text: """Implementation of the WebSocket protocol.
  
  `WebSockets <http://dev.w3.org/html5/websockets/>`_ allow for bidirectional
  communication between the browser and server.
  
  WebSockets are supported in the current versions of all major browsers,
  although older versions that do not support WebSockets are still in use
  (refer to http://caniuse.com/websockets for details).
  
  This module implements the final version of the WebSocket protocol as
  defined in `RFC 6455 <http://tools.ietf.org/html/rfc6455>`_.  Certain
  browser versions (notably Safari 5.x) implemented an earlier draft of
  the protocol (known as "draft 76") and are not compatible with this module.
  
  .. versionchanged:: 4.0
     Removed support for the draft 76 protocol version.
  """
  
  import base64
  import hashlib
  import os
  import sys
  import struct
  import tornado.escape
  import tornado.web
  from urllib.parse import urlparse
  import zlib
  
  from tornado.concurrent import Future, future_set_result_unless_cancelled
  from tornado.escape import utf8, native_str, to_unicode
  from tornado import gen, httpclient, httputil
  from tornado.ioloop import IOLoop, PeriodicCallback
  from tornado.iostream import StreamClosedError
  from tornado.log import gen_log
  from tornado import simple_httpclient
  from tornado.queues import Queue
  from tornado.tcpclient import TCPClient
  from tornado.util import _websocket_mask
  
  _default_max_message_size = 10 * 1024 * 1024
  
  
  class WebSocketError(Exception):
      pass
  
  
  class WebSocketClosedError(WebSocketError):
      """Raised by operations on a closed connection.
  
      .. versionadded:: 3.2
      """
      pass
  
  
  class _DecompressTooLargeError(Exception):
      pass
  
  
  class WebSocketHandler(tornado.web.RequestHandler):
      """Subclass this class to create a basic WebSocket handler.
  
      Override `on_message` to handle incoming messages, and use
      `write_message` to send messages to the client. You can also
      override `open` and `on_close` to handle opened and closed
      connections.
  
      Custom upgrade response headers can be sent by overriding
      `~tornado.web.RequestHandler.set_default_headers` or
      `~tornado.web.RequestHandler.prepare`.
  
      See http://dev.w3.org/html5/websockets/ for details on the
      JavaScript interface.  The protocol is specified at
      http://tools.ietf.org/html/rfc6455.
  
      Here is an example WebSocket handler that echos back all received messages
      back to the client:
  
      .. testcode::
  
        class EchoWebSocket(tornado.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")
  
      .. testoutput::
         :hide:
  
      WebSockets 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 `write_message()`, `ping()`, 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".
  
      Web browsers allow any site to open a websocket connection to any other,
      instead of using the same-origin policy that governs other network
      access from javascript.  This can be surprising and is a potential
      security hole, so since Tornado 4.0 `WebSocketHandler` requires
      applications that wish to receive cross-origin websockets to opt in
      by overriding the `~WebSocketHandler.check_origin` method (see that
      method's docs for details).  Failure to do so is the most likely
      cause of 403 errors when making a websocket connection.
  
      When using a secure websocket connection (``wss://``) with a self-signed
      certificate, the connection from a browser may fail because it wants
      to show the "accept this certificate" dialog but has nowhere to show it.
      You must first visit a regular HTML page using the same certificate
      to accept it before the websocket connection will succeed.
  
      If the application setting ``websocket_ping_interval`` has a non-zero
      value, a ping will be sent periodically, and the connection will be
      closed if a response is not received before the ``websocket_ping_timeout``.
  
      Messages larger than the ``websocket_max_message_size`` application setting
      (default 10MiB) will not be accepted.
  
      .. versionchanged:: 4.5
         Added ``websocket_ping_interval``, ``websocket_ping_timeout``, and
         ``websocket_max_message_size``.
      """
      def __init__(self, application, request, **kwargs):
          super(WebSocketHandler, self).__init__(application, request, **kwargs)
          self.ws_connection = None
          self.close_code = None
          self.close_reason = None
          self.stream = None
          self._on_close_called = False
  
      def get(self, *args, **kwargs):
          self.open_args = args
          self.open_kwargs = kwargs
  
          # Upgrade header should be present and should be equal to WebSocket
          if self.request.headers.get("Upgrade", "").lower() != 'websocket':
              self.set_status(400)
              log_msg = "Can \"Upgrade\" only to \"WebSocket\"."
              self.finish(log_msg)
              gen_log.debug(log_msg)
              return
  
