel server cannot be established, for example
because the remote URL is incorrect, or the remote application isn't
running.

Lastly, the client has been updated so that it continues to accept
connections when a connection to the server is closed. This allows
the user to correct a problem with the remote application, such as
restarting it with remote debugging enabled, without having to also
restart the process that's running RemoteSpringApplication.

Closes gh-5021

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/client/HttpTunnelConnection.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.tunnel.client;
 
 import java.io.Closeable;
 import java.io.IOException;
+import java.net.ConnectException;
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -46,6 +47,7 @@ import org.springframework.util.Assert;
  *
  * @author Phillip Webb
  * @author Rob Winch
+ * @author Andy Wilkinson
  * @since 1.3.0
  * @see TunnelClient
  * @see org.springframework.boot.devtools.tunnel.server.HttpTunnelServer
@@ -157,7 +159,13 @@ public class HttpTunnelConnection implements TunnelConnection {
 						sendAndReceive(payload);
 					}
 					catch (IOException ex) {
-						logger.trace("Unexpected connection error", ex);
+						if (ex instanceof ConnectException) {
+							logger.warn("Failed to connect to remote application at "
+									+ HttpTunnelConnection.this.uri);
+						}
+						else {
+							logger.trace("Unexpected connection error", ex);
+						}
 						closeQuietly();
 					}
 				}
@@ -188,6 +196,12 @@ public class HttpTunnelConnection implements TunnelConnection {
 				close();
 				return;
 			}
+			if (response.getStatusCode() == HttpStatus.SERVICE_UNAVAILABLE) {
+				logger.warn("Remote application responded with service unavailable. Did "
+						+ "you forget to start it with remote debugging enabled?");
+				close();
+				return;
+			}
 			if (response.getStatusCode() == HttpStatus.OK) {
 				HttpTunnelPayload payload = HttpTunnelPayload.get(response);
 				if (payload != null) {

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/client/TunnelClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.nio.ByteBuffer;
+import java.nio.channels.AsynchronousCloseException;
 import java.nio.channels.ServerSocketChannel;
 import java.nio.channels.SocketChannel;
 import java.nio.channels.WritableByteChannel;
@@ -36,6 +37,7 @@ import org.springframework.util.Assert;
  * specified port for local clients to connect to.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @since 1.3.0
  */
 public class TunnelClient implements SmartInitializingSingleton {
@@ -143,6 +145,9 @@ public class TunnelClient implements SmartInitializingSingleton {
 					try {
 						handleConnection(socket);
 					}
+					catch (AsynchronousCloseException ex) {
+						// Connection has been closed. Keep the server running
+					}
 					finally {
 						socket.close();
 					}

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/HttpTunnelServer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -88,6 +88,10 @@ import org.springframework.util.Assert;
  * <td>410 (Gone)</td>
  * <td>The target server has disconnected.</td>
  * </tr>
+ * <tr>
+ * <td>503 (Service Unavailable)</td>
+ * <td>The target server is unavailable</td>
+ * </tr>
  * </table>
  * <p>
  * Requests and responses that contain payloads include a {@code x-seq} header that
@@ -96,6 +100,7 @@ import org.springframework.util.Assert;
  * {@code 1}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @since 1.3.0
  * @see org.springframework.boot.devtools.tunnel.client.HttpTunnelConnection
  */
@@ -153,6 +158,9 @@ public class HttpTunnelServer {
 		catch (ConnectException ex) {
 			httpConnection.respond(HttpStatus.GONE);
 		}
+		catch (RemoteDebugNotRunningException ex) {
+			httpConnection.respond(HttpStatus.SERVICE_UNAVAILABLE);
+		}
 	}
 
 	/**

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/RemoteDebugNotRunningException.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2012-2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.devtools.tunnel.server;
+
+/**
+ * Exception thrown to indicate that remote debug is not running.
+ *
+ * @author Andy Wilkinson
+ */
+class RemoteDebugNotRunningException extends RuntimeException {
+
+}

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/RemoteDebugPortProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -20,12 +20,12 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.boot.lang.UsesUnsafeJava;
-import org.springframework.util.Assert;
 
 /**
  * {@link PortProvider} that provides the port being used by the Java remote debugging.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 public class RemoteDebugPortProvider implements PortProvider {
 
@@ -35,7 +35,9 @@ public class RemoteDebugPortProvider implements PortProvider {
 
 	@Override
 	public int getPort() {
-		Assert.state(isRemoteDebugRunning(), "Remote debug is not running");
+		if (!isRemoteDebugRunning()) {
+			throw new RemoteDebugNotRunningException();
+		}
 		return getRemoteDebugPort();
 	}
 

