Running a process interactively in Dart

broadcasted_stdin.dart

library broadcasted_stdin;

import 'dart:async';
import 'dart:io' as io;

class InteractiveProcess {
  Future<int> get whenExits => _whenExits;

  final BroadcastedStdin _stdin;
  Future<int> _whenExits;

  /**
   * This is the same as Process.start except it runs interactively with the
   * user.
   */
  InteractiveProcess(this._stdin, String executable,
                     List<String> arguments, {String workingDirectory}) {
    Future<io.Process> process;
    process = io.Process.start(executable, arguments,
                               workingDirectory: workingDirectory);
    _whenExits = process.then(_enableProcessInteraction);
  }

  Future<int> _enableProcessInteraction(io.Process process) {
    io.stdout.addStream(process.stdout);
    io.stderr.addStream(process.stderr);
    process.stdin.addStream(_stdin.stream);
    return process.exitCode;
  }
}

/**
 * A [BroadcastedStdin] allows for stdin to be listened to multiple times. This
 * solves the problem of wanting to pipe stdin to multiple processes.
 */
class BroadcastedStdin {
  Stream<List<int>> get stream => _stdin;

  static StreamSubscription _broadcastSubscript;
  static BroadcastedStdin _instance;
  Stream _stdin = io.stdin.asBroadcastStream(onListen: _onBroadcastListen);

  factory BroadcastedStdin() {
    if (_instance == null) {
      _instance = new BroadcastedStdin._();
    }

    return _instance;
  }

  BroadcastedStdin._();

  /**
   * This will kill all instances of this listener. Call this when program
   * execution needs to finished. Failing to call this will result in a program
   * that will never end as it will be stuck waiting on user input.
   */
  static void killAll() {
    if (_broadcastSubscript != null) {
      _broadcastSubscript.cancel();
    }
  }

  static void _onBroadcastListen(StreamSubscription streamSubscript) {
    _broadcastSubscript = streamSubscript;
  }
}