          # Connection header should be upgrade.
          # Some proxy servers/load balancers
          # might mess with it.
          headers = self.request.headers
          connection = map(lambda s: s.strip().lower(),
                           headers.get("Connection", "").split(","))
          if 'upgrade' not in connection:
              self.set_status(400)
              log_msg = "\"Connection\" must be \"Upgrade\"."
              self.finish(log_msg)
              gen_log.debug(log_msg)
              return
  
          # Handle WebSocket Origin naming convention differences
          # The difference between version 8 and 13 is that in 8 the
          # client sends a "Sec-Websocket-Origin" header and in 13 it's
          # simply "Origin".
          if "Origin" in self.request.headers:
              origin = self.request.headers.get("Origin")
          else:
              origin = self.request.headers.get("Sec-Websocket-Origin", None)
  
          # If there was an origin header, check to make sure it matches
          # according to check_origin. When the origin is None, we assume it
          # did not come from a browser and that it can be passed on.
          if origin is not None and not self.check_origin(origin):
              self.set_status(403)
              log_msg = "Cross origin websockets not allowed"
              self.finish(log_msg)
              gen_log.debug(log_msg)
              return
  
          self.ws_connection = self.get_websocket_protocol()
          if self.ws_connection:
              self.ws_connection.accept_connection()
          else:
              self.set_status(426, "Upgrade Required")
              self.set_header("Sec-WebSocket-Version", "7, 8, 13")
              self.finish()
  
      stream = None
  
      @property
      def ping_interval(self):
          """The interval for websocket keep-alive pings.
  
          Set websocket_ping_interval = 0 to disable pings.
          """
          return self.settings.get('websocket_ping_interval', None)
  
      @property
      def ping_timeout(self):
          """If no ping is received in this many seconds,
          close the websocket connection (VPNs, etc. can fail to cleanly close ws connections).
          Default is max of 3 pings or 30 seconds.
          """
          return self.settings.get('websocket_ping_timeout', None)
  
      @property
      def max_message_size(self):
          """Maximum allowed message size.
  
          If the remote peer sends a message larger than this, the connection
          will be closed.
  
          Default is 10MiB.
          """
          return self.settings.get('websocket_max_message_size', _default_max_message_size)
  
      def write_message(self, message, binary=False):
          """Sends the given message to the client of this Web Socket.
  
          The message may be either a string or a dict (which will be
          encoded as json).  If the ``binary`` argument is false, the
          message will be sent as utf8; in binary mode any byte string
          is allowed.
  
          If the connection is already closed, raises `WebSocketClosedError`.
          Returns a `.Future` which can be used for flow control.
  
          .. versionchanged:: 3.2
             `WebSocketClosedError` was added (previously a closed connection
             would raise an `AttributeError`)
  
          .. versionchanged:: 4.3
             Returns a `.Future` which can be used for flow control.
  
          .. versionchanged:: 5.0
             Consistently raises `WebSocketClosedError`. Previously could
             sometimes raise `.StreamClosedError`.
          """
          if self.ws_connection is None or self.ws_connection.is_closing():
              raise WebSocketClosedError()
          if isinstance(message, dict):
              message = tornado.escape.json_encode(message)
          return self.ws_connection.write_message(message, binary=binary)
  
      def select_subprotocol(self, subprotocols):
          """Override to implement subprotocol negotiation.
  
          ``subprotocols`` is a list of strings identifying the
          subprotocols proposed by the client.  This method may be
          overridden to return one of those strings to select it, or
          ``None`` to not select a subprotocol.
  
          Failure to select a subprotocol does not automatically abort
          the connection, although clients may close the connection if
          none of their proposed subprotocols was selected.
  
          The list may be empty, in which case this method must return
          None. This method is always called exactly once even if no
          subprotocols were proposed so that the handler can be advised
          of this fact.
  
          .. versionchanged:: 5.1
  
             Previously, this method was called with a list containing
             an empty string instead of an empty list if no subprotocols
             were proposed by the client.
          """
          return None
  
      @property
      def selected_subprotocol(self):
          """The subprotocol returned by `select_subprotocol`.
  
          .. versionadded:: 5.1
          """
          return self.ws_connection.selected_subprotocol
  
      def get_compression_options(self):
          """Override to return compression options for the connection.
  
          If this method returns None (the default), compression will
          be disabled.  If it returns a dict (even an empty one), it
          will be enabled.  The contents of the dict may be used to
          control the following compression options:
  
          ``compression_level`` specifies the compression level.
  
          ``mem_level`` specifies the amount of memory used for the internal compression state.
  
           These parameters are documented in details here:
           https://docs.python.org/3.6/library/zlib.html#zlib.compressobj
  
          .. versionadded:: 4.1
  
          .. versionchanged:: 4.5
  
             Added ``compression_level`` and ``mem_level``.
          """
          # TODO: Add wbits option.
          return None
  
      def open(self, *args, **kwargs):
          """Invoked when a new WebSocket is opened.
  
