Reapply "Active stream subscriptions".

sdk/lib/async/stream_pipe.dart

Index: sdk/lib/async/stream_pipe.dart
diff --git a/sdk/lib/async/stream_pipe.dart b/sdk/lib/async/stream_pipe.dart
index e089f6ce88dce9180a110615d26ec6df7d2b2ab0..e5aca172415406ea65dbe4da256ade70f2649958 100644
--- a/sdk/lib/async/stream_pipe.dart
+++ b/sdk/lib/async/stream_pipe.dart
@@ -69,84 +69,26 @@ abstract class _ForwardingStream<S, T> extends Stream<T> {
 
   // Override the following methods in subclasses to change the behavior.
 
-  void _handleData(S data, _EventOutputSink<T> sink) {
+  void _handleData(S data, _EventSink<T> sink) {
     var outputData = data;
-    sink._sendData(outputData);
+    sink._add(outputData);
   }
 
-  void _handleError(error, _EventOutputSink<T> sink) {
-    sink._sendError(error);
+  void _handleError(error, _EventSink<T> sink) {
+    sink._addError(error);
   }
 
-  void _handleDone(_EventOutputSink<T> sink) {
-    sink._sendDone();
+  void _handleDone(_EventSink<T> sink) {
+    sink._close();
   }
 }
 
 /**
- * Common behavior of [StreamSubscription] classes.
- *
- * Stores and allows updating of the event handlers of a [StreamSubscription].
- */
-abstract class _BaseStreamSubscription<T> implements StreamSubscription<T> {
-  // TODO(ahe): Restore type when feature is implemented in dart2js
-  // checked mode. http://dartbug.com/7733
-  var /* _DataHandler<T> */ _onData;
-  _ErrorHandler _onError;
-  _DoneHandler _onDone;
-
-  _BaseStreamSubscription(this._onData,
-                          this._onError,
-                          this._onDone) {
-    if (_onData == null) _onData = _nullDataHandler;
-    if (_onError == null) _onError = _nullErrorHandler;
-    if (_onDone == null) _onDone = _nullDoneHandler;
-  }
-
-  // StreamSubscription interface.
-  void onData(void handleData(T event)) {
-    if (handleData == null) handleData = _nullDataHandler;
-    _onData = handleData;
-  }
-
-  void onError(void handleError(error)) {
-    if (handleError == null) handleError = _nullErrorHandler;
-    _onError = handleError;
-  }
-
-  void onDone(void handleDone()) {
-    if (handleDone == null) handleDone = _nullDoneHandler;
-    _onDone = handleDone;
-  }
-
-  void pause([Future resumeSignal]);
-
-  void resume();
-
-  void cancel();
-
-  Future asFuture([var futureValue]) {
-    _FutureImpl<T> result = new _FutureImpl<T>();
-
-    // Overwrite the onDone and onError handlers.
-    onDone(() { result._setValue(futureValue); });
-    onError((error) {
-      cancel();
-      result._setError(error);
-    });
-
-    return result;
-  }
-}
-
-
-/**
  * Abstract superclass for subscriptions that forward to other subscriptions.
  */
 class _ForwardingStreamSubscription<S, T>
-    extends _BaseStreamSubscription<T> implements _EventOutputSink<T> {
+    extends _BufferingStreamSubscription<T> {
   final _ForwardingStream<S, T> _stream;
-  final bool _cancelOnError;
 
   StreamSubscription<S> _subscription;
 
@@ -154,60 +96,46 @@ class _ForwardingStreamSubscription<S, T>
                                 void onData(T data),
                                 void onError(error),
                                 void onDone(),
-                                this._cancelOnError)
-      : super(onData, onError, onDone) {
-    // Don't unsubscribe on incoming error, only if we send an error forwards.
+                                bool cancelOnError)
+      : super(onData, onError, onDone, cancelOnError) {
     _subscription =
         _stream._source.listen(_handleData,
                                onError: _handleError,
                                onDone: _handleDone);
   }
 
-  // StreamSubscription interface.
-
-  void pause([Future resumeSignal]) {
-    if (_subscription == null) return;
-    _subscription.pause(resumeSignal);
-  }
-
-  void resume() {
-    if (_subscription == null) return;
-    _subscription.resume();
-  }
+  // _StreamSink interface.
+  // Transformers sending more than one event have no way to know if the stream
+  // is canceled or closed after the first, so we just ignore remaining events.
 
