mojo: Add router for python bindings.

This is a reland of https://codereview.chromium.org/607513003 with the
fix for the failing test.

BUG=417707
TBR=sdefresne@chromium.org

Review URL: https://codereview.chromium.org/612443002

Cr-Commit-Position: refs/heads/master@{#296958}

mojo/public/python/mojo/bindings/messaging.py

@@ -5,18 +5,140 @@
 """Utility classes to handle sending and receiving messages."""
 
 
+import struct
 import weakref
 
 # pylint: disable=F0401
+import mojo.bindings.serialization as serialization
 import mojo.system as system
 
 
+# The flag values for a message header.
+NO_FLAG = 0
+MESSAGE_EXPECTS_RESPONSE_FLAG = 1 << 0
+MESSAGE_IS_RESPONSE_FLAG = 1 << 1
+
+
+class MessageHeader(object):
+  """The header of a mojo message."""
+
+  _SIMPLE_MESSAGE_NUM_FIELDS = 2
+  _SIMPLE_MESSAGE_STRUCT = struct.Struct("=IIII")
+
+  _REQUEST_ID_STRUCT = struct.Struct("=Q")
+  _REQUEST_ID_OFFSET = _SIMPLE_MESSAGE_STRUCT.size
+
+  _MESSAGE_WITH_REQUEST_ID_NUM_FIELDS = 3
+  _MESSAGE_WITH_REQUEST_ID_SIZE = (
+      _SIMPLE_MESSAGE_STRUCT.size + _REQUEST_ID_STRUCT.size)
+
+  def __init__(self, message_type, flags, request_id=0, data=None):
+    self._message_type = message_type
+    self._flags = flags
+    self._request_id = request_id
+    self._data = data
+
+  @classmethod
+  def Deserialize(cls, data):
+    buf = buffer(data)
+    if len(data) < cls._SIMPLE_MESSAGE_STRUCT.size:
+      raise serialization.DeserializationException('Header is too short.')
+    (size, version, message_type, flags) = (
+        cls._SIMPLE_MESSAGE_STRUCT.unpack_from(buf))
+    if (version < cls._SIMPLE_MESSAGE_NUM_FIELDS):
+      raise serialization.DeserializationException('Incorrect version.')
+    request_id = 0
+    if _HasRequestId(flags):
+      if version < cls._MESSAGE_WITH_REQUEST_ID_NUM_FIELDS:
+        raise serialization.DeserializationException('Incorrect version.')
+      if (size < cls._MESSAGE_WITH_REQUEST_ID_SIZE or
+          len(data) < cls._MESSAGE_WITH_REQUEST_ID_SIZE):
+        raise serialization.DeserializationException('Header is too short.')
+      (request_id, ) = cls._REQUEST_ID_STRUCT.unpack_from(
+          buf, cls._REQUEST_ID_OFFSET)
+    return MessageHeader(message_type, flags, request_id, data)
+
+  @property
+  def message_type(self):
+    return self._message_type
+
+  # pylint: disable=E0202
+  @property
+  def request_id(self):
+    assert self.has_request_id
+    return self._request_id
+
+  # pylint: disable=E0202
+  @request_id.setter
+  def request_id(self, request_id):
+    assert self.has_request_id
+    self._request_id = request_id
+    self._REQUEST_ID_STRUCT.pack_into(self._data, self._REQUEST_ID_OFFSET,
+                                      request_id)
+
+  @property
+  def has_request_id(self):
+    return _HasRequestId(self._flags)
+
+  @property
+  def expects_response(self):
+    return self._HasFlag(MESSAGE_EXPECTS_RESPONSE_FLAG)
+
+  @property
+  def is_response(self):
+    return self._HasFlag(MESSAGE_IS_RESPONSE_FLAG)
+
+  @property
+  def size(self):
+    if self.has_request_id:
+      return self._MESSAGE_WITH_REQUEST_ID_SIZE
+    return self._SIMPLE_MESSAGE_STRUCT.size
+
+  def Serialize(self):
+    if not self._data:
+      self._data = bytearray(self.size)
+      version = self._SIMPLE_MESSAGE_NUM_FIELDS
+      size = self._SIMPLE_MESSAGE_STRUCT.size
+      if self.has_request_id:
+        version = self._MESSAGE_WITH_REQUEST_ID_NUM_FIELDS
+        size = self._MESSAGE_WITH_REQUEST_ID_SIZE
+      self._SIMPLE_MESSAGE_STRUCT.pack_into(self._data, 0, size, version,
+                                            self._message_type, self._flags)
+      if self.has_request_id:
+        self._REQUEST_ID_STRUCT.pack_into(self._data, self._REQUEST_ID_OFFSET,
+                                          self._request_id)
+    return self._data
+
+  def _HasFlag(self, flag):
+    return self._flags & flag != 0
+
+
 class Message(object):
   """A message for a message pipe. This contains data and handles."""
 
