/**
    * 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.hbase.http;
  
  import java.io.FileNotFoundException;
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.io.PrintStream;
  import java.net.BindException;
  import java.net.InetSocketAddress;
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletRequestWrapper;
  import javax.servlet.http.HttpServletResponse;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.HadoopIllegalArgumentException;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.CommonConfigurationKeys;
  import org.apache.hadoop.hbase.HBaseInterfaceAudience;
  import org.apache.hadoop.hbase.http.conf.ConfServlet;
  import org.apache.hadoop.hbase.http.jmx.JMXJsonServlet;
  import org.apache.hadoop.hbase.http.log.LogLevel;
  import org.apache.hadoop.hbase.util.Threads;
  import org.apache.hadoop.hbase.util.ReflectionUtils;
  import org.apache.hadoop.security.SecurityUtil;
  import org.apache.hadoop.security.UserGroupInformation;
  import org.apache.hadoop.security.authentication.server.AuthenticationFilter;
  import org.apache.hadoop.security.authorize.AccessControlList;
  import org.apache.hadoop.util.Shell;
  import org.mortbay.io.Buffer;
  import org.mortbay.jetty.Connector;
  import org.mortbay.jetty.Handler;
  import org.mortbay.jetty.MimeTypes;
  import org.mortbay.jetty.RequestLog;
  import org.mortbay.jetty.Server;
  import org.mortbay.jetty.handler.ContextHandler;
  import org.mortbay.jetty.handler.ContextHandlerCollection;
  import org.mortbay.jetty.handler.HandlerCollection;
  import org.mortbay.jetty.handler.RequestLogHandler;
  import org.mortbay.jetty.nio.SelectChannelConnector;
  import org.mortbay.jetty.security.SslSocketConnector;
  import org.mortbay.jetty.servlet.Context;
  import org.mortbay.jetty.servlet.DefaultServlet;
  import org.mortbay.jetty.servlet.FilterHolder;
  import org.mortbay.jetty.servlet.FilterMapping;
  import org.mortbay.jetty.servlet.ServletHandler;
  import org.mortbay.jetty.servlet.ServletHolder;
  import org.mortbay.jetty.webapp.WebAppContext;
  import org.mortbay.thread.QueuedThreadPool;
  import org.mortbay.util.MultiException;
  
  import com.google.common.base.Preconditions;
  import com.google.common.collect.Lists;
  import com.sun.jersey.spi.container.servlet.ServletContainer;
  
  /**
   * Create a Jetty embedded server to answer http requests. The primary goal
   * is to serve up status information for the server.
   * There are three contexts:
   *   "/logs/" -> points to the log directory
   *   "/static/" -> points to common static files (src/webapps/static)
   *   "/" -> the jsp server code from (src/webapps/<name>)
  */
 @InterfaceAudience.Private
 @InterfaceStability.Evolving
 public class HttpServer implements FilterContainer {
   private static final Log LOG = LogFactory.getLog(HttpServer.class);
   private static final String EMPTY_STRING = "";
 
   static final String FILTER_INITIALIZERS_PROPERTY
       = "hbase.http.filter.initializers";
   static final String HTTP_MAX_THREADS = "hbase.http.max.threads";
 
   public static final String HTTP_UI_AUTHENTICATION = "hbase.security.authentication.ui";
   static final String HTTP_AUTHENTICATION_PREFIX = "hbase.security.authentication.";
   static final String HTTP_SPNEGO_AUTHENTICATION_PREFIX = HTTP_AUTHENTICATION_PREFIX
       + "spnego.";
   static final String HTTP_SPNEGO_AUTHENTICATION_PRINCIPAL_SUFFIX = "kerberos.principal";
   public static final String HTTP_SPNEGO_AUTHENTICATION_PRINCIPAL_KEY =
       HTTP_SPNEGO_AUTHENTICATION_PREFIX + HTTP_SPNEGO_AUTHENTICATION_PRINCIPAL_SUFFIX;
   static final String HTTP_SPNEGO_AUTHENTICATION_KEYTAB_SUFFIX = "kerberos.keytab";
   public static final String HTTP_SPNEGO_AUTHENTICATION_KEYTAB_KEY =
       HTTP_SPNEGO_AUTHENTICATION_PREFIX + HTTP_SPNEGO_AUTHENTICATION_KEYTAB_SUFFIX;
   static final String HTTP_SPNEGO_AUTHENTICATION_KRB_NAME_SUFFIX = "kerberos.name.rules";
   public static final String HTTP_SPNEGO_AUTHENTICATION_KRB_NAME_KEY =
       HTTP_SPNEGO_AUTHENTICATION_PREFIX + HTTP_SPNEGO_AUTHENTICATION_KRB_NAME_SUFFIX;
   static final String HTTP_AUTHENTICATION_SIGNATURE_SECRET_FILE_SUFFIX =
       "signature.secret.file";
   public static final String HTTP_AUTHENTICATION_SIGNATURE_SECRET_FILE_KEY =
       HTTP_AUTHENTICATION_PREFIX + HTTP_AUTHENTICATION_SIGNATURE_SECRET_FILE_SUFFIX;
 
   // The ServletContext attribute where the daemon Configuration
   // gets stored.
   public static final String CONF_CONTEXT_ATTRIBUTE = "hbase.conf";
   public static final String ADMINS_ACL = "admins.acl";
   public static final String BIND_ADDRESS = "bind.address";
   public static final String SPNEGO_FILTER = "SpnegoFilter";
   public static final String NO_CACHE_FILTER = "NoCacheFilter";
   public static final String APP_DIR = "webapps";
 
   private final AccessControlList adminsAcl;
 
   protected final Server webServer;
   protected String appDir;
   protected String logDir;
 
   private static class ListenerInfo {
     /**
      * Boolean flag to determine whether the HTTP server should clean up the
      * listener in stop().
      */
     private final boolean isManaged;
     private final Connector listener;
     private ListenerInfo(boolean isManaged, Connector listener) {
       this.isManaged = isManaged;
       this.listener = listener;
     }
   }
 
   private final List<ListenerInfo> listeners = Lists.newArrayList();
 
   protected final WebAppContext webAppContext;
   protected final boolean findPort;
   protected final Map<Context, Boolean> defaultContexts =
       new HashMap<Context, Boolean>();
   protected final List<String> filterNames = new ArrayList<String>();
   static final String STATE_DESCRIPTION_ALIVE = " - alive";
   static final String STATE_DESCRIPTION_NOT_LIVE = " - not live";
 
