JSch-如何使用PortForwarding L从远程服务器捕获流？

Question

I tried to use InputStream and Buffer[], also BufferedReader, also PipedInputStream. For all cases i got null:

        sessionB = jSch.getSession(username, "localhost", forwardedPort);
        sessionB.connect();

          if(sessionB.isConnected()) {
             System.out.println("Connected host B!");

             channel = (ChannelExec) sessionB.openChannel("exec");   

             br = new BufferedReader(new 
             InputStreamReader(channel.getInputStream())); 
             ((ChannelExec)channel).setCommand("command");
             ((ChannelExec)channel).setErrStream(System.err);

             channel.connect();

             if(channel.isConnected()) {

                System.out.println("Channel is connected!");
            }

             String line;

                    while((line = br.readLine()) != null) {
                    System.out.println(line);
                    }

And console output:

Connected host A! Connected host B! Channel is connected!

Problem: I got nothing printed (System.out.println(line);)

There is a way to get that stream from exec channel over portforwarding ? Thanks for your help

Answer 1

get/setInputStream and get/setOutputStream only concern the standard input/output of the command, nothing to do with port forwarding. The port forwarding is done through two functions setPortForwardingL and setPortForwardingR.

You should have something like that in your code.

int assinged_port=session.setPortForwardingL(lport, rhost, rport);

As always, there is very few documentation on JSCH but a lot of detailed examples for L forwarding and R forwarding

The port forwarding is done on the session so I'm not sure you also need an active connection. But if you do, you should consider opening a 'shell' connection instead of an 'exec'. Then you wouldn't have to run a useless command just to maintain the connection.

PS: Some code is missing so it's difficult to say something precise on the example given in the question.

Answer 2

Thanks for your help. I solved it using Pipes, i share what i did:

  PipedInputStream en = new PipedInputStream();
  pin = new PipedOutputStream((PipedInputStream) en);
  BufferedReader br = new BufferedReader(new InputStreamReader((PipedInputStream) 
  channel.getInputStream()));

  channel.connect(5*1000);     


  String received=null;
  while((received=br.readLine())!=null) {
      System.out.println(received);
  }