          The arguments to `open` are extracted from the `tornado.web.URLSpec`
          regular expression, just like the arguments to
          `tornado.web.RequestHandler.get`.
  
          `open` may be a coroutine. `on_message` will not be called until
          `open` has returned.
  
          .. versionchanged:: 5.1
  
             ``open`` may be a coroutine.
          """
          pass
  
      def on_message(self, message):
          """Handle incoming messages on the WebSocket
  
          This method must be overridden.
  
          .. versionchanged:: 4.5
  
             ``on_message`` can be a coroutine.
          """
          raise NotImplementedError
  
      def ping(self, data=b''):
          """Send ping frame to the remote end.
  
          The data argument allows a small amount of data (up to 125
          bytes) to be sent as a part of the ping message. Note that not
          all websocket implementations expose this data to
          applications.
  
          Consider using the ``websocket_ping_interval`` application
          setting instead of sending pings manually.
  
          .. versionchanged:: 5.1
  
             The data argument is now optional.
  
          """
          data = utf8(data)
          if self.ws_connection is None or self.ws_connection.is_closing():
              raise WebSocketClosedError()
          self.ws_connection.write_ping(data)
  
      def on_pong(self, data):
          """Invoked when the response to a ping frame is received."""
          pass
  
      def on_ping(self, data):
          """Invoked when the a ping frame is received."""
          pass
  
      def on_close(self):
          """Invoked when the WebSocket is closed.
  
          If the connection was closed cleanly and a status code or reason
          phrase was supplied, these values will be available as the attributes
          ``self.close_code`` and ``self.close_reason``.
  
          .. versionchanged:: 4.0
  
             Added ``close_code`` and ``close_reason`` attributes.
          """
          pass
  
      def close(self, code=None, reason=None):
          """Closes this Web Socket.
  
          Once the close handshake is successful the socket will be closed.
  
          ``code`` may be a numeric status code, taken from the values
          defined in `RFC 6455 section 7.4.1
          <https://tools.ietf.org/html/rfc6455#section-7.4.1>`_.
          ``reason`` may be a textual message about why the connection is
          closing.  These values are made available to the client, but are
          not otherwise interpreted by the websocket protocol.
  
          .. versionchanged:: 4.0
  
             Added the ``code`` and ``reason`` arguments.
          """
          if self.ws_connection:
              self.ws_connection.close(code, reason)
              self.ws_connection = None
  
      def check_origin(self, origin):
          """Override to enable support for allowing alternate origins.
  
          The ``origin`` argument is the value of the ``Origin`` HTTP
          header, the url responsible for initiating this request.  This
          method is not called for clients that do not send this header;
          such requests are always allowed (because all browsers that
          implement WebSockets support this header, and non-browser
          clients do not have the same cross-site security concerns).
  
          Should return True to accept the request or False to reject it.
          By default, rejects all requests with an origin on a host other
          than this one.
  
          This is a security protection against cross site scripting attacks on
          browsers, since WebSockets are allowed to bypass the usual same-origin
          policies and don't use CORS headers.
  
          .. warning::
  
             This is an important security measure; don't disable it
             without understanding the security implications. In
             particular, if your authentication is cookie-based, you
             must either restrict the origins allowed by
             ``check_origin()`` or implement your own XSRF-like
             protection for websocket connections. See `these
             <https://www.christian-schneider.net/CrossSiteWebSocketHijacking.html>`_
             `articles
             <https://devcenter.heroku.com/articles/websocket-security>`_
             for more.
  
          To accept all cross-origin traffic (which was the default prior to
          Tornado 4.0), simply override this method to always return true::
  
              def check_origin(self, origin):
                  return True
  
          To allow connections from any subdomain of your site, you might
          do something like::
  
              def check_origin(self, origin):
                  parsed_origin = urllib.parse.urlparse(origin)
                  return parsed_origin.netloc.endswith(".mydomain.com")
  
          .. versionadded:: 4.0
  
          """
          parsed_origin = urlparse(origin)
          origin = parsed_origin.netloc
          origin = origin.lower()
  
          host = self.request.headers.get("Host")
  
          # Check to see that origin matches host directly, including ports
          return origin == host
  
      def set_nodelay(self, value):
          """Set the no-delay flag for this stream.
  
          By default, small messages may be delayed and/or combined to minimize
          the number of packets sent.  This can sometimes cause 200-500ms delays
          due to the interaction between Nagle's algorithm and TCP delayed
          ACKs.  To reduce this delay (at the expense of possibly increasing
          bandwidth usage), call ``self.set_nodelay(True)`` once the websocket
          connection is established.
  
