Implement PTY APIs

[DartBot]

This issue was originally filed by @kaendfinger

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dart:io should support PTYs. This would allow others to write things like CI Servers that can act as a terminal so that they can capture ANSI escape codes.

https://en.wikipedia.org/wiki/Pseudoterminal

Implementation in other languages:

NodeJS: https://github.com/chjj/pty.js Java: https://github.com/traff/pty4j

What if I wanted to write an IDE like WebStorm in Dart. WebStorm has a built-in terminal, which uses PTYs.

This is something that would greatly enhance dart:io. It could allow for example to build a fully-featured command line shell! I attempted to write a shell in Dart, but quickly ran into this problem.

If we want to be able to use Dart for large command line tools like shells, this is essential. It is also something that should be in the standard library, simply because it requires a lot of native code, and is cross platform (not platform specific).

[iposva-google]

Added Library-IO, Area-Library, Triaged labels.

[natebosch]

Is there any chance of this happening? Our new approach for build tools would see a benefit.

We should be able to set up a PTY in linux/mac - can we do the same in Windows?

[tejainece]

Is this fixed by https://github.com/dart-lang/sdk/issues/24716 and https://github.com/dart-lang/sdk/commit/6523896c6fb27a7ead2ced038da4d15164d894d4?

[kevmoo]

Is this fixed by #24716 and 6523896?

@zanderso ? @a-siva ?

[natebosch]

No, #24716 mitigated this issue but it's forwarding the same TTY, rather than a pseudo TTY.

Having PTY APIs would open up new possibilities but the priority is lower given that the direct solution works in many scenarios.

[tejainece]

For the time being, one can use script command on linux.

[xtyxtyx]

I've uploaded a patch that implements the PTY api: https://dart-review.googlesource.com/c/sdk/+/198940

In this patch a new process start mode ProcessStartMode.pseudoTerminal is added as well as a new method on Process that resizes the pseudo terminal.

void main() async {
  final process = await Process.start(
    'bash',
    [],
    mode: ProcessStartMode.pseudoTerminal,
  );

  // ...

  process.resizeTerminal(110, 30);
}

In this new mode a pseudo terminal is created and used to communicate with the child process. The parent process can use stdin and stdout to read from/write to the pseudo terminal.

The Windows implementation uses the ConPTY api which is available since Windows 10 1809 and Windows Server 2019, otherwise an UnsupportedError would be thrown.

[azenla]

@xtyxtyx That's awesome!

I still consider (after ~6 years) this important for inclusion in Dart, the script command workaround is not very portable, and in fact the last time I checked (a long time ago) you need to use different arguments on macOS versus Linux.

[zanderso]

/cc @aam