   /**
    * Class to construct instances of HTTP server with specific options.
    */
   public static class Builder {
     private ArrayList<URI> endpoints = Lists.newArrayList();
     private Connector connector;
     private Configuration conf;
     private String[] pathSpecs;
     private AccessControlList adminsAcl;
     private boolean securityEnabled = false;
     private String usernameConfKey;
     private String keytabConfKey;
     private boolean needsClientAuth;
 
     private String hostName;
     private String appDir = APP_DIR;
     private String logDir;
     private boolean findPort;
 
     private String trustStore;
     private String trustStorePassword;
     private String trustStoreType;
 
     private String keyStore;
     private String keyStorePassword;
     private String keyStoreType;
 
     // The -keypass option in keytool
     private String keyPassword;
 
     private String kerberosNameRulesKey;
     private String signatureSecretFileKey;
 
     @Deprecated
     private String name;
     @Deprecated
     private String bindAddress;
     @Deprecated
     private int port = -1;
 
     /**
      * Add an endpoint that the HTTP server should listen to.
      *
      * @param endpoint
      *          the endpoint of that the HTTP server should listen to. The
      *          scheme specifies the protocol (i.e. HTTP / HTTPS), the host
      *          specifies the binding address, and the port specifies the
      *          listening port. Unspecified or zero port means that the server
      *          can listen to any port.
      */
     public Builder addEndpoint(URI endpoint) {
       endpoints.add(endpoint);
       return this;
     }
 
     /**
      * Set the hostname of the http server. The host name is used to resolve the
      * _HOST field in Kerberos principals. The hostname of the first listener
      * will be used if the name is unspecified.
      */
     public Builder hostName(String hostName) {
       this.hostName = hostName;
       return this;
     }
 
     public Builder trustStore(String location, String password, String type) {
       this.trustStore = location;
       this.trustStorePassword = password;
       this.trustStoreType = type;
       return this;
     }
 
     public Builder keyStore(String location, String password, String type) {
       this.keyStore = location;
       this.keyStorePassword = password;
       this.keyStoreType = type;
       return this;
     }
 
     public Builder keyPassword(String password) {
       this.keyPassword = password;
       return this;
     }
 
     /**
      * Specify whether the server should authorize the client in SSL
      * connections.
      */
     public Builder needsClientAuth(boolean value) {
       this.needsClientAuth = value;
       return this;
     }
 
     /**
      * Use setAppDir() instead.
      */
     @Deprecated
     public Builder setName(String name){
       this.name = name;
       return this;
     }
 
     /**
      * Use addEndpoint() instead.
      */
     @Deprecated
     public Builder setBindAddress(String bindAddress){
       this.bindAddress = bindAddress;
       return this;
     }
 
     /**
      * Use addEndpoint() instead.
      */
     @Deprecated
     public Builder setPort(int port) {
       this.port = port;
       return this;
     }
 
     public Builder setFindPort(boolean findPort) {
       this.findPort = findPort;
       return this;
     }
 
     public Builder setConf(Configuration conf) {
       this.conf = conf;
       return this;
     }
 
     public Builder setConnector(Connector connector) {
       this.connector = connector;
       return this;
     }
 
     public Builder setPathSpec(String[] pathSpec) {
       this.pathSpecs = pathSpec;
       return this;
     }
 
     public Builder setACL(AccessControlList acl) {
       this.adminsAcl = acl;
       return this;
     }
 
     public Builder setSecurityEnabled(boolean securityEnabled) {
       this.securityEnabled = securityEnabled;
       return this;
     }
 
     public Builder setUsernameConfKey(String usernameConfKey) {
       this.usernameConfKey = usernameConfKey;
       return this;
     }
 
     public Builder setKeytabConfKey(String keytabConfKey) {
       this.keytabConfKey = keytabConfKey;
       return this;
     }
 
     public Builder setKerberosNameRulesKey(String kerberosNameRulesKey) {
       this.kerberosNameRulesKey = kerberosNameRulesKey;
       return this;
     }
 
     public Builder setSignatureSecretFileKey(String signatureSecretFileKey) {
       this.signatureSecretFileKey = signatureSecretFileKey;
       return this;
     }
 
     public Builder setAppDir(String appDir) {
         this.appDir = appDir;
         return this;
       }
 
     public Builder setLogDir(String logDir) {
         this.logDir = logDir;
         return this;
       }
 
     public HttpServer build() throws IOException {
 
       // Do we still need to assert this non null name if it is deprecated?
       if (this.name == null) {
         throw new HadoopIllegalArgumentException("name is not set");
       }
 
       // Make the behavior compatible with deprecated interfaces
       if (bindAddress != null && port != -1) {
         try {
           endpoints.add(0, new URI("http", "", bindAddress, port, "", "", ""));
         } catch (URISyntaxException e) {
           throw new HadoopIllegalArgumentException("Invalid endpoint: "+ e);
         }
       }
 
       if (endpoints.size() == 0 && connector == null) {
         throw new HadoopIllegalArgumentException("No endpoints specified");
       }
 
       if (hostName == null) {
         hostName = endpoints.size() == 0 ? connector.getHost() : endpoints.get(
             0).getHost();
       }
 
       if (this.conf == null) {
         conf = new Configuration();
       }
 
       HttpServer server = new HttpServer(this);
 
       if (this.securityEnabled) {
         server.initSpnego(conf, hostName, usernameConfKey, keytabConfKey, kerberosNameRulesKey,
             signatureSecretFileKey);
       }
 
       if (connector != null) {
         server.addUnmanagedListener(connector);
       }
 
       for (URI ep : endpoints) {
         Connector listener = null;
         String scheme = ep.getScheme();
         if ("http".equals(scheme)) {
           listener = HttpServer.createDefaultChannelConnector();
         } else if ("https".equals(scheme)) {
           SslSocketConnector c = new SslSocketConnectorSecure();
           c.setNeedClientAuth(needsClientAuth);
           c.setKeyPassword(keyPassword);
 
           if (keyStore != null) {
             c.setKeystore(keyStore);
             c.setKeystoreType(keyStoreType);
             c.setPassword(keyStorePassword);
           }
 
           if (trustStore != null) {
             c.setTruststore(trustStore);
             c.setTruststoreType(trustStoreType);
             c.setTrustPassword(trustStorePassword);
           }
           listener = c;
 
