Implementing SSH shell terminal in webapp using JSch

Question

I am trying to implement a shell terminal in a webapp using websocket in spring. I am able to send a single command to the JSch "exec" channel and send the output back to the websocket.

The problem I am having is:

I am not able to retain the state of the shell like working directory, when I send a second command. How can I retain the previous state? I have tried using the same session but it does not work.

 public String sendCommand(String command) {
     StringBuilder outputBuffer = new StringBuilder();

     try {
         Channel channel = sesConnection.openChannel("exec");
         ((ChannelExec) channel).setCommand(command);
         InputStream commandOutput = channel.getInputStream();
         channel.connect();
         int readByte = commandOutput.read();

         while (readByte != 0xffffffff) {
             outputBuffer.append((char) readByte);
             readByte = commandOutput.read();
         }

         channel.disconnect();
     } catch (IOException ioX) {
         logWarning(ioX.getMessage());
         return null;
     } catch (JSchException jschX) {
         logWarning(jschX.getMessage());
         return null;
     }

     return outputBuffer.toString();
 }

To send back to the websocket, in the controller I have :

private SSHManager getSSHInstance() {
    String errorMessage = null;

    if (sshInstance == null) {
        sshInstance = new SSHManager(username, password, host, "", port);
        errorMessage = sshInstance.connect();
        System.out.println("Instance created");
        if (errorMessage != null) {
            throw new RuntimeException("Could not create an ssh connection");
        }
    }
    System.out.println("Returning created instance");
    return sshInstance;
}

@MessageMapping("/user")
@SendTo("/topic/user")
public UserResponse getResponse(String command) {

    SSHManager currInstance = getSSHInstance();
    String result = currInstance.sendCommand(command);
    return new UserResponse(result);
}

I tried using the "shell" channel instead of "exec" which worked for getting the input and output through standard input and output stream but I could not get the real-time input and output from/back to the websocket and UI. I am not sure how to proceed from here. Any direction on where/what to look would be very helpful.

Here is my code for the SSH terminal through standard input/output stream:

import com.jcraft.jsch.*;

public class Terminal{
    public static void main(String[] args){

        try{
            JSch jsch=new JSch();

            String host = "127.0.0.1";
            String user = "user";
            String password = "pass";

            Session session=jsch.getSession(user, host, 5679);

            session.setPassword(password);
            session.setConfig("StrictHostKeyChecking", "no");
            session.connect(10000);

            Channel channel=session.openChannel("shell");

            channel.setInputStream(System.in);
            channel.setOutputStream(System.out);
            channel.connect(3*1000);
        }
        catch(Exception e){
            System.out.println(e.getMessage());
        }
    }
}

To send the command from the UI, I have the following:

function sendCommand() {
    if (stompClient != null) {
        stompClient.send("/app/user", {}, JSON.stringify({'command': $("#command").val()}));
    }
}

score 2 · Accepted Answer · answered Jan 19 '21 at 06:44

If you want to implement an interactive shell, you have to use the "shell" channel, not the "exec" channel. The "exec" channel is intended for automating individual commands.

Some references:

Implementing SSH shell terminal in webapp using JSch

1 Answers1