-  bool get isPaused {
-    if (_subscription == null) return false;
-    return _subscription.isPaused;
+  void _add(T data) {
+    if (_isClosed) return;
+    super._add(data);
   }
 
-  void cancel() {
-    if (_subscription != null) {
-      _subscription.cancel();
-      _subscription = null;
-    }
+  void _addError(Object error) {
+    if (_isClosed) return;
+    super._addError(error);
   }
 
-  // _EventOutputSink interface. Sends data to this subscription.
+  // StreamSubscription callbacks.
 
-  void _sendData(T data) {
-    _onData(data);
+  void _onPause() {
+    if (_subscription == null) return;
+    _subscription.pause();
   }
 
-  void _sendError(error) {
-    _onError(error);
-    if (_cancelOnError) {
-      _subscription.cancel();
-      _subscription = null;
-    }
+  void _onResume() {
+    if (_subscription == null) return;
+    _subscription.resume();
   }
 
-  void _sendDone() {
-    // If the transformation sends a done signal, we stop the subscription.
+  void _onCancel() {
     if (_subscription != null) {
-      _subscription.cancel();
+      StreamSubscription subscription = _subscription;
       _subscription = null;
+      subscription.cancel();
     }
-    _onDone();
   }
 
   // Methods used as listener on source subscription.
@@ -241,16 +169,16 @@ class _WhereStream<T> extends _ForwardingStream<T, T> {
   _WhereStream(Stream<T> source, bool test(T value))
       : _test = test, super(source);
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     bool satisfies;
     try {
       satisfies = _test(inputEvent);
     } catch (e, s) {
-      sink._sendError(_asyncError(e, s));
+      sink._addError(_asyncError(e, s));
       return;
     }
     if (satisfies) {
-      sink._sendData(inputEvent);
+      sink._add(inputEvent);
     }
   }
 }
@@ -267,15 +195,15 @@ class _MapStream<S, T> extends _ForwardingStream<S, T> {
   _MapStream(Stream<S> source, T transform(S event))
       : this._transform = transform, super(source);
 
-  void _handleData(S inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(S inputEvent, _EventSink<T> sink) {
     T outputEvent;
     try {
       outputEvent = _transform(inputEvent);
     } catch (e, s) {
-      sink._sendError(_asyncError(e, s));
+      sink._addError(_asyncError(e, s));
       return;
     }
-    sink._sendData(outputEvent);
+    sink._add(outputEvent);
   }
 }
 
@@ -288,15 +216,15 @@ class _ExpandStream<S, T> extends _ForwardingStream<S, T> {
   _ExpandStream(Stream<S> source, Iterable<T> expand(S event))
       : this._expand = expand, super(source);
 
-  void _handleData(S inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(S inputEvent, _EventSink<T> sink) {
     try {
       for (T value in _expand(inputEvent)) {
-        sink._sendData(value);
+        sink._add(value);
       }
     } catch (e, s) {
       // If either _expand or iterating the generated iterator throws,
       // we abort the iteration.
-      sink._sendError(_asyncError(e, s));
+      sink._addError(_asyncError(e, s));
     }
   }
 }
@@ -318,13 +246,13 @@ class _HandleErrorStream<T> extends _ForwardingStream<T, T> {
                     bool test(error))
       : this._transform = transform, this._test = test, super(source);
 