         } else {
           throw new HadoopIllegalArgumentException(
               "unknown scheme for endpoint:" + ep);
         }
         listener.setHeaderBufferSize(1024*64);
         listener.setHost(ep.getHost());
         listener.setPort(ep.getPort() == -1 ? 0 : ep.getPort());
         server.addManagedListener(listener);
       }
 
       server.loadListeners();
       return server;
 
     }
 
   }
 
   /** Same as this(name, bindAddress, port, findPort, null); */
   @Deprecated
   public HttpServer(String name, String bindAddress, int port, boolean findPort
       ) throws IOException {
     this(name, bindAddress, port, findPort, new Configuration());
   }
 
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf, Connector connector) throws IOException {
     this(name, bindAddress, port, findPort, conf, null, connector, null);
   }
 
   /**
    * Create a status server on the given port. Allows you to specify the
    * path specifications that this server will be serving so that they will be
    * added to the filters properly.
    *
    * @param name The name of the server
    * @param bindAddress The address for this server
    * @param port The port to use on the server
    * @param findPort whether the server should start at the given port and
    *        increment by 1 until it finds a free port.
    * @param conf Configuration
    * @param pathSpecs Path specifications that this httpserver will be serving.
    *        These will be added to any filters.
    */
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf, String[] pathSpecs) throws IOException {
     this(name, bindAddress, port, findPort, conf, null, null, pathSpecs);
   }
 
   /**
    * Create a status server on the given port.
    * The jsp scripts are taken from src/webapps/&lt;name&gt;.
    * @param name The name of the server
    * @param port The port to use on the server
    * @param findPort whether the server should start at the given port and
    *        increment by 1 until it finds a free port.
    * @param conf Configuration
    */
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf) throws IOException {
     this(name, bindAddress, port, findPort, conf, null, null, null);
   }
 
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf, AccessControlList adminsAcl)
       throws IOException {
     this(name, bindAddress, port, findPort, conf, adminsAcl, null, null);
   }
 
   /**
    * Create a status server on the given port.
    * The jsp scripts are taken from src/webapps/&lt;name&gt;.
    * @param name The name of the server
    * @param bindAddress The address for this server
    * @param port The port to use on the server
    * @param findPort whether the server should start at the given port and
    *        increment by 1 until it finds a free port.
    * @param conf Configuration
    * @param adminsAcl {@link AccessControlList} of the admins
    * @param connector The jetty {@link Connector} to use
    */
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf, AccessControlList adminsAcl,
       Connector connector) throws IOException {
     this(name, bindAddress, port, findPort, conf, adminsAcl, connector, null);
   }
 
   /**
    * Create a status server on the given port.
    * The jsp scripts are taken from src/webapps/&lt;name&gt;.
    * @param name The name of the server
    * @param bindAddress The address for this server
    * @param port The port to use on the server
    * @param findPort whether the server should start at the given port and
    *        increment by 1 until it finds a free port.
    * @param conf Configuration
    * @param adminsAcl {@link AccessControlList} of the admins
    * @param connector A jetty connection listener
    * @param pathSpecs Path specifications that this httpserver will be serving.
    *        These will be added to any filters.
    */
   @Deprecated
   public HttpServer(String name, String bindAddress, int port,
       boolean findPort, Configuration conf, AccessControlList adminsAcl,
       Connector connector, String[] pathSpecs) throws IOException {
     this(new Builder().setName(name)
         .addEndpoint(URI.create("http://" + bindAddress + ":" + port))
         .setFindPort(findPort).setConf(conf).setACL(adminsAcl)
         .setConnector(connector).setPathSpec(pathSpecs));
   }
 
   private HttpServer(final Builder b) throws IOException {
     this.appDir = b.appDir;
     this.logDir = b.logDir;
     final String appDir = getWebAppsPath(b.name);
     this.webServer = new Server();
     this.adminsAcl = b.adminsAcl;
     this.webAppContext = createWebAppContext(b.name, b.conf, adminsAcl, appDir);
     this.findPort = b.findPort;
     initializeWebServer(b.name, b.hostName, b.conf, b.pathSpecs);
   }
 
   private void initializeWebServer(String name, String hostName,
       Configuration conf, String[] pathSpecs)
       throws FileNotFoundException, IOException {
 
     Preconditions.checkNotNull(webAppContext);
 
     int maxThreads = conf.getInt(HTTP_MAX_THREADS, -1);
     // If HTTP_MAX_THREADS is not configured, QueueThreadPool() will use the
     // default value (currently 250).
     QueuedThreadPool threadPool = maxThreads == -1 ? new QueuedThreadPool()
         : new QueuedThreadPool(maxThreads);
     threadPool.setDaemon(true);
     webServer.setThreadPool(threadPool);
 