   def __init__(self, data=None, handles=None):
     self.data = data
     self.handles = handles
+    self._header = None
+    self._payload = None
+
+  @property
+  def header(self):
+    if self._header is None:
+      self._header = MessageHeader.Deserialize(self.data)
+    return self._header
+
+  @property
+  def payload(self):
+    if self._payload is None:
+      self._payload = Message(self.data[self.header.size:], self.handles)
+    return self._payload
+
+  def SetRequestId(self, request_id):
+    header = self.header
+    header.request_id = request_id
+    (data, _) = header.Serialize()
+    self.data[:header.Size] = data[:header.Size]
 
 
 class MessageReceiver(object):
@@ -111,6 +233,12 @@ class Connector(MessageReceiver):
     result = self._handle.WriteMessage(message.data, message.handles)
     return result == system.RESULT_OK
 
+  def Close(self):
+    if self._cancellable:
+      self._cancellable()
+      self._cancellable = None
+    self._handle.Close()
+
   def _OnAsyncWaiterResult(self, result):
     self._cancellable = None
     if result == system.RESULT_OK:
@@ -141,6 +269,96 @@ class Connector(MessageReceiver):
     self._OnError(result)
 
 
+class Router(MessageReceiverWithResponder):
+  """
+  A Router will handle mojo message and forward those to a Connector. It deals
+  with parsing of headers and adding of request ids in order to be able to match
+  a response to a request.
+  """
+
+  def __init__(self, handle):
+    MessageReceiverWithResponder.__init__(self)
+    self._incoming_message_receiver = None
+    self._next_request_id = 1
+    self._responders = {}
+    self._connector = Connector(handle)
+    self._connector.SetIncomingMessageReceiver(
+        ForwardingMessageReceiver(self._HandleIncomingMessage))
+
+  def Start(self):
+    self._connector.Start()
+
+  def SetIncomingMessageReceiver(self, message_receiver):
+    """
+    Set the MessageReceiver that will receive message from the owned message
+    pipe.
+    """
+    self._incoming_message_receiver = message_receiver
+
+  def SetErrorHandler(self, error_handler):
+    """
+    Set the ConnectionErrorHandler that will be notified of errors on the owned
+    message pipe.
+    """
+    self._connector.SetErrorHandler(error_handler)
+
+  def Accept(self, message):
+    # A message without responder is directly forwarded to the connector.
+    return self._connector.Accept(message)
+
+  def AcceptWithResponder(self, message, responder):
+    # The message must have a header.
+    header = message.header
+    assert header.expects_response
+    request_id = self.NextRequestId()
+    header.request_id = request_id
+    if not self._connector.Accept(message):
+      return False
+    self._responders[request_id] = responder
+    return True
+
+  def Close(self):
+    self._connector.Close()
+
+  def _HandleIncomingMessage(self, message):
+    header = message.header
+    if header.expects_response:
+      if self._incoming_message_receiver:
+        return self._incoming_message_receiver.AcceptWithResponder(
+            message, self)
+      # If we receive a request expecting a response when the client is not
+      # listening, then we have no choice but to tear down the pipe.
+      self.Close()
+      return False
+    if header.is_response:
+      request_id = header.request_id
+      responder = self._responders.pop(request_id, None)
+      if responder is None:
+        return False
+      return responder.Accept(message)
+    if self._incoming_message_receiver:
+      return self._incoming_message_receiver.Accept(message)
+    # Ok to drop the message
+    return False
+
+  def NextRequestId(self):
+    request_id = self._next_request_id
+    while request_id == 0 or request_id in self._responders:
+      request_id = (request_id + 1) % (1 << 64)
+    self._next_request_id = (request_id + 1) % (1 << 64)
+    return request_id
+
+class ForwardingMessageReceiver(MessageReceiver):
+  """A MessageReceiver that forward calls to |Accept| to a callable."""
+
+  def __init__(self, callback):
+    MessageReceiver.__init__(self)
+    self._callback = callback
+
+  def Accept(self, message):
+    return self._callback(message)
+
+
 def _WeakCallback(callback):
   func = callback.im_func
   self = callback.im_self
@@ -165,3 +383,5 @@ def _ReadAndDispatchMessage(handle, message_receiver):
     message_receiver.Accept(Message(data[0], data[1]))
   return result
 
