Dart: Simplifies the handle watcher. Various cleanups and bugfixes.

mojo/public/dart/src/interface.dart

 // Copyright 2014 The Chromium Authors. 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 bindings;
 
 abstract class Interface {
   core.MojoMessagePipeEndpoint _endpoint;
   core.MojoHandle _handle;
   List _sendQueue;
   bool _isOpen;
 
-  Message handleMessage(MessageReader reader);
+  Future<Message> handleMessage(MessageReader reader);
 
-  Interface(this._endpoint) {
+  Interface(core.MojoMessagePipeEndpoint endpoint) :
+      _endpoint = endpoint,
+      _sendQueue = [],
+      _handle = new core.MojoHandle(endpoint.handle),
+      _isOpen = false;
+
+  Interface.fromHandle(int handle) {
+    _endpoint =
+        new core.MojoMessagePipeEndpoint(new core.RawMojoHandle(handle));
     _sendQueue = [];
     _handle = new core.MojoHandle(_endpoint.handle);
     _isOpen = false;
   }
 
+  void _doRead() {
+    assert(_handle.readyRead);
+
+    // Query how many bytes are available.
+    var result = _endpoint.query();
+    if (!result.status.isOk && !result.status.isResourceExhausted) {
+      // If something else happens, it means the handle wasn't really ready
+      // for reading, which indicates a bug in MojoHandle or the
+      // handle watcher.
+      throw "message pipe query failed: ${result.status} for $_handle";
+    }
+
+    // Read the data and view as a message.
+    var bytes = new ByteData(result.bytesRead);
+    var handles = new List<core.RawMojoHandle>(result.handlesRead);
+    result = _endpoint.read(bytes, result.bytesRead, handles);
+    if (!result.status.isOk && !result.status.isResourceExhausted) {
+      // If something else happens, it means the handle wasn't really ready
+      // for reading, which indicates a bug in MojoHandle or the
+      // handle watcher.
+      throw "message pipe read failed: ${result.status}";
+    }
+    var message = new Message(bytes, handles);
+    var reader = new MessageReader(message);
+
+    // Prepare the response.
+    var responseFuture = handleMessage(reader);
+
+    // If there's a response, queue it up for sending.
+    if (responseFuture != null) {
+      responseFuture.then((response) {
+        _sendQueue.add(response);
+        if (_sendQueue.length == 1) {
+          _handle.enableWriteEvents();
+        }
+      });
+    }
+  }
+
+  void _doWrite() {
+    if (_sendQueue.length > 0) {
+      assert(_handle.readyWrite);
+      var responseMessage = _sendQueue.removeAt(0);
+      _endpoint.write(responseMessage.buffer,
+                      responseMessage.buffer.lengthInBytes,
+                      responseMessage.handles);
+      if (!_endpoint.status.isOk) {
+        throw "message pipe write failed: ${_endpoint.status}";
+      }
+    }
+  }
+
   StreamSubscription<int> listen() {
     _isOpen = true;
-    return _handle.listen((int mojoSignal) {
-      if (core.MojoHandleSignals.isReadable(mojoSignal)) {
-        // Query how many bytes are available.
-        var result = _endpoint.query();
-        if (!result.status.isOk && !result.status.isResourceExhausted) {
-          // If something else happens, it means the handle wasn't really ready
-          // for reading, which indicates a bug in MojoHandle or the
-          // event listener.
-          throw new Exception("message pipe query failed: ${result.status}");
-        }
+    return _handle.listen((List<int> event) {
+      var signalsWatched = new core.MojoHandleSignals(event[0]);
+      var signalsReceived = new core.MojoHandleSignals(event[1]);
+      if (signalsReceived.isPeerClosed) {
+        close();
+        return;
+      }
 
-        // Read the data and view as a message.
-        var bytes = new ByteData(result.bytesRead);
-        var handles = new List<core.RawMojoHandle>(result.handlesRead);
-        result = _endpoint.read(bytes, result.bytesRead, handles);
-        if (!result.status.isOk && !result.status.isResourceExhausted) {
-          // If something else happens, it means the handle wasn't really ready
-          // for reading, which indicates a bug in MojoHandle or the
-          // event listener.
-          throw new Exception("message pipe read failed: ${result.status}");
-        }
-        var message = new Message(bytes, handles);
-        var reader = new MessageReader(message);
+      if (signalsReceived.isReadable) {
+        _doRead();
+      }
 
-        // Prepare the response.
-        var responseMessage = handleMessage(reader);
-        // If there's a response, queue it up for sending.
-        if (responseMessage != null) {
-          _sendQueue.add(responseMessage);
-          if ((_sendQueue.length > 0) && !_handle.writeEnabled()) {
-            _handle.enableWriteEvents();
-          }
-        }
+      if (signalsReceived.isWritable) {
+        _doWrite();
       }
-      if (core.MojoHandleSignals.isWritable(mojoSignal)) {
-        if (_sendQueue.length > 0) {
-          var responseMessage = _sendQueue.removeAt(0);
-          _endpoint.write(responseMessage.buffer,
-                          responseMessage.buffer.lengthInBytes,
-                          responseMessage.handles);
-          if (!_endpoint.status.isOk) {
-            throw new Exception("message pipe write failed");
-          }
-        }
-        if ((_sendQueue.length == 0) && _handle.writeEnabled()) {
-          _handle.disableWriteEvents();
-        }
-      }
-      if (core.MojoHandleSignals.isNone(mojoSignal)) {
-        // The handle watcher will send MojoHandleSignals.NONE when the other
-        // endpoint of the pipe is closed.
-        _handle.close();
+
+      if (_sendQueue.length == 0) {
+        var withoutWritable = signalsWatched - core.MojoHandleSignals.WRITABLE;
+        _handle.enableSignals(withoutWritable);
+      } else {
+        _handle.enableSignals(signalsWatched);
       }
     });
   }
 
+  void close() {
+    if (_isOpen) {
+      _handle.close();
+      _isOpen = false;
+      _handle = null;
+    }
+  }
+
   Message buildResponse(Type t, int name, Object response) {
     var builder = new MessageBuilder(name, align(getEncodedSize(t)));
     builder.encodeStruct(t, response);
     return builder.finish();
   }
 
   Message buildResponseWithID(
       Type t, int name, int id, int flags, Object response) {
     var builder = new MessageWithRequestIDBuilder(
         name, align(getEncodedSize(t)), id, flags);
     builder.encodeStruct(t, response);
     return builder.finish();
   }
 
   void enqueueMessage(Type t, int name, Object msg) {
     var builder = new MessageBuilder(name, align(getEncodedSize(t)));
     builder.encodeStruct(t, msg);
     var message = builder.finish();
     _sendQueue.add(message);
-    if (!_handle.writeEnabled()) {
-      _handle.enableWriteEvents();
-    }
+    _handle.enableWriteEvents();
   }
 
   Future enqueueMessageWithRequestID(Type t, int name, int id, Object msg) {
-    throw new Exception("The client Mixin should not expect a response");
+    // TODO(zra): Is this correct?
+    throw "The client interface should not expect a response";
   }
 
   bool get isOpen => _isOpen;
+  core.MojoMessagePipeEndpoint get endpoint => _endpoint;
 }