Is it possible to cancel SshCommand?

[MistyKuu]

There is CancelAsync method but it seems to only cancel connection between client and server. Is there a way to stop the command from running? Similarly to CTRL+C while running in BASH shell.

[lifeincha0s]

No, using RunCommand, the Execute method blocks until all data is returned from the command, so nothing can be sent to stop the command. You need to use CreateShellStream to kill a running process, which allows writing data while reading data. You can then send Ctrl^C (\x3) to the output stream and kill the process.

[bsmithcompsci]

I solved this after a long day trying to force this to cancel, by hijacking the SSHCommand via reflection. This is nasty, please contributors/maintainers make a proper fix for this, this hurts production code.

Answer

token.Register(() => {
  FieldInfo? _sessionErrorOccuredWaitHandleField = sshCommand.GetType().GetField("_sessionErrorOccuredWaitHandle", BindingFlags.NonPublic | BindingFlags.Instance);
  if (_sessionErrorOccuredWaitHandleField != null)
  {
      object? _sessionErrorOccuredWaitHandle = _sessionErrorOccuredWaitHandleField.GetValue(sshCommand);
      MethodInfo[] methods = _sessionErrorOccuredWaitHandleField.FieldType.GetMethods();
      MethodInfo? Set = _sessionErrorOccuredWaitHandleField.FieldType.GetMethod("Set");
      if (Set != null)
          Set.Invoke(_sessionErrorOccuredWaitHandle, new object[] { });
  }
   sshCommand.CancelAsync();
   client.Disconnect();
});

Diagnoses

To start, what's the issue. EndExecute() blocks the thread. This as expected to do, but we should be able to have a CancellationToken to cancel a asynchronous task.

Using CancelAsync() just calls a dispose.... not greatly helpful.

Okay, let's kill the client Disconnect()... nothing.... Well, let's understand how the Client communicates to the SSHCommand; we can see that the ctor of SSHCommand will append delegates for client callbacks.

And we can see that, Session_Disconnect() calls something called _sessionErrorOccuredWaitHandle.Set(), which is interesting.

So, I believe there's a bug on the disposal of SSHCommand, when it comes to _isDisposed I cannot find exactly why, this may be the case.

Okay, so lets get our hands a little dirty. Let's touch the AsyncWaitHandle variable on sshCommand var. Well, we cannot simply Close() on the AsyncWaitHandle.... because that also will just do nothing....

But... while diving into SSH.NET code, I found something interesting that I can hijack with some reflection.
DONT TRY AT HOME

I can get around this problem today with some nasty hacks, but I hope in the future SSH.NET has a fix for this.
I hope this diagnoses was informational. Thanks, and take care!