+def _HasRequestId(flags):
+  return flags & (MESSAGE_EXPECTS_RESPONSE_FLAG|MESSAGE_IS_RESPONSE_FLAG) != 0

mojo/python/tests/messaging_unittest.py

@@ -10,16 +10,6 @@ from mojo.bindings import messaging
 from mojo import system
 
 
-class _ForwardingMessageReceiver(messaging.MessageReceiver):
-
-  def __init__(self, callback):
-    self._callback = callback
-
-  def Accept(self, message):
-    self._callback(message)
-    return True
-
-
 class _ForwardingConnectionErrorHandler(messaging.ConnectionErrorHandler):
 
   def __init__(self, callback):
@@ -29,7 +19,7 @@ class _ForwardingConnectionErrorHandler(messaging.ConnectionErrorHandler):
     self._callback(result)
 
 
-class MessagingTest(unittest.TestCase):
+class ConnectorTest(unittest.TestCase):
 
   def setUp(self):
     mojo.embedder.Init()
@@ -38,12 +28,13 @@ class MessagingTest(unittest.TestCase):
     self.received_errors = []
     def _OnMessage(message):
       self.received_messages.append(message)
+      return True
     def _OnError(result):
       self.received_errors.append(result)
     handles = system.MessagePipe()
     self.connector = messaging.Connector(handles.handle1)
     self.connector.SetIncomingMessageReceiver(
-        _ForwardingMessageReceiver(_OnMessage))
+        messaging.ForwardingMessageReceiver(_OnMessage))
     self.connector.SetErrorHandler(
         _ForwardingConnectionErrorHandler(_OnError))
     self.connector.Start()
@@ -79,3 +70,138 @@ class MessagingTest(unittest.TestCase):
     self.connector = None
     (result, _, _) = self.handle.ReadMessage()
     self.assertEquals(result, system.RESULT_FAILED_PRECONDITION)
+
+
+class HeaderTest(unittest.TestCase):
+
+  def testSimpleMessageHeader(self):
+    header = messaging.MessageHeader(0xdeadbeaf, messaging.NO_FLAG)
+    self.assertEqual(header.message_type, 0xdeadbeaf)
+    self.assertFalse(header.has_request_id)
+    self.assertFalse(header.expects_response)
+    self.assertFalse(header.is_response)
+    data = header.Serialize()
+    other_header = messaging.MessageHeader.Deserialize(data)
+    self.assertEqual(other_header.message_type, 0xdeadbeaf)
+    self.assertFalse(other_header.has_request_id)
+    self.assertFalse(other_header.expects_response)
+    self.assertFalse(other_header.is_response)
+
+  def testMessageHeaderWithRequestID(self):
+    # Request message.
+    header = messaging.MessageHeader(0xdeadbeaf,
+                                     messaging.MESSAGE_EXPECTS_RESPONSE_FLAG)
+
+    self.assertEqual(header.message_type, 0xdeadbeaf)
+    self.assertTrue(header.has_request_id)
+    self.assertTrue(header.expects_response)
+    self.assertFalse(header.is_response)
+    self.assertEqual(header.request_id, 0)
+
+    data = header.Serialize()
+    other_header = messaging.MessageHeader.Deserialize(data)
+
+    self.assertEqual(other_header.message_type, 0xdeadbeaf)
+    self.assertTrue(other_header.has_request_id)
+    self.assertTrue(other_header.expects_response)
+    self.assertFalse(other_header.is_response)
+    self.assertEqual(other_header.request_id, 0)
+
+    header.request_id = 0xdeadbeafdeadbeaf
+    data = header.Serialize()
+    other_header = messaging.MessageHeader.Deserialize(data)
+
+    self.assertEqual(other_header.request_id, 0xdeadbeafdeadbeaf)
+
+    # Response message.
+    header = messaging.MessageHeader(0xdeadbeaf,
+                                     messaging.MESSAGE_IS_RESPONSE_FLAG,
+                                     0xdeadbeafdeadbeaf)
