Command line keyboard events

[idraper]

Dart SDK Version: Dart VM version: 2.4.0
OS: Windows 10 x64

I am working on a command line dart application and am looking for the ability to detect keyboard events. For example, if the user presses ctrl (or cmd), this would cause different behavior as the program executes tasks. I have found a few instances that seem to get close, but do not have the complete extendability I am looking for. Specifically:

• https://pub.dev/packages/hotkey - this one is simply out of date, but also seems like it is only for html applications, same as current keyboard support (the dart:html library).
• POSIX signal handling (SIGINT, SIGTERM, SIGHUP, etc) #15188 - this is useful for special cases but does not extend beyond signals

I tried a very simple test, but similarly, it does not get very far:

import 'dart:io';
void main() {
  stdin.echoMode = false;
  stdin.lineMode = false;

  stdin.listen((data) {
    print (data);
  });
}

since it only prints out on pressing down (cannot detect holding a key) and does not recognize when the shift or ctrl key are pressed alone since they do not write alone.

Another thought that I have not tried yet was starting a separate process and try to detect keyboard input through a separate pipe, but this seems clunky and does not solve the root problem of lower-level access to keyboard interaction.

I am wondering if there is planned support for handling more advanced keyboard combinations (non-blocking) with special keys like ctrl and shift for command-line written dart applications. If there is not, whether any community libraries have been written. Lastly, if the answer is no to both questions, possible (preferably simple 😄) implementations. What would be of most importance is regarding holding ctrl or shift. Thanks!

[devoncarew]

If lineMode doesn't do what you want, then your use case likely isn't covered by dart:io currently. Routing to the dart:io owners.

[natebosch]

does not recognize when the shift or ctrl key are pressed alone since they do not write alone.

This isn't, as far as I'm aware, information available to something running inside of a shell. The combined input (like control + some character) is available, but not a modifier key pressed on its own.

handling more advanced keyboard combinations (non-blocking) with special keys like ctrl and shift

You'll get different bytes on stdin depending on whether a modifier was used, but you won't get things like keydown/keyup. These things aren't possible in a terminal.

[idraper]

Thanks for the responses. I kinda figured this would be the case and have been working towards a new design to avoid keyboard input. However... out of curiosity:

Would it be possible to write an asynchronous native extension (os specific) to detect key presses (eg KeyUp/KeyDown)? Having not written a native extension yet (and just noticed them), are they similar to Python extensions? At first glance, it looks like a very similar concept (sorry if this is slightly off-topic).

[natebosch]

Would it be possible

I'm not sure - I don't know the details of having something running that has full access to read from the keyboard. I'd imagine we won't have a full answer to that unless Flutter desktop becomes fully supported.

I think for now this isn't something we want to try to bake in to the Dart SDK so I'll close the issue - you may want to file an issue against flutter desktop asking about this support.

[timsneath]

Adding @mit-mit; might be interesting to consider this in the context of Dart native console applications. This also affects our ability to read keyboard arrow keys. I think we want at some point to be able to retrieve keyboard scan codes.

(I also ran into this, for what it's worth.)

[jtmcdole]

I, too, have run into the need for reading arrow keys from the command line (interactive dart shell programs)

Edit: I'm able to get when the arrow keys are pressed (yay), but I don't know when they are released, nor can I get modifier keys other than "Alt".

[mit-mit]

Re-opening as desktop is now indeed a supported platform

[mit-mit]

cc @a-siva

[timsneath]

Just in case it's handy, @jtmcdole, I wound up writing a console package that solves for a lot of command-line problems. It's PM-quality code, so your mileage may vary :) but it's sophisticated enough to support a port of a simple full-screen text editor to Dart.

[jtmcdole]

That's awesome! FYI; There is also https://github.com/DirectMyFile/console.dart I'm not sure this handle modifier keys though.