          See `.BaseIOStream.set_nodelay` for additional details.
  
          .. versionadded:: 3.1
          """
          self.stream.set_nodelay(value)
  
      def on_connection_close(self):
          if self.ws_connection:
              self.ws_connection.on_connection_close()
              self.ws_connection = None
          if not self._on_close_called:
              self._on_close_called = True
              self.on_close()
              self._break_cycles()
  
      def _break_cycles(self):
          # WebSocketHandlers call finish() early, but we don't want to
          # break up reference cycles (which makes it impossible to call
          # self.render_string) until after we've really closed the
          # connection (if it was established in the first place,
          # indicated by status code 101).
          if self.get_status() != 101 or self._on_close_called:
              super(WebSocketHandler, self)._break_cycles()
  
      def send_error(self, *args, **kwargs):
          if self.stream is None:
              super(WebSocketHandler, self).send_error(*args, **kwargs)
          else:
              # If we get an uncaught exception during the handshake,
              # we have no choice but to abruptly close the connection.
              # TODO: for uncaught exceptions after the handshake,
              # we can close the connection more gracefully.
              self.stream.close()
  
      def get_websocket_protocol(self):
          websocket_version = self.request.headers.get("Sec-WebSocket-Version")
          if websocket_version in ("7", "8", "13"):
              return WebSocketProtocol13(
                  self, compression_options=self.get_compression_options())
  
      def _attach_stream(self):
          self.stream = self.detach()
          self.stream.set_close_callback(self.on_connection_close)
          # disable non-WS methods
          for method in ["write", "redirect", "set_header", "set_cookie",
                         "set_status", "flush", "finish"]:
              setattr(self, method, _raise_not_supported_for_websockets)
  
  
  def _raise_not_supported_for_websockets(*args, **kwargs):
      raise RuntimeError("Method not supported for Web Sockets")
  
  
  class WebSocketProtocol(object):
      """Base class for WebSocket protocol versions.
      """
      def __init__(self, handler):
          self.handler = handler
          self.request = handler.request
          self.stream = handler.stream
          self.client_terminated = False
          self.server_terminated = False
  
      def _run_callback(self, callback, *args, **kwargs):
          """Runs the given callback with exception handling.
  
          If the callback is a coroutine, returns its Future. On error, aborts the
          websocket connection and returns None.
          """
          try:
              result = callback(*args, **kwargs)
          except Exception:
              self.handler.log_exception(*sys.exc_info())
              self._abort()
          else:
              if result is not None:
                  result = gen.convert_yielded(result)
                  self.stream.io_loop.add_future(result, lambda f: f.result())
              return result
  
      def on_connection_close(self):
          self._abort()
  
      def _abort(self):
          """Instantly aborts the WebSocket connection by closing the socket"""
          self.client_terminated = True
          self.server_terminated = True
          self.stream.close()  # forcibly tear down the connection
          self.close()  # let the subclass cleanup
  
  
  class _PerMessageDeflateCompressor(object):
      def __init__(self, persistent, max_wbits, compression_options=None):
          if max_wbits is None:
              max_wbits = zlib.MAX_WBITS
          # There is no symbolic constant for the minimum wbits value.
          if not (8 <= max_wbits <= zlib.MAX_WBITS):
              raise ValueError("Invalid max_wbits value %r; allowed range 8-%d",
                               max_wbits, zlib.MAX_WBITS)
          self._max_wbits = max_wbits
  
          if compression_options is None or 'compression_level' not in compression_options:
              self._compression_level = tornado.web.GZipContentEncoding.GZIP_LEVEL
          else:
              self._compression_level = compression_options['compression_level']
  
          if compression_options is None or 'mem_level' not in compression_options:
              self._mem_level = 8
          else:
              self._mem_level = compression_options['mem_level']
  
          if persistent:
              self._compressor = self._create_compressor()
          else:
              self._compressor = None
  
      def _create_compressor(self):
          return zlib.compressobj(self._compression_level,
                                  zlib.DEFLATED, -self._max_wbits, self._mem_level)
  
      def compress(self, data):
          compressor = self._compressor or self._create_compressor()
          data = (compressor.compress(data) +
                  compressor.flush(zlib.Z_SYNC_FLUSH))
          assert data.endswith(b'\x00\x00\xff\xff')
          return data[:-4]
  
  
  class _PerMessageDeflateDecompressor(object):
      def __init__(self, persistent, max_wbits, max_message_size, compression_options=None):
          self._max_message_size = max_message_size
          if max_wbits is None:
              max_wbits = zlib.MAX_WBITS
          if not (8 <= max_wbits <= zlib.MAX_WBITS):
              raise ValueError("Invalid max_wbits value %r; allowed range 8-%d",
                               max_wbits, zlib.MAX_WBITS)
          self._max_wbits = max_wbits
          if persistent:
              self._decompressor = self._create_decompressor()
          else:
              self._decompressor = None
  
