HADOOP-6434 Make HttpServer slightly easier to manage/diagnose faults with

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@893485 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/hadoop/http/HttpServer.java

@@ -85,6 +85,8 @@ public class HttpServer implements FilterContainer {
       new HashMap<Context, Boolean>();
   protected final List<String> filterNames = new ArrayList<String>();
   private static final int MAX_RETRIES = 10;
+  static final String STATE_DESCRIPTION_ALIVE = " - alive";
+  static final String STATE_DESCRIPTION_NOT_LIVE = " - not live";
 
   /** Same as this(name, bindAddress, port, findPort, null); */
   public HttpServer(String name, String bindAddress, int port, boolean findPort
@@ -502,7 +504,11 @@ public void start() throws IOException {
           // then try the next port number.
           if (ex instanceof BindException) {
             if (!findPort) {
-              throw (BindException) ex;
+              BindException be = new BindException(
+                      "Port in use: " + listener.getHost()
+                              + ":" + listener.getPort());
+              be.initCause(ex);
+              throw be;
             }
           } else {
             LOG.info("HttpServer.start() threw a non Bind IOException"); 
@@ -533,6 +539,26 @@ public void join() throws InterruptedException {
     webServer.join();
   }
 
+  /**
+   * Test for the availability of the web server
+   * @return true if the web server is started, false otherwise
+   */
+  public boolean isAlive() {
+    return webServer != null && webServer.isStarted();
+  }
+
+  /**
+   * Return the host and port of the HttpServer, if live
+   * @return the classname and any HTTP URL
+   */
+  @Override
+  public String toString() {
+    return listener != null ?
+        ("HttpServer at http://" + listener.getHost() + ":" + listener.getLocalPort() + "/"
+            + (isAlive() ? STATE_DESCRIPTION_ALIVE : STATE_DESCRIPTION_NOT_LIVE))
+        : "Inactive HttpServer";
+  }
+
   /**
    * A very simple servlet to serve up a text representation of the current
    * stack traces. It both returns the stacks to the caller and logs them.

src/test/core/org/apache/hadoop/http/TestHttpServerLifecycle.java

@@ -0,0 +1,145 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.hadoop.http;
+
+import static org.junit.Assert.assertTrue;
+import org.junit.Test;
+
+import java.io.File;
+
+public class TestHttpServerLifecycle {
+
+
+  /**
+   * Create but do not start the server
+   * @return the server instance in the member variable "server"
+   * @throws Exception on any failure
+   */
+  private HttpServer createServer() throws Exception {
+    new File(System.getProperty("build.webapps", "build/webapps") + "/test"
+             ).mkdirs();
+    HttpServer server = new HttpServer("test", "0.0.0.0", 0, true);
+    return server;
+  }
+
+  /**
+   * Create and start the server
+   * @return the newly started server
+   * @throws Exception on any failure
+   */
+  private HttpServer createAndStartServer() throws Exception {
+    HttpServer server = createServer();
+    server.start();
+    return server;
+  }
+
+  /**
+   * If the server is non null, stop it
+   * @throws Exception on any failure
+   */
+  private void stop(HttpServer server) throws Exception {
+    if (server != null) {
+      server.stop();
+    }
+  }
+
+  /**
+   * Check that a server is alive by probing the {@link HttpServer#isAlive()} method
+   * and the text of its toString() description
+   * @param server server
+   */
+  private void assertAlive(HttpServer server) {
+    assertTrue("Server is not alive", server.isAlive());
+    assertToStringContains(server, HttpServer.STATE_DESCRIPTION_ALIVE);
+  }
+
+  private void assertNotLive(HttpServer server) {
+    assertTrue("Server should not be live", !server.isAlive());
+    assertToStringContains(server, HttpServer.STATE_DESCRIPTION_NOT_LIVE);
+  }
+
+  /**
+   * Test that the server is alive once started
+   *
+   * @throws Throwable on failure
+   */
+  @Test public void testCreatedServerIsNotAlive() throws Throwable {
+    HttpServer server = createServer();
+    assertNotLive(server);
+  }
+
+  @Test public void testStopUnstartedServer() throws Throwable {
+    HttpServer server = createServer();
+    stop(server);
+  }
+
+  /**
+   * Test that the server is alive once started
+   *
+   * @throws Throwable on failure
+   */
+  @Test public void testStartedServerIsAlive() throws Throwable {
+    HttpServer server = null;
+    try {
+      server = createServer();
+      assertNotLive(server);
+      server.start();
+      assertAlive(server);
+    } finally {
+      stop(server);
+    }
+  }
+
+  /**
+   * Assert that the result of {@link HttpServer#toString()} contains the specific text
+   * @param server server to examine
+   * @param text text to search for
+   */
+  private void assertToStringContains(HttpServer server, String text) {
+    String description = server.toString();
+    assertTrue("Did not find \"" + text + "\" in \"" + description + "\"",
+               description.contains(text));
+  }
+
+  /**
+   * Test that the server is not alive once stopped
+   *
+   * @throws Throwable on failure
+   */
+  @Test public void testStoppedServerIsNotAlive() throws Throwable {
+    HttpServer server = createAndStartServer();
+    assertAlive(server);
+    stop(server);
+    assertNotLive(server);
+  }
+
+  /**
+   * Test that the server is not alive once stopped
+   *
+   * @throws Throwable on failure
+   */
+  @Test public void testStoppingTwiceServerIsAllowed() throws Throwable {
+    HttpServer server = createAndStartServer();
+    assertAlive(server);
+    stop(server);
+    assertNotLive(server);
+    stop(server);
+    assertNotLive(server);
+  }
+
+}