Optmize detached socket to not contain a extra stream controller/subscription, but simly forward ca…

sdk/lib/io/http_parser.dart

Index: sdk/lib/io/http_parser.dart
diff --git a/sdk/lib/io/http_parser.dart b/sdk/lib/io/http_parser.dart
index 8856c103df260d6941f7fd3030594fb952218345..dee7371687749e0f3e0ae4bb8b65e22eaf254879 100644
--- a/sdk/lib/io/http_parser.dart
+++ b/sdk/lib/io/http_parser.dart
@@ -96,68 +96,119 @@ class _MessageType {
   static const int RESPONSE = 0;
 }
 
-class _HttpDetachedIncoming extends Stream<List<int>> {
-  StreamController<List<int>> controller;
-  final StreamSubscription subscription;
 
-  List<int> bufferedData;
-  bool paused;
+/**
+ * The _HttpDetachedStreamSubscription takes a subscription and some extra data,
+ * and makes it possible to "inject" the data in from of other data events
+ * from the subscription.
+ *
+ * It does so by overriding pause/resume, so that once the
+ * _HttpDetachedStreamSubscription is resumed, it'll deliver the data before
+ * resuming the underlaying subscription.
+ */
+class _HttpDetachedStreamSubscription implements StreamSubscription<List<int>> {
+  StreamSubscription<List<int>> _subscription;
+  List<int> _injectData;
+  bool _isCanceled = false;
+  int _pauseCount = 1;
+  Function _userOnData;
+  bool _scheduled = false;
+
+  _HttpDetachedStreamSubscription(this._subscription,
+                                  this._injectData,
+                                  this._userOnData);
+
+  bool get isPaused => _subscription.isPaused;
+
+  Future asFuture([futureValue]) => _subscription.asFuture(futureValue);
+
+  Future cancel() {
+    _isCanceled = true;
+    _injectData = null;
+    return _subscription.cancel();
+  }
 
-  Completer resumeCompleter;
+  void onData(void handleData(List<int> data)) {
+    _userOnData = handleData;
+    _subscription.onData(handleData);
+  }
 
-  _HttpDetachedIncoming(this.subscription, this.bufferedData) {
-    controller = new StreamController<List<int>>(
-        sync: true,
-        onListen: resume,
-        onPause: pause,
-        onResume: resume,
-        onCancel: () => subscription.cancel());
-    if (subscription == null) {
-      // Socket was already closed.
-      if (bufferedData != null) controller.add(bufferedData);
-      controller.close();
-    } else {
-      pause();
-      subscription
-          ..resume()
-          ..onData(controller.add)
-          ..onDone(controller.close)
-          ..onError(controller.addError);
-    }
+  void onDone(void handleDone()) {
+    _subscription.onDone(handleDone);
   }
 
-  StreamSubscription<List<int>> listen(void onData(List<int> event),
-                                       {Function onError,
-                                        void onDone(),
-                                        bool cancelOnError}) {
-    return controller.stream.listen(
-        onData,
-        onError: onError,
-        onDone: onDone,
-        cancelOnError: cancelOnError);
+  void onError(Function handleError) {
+    _subscription.onError(handleError);
   }
 
-  void resume() {
-    paused = false;
-    if (bufferedData != null) {
-      var data = bufferedData;
-      bufferedData = null;
-      controller.add(data);
-      // If the consumer pauses again after the carry-over data, we'll not
-      // continue our subscriber until the next resume.
-      if (paused) return;
+  void pause([Future resumeSignal]) {
+    if (_injectData == null) {
+      _subscription.pause(resumeSignal);
+    } else {
+      _pauseCount++;
+      if (resumeSignal != null) {
+        resumeSignal.whenComplete(resume);
+      }
     }
-    if (resumeCompleter != null) {
-      resumeCompleter.complete();
-      resumeCompleter = null;
+  }
+
+  void resume() {
+    if (_injectData == null) {
+      _subscription.resume();
+    } else {
+      _pauseCount--;
+      _maybeScheduleData();
     }
   }
 
-  void pause() {
-    paused = true;
-    if (resumeCompleter == null) {
-      resumeCompleter = new Completer();
-      subscription.pause(resumeCompleter.future);
+  void _maybeScheduleData() {
+    if (_scheduled) return;
+    if (_pauseCount != 0) return;
+    _scheduled = true;
+    scheduleMicrotask(() {
+      _scheduled = false;
+      if (_pauseCount > 0 || _isCanceled) return;
+      var data = _injectData;
+      _injectData = null;
+      // To ensure that 'subscription.isPaused' is false, we resume the
+      // subscription here. This is fine as potential events are delayed.
+      _subscription.resume();
+      if (_userOnData != null) {
+        _userOnData(data);
+      }
+    });
+  }
+}
+
+
+class _HttpDetachedIncoming extends Stream<List<int>> {
+  final StreamSubscription subscription;
+  final List<int> bufferedData;
+
+  _HttpDetachedIncoming(this.subscription, this.bufferedData);
+
+  StreamSubscription<List<int>> listen(void onData(List<int> event),
+                                       {Function onError,
+                                        void onDone(),
+                                        bool cancelOnError}) {
+    if (subscription != null) {
+      subscription
+        ..onData(onData)
+        ..onError(onError)
+        ..onDone(onDone);
+      if (bufferedData == null) {
+        return subscription..resume();
+      }
+      return new _HttpDetachedStreamSubscription(subscription,
+                                                 bufferedData,
+                                                 onData)
+        ..resume();
+    } else {
+      return new Stream.fromIterable(bufferedData)
+          .listen(onData,
+                  onError: onError,
+                  onDone: onDone,
+                  cancelOnError: cancelOnError);
     }
   }
 }