      def _create_decompressor(self):
          return zlib.decompressobj(-self._max_wbits)
  
      def decompress(self, data):
          decompressor = self._decompressor or self._create_decompressor()
          result = decompressor.decompress(data + b'\x00\x00\xff\xff', self._max_message_size)
          if decompressor.unconsumed_tail:
              raise _DecompressTooLargeError()
          return result
  
  
  class WebSocketProtocol13(WebSocketProtocol):
      """Implementation of the WebSocket protocol from RFC 6455.
  
      This class supports versions 7 and 8 of the protocol in addition to the
      final version 13.
      """
      # Bit masks for the first byte of a frame.
      FIN = 0x80
      RSV1 = 0x40
      RSV2 = 0x20
      RSV3 = 0x10
      RSV_MASK = RSV1 | RSV2 | RSV3
      OPCODE_MASK = 0x0f
  
      def __init__(self, handler, mask_outgoing=False,
                   compression_options=None):
          WebSocketProtocol.__init__(self, handler)
          self.mask_outgoing = mask_outgoing
          self._final_frame = False
          self._frame_opcode = None
          self._masked_frame = None
          self._frame_mask = None
          self._frame_length = None
          self._fragmented_message_buffer = None
          self._fragmented_message_opcode = None
          self._waiting = None
          self._compression_options = compression_options
          self._decompressor = None
          self._compressor = None
          self._frame_compressed = None
          # The total uncompressed size of all messages received or sent.
          # Unicode messages are encoded to utf8.
          # Only for testing; subject to change.
          self._message_bytes_in = 0
          self._message_bytes_out = 0
          # The total size of all packets received or sent.  Includes
          # the effect of compression, frame overhead, and control frames.
          self._wire_bytes_in = 0
          self._wire_bytes_out = 0
          self.ping_callback = None
          self.last_ping = 0
          self.last_pong = 0
  
      def accept_connection(self):
          try:
              self._handle_websocket_headers()
          except ValueError:
              self.handler.set_status(400)
              log_msg = "Missing/Invalid WebSocket headers"
              self.handler.finish(log_msg)
              gen_log.debug(log_msg)
              return
  
          try:
              self._accept_connection()
          except ValueError:
              gen_log.debug("Malformed WebSocket request received",
                            exc_info=True)
              self._abort()
              return
  
      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
          """
          fields = ("Host", "Sec-Websocket-Key", "Sec-Websocket-Version")
          if not all(map(lambda f: self.request.headers.get(f), fields)):
              raise ValueError("Missing/Invalid WebSocket headers")
  
      @staticmethod
      def compute_accept_value(key):
          """Computes the value for the Sec-WebSocket-Accept header,
          given the value for Sec-WebSocket-Key.
          """
          sha1 = hashlib.sha1()
          sha1.update(utf8(key))
          sha1.update(b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11")  # Magic value
          return native_str(base64.b64encode(sha1.digest()))
  
      def _challenge_response(self):
          return WebSocketProtocol13.compute_accept_value(
              self.request.headers.get("Sec-Websocket-Key"))
  
      @gen.coroutine
      def _accept_connection(self):
          subprotocol_header = self.request.headers.get("Sec-WebSocket-Protocol")
          if subprotocol_header:
              subprotocols = [s.strip() for s in subprotocol_header.split(',')]
          else:
              subprotocols = []
          self.selected_subprotocol = self.handler.select_subprotocol(subprotocols)
          if self.selected_subprotocol:
              assert self.selected_subprotocol in subprotocols
              self.handler.set_header("Sec-WebSocket-Protocol", self.selected_subprotocol)
  
          extensions = self._parse_extensions_header(self.request.headers)
          for ext in extensions:
              if (ext[0] == 'permessage-deflate' and
                      self._compression_options is not None):
                  # TODO: negotiate parameters if compression_options
                  # specifies limits.
                  self._create_compressors('server', ext[1], self._compression_options)
                  if ('client_max_window_bits' in ext[1] and
                          ext[1]['client_max_window_bits'] is None):
                      # Don't echo an offered client_max_window_bits
                      # parameter with no value.
                      del ext[1]['client_max_window_bits']
                  self.handler.set_header("Sec-WebSocket-Extensions",
                                          httputil._encode_header(
                                              'permessage-deflate', ext[1]))
                  break
  