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/test/MockClientHttpRequestFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -37,12 +37,13 @@ import org.springframework.mock.http.client.MockClientHttpResponse;
  * Mock {@link ClientHttpRequestFactory}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 public class MockClientHttpRequestFactory implements ClientHttpRequestFactory {
 
 	private AtomicLong seq = new AtomicLong();
 
-	private Deque<Response> responses = new ArrayDeque<Response>();
+	private Deque<Object> responses = new ArrayDeque<Object>();
 
 	private List<MockClientHttpRequest> executedRequests = new ArrayList<MockClientHttpRequest>();
 
@@ -58,6 +59,12 @@ public class MockClientHttpRequestFactory implements ClientHttpRequestFactory {
 		}
 	}
 
+	public void willRespond(IOException... response) {
+		for (IOException exception : response) {
+			this.responses.addLast(exception);
+		}
+	}
+
 	public void willRespond(String... response) {
 		for (String payload : response) {
 			this.responses.add(new Response(0, payload.getBytes(), HttpStatus.OK));
@@ -81,11 +88,15 @@ public class MockClientHttpRequestFactory implements ClientHttpRequestFactory {
 		@Override
 		protected ClientHttpResponse executeInternal() throws IOException {
 			MockClientHttpRequestFactory.this.executedRequests.add(this);
-			Response response = MockClientHttpRequestFactory.this.responses.pollFirst();
+			Object response = MockClientHttpRequestFactory.this.responses.pollFirst();
+			if (response instanceof IOException) {
+				throw (IOException) response;
+			}
 			if (response == null) {
 				response = new Response(0, null, HttpStatus.GONE);
 			}
-			return response.asHttpResponse(MockClientHttpRequestFactory.this.seq);
+			return ((Response) response)
+					.asHttpResponse(MockClientHttpRequestFactory.this.seq);
 		}
 
 	}

spring-boot-devtools/src/test/java/org/springframework/boot/devtools/tunnel/client/HttpTunnelConnectionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -19,6 +19,7 @@ package org.springframework.boot.devtools.tunnel.client;
 import java.io.ByteArrayOutputStream;
 import java.io.Closeable;
 import java.io.IOException;
+import java.net.ConnectException;
 import java.nio.ByteBuffer;
 import java.nio.channels.Channels;
 import java.nio.channels.WritableByteChannel;
@@ -33,11 +34,14 @@ import org.mockito.MockitoAnnotations;
 
 import org.springframework.boot.devtools.test.MockClientHttpRequestFactory;
 import org.springframework.boot.devtools.tunnel.client.HttpTunnelConnection.TunnelChannel;
+import org.springframework.boot.test.OutputCapture;
 import org.springframework.http.HttpStatus;
 import org.springframework.util.SocketUtils;
 
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertThat;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.times;
@@ -48,12 +52,16 @@ import static org.mockito.Mockito.verify;
  *
  * @author Phillip Webb
  * @author Rob Winch
+ * @author Andy Wilkinson
  */
 public class HttpTunnelConnectionTests {
 
 	@Rule
 	public ExpectedException thrown = ExpectedException.none();
 
+	@Rule
+	public OutputCapture outputCapture = new OutputCapture();
+
 	private int port = SocketUtils.findAvailableTcpPort();
 
 	private String url;
@@ -144,6 +152,25 @@ public class HttpTunnelConnectionTests {
 		assertThat(this.requestFactory.getExecutedRequests().size(), greaterThan(10));
 	}
 
+	@Test
+	public void serviceUnavailableResponseLogsWarningAndClosesTunnel() throws Exception {
+		this.requestFactory.willRespond(HttpStatus.SERVICE_UNAVAILABLE);
+		TunnelChannel tunnel = openTunnel(true);
+		assertThat(tunnel.isOpen(), is(false));
+		this.outputCapture.expect(containsString(
+				"Did you forget to start it with remote debugging enabled?"));
+	}
+
+	@Test
+	public void connectFailureLogsWarning() throws Exception {
+		this.requestFactory.willRespond(new ConnectException());
+		TunnelChannel tunnel = openTunnel(true);
+		assertThat(tunnel.isOpen(), is(false));
+		this.outputCapture.expect(containsString(
+				"Failed to connect to remote application at http://localhost:"
+						+ this.port));
+	}
+
 	private void write(TunnelChannel channel, String string) throws IOException {
 		channel.write(ByteBuffer.wrap(string.getBytes()));
 	}