     ContextHandlerCollection contexts = new ContextHandlerCollection();
     RequestLog requestLog = HttpRequestLog.getRequestLog(name);
 
     if (requestLog != null) {
       RequestLogHandler requestLogHandler = new RequestLogHandler();
       requestLogHandler.setRequestLog(requestLog);
       HandlerCollection handlers = new HandlerCollection();
       handlers.setHandlers(new Handler[] { requestLogHandler, contexts });
       webServer.setHandler(handlers);
     } else {
       webServer.setHandler(contexts);
     }
 
     final String appDir = getWebAppsPath(name);
 
     webServer.addHandler(webAppContext);
 
     addDefaultApps(contexts, appDir, conf);
 
     addGlobalFilter("safety", QuotingInputFilter.class.getName(), null);
     Map<String, String> params = new HashMap<String, String>();
     params.put("xframeoptions", conf.get("hbase.http.filter.xframeoptions.mode", "DENY"));
     addGlobalFilter("clickjackingprevention",
             ClickjackingPreventionFilter.class.getName(), params);
     final FilterInitializer[] initializers = getFilterInitializers(conf);
     if (initializers != null) {
       conf = new Configuration(conf);
       conf.set(BIND_ADDRESS, hostName);
       for (FilterInitializer c : initializers) {
         c.initFilter(this, conf);
       }
     }
 
     addDefaultServlets();
 
     if (pathSpecs != null) {
       for (String path : pathSpecs) {
         LOG.info("adding path spec: " + path);
         addFilterPathMapping(path, webAppContext);
       }
     }
   }
 
   private void addUnmanagedListener(Connector connector) {
     listeners.add(new ListenerInfo(false, connector));
   }
 
   private void addManagedListener(Connector connector) {
     listeners.add(new ListenerInfo(true, connector));
   }
 
   private static WebAppContext createWebAppContext(String name,
       Configuration conf, AccessControlList adminsAcl, final String appDir) {
     WebAppContext ctx = new WebAppContext();
     ctx.setDisplayName(name);
     ctx.setContextPath("/");
     ctx.setWar(appDir + "/" + name);
     ctx.getServletContext().setAttribute(CONF_CONTEXT_ATTRIBUTE, conf);
     // for org.apache.hadoop.metrics.MetricsServlet
     ctx.getServletContext().setAttribute(
       org.apache.hadoop.http.HttpServer2.CONF_CONTEXT_ATTRIBUTE, conf);
     ctx.getServletContext().setAttribute(ADMINS_ACL, adminsAcl);
     addNoCacheFilter(ctx);
     return ctx;
   }
 
   private static void addNoCacheFilter(WebAppContext ctxt) {
     defineFilter(ctxt, NO_CACHE_FILTER, NoCacheFilter.class.getName(),
         Collections.<String, String> emptyMap(), new String[] { "/*" });
   }
 
   /**
    * Create a required listener for the Jetty instance listening on the port
    * provided. This wrapper and all subclasses must create at least one
    * listener.
    */
   public Connector createBaseListener(Configuration conf) throws IOException {
     return HttpServer.createDefaultChannelConnector();
   }
 
   @InterfaceAudience.Private
   public static Connector createDefaultChannelConnector() {
     SelectChannelConnector ret = new SelectChannelConnector();
     ret.setLowResourceMaxIdleTime(10000);
     ret.setAcceptQueueSize(128);
     ret.setResolveNames(false);
     ret.setUseDirectBuffers(false);
     if(Shell.WINDOWS) {
       // result of setting the SO_REUSEADDR flag is different on Windows
       // http://msdn.microsoft.com/en-us/library/ms740621(v=vs.85).aspx
       // without this 2 NN's can start on the same machine and listen on
       // the same port with indeterminate routing of incoming requests to them
       ret.setReuseAddress(false);
     }
     return ret;
   }
 
   /** Get an array of FilterConfiguration specified in the conf */
   private static FilterInitializer[] getFilterInitializers(Configuration conf) {
     if (conf == null) {
       return null;
     }
 
     Class<?>[] classes = conf.getClasses(FILTER_INITIALIZERS_PROPERTY);
     if (classes == null) {
       return null;
     }
 
     FilterInitializer[] initializers = new FilterInitializer[classes.length];
     for(int i = 0; i < classes.length; i++) {
       initializers[i] = (FilterInitializer)ReflectionUtils.newInstance(classes[i]);
     }
     return initializers;
   }
 
   /**
    * Add default apps.
    * @param appDir The application directory
    * @throws IOException
    */
   protected void addDefaultApps(ContextHandlerCollection parent,
       final String appDir, Configuration conf) throws IOException {
     // set up the context for "/logs/" if "hadoop.log.dir" property is defined.
     String logDir = this.logDir;
     if (logDir == null) {
         logDir = System.getProperty("hadoop.log.dir");
     }
     if (logDir != null) {
       Context logContext = new Context(parent, "/logs");
       logContext.setResourceBase(logDir);
       logContext.addServlet(AdminAuthorizedServlet.class, "/*");
       if (conf.getBoolean(
           ServerConfigurationKeys.HBASE_JETTY_LOGS_SERVE_ALIASES,
           ServerConfigurationKeys.DEFAULT_HBASE_JETTY_LOGS_SERVE_ALIASES)) {
         @SuppressWarnings("unchecked")
         Map<String, String> params = logContext.getInitParams();
         params.put(
             "org.mortbay.jetty.servlet.Default.aliases", "true");
       }
       logContext.setDisplayName("logs");
       setContextAttributes(logContext, conf);
       addNoCacheFilter(webAppContext);
       defaultContexts.put(logContext, true);
     }
     // set up the context for "/static/*"
     Context staticContext = new Context(parent, "/static");
     staticContext.setResourceBase(appDir + "/static");
     staticContext.addServlet(DefaultServlet.class, "/*");
     staticContext.setDisplayName("static");
     setContextAttributes(staticContext, conf);
     defaultContexts.put(staticContext, true);
   }
 
   private void setContextAttributes(Context context, Configuration conf) {
     context.getServletContext().setAttribute(CONF_CONTEXT_ATTRIBUTE, conf);
     context.getServletContext().setAttribute(ADMINS_ACL, adminsAcl);
   }
 
   /**
    * Add default servlets.
    */
   protected void addDefaultServlets() {
     // set up default servlets
     addServlet("stacks", "/stacks", StackServlet.class);
     addServlet("logLevel", "/logLevel", LogLevel.Servlet.class);
     addServlet("jmx", "/jmx", JMXJsonServlet.class);
     addServlet("conf", "/conf", ConfServlet.class);
     try {
       Class<? extends HttpServlet> clazz = (Class<? extends HttpServlet>)
         Class.forName("org.apache.hadoop.metrics.MetricsServlet");
       addServlet("metrics", "/metrics", clazz);
     } catch (Exception e) {
       LOG.warn("MetricsServlet class not found, metrics servlet will not start", e);
     }
   }
 
   public void addContext(Context ctxt, boolean isFiltered)
       throws IOException {
     webServer.addHandler(ctxt);
     addNoCacheFilter(webAppContext);
     defaultContexts.put(ctxt, isFiltered);
   }
 
