Implement Process methods from dart:io

[jimmyff]

Hey, I'm using this library in the context of a firebase cloud function. I'm trying to utilise imagemagik from the cloud function. In JS this would be exec(...) and with dart:io i'd use Process.run(...). I can't find an alternative in node_io?

Thanks

[pulyaevskiy]

Hi, you are right. I haven't had a chance to implement Process interface from dart:io yet.

There are bindings for Node's child_process module in package:node_interop/child_process.dart though.

I can take a look at this later this week or during the weekend. You are also welcome to submit a pull request if you need this sooner.

[jimmyff]

ah okay great, I think package:node_interop/child_process.dart should cover my needs! Thanks very much

[jimmyff]

Hey @pulyaevskiy I'm having difficulty with assigning a listener for ChildProcess events. Don't suppose you can see anything obvious?

    final resize = childProcess.spawn('convert', [ ... ]);
    resize
      ..on('error', (error) { ... })
      ..on('close', (int code, String signal) { ...  })
      ..on('exit', (int code, String signal) { ... });

I'm getting the following error:

TypeError: "listener" argument must be a function
    at _addListener (events.js:216:11)
    at ChildProcess.addListener (events.js:276:10)
    at ch.b8 (/user_code/build/node/functions.dart.js:334:29)
    at J.c4 (/user_code/build/node/functions.dart.js:7921:36)
    at /user_code/build/node/functions.dart.js:7823:3
    at oD.a (/user_code/build/node/functions.dart.js:2372:72)
    at oD.$2 (/user_code/build/node/functions.dart.js:2521:23)
    at og.$1 (/user_code/build/node/functions.dart.js:2517:30)
    at nm.c6 (/user_code/build/node/functions.dart.js:3261:23)
    at mH.$0 (/user_code/build/node/functions.dart.js:2844:14)

I've tried using the other EventEmitter methods like once, addListener etc but not having any luck.

Thanks

[pulyaevskiy]

Hey, yes.

Any function you pass from Dart to JS must be wrapped with allowInterop or allowInteropCaptureThis.

In your example it would be something like:

    final resize = childProcess.spawn('convert', [ ... ]);
    resize
      ..on('error', allowInterop((error) { ... }))
      ..on('close', allowInterop((int code, String signal) { ...  }))
      ..on('exit', allowInterop((int code, String signal) { ... }));

[jimmyff]

Ahh - I did briefly consider that but I assumed that the library would be handling that.

Having said that I had the child_prcess.dart open and could see what it was doing, clearly not got my head in gear for 2019 yet! :)

Thanks

[pulyaevskiy]

but I assumed that the library would be handling that.

node_interop package only provides JS interop bindings based on package:js. You can read how bindings work in the docs of that package.

This is why I also created node_io which hides all the complexity of dealing with JS interop by wrapping Node.js APIs with standard dart:io interfaces.

I'll try to find some time for the Process APIs in node_io in the next couple of weeks.