websocket.py

# Author: Jacob Kristhammar, 2010
#
# Updated version of websocket.py[1] that implements latest[2] stable version
# of the websocket protocol.
#
# NB. It's no longer possible to manually select which callback that should
#     be invoked upon message reception. Instead you must override the
#     on_message(message) method to handle incoming messsages.
#     This also means that you don't have to explicitly invoke 
#     receive_message, in fact you shouldn't.
#
# [1] http://github.com/facebook/tornado/blob/
#     2c89b89536bbfa081745336bb5ab5465c448cb8a/tornado/websocket.py
# [2] http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-76

import functools
import hashlib
import logging
import re
import struct
import time
import tornado.escape
import tornado.web


class WebSocketHandler(tornado.web.RequestHandler):
    """Subclass this class to create a basic WebSocket handler.

    Override on_message to handle incoming messages. You can also override 
    open and on_close to handle opened and closed connections.

    See http://www.w3.org/TR/2009/WD-websockets-20091222/ for details on the
    JavaScript interface. This implement the protocol as specified at
    http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-76.
 
    Here is an example Web Socket handler that echos back all received messages
    back to the client:
 
      class EchoWebSocket(websocket.WebSocketHandler):
          def open(self):
              print "WebSocket opened"
 
          def on_message(self, message):
              self.write_message(u"You said: " + message)

          def on_close(self):
              print "WebSocket closed"
 
    Web Sockets are not standard HTTP connections. The "handshake" is HTTP,
    but after the handshake, the protocol is message-based. Consequently,
    most of the Tornado HTTP facilities are not available in handlers of this
    type. The only communication methods available to you are send_message()
    and close(). Likewise, your request handler class should
    implement open() method rather than get() or post().
 
    If you map the handler above to "/websocket" in your application, you can
    invoke it in JavaScript with:
 
      var ws = new WebSocket("ws://localhost:8888/websocket");
      ws.onopen = function() {
         ws.send("Hello, world");
      };
      ws.onmessage = function (evt) {
         alert(evt.data);
      };
 
    This script pops up an alert box that says "You said: Hello, world".
    """
    def __init__(self, application, request):
        tornado.web.RequestHandler.__init__(self, application, request)
        self.stream = request.connection.stream
        self.client_terminated = False
        self._waiting = None

    def _execute(self, transforms, *args, **kwargs):
        self.open_args = args
        self.open_kwargs = kwargs
        try:
            self.ws_request = WebSocketRequest(self.request)
        except ValueError:
            logging.debug("Malformed WebSocket request received")
            self._abort()
            return
        self.stream.read_bytes(8, self._handle_challenge)

    def _handle_challenge(self, challenge):
        try:
            challenge_response = self.ws_request.challenge_response(challenge)
        except ValueError:
            logging.debug("Malformed key data in WebSocket request")
            self._abort()
            return
        self._write_response(challenge_response)

    def _write_response(self, challenge):
        self.stream.write(
            "HTTP/1.1 101 Web Socket Protocol Handshake\r\n"
            "Upgrade: WebSocket\r\n"
            "Connection: Upgrade\r\n"
            "Server: TornadoServer/0.1\r\n"
            "Sec-WebSocket-Origin: %s\r\n"
            "Sec-WebSocket-Location: ws://%s%s\r\n"
            "\r\n%s" % (self.request.headers["Origin"], self.request.host, 
             self.request.path, challenge))
        self.async_callback(self.open)(*self.open_args, **self.open_kwargs)
        self._receive_message()

    def write_message(self, message):
        """Sends the given message to the client of this Web Socket."""
        if isinstance(message, dict):
            message = tornado.escape.json_encode(message)
        if isinstance(message, unicode):
            message = message.encode("utf-8")
        assert isinstance(message, str)
        self.stream.write("\x00" + message + "\xff")

    def open(self, *args, **kwargs):
        """Invoked when a new WebSocket is opened."""
        pass

    def on_message(self, message):
        """Handle incoming messages on the WebSocket
        
        This method must be overloaded
        """
        raise NotImplementedError

    def on_close(self):
        """Invoked when the WebSocket is closed."""
        pass


    def close(self):
        """Closes this Web Socket.
        