-  void _handleError(Object error, _EventOutputSink<T> sink) {
+  void _handleError(Object error, _EventSink<T> sink) {
     bool matches = true;
     if (_test != null) {
       try {
         matches = _test(error);
       } catch (e, s) {
-        sink._sendError(_asyncError(e, s));
+        sink._addError(_asyncError(e, s));
         return;
       }
     }
@@ -332,11 +260,11 @@ class _HandleErrorStream<T> extends _ForwardingStream<T, T> {
       try {
         _transform(error);
       } catch (e, s) {
-        sink._sendError(_asyncError(e, s));
+        sink._addError(_asyncError(e, s));
         return;
       }
     } else {
-      sink._sendError(error);
+      sink._addError(error);
     }
   }
 }
@@ -352,14 +280,14 @@ class _TakeStream<T> extends _ForwardingStream<T, T> {
     if (count is! int) throw new ArgumentError(count);
   }
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     if (_remaining > 0) {
-      sink._sendData(inputEvent);
+      sink._add(inputEvent);
       _remaining -= 1;
       if (_remaining == 0) {
         // Closing also unsubscribes all subscribers, which unsubscribes
         // this from source.
-        sink._sendDone();
+        sink._close();
       }
     }
   }
@@ -372,20 +300,20 @@ class _TakeWhileStream<T> extends _ForwardingStream<T, T> {
   _TakeWhileStream(Stream<T> source, bool test(T value))
       : this._test = test, super(source);
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     bool satisfies;
     try {
       satisfies = _test(inputEvent);
     } catch (e, s) {
-      sink._sendError(_asyncError(e, s));
+      sink._addError(_asyncError(e, s));
       // The test didn't say true. Didn't say false either, but we stop anyway.
-      sink._sendDone();
+      sink._close();
       return;
     }
     if (satisfies) {
-      sink._sendData(inputEvent);
+      sink._add(inputEvent);
     } else {
-      sink._sendDone();
+      sink._close();
     }
   }
 }
@@ -400,12 +328,12 @@ class _SkipStream<T> extends _ForwardingStream<T, T> {
     if (count is! int || count < 0) throw new ArgumentError(count);
   }
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     if (_remaining > 0) {
       _remaining--;
       return;
     }
-    return sink._sendData(inputEvent);
+    return sink._add(inputEvent);
   }
 }
 
@@ -416,23 +344,23 @@ class _SkipWhileStream<T> extends _ForwardingStream<T, T> {
   _SkipWhileStream(Stream<T> source, bool test(T value))
       : this._test = test, super(source);
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     if (_hasFailed) {
-      sink._sendData(inputEvent);
+      sink._add(inputEvent);
       return;
     }
     bool satisfies;
     try {
       satisfies = _test(inputEvent);
     } catch (e, s) {
-      sink._sendError(_asyncError(e, s));
+      sink._addError(_asyncError(e, s));
       // A failure to return a boolean is considered "not matching".
       _hasFailed = true;
       return;
     }
     if (!satisfies) {
       _hasFailed = true;
-      sink._sendData(inputEvent);
+      sink._add(inputEvent);
     }
   }
 }
@@ -448,10 +376,10 @@ class _DistinctStream<T> extends _ForwardingStream<T, T> {
   _DistinctStream(Stream<T> source, bool equals(T a, T b))
       : _equals = equals, super(source);
 
-  void _handleData(T inputEvent, _EventOutputSink<T> sink) {
+  void _handleData(T inputEvent, _EventSink<T> sink) {
     if (identical(_previous, _SENTINEL)) {
       _previous = inputEvent;
-      return sink._sendData(inputEvent);
+      return sink._add(inputEvent);
     } else {
       bool isEqual;
       try {
@@ -461,11 +389,11 @@ class _DistinctStream<T> extends _ForwardingStream<T, T> {
           isEqual = _equals(_previous, inputEvent);
         }
       } catch (e, s) {
-        sink._sendError(_asyncError(e, s));
+        sink._addError(_asyncError(e, s));
         return null;
       }
       if (!isEqual) {
-        sink._sendData(inputEvent);
+        sink._add(inputEvent);
         _previous = inputEvent;
       }
     }