Adding to a closed sink throws.

sdk/lib/async/stream_transformers.dart

 // Copyright (c) 2013, 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.
 
 part of dart.async;
 
 /**
  * Wraps an [_EventSink] so it exposes only the [EventSink] interface.
  */
 class _EventSinkWrapper<T> implements EventSink<T> {
@@ skipping 202 matching lines @@
 
   _HandlerEventSink(
       this._handleData, this._handleError, this._handleDone, this._sink) {
     if (_sink == null) {
       throw new ArgumentError("The provided sink must not be null.");
     }
   }
 
   bool get _isClosed => _sink == null;
 
-  _reportClosedSink() {
-    // TODO(29554): throw a StateError, and don't just report the problem.
-    Zone.ROOT
-      ..print("Sink is closed and adding to it is an error.")
-      ..print("  See http://dartbug.com/29554.")
-      ..print(StackTrace.current.toString());
-  }
-
   void add(S data) {
     if (_isClosed) {
-      _reportClosedSink();
+      throw new StateError("Sink is closed");
     }
     if (_handleData != null) {
       _handleData(data, _sink);
     } else {
       _sink.add(data as T);
     }
   }
 
   void addError(Object error, [StackTrace stackTrace]) {
     if (_isClosed) {
-      _reportClosedSink();
+      throw new StateError("Sink is closed");
     }
     if (_handleError != null) {
       _handleError(error, stackTrace, _sink);
     } else {
       _sink.addError(error, stackTrace);
     }
   }
 
   void close() {
     if (_isClosed) return;
@@ skipping 68 matching lines @@
   StreamSubscription<T> listen(void onData(T event),
       {Function onError, void onDone(), bool cancelOnError}) {
     cancelOnError = identical(true, cancelOnError);
     StreamSubscription<T> result = _onListen(_stream, cancelOnError);
     result.onData(onData);
     result.onError(onError);
     result.onDone(onDone);
     return result;
   }
 }