   /**
    * Add a context
    * @param pathSpec The path spec for the context
    * @param dir The directory containing the context
    * @param isFiltered if true, the servlet is added to the filter path mapping
    * @throws IOException
    */
   protected void addContext(String pathSpec, String dir, boolean isFiltered) throws IOException {
     if (0 == webServer.getHandlers().length) {
       throw new RuntimeException("Couldn't find handler");
     }
     WebAppContext webAppCtx = new WebAppContext();
     webAppCtx.setContextPath(pathSpec);
     webAppCtx.setWar(dir);
     addContext(webAppCtx, true);
   }
 
   /**
    * Set a value in the webapp context. These values are available to the jsp
    * pages as "application.getAttribute(name)".
    * @param name The name of the attribute
    * @param value The value of the attribute
    */
   public void setAttribute(String name, Object value) {
     webAppContext.setAttribute(name, value);
   }
 
   /**
    * Add a Jersey resource package.
    * @param packageName The Java package name containing the Jersey resource.
    * @param pathSpec The path spec for the servlet
    */
   public void addJerseyResourcePackage(final String packageName,
       final String pathSpec) {
     LOG.info("addJerseyResourcePackage: packageName=" + packageName
         + ", pathSpec=" + pathSpec);
     final ServletHolder sh = new ServletHolder(ServletContainer.class);
     sh.setInitParameter("com.sun.jersey.config.property.resourceConfigClass",
         "com.sun.jersey.api.core.PackagesResourceConfig");
     sh.setInitParameter("com.sun.jersey.config.property.packages", packageName);
     webAppContext.addServlet(sh, pathSpec);
   }
 
   /**
    * Add a servlet in the server.
    * @param name The name of the servlet (can be passed as null)
    * @param pathSpec The path spec for the servlet
    * @param clazz The servlet class
    */
   public void addServlet(String name, String pathSpec,
       Class<? extends HttpServlet> clazz) {
     addInternalServlet(name, pathSpec, clazz, false);
     addFilterPathMapping(pathSpec, webAppContext);
   }
 
   /**
    * Add an internal servlet in the server.
    * Note: This method is to be used for adding servlets that facilitate
    * internal communication and not for user facing functionality. For
    * servlets added using this method, filters are not enabled.
    *
    * @param name The name of the servlet (can be passed as null)
    * @param pathSpec The path spec for the servlet
    * @param clazz The servlet class
    */
   public void addInternalServlet(String name, String pathSpec,
       Class<? extends HttpServlet> clazz) {
     addInternalServlet(name, pathSpec, clazz, false);
   }
 
   /**
    * Add an internal servlet in the server, specifying whether or not to
    * protect with Kerberos authentication.
    * Note: This method is to be used for adding servlets that facilitate
    * internal communication and not for user facing functionality. For
    +   * servlets added using this method, filters (except internal Kerberos
    * filters) are not enabled.
    *
    * @param name The name of the servlet (can be passed as null)
    * @param pathSpec The path spec for the servlet
    * @param clazz The servlet class
    * @param requireAuth Require Kerberos authenticate to access servlet
    */
   public void addInternalServlet(String name, String pathSpec,
       Class<? extends HttpServlet> clazz, boolean requireAuth) {
     ServletHolder holder = new ServletHolder(clazz);
     if (name != null) {
       holder.setName(name);
     }
     webAppContext.addServlet(holder, pathSpec);
 
     if(requireAuth && UserGroupInformation.isSecurityEnabled()) {
        LOG.info("Adding Kerberos (SPNEGO) filter to " + name);
        ServletHandler handler = webAppContext.getServletHandler();
        FilterMapping fmap = new FilterMapping();
        fmap.setPathSpec(pathSpec);
        fmap.setFilterName(SPNEGO_FILTER);
        fmap.setDispatches(Handler.ALL);
        handler.addFilterMapping(fmap);
     }
   }
 
   @Override
   public void addFilter(String name, String classname,
       Map<String, String> parameters) {
 
     final String[] USER_FACING_URLS = { "*.html", "*.jsp" };
     defineFilter(webAppContext, name, classname, parameters, USER_FACING_URLS);
     LOG.info("Added filter " + name + " (class=" + classname
         + ") to context " + webAppContext.getDisplayName());
     final String[] ALL_URLS = { "/*" };
     for (Map.Entry<Context, Boolean> e : defaultContexts.entrySet()) {
       if (e.getValue()) {
         Context ctx = e.getKey();
         defineFilter(ctx, name, classname, parameters, ALL_URLS);
         LOG.info("Added filter " + name + " (class=" + classname
             + ") to context " + ctx.getDisplayName());
       }
     }
     filterNames.add(name);
   }
 
   @Override
   public void addGlobalFilter(String name, String classname,
       Map<String, String> parameters) {
     final String[] ALL_URLS = { "/*" };
     defineFilter(webAppContext, name, classname, parameters, ALL_URLS);
     for (Context ctx : defaultContexts.keySet()) {
       defineFilter(ctx, name, classname, parameters, ALL_URLS);
     }
     LOG.info("Added global filter '" + name + "' (class=" + classname + ")");
   }
 
   /**
    * Define a filter for a context and set up default url mappings.
    */
   public static void defineFilter(Context ctx, String name,
       String classname, Map<String,String> parameters, String[] urls) {
 
     FilterHolder holder = new FilterHolder();
     holder.setName(name);
     holder.setClassName(classname);
     holder.setInitParameters(parameters);
     FilterMapping fmap = new FilterMapping();
     fmap.setPathSpecs(urls);
     fmap.setDispatches(Handler.ALL);
     fmap.setFilterName(name);
     ServletHandler handler = ctx.getServletHandler();
     handler.addFilter(holder, fmap);
   }
 
