Pausing readline pauses SIGINTs

[devsnek]

So lets say you are making a cute little CLI app, and you write this code:

const rl = readline.createInterface(...);
rl.on('SIGINT', () => {
  console.log('bye!');
  process.exit();
});
rl.on('line', (line) => {
  rl.pause();
  compute(line).then(() => {
    rl.resume();
  });
});

You will discover that, while the interface is paused, the SIGINT event stops working. This is because pausing readline just pauses the underlying input stream. To fix this I think we would need to decouple that and have readline have an internal buffer of events. Alternatively we could say that people just shouldn't use readline pausing in this case, and do the line buffering themselves (that being said, I don't know how you would do this yourself or if it is even possible).

cc @nodejs/readline

[devsnek]

I came up with a weird hack where I create a second instance of stdin using new tty.ReadStream(process.stdin.fd, ...) and watch for Ctrl+C events using it. Not sure how portable it is.

[bnoordhuis]

Does making.pause() and .resume() call this._setRawMode(on) with on=false and on=true respectively work?

(TBD how to interact with the SIGCONT handler.)

[devsnek]

@bnoordhuis well the ^C seems to be handled, but by node instead of bubbling through the readline event. I guess with some additional plumbing this could work?

Also worth noting that because its not in raw mode, stdin gets echoed back to the terminal while its paused.

[bnoordhuis]

the ^C seems to be handled, but by node instead of bubbling through the readline event

I'd say that's the expected behavior, given that the readline instance is paused. I'd find it surprising if it did emit an event.

because its not in raw mode, stdin gets echoed back to the terminal while its paused

That can be fixed by just flipping the ISIG bit with a call to tcsetattr(). Libuv only knows how to switch from fully cooked to fully raw mode but node can be cleverer about that.