Use StreamChannel.

lib/src/channel_manager.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:stream_channel/stream_channel.dart';
+
+/// Wraps a [StreamChannel] and handles logic that's shared between [Server],
+/// [Client], and [Peer].
+///
+/// These classes don't provide the user direct access to a
+/// [StreamSubscription]. Instead, they use the future returned by [listen] to
+/// notify the user of the remote endpoint closing or producing an error.
+class ChannelManager {
+  /// The name of the component whose channel is wrapped (e.g. "Server").
+  ///
+  /// Used for error reporting.
+  final String _name;
+
+  /// The underlying channel.
+  final StreamChannel _channel;
+
+  /// Returns a [Future] that completes when the connection is closed.
+  ///
+  /// This is the same future that's returned by [listen].
+  Future get done => _doneCompleter.future;
+  final _doneCompleter = new Completer();
+
+  /// Whether the underlying communication channel is closed.
+  bool get isClosed => _doneCompleter.isCompleted;
+
+  /// Whether [listen] has been called.
+  bool _listenCalled = false;
+
+  /// Whether [close] has been called.
+  ///
+  /// Note that [isClosed] tracks whether the underlying connection is closed,
+  /// whereas this tracks only whether it was explicitly closed from this end.
+  bool _closeCalled = false;
+
+  ChannelManager(this._name, this._channel);
+
+  /// Starts listening to the channel.
+  ///
+  /// The returned Future will complete when the input stream is closed. If the
+  /// input stream emits an error, that will be piped to the returned Future.
+  Future listen(void handleInput(input)) {
+    if (_listenCalled) {
+      throw new StateError("Can only call $_name.listen() once.");
+    }
+    _listenCalled = true;
+
+    _channel.stream.listen(handleInput,
+        onError: (error, stackTrace) {
+          _doneCompleter.completeError(error, stackTrace);
+          _channel.sink.close();
+        },
+        onDone: _doneCompleter.complete,
+        cancelOnError: true);
+
+    return done;
+  }
+
+  /// Emit [event].
+  void add(event) {
+    if (isClosed && !_closeCalled) return;
+    _channel.sink.add(event);
+  }
+
+  /// Closes the channel.
+  Future close() {
+    _closeCalled = true;
+    if (!_doneCompleter.isCompleted) {
+      _doneCompleter.complete(_channel.sink.close());
+    }
+    return done;
+  }
+}