   /**
    * Add the path spec to the filter path mapping.
    * @param pathSpec The path spec
    * @param webAppCtx The WebApplicationContext to add to
    */
   protected void addFilterPathMapping(String pathSpec,
       Context webAppCtx) {
     ServletHandler handler = webAppCtx.getServletHandler();
     for(String name : filterNames) {
       FilterMapping fmap = new FilterMapping();
       fmap.setPathSpec(pathSpec);
       fmap.setFilterName(name);
       fmap.setDispatches(Handler.ALL);
       handler.addFilterMapping(fmap);
     }
   }
 
   /**
    * Get the value in the webapp context.
    * @param name The name of the attribute
    * @return The value of the attribute
    */
   public Object getAttribute(String name) {
     return webAppContext.getAttribute(name);
   }
 
   public WebAppContext getWebAppContext(){
     return this.webAppContext;
   }
 
   public String getWebAppsPath(String appName) throws FileNotFoundException {
       return getWebAppsPath(this.appDir, appName);
   }
 
   /**
    * Get the pathname to the webapps files.
    * @param appName eg "secondary" or "datanode"
    * @return the pathname as a URL
    * @throws FileNotFoundException if 'webapps' directory cannot be found on CLASSPATH.
    */
   protected String getWebAppsPath(String webapps, String appName) throws FileNotFoundException {
     URL url = getClass().getClassLoader().getResource(webapps + "/" + appName);
     if (url == null)
       throw new FileNotFoundException(webapps + "/" + appName
           + " not found in CLASSPATH");
     String urlString = url.toString();
     return urlString.substring(0, urlString.lastIndexOf('/'));
   }
 
   /**
    * Get the port that the server is on
    * @return the port
    */
   @Deprecated
   public int getPort() {
     return webServer.getConnectors()[0].getLocalPort();
   }
 
   /**
    * Get the address that corresponds to a particular connector.
    *
    * @return the corresponding address for the connector, or null if there's no
    *         such connector or the connector is not bounded.
    */
   public InetSocketAddress getConnectorAddress(int index) {
     Preconditions.checkArgument(index >= 0);
     if (index > webServer.getConnectors().length)
       return null;
 
     Connector c = webServer.getConnectors()[index];
     if (c.getLocalPort() == -1) {
       // The connector is not bounded
       return null;
     }
 
     return new InetSocketAddress(c.getHost(), c.getLocalPort());
   }
 
   /**
    * Set the min, max number of worker threads (simultaneous connections).
    */
   public void setThreads(int min, int max) {
     QueuedThreadPool pool = (QueuedThreadPool) webServer.getThreadPool();
     pool.setMinThreads(min);
     pool.setMaxThreads(max);
   }
 
   private void initSpnego(Configuration conf, String hostName,
       String usernameConfKey, String keytabConfKey, String kerberosNameRuleKey,
       String signatureSecretKeyFileKey) throws IOException {
     Map<String, String> params = new HashMap<String, String>();
     String principalInConf = getOrEmptyString(conf, usernameConfKey);
     if (!principalInConf.isEmpty()) {
       params.put(HTTP_SPNEGO_AUTHENTICATION_PRINCIPAL_SUFFIX, SecurityUtil.getServerPrincipal(
           principalInConf, hostName));
     }
     String httpKeytab = getOrEmptyString(conf, keytabConfKey);
     if (!httpKeytab.isEmpty()) {
       params.put(HTTP_SPNEGO_AUTHENTICATION_KEYTAB_SUFFIX, httpKeytab);
     }
     String kerberosNameRule = getOrEmptyString(conf, kerberosNameRuleKey);
     if (!kerberosNameRule.isEmpty()) {
       params.put(HTTP_SPNEGO_AUTHENTICATION_KRB_NAME_SUFFIX, kerberosNameRule);
     }
     String signatureSecretKeyFile = getOrEmptyString(conf, signatureSecretKeyFileKey);
     if (!signatureSecretKeyFile.isEmpty()) {
       params.put(HTTP_AUTHENTICATION_SIGNATURE_SECRET_FILE_SUFFIX,
           signatureSecretKeyFile);
     }
     params.put(AuthenticationFilter.AUTH_TYPE, "kerberos");
 
     // Verify that the required options were provided
     if (isMissing(params.get(HTTP_SPNEGO_AUTHENTICATION_PRINCIPAL_SUFFIX)) ||
             isMissing(params.get(HTTP_SPNEGO_AUTHENTICATION_KEYTAB_SUFFIX))) {
       throw new IllegalArgumentException(usernameConfKey + " and "
           + keytabConfKey + " are both required in the configuration "
           + "to enable SPNEGO/Kerberos authentication for the Web UI");
     }
 
     addGlobalFilter(SPNEGO_FILTER, AuthenticationFilter.class.getName(), params);
   }
 
   /**
    * Returns true if the argument is non-null and not whitespace
    */
   private boolean isMissing(String value) {
     if (null == value) {
       return true;
     }
     return value.trim().isEmpty();
   }
 
   /**
    * Extracts the value for the given key from the configuration of returns a string of
    * zero length.
    */
   private String getOrEmptyString(Configuration conf, String key) {
     if (null == key) {
       return EMPTY_STRING;
     }
     final String value = conf.get(key.trim());
     return null == value ? EMPTY_STRING : value;
   }
 
   /**
    * Start the server. Does not wait for the server to start.
    */
   public void start() throws IOException {
     try {
       try {
         openListeners();
         webServer.start();
       } catch (IOException ex) {
         LOG.info("HttpServer.start() threw a non Bind IOException", ex);
         throw ex;
       } catch (MultiException ex) {
         LOG.info("HttpServer.start() threw a MultiException", ex);
         throw ex;
       }
       // Make sure there is no handler failures.
       Handler[] handlers = webServer.getHandlers();
       for (int i = 0; i < handlers.length; i++) {
         if (handlers[i].isFailed()) {
           throw new IOException(
               "Problem in starting http server. Server handlers failed");
         }
       }
       // Make sure there are no errors initializing the context.
       Throwable unavailableException = webAppContext.getUnavailableException();
       if (unavailableException != null) {
         // Have to stop the webserver, or else its non-daemon threads
         // will hang forever.
         webServer.stop();
         throw new IOException("Unable to initialize WebAppContext",
             unavailableException);
       }
     } catch (IOException e) {
       throw e;
     } catch (InterruptedException e) {
       throw (IOException) new InterruptedIOException(
           "Interrupted while starting HTTP server").initCause(e);
     } catch (Exception e) {
       throw new IOException("Problem starting http server", e);
     }
   }
 
   private void loadListeners() {
     for (ListenerInfo li : listeners) {
       webServer.addConnector(li.listener);
     }
   }
 
