/*
    * 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.commons.vfs2.provider.sftp;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.net.Socket;
  
  import org.apache.commons.vfs2.FileSystemOptions;
  
  import com.jcraft.jsch.ChannelExec;
  import com.jcraft.jsch.Proxy;
  import com.jcraft.jsch.Session;
  import com.jcraft.jsch.SocketFactory;
  
  /**
   * Stream based proxy for JSch.
   *
   * <p>
   * Use a command on the proxy that will forward the SSH stream to the target host and port.
   * </p>
   *
   * @since 2.1
   */
  public class SftpStreamProxy implements Proxy {
      /**
       * Command format using bash built-in TCP stream.
       */
      public static final String BASH_TCP_COMMAND = "/bin/bash -c 'exec 3<>/dev/tcp/%s/%d; cat <&3 & cat >&3; kill $!";
  
      /**
       * Command format using netcat command.
       */
      public static final String NETCAT_COMMAND = "nc -q 0 %s %d";
  
      private ChannelExec channel;
  
      /**
       * Command pattern to execute on the proxy host.
       * <p>
       * When run, the command output should be forwarded to the target host and port, and its input should be forwarded from the target host and port.
       * </p>
       * <p>
       * The command will be created for each host/port pair by using {@linkplain String#format(String, Object...)} with two objects: the target host name
       * ({@linkplain String}) and the target port ({@linkplain Integer}).
       * </p>
       * <p>
       * Here are two examples (that can be easily used by using the static members of this class):
       * </p>
       * <ul>
       * <li>{@code nc -q 0 %s %d} to use the netcat command ({@linkplain #NETCAT_COMMAND})</li>
       * <li>{@code /bin/bash -c 'exec 3<>/dev/tcp/%s/%d; cat <&3 & cat >&3; kill $!} will use bash built-in TCP stream, which can be useful when there is no
       * netcat available. ({@linkplain #BASH_TCP_COMMAND})</li>
       * </ul>
       */
      private final String commandFormat;
  
      /**
       * Hostname used to connect to the proxy host.
       */
      private final String proxyHost;
  
      /**
       * The options for connection.
       */
      private final FileSystemOptions proxyOptions;
  
      /**
       * The password to be used for connection.
       */
      private final String proxyPassword;
  
      /**
       * Port used to connect to the proxy host.
       */
      private final int proxyPort;
  
      /**
       * User name used to connect to the proxy host.
       */
      private final String proxyUser;
  
      private Session session;
 
     /**
      * Creates a stream proxy.
      *
      * @param commandFormat A format string that will be used to create the command to execute on the proxy host using
      *            {@linkplain String#format(String, Object...)}. Two parameters are given to the format command, the
      *            target host name (String) and port (Integer).
      *
      * @param proxyUser The proxy user
      * @param proxyPassword The proxy password
      * @param proxyHost The proxy host
      * @param proxyPort The port to connect to on the proxy
      * @param proxyOptions Options used when connecting to the proxy
      */
     public SftpStreamProxy(final String commandFormat, final String proxyUser, final String proxyHost,
             final int proxyPort, final String proxyPassword, final FileSystemOptions proxyOptions) {
         this.proxyHost = proxyHost;
         this.proxyPort = proxyPort;
         this.proxyUser = proxyUser;
         this.proxyPassword = proxyPassword;
         this.commandFormat = commandFormat;
         this.proxyOptions = proxyOptions;
     }
 
     @Override
     public void close() {
         if (channel != null) {
             channel.disconnect();
         }
         if (session != null) {
             session.disconnect();
         }
     }
 
     @Override
     public void connect(final SocketFactory socketFactory, final String targetHost, final int targetPort,
             final int timeout) throws Exception {
         session = SftpClientFactory.createConnection(proxyHost, proxyPort, proxyUser.toCharArray(),
                 proxyPassword.toCharArray(), proxyOptions);
         channel = (ChannelExec) session.openChannel("exec");
         channel.setCommand(String.format(commandFormat, targetHost, targetPort));
         channel.connect(timeout);
     }
 
     @Override
     public InputStream getInputStream() {
         try {
             return channel.getInputStream();
         } catch (final IOException e) {
             throw new IllegalStateException("IOException getting the SSH proxy input stream", e);
         }
     }
 
     @Override
     public OutputStream getOutputStream() {
         try {
             return channel.getOutputStream();
         } catch (final IOException e) {
             throw new IllegalStateException("IOException getting the SSH proxy output stream", e);
         }
     }
 
     @Override
     public Socket getSocket() {
         return null;
     }
 }