Add support for tunneling TCP/IP connections.

examples/src/main/java/net/schmizz/sshj/examples/Jump.java

@@ -0,0 +1,50 @@
+package net.schmizz.sshj.examples;
+
+import net.schmizz.sshj.SSHClient;
+import net.schmizz.sshj.common.IOUtils;
+import net.schmizz.sshj.connection.channel.direct.DirectConnection;
+import net.schmizz.sshj.connection.channel.direct.Session;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * This example demonstrates connecting via an intermediate "jump" server using a direct TCP/IP channel.
+ */
+public class Jump {
+    public static void main(String... args)
+            throws IOException {
+        SSHClient firstHop = new SSHClient();
+
+        firstHop.loadKnownHosts();
+
+        firstHop.connect("localhost");
+        try {
+
+            firstHop.authPublickey(System.getProperty("user.name"));
+
+            DirectConnection tunnel = firstHop.newDirectConnection("localhost", 22);
+
+            SSHClient ssh = new SSHClient();
+            try {
+                ssh.loadKnownHosts();
+                ssh.connectVia(tunnel);
+                ssh.authPublickey(System.getProperty("user.name"));
+
+                final Session session = ssh.startSession();
+                try {
+                    final Session.Command cmd = session.exec("ping -c 1 google.com");
+                    System.out.println(IOUtils.readFully(cmd.getInputStream()).toString());
+                    cmd.join(5, TimeUnit.SECONDS);
+                    System.out.println("\n** exit status: " + cmd.getExitStatus());
+                } finally {
+                    session.close();
+                }
+            } finally {
+                ssh.disconnect();
+            }
+        } finally {
+            firstHop.disconnect();
+        }
+    }
+}

src/main/java/net/schmizz/sshj/SSHClient.java

@@ -23,6 +23,7 @@ import net.schmizz.sshj.common.SecurityUtils;
 import net.schmizz.sshj.connection.Connection;
 import net.schmizz.sshj.connection.ConnectionException;
 import net.schmizz.sshj.connection.ConnectionImpl;
+import net.schmizz.sshj.connection.channel.direct.DirectConnection;
 import net.schmizz.sshj.connection.channel.direct.LocalPortForwarder;
 import net.schmizz.sshj.connection.channel.direct.Session;
 import net.schmizz.sshj.connection.channel.direct.SessionChannel;
@@ -672,6 +673,20 @@ public class SSHClient
         return forwarder;
     }
 
+    /** Create a {@link DirectConnection} channel that connects to a remote address from the server.
+     *
+     * This can be used to open a tunnel to, for example, an HTTP server that is only
+     * accessible from the SSH server, or opening an SSH connection via a 'jump' server.
+     *
+     * @param hostname name of the host to connect to from the server.
+     * @param port remote port number.
+     */
+    public DirectConnection newDirectConnection(String hostname, int port) throws IOException {
+        DirectConnection tunnel = new DirectConnection(conn, hostname, port);
+        tunnel.open();
+        return tunnel;
+    }
+
     /**
      * Register a {@code listener} for handling forwarded X11 channels. Without having done this, an incoming X11
      * forwarding will be summarily rejected.

src/main/java/net/schmizz/sshj/SocketClient.java

@@ -17,6 +17,7 @@ package net.schmizz.sshj;
 
 import com.hierynomus.sshj.backport.JavaVersion;
 import com.hierynomus.sshj.backport.Jdk7HttpProxySocket;
+import net.schmizz.sshj.connection.channel.direct.DirectConnection;
 
 import javax.net.SocketFactory;
 import java.io.IOException;
@@ -43,6 +44,9 @@ public abstract class SocketClient {
     private int timeout = 0;
 
     private String hostname;
+    private int port;
+
+    private boolean tunneled = false;
 