   /**
    * Open the main listener for the server
    * @throws Exception
    */
   void openListeners() throws Exception {
     for (ListenerInfo li : listeners) {
       Connector listener = li.listener;
       if (!li.isManaged || li.listener.getLocalPort() != -1) {
         // This listener is either started externally or has been bound
         continue;
       }
       int port = listener.getPort();
       while (true) {
         // jetty has a bug where you can't reopen a listener that previously
         // failed to open w/o issuing a close first, even if the port is changed
         try {
           listener.close();
           listener.open();
           LOG.info("Jetty bound to port " + listener.getLocalPort());
           break;
         } catch (BindException ex) {
           if (port == 0 || !findPort) {
             BindException be = new BindException("Port in use: "
                 + listener.getHost() + ":" + listener.getPort());
             be.initCause(ex);
             throw be;
           }
         }
         // try the next port number
         listener.setPort(++port);
         Thread.sleep(100);
       }
     }
   }
 
   /**
    * stop the server
    */
   public void stop() throws Exception {
     MultiException exception = null;
     for (ListenerInfo li : listeners) {
       if (!li.isManaged) {
         continue;
       }
 
       try {
         li.listener.close();
       } catch (Exception e) {
         LOG.error(
             "Error while stopping listener for webapp"
                 + webAppContext.getDisplayName(), e);
         exception = addMultiException(exception, e);
       }
     }
 
     try {
       // clear & stop webAppContext attributes to avoid memory leaks.
       webAppContext.clearAttributes();
       webAppContext.stop();
     } catch (Exception e) {
       LOG.error("Error while stopping web app context for webapp "
           + webAppContext.getDisplayName(), e);
       exception = addMultiException(exception, e);
     }
 
     try {
       webServer.stop();
     } catch (Exception e) {
       LOG.error("Error while stopping web server for webapp "
           + webAppContext.getDisplayName(), e);
       exception = addMultiException(exception, e);
     }
 
     if (exception != null) {
       exception.ifExceptionThrow();
     }
 
   }
 
   private MultiException addMultiException(MultiException exception, Exception e) {
     if(exception == null){
       exception = new MultiException();
     }
     exception.add(e);
     return exception;
   }
 
   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() {
     if (listeners.size() == 0) {
       return "Inactive HttpServer";
     } else {
       StringBuilder sb = new StringBuilder("HttpServer (")
         .append(isAlive() ? STATE_DESCRIPTION_ALIVE : STATE_DESCRIPTION_NOT_LIVE).append("), listening at:");
       for (ListenerInfo li : listeners) {
         Connector l = li.listener;
         sb.append(l.getHost()).append(":").append(l.getPort()).append("/,");
       }
       return sb.toString();
     }
   }
 
   /**
    * Checks the user has privileges to access to instrumentation servlets.
    * <p>
    * If <code>hadoop.security.instrumentation.requires.admin</code> is set to FALSE
    * (default value) it always returns TRUE.
    * </p><p>
    * If <code>hadoop.security.instrumentation.requires.admin</code> is set to TRUE
    * it will check that if the current user is in the admin ACLS. If the user is
    * in the admin ACLs it returns TRUE, otherwise it returns FALSE.
    * </p>
    *
    * @param servletContext the servlet context.
    * @param request the servlet request.
    * @param response the servlet response.
    * @return TRUE/FALSE based on the logic decribed above.
    */
   public static boolean isInstrumentationAccessAllowed(
     ServletContext servletContext, HttpServletRequest request,
     HttpServletResponse response) throws IOException {
     Configuration conf =
       (Configuration) servletContext.getAttribute(CONF_CONTEXT_ATTRIBUTE);
 
     boolean access = true;
     boolean adminAccess = conf.getBoolean(
       CommonConfigurationKeys.HADOOP_SECURITY_INSTRUMENTATION_REQUIRES_ADMIN,
       false);
     if (adminAccess) {
       access = hasAdministratorAccess(servletContext, request, response);
     }
     return access;
   }
 
   /**
    * Does the user sending the HttpServletRequest has the administrator ACLs? If
    * it isn't the case, response will be modified to send an error to the user.
    *
    * @param servletContext
    * @param request
    * @param response used to send the error response if user does not have admin access.
    * @return true if admin-authorized, false otherwise
    * @throws IOException
    */
   public static boolean hasAdministratorAccess(
       ServletContext servletContext, HttpServletRequest request,
       HttpServletResponse response) throws IOException {
     Configuration conf =
         (Configuration) servletContext.getAttribute(CONF_CONTEXT_ATTRIBUTE);
     // If there is no authorization, anybody has administrator access.
     if (!conf.getBoolean(
         CommonConfigurationKeys.HADOOP_SECURITY_AUTHORIZATION, false)) {
       return true;
     }
 
     String remoteUser = request.getRemoteUser();
     if (remoteUser == null) {
       response.sendError(HttpServletResponse.SC_UNAUTHORIZED,
                          "Unauthenticated users are not " +
                          "authorized to access this page.");
       return false;
     }
 
     if (servletContext.getAttribute(ADMINS_ACL) != null &&
         !userHasAdministratorAccess(servletContext, remoteUser)) {
       response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "User "
           + remoteUser + " is unauthorized to access this page.");
       return false;
     }
 
     return true;
   }
 
   /**
    * Get the admin ACLs from the given ServletContext and check if the given
    * user is in the ACL.
    *
    * @param servletContext the context containing the admin ACL.
    * @param remoteUser the remote user to check for.
    * @return true if the user is present in the ACL, false if no ACL is set or
    *         the user is not present
    */
   public static boolean userHasAdministratorAccess(ServletContext servletContext,
       String remoteUser) {
     AccessControlList adminsAcl = (AccessControlList) servletContext
         .getAttribute(ADMINS_ACL);
     UserGroupInformation remoteUserUGI =
         UserGroupInformation.createRemoteUser(remoteUser);
     return adminsAcl != null && adminsAcl.isUserAllowed(remoteUserUGI);
   }
 
