CODEWITHSUNDEEP
c#node.jssshssh.netssh2
Fizz
Fizz

Reputation: 3487

Possible to have C# SSH client communicate with a NodeJS SSH Server?

I have a C# application that needs to run certain commands on a piece of hardware over SSH. The application is using SSH.Net to make the connection, send the command, and the read the result. I have this working if I connect to my local machine using OpenSSH. Finally, I wanted to go a step further and setup my own SSH server so I could simulate multiple hardware devices at one time (need to simulate having 50+ devices to SSH into).

For this I have setup a simple SSH server using nodejs and the ssh2 package. So far I have the client connected, authenticated (all connections are accepted for now), and I can see a session object being created. Although where I'm hitting a wall is with the execution of commands sent by the client. I noticed that ssh2 has an event for exec on the session object but this never seems to trigger (regardless of what i put in SSH.Net's ShellStream).

The C# client code that initiates the connection is the following (command is already defined that the command string to be executed):

using(SshClient client = new SshClient(hostname, port, username, password))
{
    try
    {
        client.ErrorOccurred += Client_ErrorOccurred;
        client.Connect();

        ShellStream shellStream = client.CreateShellStream("xterm", Columns, Rows, Width, Height, BufferSize, terminalModes);

        var initialPrompt = await ReadDataAsync(shellStream);

        // The command I write to the stream will get executed on OpenSSH
        // but not on the nodejs SSH server
        shellStream.WriteLine(command);
        var output = await ReadDataAsync(shellStream);
        var results = $"Command: {command} \nResult: {output}";

        client.Disconnect();

        Console.WriteLine($"Prompt: {initialPrompt} \n{results}\n");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Exception during SSH connection: {ex.ToString()}");
    }
}

The nodejs server code that set ups the ssh2 server is following:

new ssh2.Server({
  hostKeys: [fs.readFileSync('host.key')]
}, function(client) {
  console.log('Client connected!');

  client.on('authentication', function(ctx) {
    ctx.accept();
  }).on('ready', function() {
    console.log('Client authenticated!');

    client.on('session', function(accept, reject) {
      var session = accept();

      // Code gets here but never triggers the exec
      session.once('exec', function(accept, reject, info) {
        console.log('Client wants to execute: ' + inspect(info.command));
        var stream = accept();
        stream.write('returned result\n');
        stream.exit(0);
        stream.end();
      });
    });
  }).on('end', function() {
    console.log('Client disconnected');
  });
}).listen(port, '127.0.0.1', function() {
  console.log('Listening on port ' + this.address().port);
});

I have seen various ssh2 client examples invoking a client.exec function but I was assuming that it did not matter that my client was not using the ssh2 node package. Is there something that I'm missing here?

Upvotes: 3

Views: 820

Answers (1)

Martin Prikryl
Martin Prikryl

Reputation: 202534

The "exec" Node.js server session event is for "non-interactive (exec) command execution". By which they most likely mean SSH "exec" channel (which is intended for "non-interactive command execution").

To execute a command using "exec" SSH channel in SSH.NET, use SshClient.RunCommand.

On the contrary SshClient.CreateShellStream uses SSH "shell" channel, which is intended for implementing an interactive shell session.

For that, you need to handle "shell" Node.js server session event.

Upvotes: 1

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