     SocketClient(int defaultPort) {
         this.defaultPort = defaultPort;
@@ -71,6 +75,7 @@ public abstract class SocketClient {
     @Deprecated
     public void connect(String hostname, int port, Proxy proxy) throws IOException {
         this.hostname = hostname;
+        this.port = port;
         if (JavaVersion.isJava7OrEarlier() && proxy.type() == Proxy.Type.HTTP) {
             // Java7 and earlier have no support for HTTP Connect proxies, return our custom socket.
             socket = new Jdk7HttpProxySocket(proxy);
@@ -103,6 +108,7 @@ public abstract class SocketClient {
      */
     @Deprecated
     public void connect(InetAddress host, int port, Proxy proxy) throws IOException {
+        this.port = port;
         if (JavaVersion.isJava7OrEarlier() && proxy.type() == Proxy.Type.HTTP) {
             // Java7 and earlier have no support for HTTP Connect proxies, return our custom socket.
             socket = new Jdk7HttpProxySocket(proxy);
@@ -122,6 +128,7 @@ public abstract class SocketClient {
             connect(InetAddress.getByName(null), port);
         } else {
             this.hostname = hostname;
+            this.port = port;
             socket = socketFactory.createSocket();
             socket.connect(new InetSocketAddress(hostname, port), connectTimeout);
             onConnect();
@@ -133,6 +140,7 @@ public abstract class SocketClient {
             connect(InetAddress.getByName(null), port, localAddr, localPort);
         } else {
             this.hostname = hostname;
+            this.port = port;
             socket = socketFactory.createSocket();
             socket.bind(new InetSocketAddress(localAddr, localPort));
             socket.connect(new InetSocketAddress(hostname, port), connectTimeout);
@@ -140,11 +148,22 @@ public abstract class SocketClient {
         }
     }
 
+    /** Connect to a remote address via a direct TCP/IP connection from the server. */
+    public void connectVia(DirectConnection directConnection) throws IOException {
+        this.hostname = directConnection.getRemoteHost();
+        this.port = directConnection.getRemotePort();
+        this.input = directConnection.getInputStream();
+        this.output = directConnection.getOutputStream();
+        this.tunneled = true;
+        onConnect();
+    }
+
     public void connect(InetAddress host) throws IOException {
         connect(host, defaultPort);
     }
 
     public void connect(InetAddress host, int port) throws IOException {
+        this.port = port;
         socket = socketFactory.createSocket();
         socket.connect(new InetSocketAddress(host, port), connectTimeout);
         onConnect();
@@ -152,6 +171,7 @@ public abstract class SocketClient {
 
     public void connect(InetAddress host, int port, InetAddress localAddr, int localPort)
             throws IOException {
+        this.port = port;
         socket = socketFactory.createSocket();
         socket.bind(new InetSocketAddress(localAddr, localPort));
         socket.connect(new InetSocketAddress(host, port), connectTimeout);
@@ -174,15 +194,15 @@ public abstract class SocketClient {
     }
 
     public boolean isConnected() {
-        return (socket != null) && socket.isConnected();
+        return tunneled || ((socket != null) && socket.isConnected());
     }
 
     public int getLocalPort() {
-        return socket.getLocalPort();
+        return tunneled ? 65536 : socket.getLocalPort();
     }
 
     public InetAddress getLocalAddress() {
-        return socket.getLocalAddress();
+        return socket == null ? null : socket.getLocalAddress();
     }
 
     public String getRemoteHostname() {
@@ -190,11 +210,11 @@ public abstract class SocketClient {
     }
 
     public int getRemotePort() {
-        return socket.getPort();
+        return socket == null ? this.port : socket.getPort();
     }
 
     public InetAddress getRemoteAddress() {
-        return socket.getInetAddress();
+        return socket == null ? null : socket.getInetAddress();
     }
 
     public void setSocketFactory(SocketFactory factory) {
@@ -238,9 +258,11 @@ public abstract class SocketClient {
     }
 
     void onConnect() throws IOException {
-        socket.setSoTimeout(timeout);
-        input = socket.getInputStream();
-        output = socket.getOutputStream();
+        if (socket != null) {
+          socket.setSoTimeout(timeout);
+          input = socket.getInputStream();
+          output = socket.getOutputStream();
+        }
     }
 
 }

src/main/java/net/schmizz/sshj/connection/channel/direct/DirectConnection.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed 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 net.schmizz.sshj.connection.channel.direct;
+
+import net.schmizz.sshj.common.SSHPacket;
+import net.schmizz.sshj.connection.Connection;
+
+/** A channel for creating a direct TCP/IP connection from the server to a remote address. */
+public class DirectConnection extends AbstractDirectChannel {
+    private final String remoteHost;
+    private final int remotePort;
+
+    public DirectConnection(Connection conn, String remoteHost, int remotePort) {
+        super(conn, "direct-tcpip");
+        this.remoteHost = remoteHost;
+        this.remotePort = remotePort;
+    }
+
+    @Override protected SSHPacket buildOpenReq() {
+        return super.buildOpenReq()
+                .putString(getRemoteHost())
+                .putUInt32(getRemotePort())
+                .putString("localhost")
+                .putUInt32(65536); // it looks like OpenSSH uses this value in stdio-forward
+    }
+
+    public String getRemoteHost() {
+        return remoteHost;
+    }
+
+    public int getRemotePort() {
+        return remotePort;
+    }
+}