   /**
    * 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.
    * Currently the stack traces are done sequentially rather than exactly the
    * same data.
    */
   public static class StackServlet extends HttpServlet {
     private static final long serialVersionUID = -6284183679759467039L;
 
     @Override
     public void doGet(HttpServletRequest request, HttpServletResponse response)
       throws ServletException, IOException {
       if (!HttpServer.isInstrumentationAccessAllowed(getServletContext(),
                                                      request, response)) {
         return;
       }
       response.setContentType("text/plain; charset=UTF-8");
       try (PrintStream out = new PrintStream(
         response.getOutputStream(), false, "UTF-8")) {
         Threads.printThreadInfo(out, "");
         out.flush();
       }
       ReflectionUtils.logThreadInfo(LOG, "jsp requested", 1);
     }
   }
 
   /**
    * A Servlet input filter that quotes all HTML active characters in the
    * parameter names and values. The goal is to quote the characters to make
    * all of the servlets resistant to cross-site scripting attacks.
    */
   @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.CONFIG)
   public static class QuotingInputFilter implements Filter {
     private FilterConfig config;
 
     public static class RequestQuoter extends HttpServletRequestWrapper {
       private final HttpServletRequest rawRequest;
       public RequestQuoter(HttpServletRequest rawRequest) {
         super(rawRequest);
         this.rawRequest = rawRequest;
       }
 
       /**
        * Return the set of parameter names, quoting each name.
        */
       @SuppressWarnings("unchecked")
       @Override
       public Enumeration<String> getParameterNames() {
         return new Enumeration<String>() {
           private Enumeration<String> rawIterator =
             rawRequest.getParameterNames();
           @Override
           public boolean hasMoreElements() {
             return rawIterator.hasMoreElements();
           }
 
           @Override
           public String nextElement() {
             return HtmlQuoting.quoteHtmlChars(rawIterator.nextElement());
           }
         };
       }
 
       /**
        * Unquote the name and quote the value.
        */
       @Override
       public String getParameter(String name) {
         return HtmlQuoting.quoteHtmlChars(rawRequest.getParameter
                                      (HtmlQuoting.unquoteHtmlChars(name)));
       }
 
       @Override
       public String[] getParameterValues(String name) {
         String unquoteName = HtmlQuoting.unquoteHtmlChars(name);
         String[] unquoteValue = rawRequest.getParameterValues(unquoteName);
         if (unquoteValue == null) {
           return null;
         }
         String[] result = new String[unquoteValue.length];
         for(int i=0; i < result.length; ++i) {
           result[i] = HtmlQuoting.quoteHtmlChars(unquoteValue[i]);
         }
         return result;
       }
 
       @SuppressWarnings("unchecked")
       @Override
       public Map<String, String[]> getParameterMap() {
         Map<String, String[]> result = new HashMap<String,String[]>();
         Map<String, String[]> raw = rawRequest.getParameterMap();
         for (Map.Entry<String,String[]> item: raw.entrySet()) {
           String[] rawValue = item.getValue();
           String[] cookedValue = new String[rawValue.length];
           for(int i=0; i< rawValue.length; ++i) {
             cookedValue[i] = HtmlQuoting.quoteHtmlChars(rawValue[i]);
           }
           result.put(HtmlQuoting.quoteHtmlChars(item.getKey()), cookedValue);
         }
         return result;
       }
 
       /**
        * Quote the url so that users specifying the HOST HTTP header
        * can't inject attacks.
        */
       @Override
       public StringBuffer getRequestURL(){
         String url = rawRequest.getRequestURL().toString();
         return new StringBuffer(HtmlQuoting.quoteHtmlChars(url));
       }
 
       /**
        * Quote the server name so that users specifying the HOST HTTP header
        * can't inject attacks.
        */
       @Override
       public String getServerName() {
         return HtmlQuoting.quoteHtmlChars(rawRequest.getServerName());
       }
     }
 
     @Override
     public void init(FilterConfig config) throws ServletException {
       this.config = config;
     }
 
     @Override
     public void destroy() {
     }
 
     @Override
     public void doFilter(ServletRequest request,
                          ServletResponse response,
                          FilterChain chain
                          ) throws IOException, ServletException {
       HttpServletRequestWrapper quoted =
         new RequestQuoter((HttpServletRequest) request);
       HttpServletResponse httpResponse = (HttpServletResponse) response;
 
       String mime = inferMimeType(request);
       if (mime == null) {
         httpResponse.setContentType("text/plain; charset=utf-8");
       } else if (mime.startsWith("text/html")) {
         // HTML with unspecified encoding, we want to
         // force HTML with utf-8 encoding
         // This is to avoid the following security issue:
         // http://openmya.hacker.jp/hasegawa/security/utf7cs.html
         httpResponse.setContentType("text/html; charset=utf-8");
       } else if (mime.startsWith("application/xml")) {
         httpResponse.setContentType("text/xml; charset=utf-8");
       }
       chain.doFilter(quoted, httpResponse);
     }
 
     /**
      * Infer the mime type for the response based on the extension of the request
      * URI. Returns null if unknown.
      */
     private String inferMimeType(ServletRequest request) {
       String path = ((HttpServletRequest)request).getRequestURI();
       ContextHandler.SContext sContext = (ContextHandler.SContext)config.getServletContext();
       MimeTypes mimes = sContext.getContextHandler().getMimeTypes();
       Buffer mimeBuffer = mimes.getMimeByExtension(path);
       return (mimeBuffer == null) ? null : mimeBuffer.toString();
     }
 
   }
 
 }