        Once the close handshake is successful the socket will be closed.
        """
        if self.client_terminated and self._waiting:
            tornado.ioloop.IOLoop.instance().remove_timeout(self._waiting)
            self.stream.close()
        else:
            self.stream.write("\xff\x00")
            self._waiting = tornado.ioloop.IOLoop.instance().add_timeout(
                                time.time() + 5, self._abort)

    def async_callback(self, callback, *args, **kwargs):
        """Wrap callbacks with this if they are used on asynchronous requests.

        Catches exceptions properly and closes this Web Socket if an exception
        is uncaught.
        """
        if args or kwargs:
            callback = functools.partial(callback, *args, **kwargs)
        def wrapper(*args, **kwargs):
            try:
                return callback(*args, **kwargs)
            except Exception, e:
                logging.error("Uncaught exception in %s",
                              self.request.path, exc_info=True)
                self._abort()
        return wrapper

    def _abort(self):
        """Instantly aborts the WebSocket connection by closing the socket"""
        self.client_terminated = True
        self.stream.close()

    def _receive_message(self):
        self.stream.read_bytes(1, self._on_frame_type)

    def _on_frame_type(self, byte):
        frame_type = ord(byte)
        if frame_type == 0x00:
            self.stream.read_until("\xff", self._on_end_delimiter)
        elif frame_type == 0xff:
            self.stream.read_bytes(1, self._on_length_indicator)
        else:
            self._abort()

    def _on_end_delimiter(self, frame):
        if not self.client_terminated:
            self.async_callback(self.on_message)(
                    frame[:-1].decode("utf-8", "replace"))
            self._receive_message()

    def _on_length_indicator(self, byte):
        if ord(byte) != 0x00:
            self._abort()
            return
        self.client_terminated = True
        self.close()
    
    def on_connection_close(self):
        self.client_terminated = True
        self.on_close()

    def _not_supported(self, *args, **kwargs):
        raise Exception("Method not supported for Web Sockets")


for method in ["write", "redirect", "set_header", "send_error", "set_cookie",
               "set_status", "flush", "finish"]:
    setattr(WebSocketHandler, method, WebSocketHandler._not_supported)


class WebSocketRequest(object):
    """A single WebSocket request.

    This class provides basic functionality to process WebSockets requests as
    specified in 
    http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-76
    """
    def __init__(self, request):
        self.request = request
        self.challenge = None
        self._handle_websocket_headers()

    def challenge_response(self, challenge):
        """Generates the challange response that's needed in the handshake

        The challenge parameter should be the raw bytes as sent from the
        client.
        """
        key_1 = self.request.headers.get("Sec-Websocket-Key1")
        key_2 = self.request.headers.get("Sec-Websocket-Key2")
        try:
            part_1 = self._calculate_part(key_1)
            part_2 = self._calculate_part(key_2)
        except ValueError:
            raise ValueError("Invalid Keys/Challenge")
        return self._generate_challenge_response(part_1, part_2, challenge)

    def _handle_websocket_headers(self):
        """Verifies all invariant- and required headers

        If a header is missing or have an incorrect value ValueError will be
        raised
        """
        headers = self.request.headers
        fields = ("Origin", "Host", "Sec-Websocket-Key1", 
                  "Sec-Websocket-Key2")
        if headers.get("Upgrade", '').lower() != "websocket" or \
           headers.get("Connection", '').lower() != "upgrade" or \
           not all(map(lambda f: self.request.headers.get(f), fields)):
            raise ValueError("Missing/Invalid WebSocket headers")

    def _calculate_part(self, key):
        """Processes the key headers and calculates their key value.

        Raises ValueError when feed invalid key."""
        number, spaces = filter(str.isdigit, key), filter(str.isspace, key)
        try:
            key_number = int(number) / len(spaces)
        except (ValueError, ZeroDivisionError):
            raise ValueError
        return struct.pack(">I", key_number)

    def _generate_challenge_response(self, part_1, part_2, part_3):
        m = hashlib.md5()
        m.update(part_1)
        m.update(part_2)
        m.update(part_3)
        return m.digest()