java - How to use jsch with ProxyCommands for portforwarding

Question

I want to ssh to a machine which is behind a proxy and do a portforwarding after that in my java program. (To be able to ssh to the box I should have ssh'ed to the proxy machine first). I usually do that by having the following entries in my ~/.ssh/config file:

ProxyCommand ssh proxyhost.com -t nc %h %p
IdentityFile /home/username/username_dsa_key

And then I run the following to do portforwarding to map hostmachine.com:54321 to my localhost:12345:

ssh -A -L12345:localhost:54321 hostmachine.com

Now I want to do these with Jsch library but I can't figure out how to connect to the second host after opening the channel on the session:

        String proxyHost = "proxyhost.com";
        String host = "hostmachine.com";
        int lport = 12345;
        String rhost = "localhost";
        int rport = 54321;

        JSch jsch=new JSch();
        jsch.setKnownHosts("/home/{user}/.ssh/known_hosts");
        jsch.addIdentity("/home/{user}/.ssh/{user}_dsa_key",passphrase);

        Session session1 = jsch.getSession(user,proxyHost,22);
        session1.connect(3000);
        System.out.println(session1.isConnected());
        Channel channel = session1.openChannel("shell");

        ////// Now what? :)


        channel.disconnect();
        session1.disconnect();

Any idea?

p.s: I have read the samples in www.jcraft.com/jsch/examples/ but they didn't help in this case unfortunately.

Thanks!

Answer 1

I'll suggest you to try

http://www.jcraft.com/jsch/examples/JumpHosts.java.html

, but if it is important to use the native "ssh" command, you will find the class ProxyCommand in the comment of Session.java of jsch-0.1.50,

/*
// setProxyCommand("ssh -l user2 host2 -o 'ProxyCommand ssh user1@host1 nc host2 22' nc %h %p")
public void setProxyCommand(String command){
  setProxy(new ProxyCommand(command));
}

class ProxyCommand implements Proxy {
  String command;
  Process p = null;
  InputStream in = null;
  OutputStream out = null;
  ProxyCommand(String command){
    this.command = command;
  }
  public void connect(SocketFactory socket_factory, String host, int port, int timeout) throws Exception {
    String _command = command.replace("%h", host);
    _command = _command.replace("%p", new Integer(port).toString());
    p = Runtime.getRuntime().exec(_command);
    in = p.getInputStream();
    out = p.getOutputStream();
  }
  public Socket getSocket() { return null; }
  public InputStream getInputStream() { return in; }
  public OutputStream getOutputStream() { return out; }
  public void close() {
    try{
      if(p!=null){
        p.getErrorStream().close();
        p.getOutputStream().close();
        p.getInputStream().close();
        p.destroy();
        p=null;
      }
    }
    catch(IOException e){
    }
  }
}
*/