YARN-4591. YARN Web UIs should provide a robots.txt. (Sidharta Seethana via wangda)

(cherry picked from commit 5a58bfee30)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/webapp/Dispatcher.java

@@ -35,6 +35,7 @@ import org.apache.hadoop.http.HtmlQuoting;
 import org.apache.hadoop.yarn.webapp.Controller.RequestContext;
 import org.apache.hadoop.yarn.webapp.Router.Dest;
 import org.apache.hadoop.yarn.webapp.view.ErrorPage;
+import org.apache.hadoop.yarn.webapp.view.RobotsTextPage;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -117,6 +118,14 @@ public class Dispatcher extends HttpServlet {
     }
     Controller.RequestContext rc =
         injector.getInstance(Controller.RequestContext.class);
+
+    //short-circuit robots.txt serving for all YARN webapps.
+    if (uri.equals(RobotsTextPage.ROBOTS_TXT_PATH)) {
+      rc.setStatus(HttpServletResponse.SC_FOUND);
+      render(RobotsTextPage.class);
+      return;
+    }
+
     if (setCookieParams(rc, req) > 0) {
       Cookie ec = rc.cookies().get(ERROR_COOKIE);
       if (ec != null) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/webapp/WebApp.java

@@ -29,6 +29,7 @@ import java.util.Map;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.http.HttpServer2;
+import org.apache.hadoop.yarn.webapp.view.RobotsTextPage;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -158,7 +159,8 @@ public abstract class WebApp extends ServletModule {
   public void configureServlets() {
     setup();
 
-    serve("/", "/__stop").with(Dispatcher.class);
+    serve("/", "/__stop", RobotsTextPage.ROBOTS_TXT_PATH)
+        .with(Dispatcher.class);
 
     for (String path : this.servePathSpecs) {
       serve(path).with(Dispatcher.class);

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/webapp/view/RobotsTextPage.java

@@ -0,0 +1,39 @@
+/*
+ * *
+ *  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.yarn.webapp.view;
+
+/**
+ * Simple class that renders a robot.txt page that disallows crawling.
+ */
+
+public class RobotsTextPage extends TextPage {
+  public static final String ROBOTS_TXT = "robots.txt";
+  public static final String ROBOTS_TXT_PATH = "/" + ROBOTS_TXT;
+
+  static final String USER_AGENT_LINE = "User-agent: *";
+  static final String DISALLOW_LINE = "Disallow: /";
+
+  @Override
+  public void render() {
+    putWithoutEscapeHtml(USER_AGENT_LINE);
+    putWithoutEscapeHtml(DISALLOW_LINE);
+  }
+}

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-common/src/test/java/org/apache/hadoop/yarn/webapp/TestWebApp.java

@@ -38,6 +38,7 @@ import org.apache.commons.lang.ArrayUtils;
 import org.apache.hadoop.yarn.MockApps;
 import org.apache.hadoop.yarn.webapp.view.HtmlPage;
 import org.apache.hadoop.yarn.webapp.view.JQueryUI;
+import org.apache.hadoop.yarn.webapp.view.RobotsTextPage;
 import org.apache.hadoop.yarn.webapp.view.TextPage;
 import org.junit.Test;
 import org.slf4j.Logger;
@@ -260,6 +261,31 @@ public class TestWebApp {
     }
   }
 
+  @Test public void testRobotsText() throws Exception {
+    WebApp app =
+        WebApps.$for("test", TestWebApp.class, this, "ws").start(new WebApp() {
+          @Override
+          public void setup() {
+            bind(MyTestJAXBContextResolver.class);
+            bind(MyTestWebService.class);
+          }
+        });
+    String baseUrl = baseUrl(app);
+    try {
+      //using system line separator here since that is what
+      // TextView (via PrintWriter) seems to use.
+      String[] robotsTxtOutput = getContent(baseUrl +
+          RobotsTextPage.ROBOTS_TXT).trim().split(System.getProperty("line"
+          + ".separator"));
+
+      assertEquals(2, robotsTxtOutput.length);
+      assertEquals("User-agent: *", robotsTxtOutput[0]);
+      assertEquals("Disallow: /", robotsTxtOutput[1]);
+    } finally {
+      app.stop();
+    }
+  }
+
   // This is to test the GuiceFilter should only be applied to webAppContext,
   // not to logContext;
   @Test public void testYARNWebAppContext() throws Exception {