commons-vfs2/src/main/java/org/apache/commons/vfs2/provider/sftp/SftpStreamProxy.java

/*
 * 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>
     * <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;

    /**
     * Username 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;
    }
}