          self.handler.clear_header("Content-Type")
          self.handler.set_status(101)
          self.handler.set_header("Upgrade", "websocket")
          self.handler.set_header("Connection", "Upgrade")
          self.handler.set_header("Sec-WebSocket-Accept", self._challenge_response())
          self.handler.finish()
  
          self.handler._attach_stream()
          self.stream = self.handler.stream
  
          self.start_pinging()
          open_result = self._run_callback(self.handler.open, *self.handler.open_args,
                                           **self.handler.open_kwargs)
          if open_result is not None:
              yield open_result
          yield self._receive_frame_loop()
  
      def _parse_extensions_header(self, headers):
          extensions = headers.get("Sec-WebSocket-Extensions", '')
          if extensions:
              return [httputil._parse_header(e.strip())
                      for e in extensions.split(',')]
          return []
  
      def _process_server_headers(self, key, headers):
          """Process the headers sent by the server to this client connection.
  
          'key' is the websocket handshake challenge/response key.
          """
          assert headers['Upgrade'].lower() == 'websocket'
          assert headers['Connection'].lower() == 'upgrade'
          accept = self.compute_accept_value(key)
          assert headers['Sec-Websocket-Accept'] == accept
  
          extensions = self._parse_extensions_header(headers)
          for ext in extensions:
              if (ext[0] == 'permessage-deflate' and
                      self._compression_options is not None):
                  self._create_compressors('client', ext[1])
              else:
                  raise ValueError("unsupported extension %r", ext)
  
          self.selected_subprotocol = headers.get('Sec-WebSocket-Protocol', None)
  
      def _get_compressor_options(self, side, agreed_parameters, compression_options=None):
          """Converts a websocket agreed_parameters set to keyword arguments
          for our compressor objects.
          """
          options = dict(
              persistent=(side + '_no_context_takeover') not in agreed_parameters)
          wbits_header = agreed_parameters.get(side + '_max_window_bits', None)
          if wbits_header is None:
              options['max_wbits'] = zlib.MAX_WBITS
          else:
              options['max_wbits'] = int(wbits_header)
          options['compression_options'] = compression_options
          return options
  
      def _create_compressors(self, side, agreed_parameters, compression_options=None):
          # TODO: handle invalid parameters gracefully
          allowed_keys = set(['server_no_context_takeover',
                              'client_no_context_takeover',
                              'server_max_window_bits',
                              'client_max_window_bits'])
          for key in agreed_parameters:
              if key not in allowed_keys:
                  raise ValueError("unsupported compression parameter %r" % key)
          other_side = 'client' if (side == 'server') else 'server'
          self._compressor = _PerMessageDeflateCompressor(
              **self._get_compressor_options(side, agreed_parameters, compression_options))
          self._decompressor = _PerMessageDeflateDecompressor(
              max_message_size=self.handler.max_message_size,
              **self._get_compressor_options(other_side, agreed_parameters, compression_options))
  
      def _write_frame(self, fin, opcode, data, flags=0):
          data_len = len(data)
          if opcode & 0x8:
              # All control frames MUST have a payload length of 125
              # bytes or less and MUST NOT be fragmented.
              if not fin:
                  raise ValueError("control frames may not be fragmented")
              if data_len > 125:
                  raise ValueError("control frame payloads may not exceed 125 bytes")
          if fin:
              finbit = self.FIN
          else:
              finbit = 0
          frame = struct.pack("B", finbit | opcode | flags)
          if self.mask_outgoing:
              mask_bit = 0x80
          else:
              mask_bit = 0
          if data_len < 126:
              frame += struct.pack("B", data_len | mask_bit)
          elif data_len <= 0xFFFF:
              frame += struct.pack("!BH", 126 | mask_bit, data_len)
          else:
              frame += struct.pack("!BQ", 127 | mask_bit, data_len)
          if self.mask_outgoing:
              mask = os.urandom(4)
              data = mask + _websocket_mask(mask, data)
          frame += data
          self._wire_bytes_out += len(frame)
          return self.stream.write(frame)
  
      def write_message(self, message, binary=False):
          """Sends the given message to the client of this Web Socket."""
          if binary:
              opcode = 0x2
          else:
              opcode = 0x1
          message = tornado.escape.utf8(message)
          assert isinstance(message, bytes)
          self._message_bytes_out += len(message)
          flags = 0
          if self._compressor:
              message = self._compressor.compress(message)
              flags |= self.RSV1
          # For historical reasons, write methods in Tornado operate in a semi-synchronous
          # mode in which awaiting the Future they return is optional (But errors can
          # still be raised). This requires us to go through an awkward dance here
          # to transform the errors that may be returned while presenting the same
          # semi-synchronous interface.
          try:
              fut = self._write_frame(True, opcode, message, flags=flags)
          except StreamClosedError:
              raise WebSocketClosedError()
  
