Fix datagram issue where available is not correctly updated upon receive.

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 550 matching lines @@
   }
 
   Datagram receive() {
     if (isClosing || isClosed) return null;
     var result = nativeRecvFrom();
     if (result is OSError) {
       reportError(result, "Receive failed");
       return null;
     }
     if (result != null) {
-      if (Platform.isMacOS) {
-        // Mac includes the header size, so we need to query the actual
-        // available.
-        available = nativeAvailable();
-      } else {
-        available -= result.data.length;
-      }
+      // Read the next available. Available is only for the next datagram, not
+      // the sum of all datagrams pending, so we need to call after each
+      // receive. If available becomes > 0, the _NativeSocket will continue to
+      // emit read events.
+      available = nativeAvailable();
       totalRead += result.data.length;
     }
     readCount++;
     lastRead = timestamp;
     return result;
   }
 
   int write(List<int> buffer, int offset, int bytes) {
     if (buffer is! List) throw new ArgumentError();
     if (offset == null) offset = 0;
@@ skipping 1341 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();