Make the event-handler handle backpreasure.

runtime/bin/socket_patch.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.
 
 patch class RawServerSocket {
   /* patch */ static Future<RawServerSocket> bind(address,
                                                   int port,
                                                   {int backlog: 0,
                                                    bool v6Only: false}) {
     return _RawServerSocket.bind(address, port, backlog, v6Only);
@@ skipping 337 matching lines @@
   static const int ERROR_EVENT = 2;
   static const int CLOSED_EVENT = 3;
   static const int DESTROYED_EVENT = 4;
   static const int FIRST_EVENT = READ_EVENT;
   static const int LAST_EVENT = DESTROYED_EVENT;
   static const int EVENT_COUNT = LAST_EVENT - FIRST_EVENT + 1;
 
   static const int CLOSE_COMMAND = 8;
   static const int SHUTDOWN_READ_COMMAND = 9;
   static const int SHUTDOWN_WRITE_COMMAND = 10;
+  static const int RETURN_TOKEN_COMMAND = 11;
   static const int FIRST_COMMAND = CLOSE_COMMAND;
-  static const int LAST_COMMAND = SHUTDOWN_WRITE_COMMAND;
+  static const int LAST_COMMAND = RETURN_TOKEN_COMMAND;
 
   // Type flag send to the eventhandler providing additional
   // information on the type of the file descriptor.
   static const int LISTENING_SOCKET = 16;
   static const int PIPE_SOCKET = 17;
   static const int TYPE_NORMAL_SOCKET = 0;
   static const int TYPE_LISTENING_SOCKET = 1 << LISTENING_SOCKET;
   static const int TYPE_PIPE = 1 << PIPE_SOCKET;
   static const int TYPE_TYPE_MASK = TYPE_LISTENING_SOCKET | PIPE_SOCKET;
 
@@ skipping 440 matching lines @@
           if (!isClosing) {
             reportError(nativeGetError(), "");
           }
         } else if (!isClosed) {
           // If the connection is closed right after it's accepted, there's a
           // chance the close-handler is not set.
           if (handler != null) handler();
         }
       }
     }
+    if (eventPort != null && !isClosing && !isClosed) {
+      sendToEventHandler(1 << RETURN_TOKEN_COMMAND);
+    }
   }
 
   void setHandlers({read, write, error, closed, destroyed}) {
     eventHandlers[READ_EVENT] = read;
     eventHandlers[WRITE_EVENT] = write;
     eventHandlers[ERROR_EVENT] = error;
     eventHandlers[CLOSED_EVENT] = closed;
     eventHandlers[DESTROYED_EVENT] = destroyed;
   }
 
   void setListening({read: true, write: true}) {
     sendReadEvents = read;
     sendWriteEvents = write;
     if (read) issueReadEvent();
     if (write) issueWriteEvent();
-    if (eventPort == null) {
+    if (eventPort == null && !isClosing && !isClosed) {
       int flags = typeFlags & TYPE_TYPE_MASK;
       if (!isClosedRead) flags |= 1 << READ_EVENT;
       if (!isClosedWrite) flags |= 1 << WRITE_EVENT;
       sendToEventHandler(flags);
     }
   }
 
   Future close() {
     if (!isClosing && !isClosed) {
       sendToEventHandler(1 << CLOSE_COMMAND);
@@ skipping 36 matching lines @@
       if (isClosedWrite) {
         close();
       } else {
         sendToEventHandler(1 << SHUTDOWN_READ_COMMAND);
       }
       isClosedRead = true;
     }
   }
 
   void sendToEventHandler(int data) {
-    assert(!isClosed);
+    assert(!isClosing);
     connectToEventHandler();
     _EventHandler._sendData(this, eventPort, data);
   }
 
   void connectToEventHandler() {
     if (eventPort == null) {
       eventPort = new RawReceivePort(multiplex);
       _SocketsObservatory.add(this);
     }
   }
@@ skipping 847 matching lines @@
                        String address,
                        List<int> in_addr,
                        int port) {
   return new Datagram(
       data,
       new _InternetAddress(address, null, in_addr),
       port);
 }
 
 String _socketsStats() => _SocketsObservatory.toJSON();