          @gen.coroutine
          def wrapper():
              try:
                  yield fut
              except StreamClosedError:
                  raise WebSocketClosedError()
          return wrapper()
  
      def write_ping(self, data):
          """Send ping frame."""
          assert isinstance(data, bytes)
          self._write_frame(True, 0x9, data)
  
      @gen.coroutine
      def _receive_frame_loop(self):
          try:
              while not self.client_terminated:
                  yield self._receive_frame()
          except StreamClosedError:
              self._abort()
  
      def _read_bytes(self, n):
          self._wire_bytes_in += n
          return self.stream.read_bytes(n)
  
      @gen.coroutine
      def _receive_frame(self):
          # Read the frame header.
          data = yield self._read_bytes(2)
          header, mask_payloadlen = struct.unpack("BB", data)
          is_final_frame = header & self.FIN
          reserved_bits = header & self.RSV_MASK
          opcode = header & self.OPCODE_MASK
          opcode_is_control = opcode & 0x8
          if self._decompressor is not None and opcode != 0:
              # Compression flag is present in the first frame's header,
              # but we can't decompress until we have all the frames of
              # the message.
              self._frame_compressed = bool(reserved_bits & self.RSV1)
              reserved_bits &= ~self.RSV1
          if reserved_bits:
              # client is using as-yet-undefined extensions; abort
              self._abort()
              return
          is_masked = bool(mask_payloadlen & 0x80)
          payloadlen = mask_payloadlen & 0x7f
  
          # Parse and validate the length.
          if opcode_is_control and payloadlen >= 126:
              # control frames must have payload < 126
              self._abort()
              return
          if payloadlen < 126:
              self._frame_length = payloadlen
          elif payloadlen == 126:
              data = yield self._read_bytes(2)
              payloadlen = struct.unpack("!H", data)[0]
          elif payloadlen == 127:
              data = yield self._read_bytes(8)
              payloadlen = struct.unpack("!Q", data)[0]
          new_len = payloadlen
          if self._fragmented_message_buffer is not None:
              new_len += len(self._fragmented_message_buffer)
          if new_len > self.handler.max_message_size:
              self.close(1009, "message too big")
              self._abort()
              return
  
          # Read the payload, unmasking if necessary.
          if is_masked:
              self._frame_mask = yield self._read_bytes(4)
          data = yield self._read_bytes(payloadlen)
          if is_masked:
              data = _websocket_mask(self._frame_mask, data)
  
          # Decide what to do with this frame.
          if opcode_is_control:
              # control frames may be interleaved with a series of fragmented
              # data frames, so control frames must not interact with
              # self._fragmented_*
              if not is_final_frame:
                  # control frames must not be fragmented
                  self._abort()
                  return
          elif opcode == 0:  # continuation frame
              if self._fragmented_message_buffer is None:
                  # nothing to continue
                  self._abort()
                  return
              self._fragmented_message_buffer += data
              if is_final_frame:
                  opcode = self._fragmented_message_opcode
                  data = self._fragmented_message_buffer
                  self._fragmented_message_buffer = None
          else:  # start of new data message
              if self._fragmented_message_buffer is not None:
                  # can't start new message until the old one is finished
                  self._abort()
                  return
              if not is_final_frame:
                  self._fragmented_message_opcode = opcode
                  self._fragmented_message_buffer = data
  
          if is_final_frame:
              handled_future = self._handle_message(opcode, data)
              if handled_future is not None:
                  yield handled_future
  
      def _handle_message(self, opcode, data):
          """Execute on_message, returning its Future if it is a coroutine."""
          if self.client_terminated:
              return
  
          if self._frame_compressed:
              try:
                  data = self._decompressor.decompress(data)
              except _DecompressTooLargeError:
                  self.close(1009, "message too big after decompression")
                  self._abort()
                  return
  
          if opcode == 0x1:
              # UTF-8 data
              self._message_bytes_in += len(data)
              try:
                  decoded = data.decode("utf-8")
              except UnicodeDecodeError:
                  self._abort()
                  return
              return self._run_callback(self.handler.on_message, decoded)
          elif opcode == 0x2:
              # Binary data
              self._message_bytes_in += len(data)
              return self._run_callback(self.handler.on_message, data)
          elif opcode == 0x8:
              # Close
              self.client_terminated = True
              if len(data) >= 2:
                  self.handler.close_code = struct.unpack('>H', data[:2])[0]
              if len(data) > 2:
                  self.handler.close_reason = to_unicode(data[2:])
              # Echo the received close code, if any (RFC 6455 section 5.5.1).
              self.close(self.handler.close_code)
          elif opcode == 0x9:
              # Ping
              try:
                  self._write_frame(True, 0xA, data)
              except StreamClosedError:
                  self._abort()
              self._run_callback(self.handler.on_ping, data)
          elif opcode == 0xA:
              # Pong
              self.last_pong = IOLoop.current().time()
              return self._run_callback(self.handler.on_pong, data)
          else:
              self._abort()
  