+
+    self.assertEqual(header.message_type, 0xdeadbeaf)
+    self.assertTrue(header.has_request_id)
+    self.assertFalse(header.expects_response)
+    self.assertTrue(header.is_response)
+    self.assertEqual(header.request_id, 0xdeadbeafdeadbeaf)
+
+    data = header.Serialize()
+    other_header = messaging.MessageHeader.Deserialize(data)
+
+    self.assertEqual(other_header.message_type, 0xdeadbeaf)
+    self.assertTrue(other_header.has_request_id)
+    self.assertFalse(other_header.expects_response)
+    self.assertTrue(other_header.is_response)
+    self.assertEqual(other_header.request_id, 0xdeadbeafdeadbeaf)
+
+
+class RouterTest(unittest.TestCase):
+
+  def setUp(self):
+    mojo.embedder.Init()
+    self.loop = system.RunLoop()
+    self.received_messages = []
+    self.received_errors = []
+    def _OnMessage(message):
+      self.received_messages.append(message)
+      return True
+    def _OnError(result):
+      self.received_errors.append(result)
+    handles = system.MessagePipe()
+    self.router = messaging.Router(handles.handle1)
+    self.router.SetIncomingMessageReceiver(
+        messaging.ForwardingMessageReceiver(_OnMessage))
+    self.router.SetErrorHandler(
+        _ForwardingConnectionErrorHandler(_OnError))
+    self.router.Start()
+    self.handle = handles.handle0
+
+  def tearDown(self):
+    self.router = None
+    self.handle = None
+    self.loop = None
+
+  def testSimpleMessage(self):
+    header_data = messaging.MessageHeader(0, messaging.NO_FLAG).Serialize()
+    message = messaging.Message(header_data)
+    self.router.Accept(message)
+    self.loop.RunUntilIdle()
+    self.assertFalse(self.received_errors)
+    self.assertFalse(self.received_messages)
+    (res, data, _) = self.handle.ReadMessage(bytearray(len(header_data)))
+    self.assertEquals(system.RESULT_OK, res)
+    self.assertEquals(data[0], header_data)
+
+  def testSimpleReception(self):
+    header_data = messaging.MessageHeader(0, messaging.NO_FLAG).Serialize()
+    self.handle.WriteMessage(header_data)
+    self.loop.RunUntilIdle()
+    self.assertFalse(self.received_errors)
+    self.assertEquals(len(self.received_messages), 1)
+    self.assertEquals(self.received_messages[0].data, header_data)
+
+  def testRequestResponse(self):
+    header_data = messaging.MessageHeader(
+        0, messaging.MESSAGE_EXPECTS_RESPONSE_FLAG).Serialize()
+    message = messaging.Message(header_data)
+    back_messages = []
+    def OnBackMessage(message):
+      back_messages.append(message)
+    self.router.AcceptWithResponder(message,
+                                    messaging.ForwardingMessageReceiver(
+                                        OnBackMessage))
+    self.loop.RunUntilIdle()
+    self.assertFalse(self.received_errors)
+    self.assertFalse(self.received_messages)
+    (res, data, _) = self.handle.ReadMessage(bytearray(len(header_data)))
+    self.assertEquals(system.RESULT_OK, res)
+    message_header = messaging.MessageHeader.Deserialize(data[0])
+    self.assertNotEquals(message_header.request_id, 0)
+    response_header_data = messaging.MessageHeader(
+        0,
+        messaging.MESSAGE_IS_RESPONSE_FLAG,
+        message_header.request_id).Serialize()
+    self.handle.WriteMessage(response_header_data)
+    self.loop.RunUntilIdle()
+    self.assertFalse(self.received_errors)
+    self.assertEquals(len(back_messages), 1)
+    self.assertEquals(back_messages[0].data, response_header_data)