      def close(self, code=None, reason=None):
          """Closes the WebSocket connection."""
          if not self.server_terminated:
              if not self.stream.closed():
                  if code is None and reason is not None:
                      code = 1000  # "normal closure" status code
                  if code is None:
                      close_data = b''
                  else:
                      close_data = struct.pack('>H', code)
                  if reason is not None:
                      close_data += utf8(reason)
                  try:
                      self._write_frame(True, 0x8, close_data)
                  except StreamClosedError:
                      self._abort()
              self.server_terminated = True
          if self.client_terminated:
              if self._waiting is not None:
                  self.stream.io_loop.remove_timeout(self._waiting)
                  self._waiting = None
              self.stream.close()
          elif self._waiting is None:
              # Give the client a few seconds to complete a clean shutdown,
              # otherwise just close the connection.
              self._waiting = self.stream.io_loop.add_timeout(
                  self.stream.io_loop.time() + 5, self._abort)
  
      def is_closing(self):
          """Return true if this connection is closing.
  
          The connection is considered closing if either side has
          initiated its closing handshake or if the stream has been
          shut down uncleanly.
          """
          return (self.stream.closed() or
                  self.client_terminated or
                  self.server_terminated)
  
      @property
      def ping_interval(self):
          interval = self.handler.ping_interval
          if interval is not None:
              return interval
          return 0
  
      @property
      def ping_timeout(self):
          timeout = self.handler.ping_timeout
          if timeout is not None:
              return timeout
          return max(3 * self.ping_interval, 30)
  
      def start_pinging(self):
          """Start sending periodic pings to keep the connection alive"""
          if self.ping_interval > 0:
              self.last_ping = self.last_pong = IOLoop.current().time()
              self.ping_callback = PeriodicCallback(
                  self.periodic_ping, self.ping_interval * 1000)
              self.ping_callback.start()
  
      def periodic_ping(self):
          """Send a ping to keep the websocket alive
  
          Called periodically if the websocket_ping_interval is set and non-zero.
          """
          if self.is_closing() and self.ping_callback is not None:
              self.ping_callback.stop()
              return
  
          # Check for timeout on pong. Make sure that we really have
          # sent a recent ping in case the machine with both server and
          # client has been suspended since the last ping.
          now = IOLoop.current().time()
          since_last_pong = now - self.last_pong
          since_last_ping = now - self.last_ping
          if (since_last_ping < 2 * self.ping_interval and
                  since_last_pong > self.ping_timeout):
              self.close()
              return
  
          self.write_ping(b'')
          self.last_ping = now
  
  
  class WebSocketClientConnection(simple_httpclient._HTTPConnection):
      """WebSocket client connection.
  
      This class should not be instantiated directly; use the
      `websocket_connect` function instead.
      """
      def __init__(self, request, on_message_callback=None,
                   compression_options=None, ping_interval=None, ping_timeout=None,
                   max_message_size=None, subprotocols=[]):
          self.compression_options = compression_options
          self.connect_future = Future()
          self.protocol = None
          self.read_queue = Queue(1)
          self.key = base64.b64encode(os.urandom(16))
          self._on_message_callback = on_message_callback
          self.close_code = self.close_reason = None
          self.ping_interval = ping_interval
          self.ping_timeout = ping_timeout
          self.max_message_size = max_message_size
  
          scheme, sep, rest = request.url.partition(':')
          scheme = {'ws': 'http', 'wss': 'https'}[scheme]
          request.url = scheme + sep + rest
          request.headers.update({
              'Upgrade': 'websocket',
              'Connection': 'Upgrade',
              'Sec-WebSocket-Key': self.key,
              'Sec-WebSocket-Version': '13',
          })
          if subprotocols is not None:
              request.headers['Sec-WebSocket-Protocol'] = ','.join(subprotocols)
          if self.compression_options is not None:
              # Always offer to let the server set our max_wbits (and even though
              # we don't offer it, we will accept a client_no_context_takeover
              # from the server).
              # TODO: set server parameters for deflate extension
              # if requested in self.compression_options.
              request.headers['Sec-WebSocket-Extensions'] = (
                  'permessage-deflate; client_max_window_bits')
  
          self.tcp_client = TCPClient()
          super(WebSocketClientConnection, self).__init__(
              None, request, lambda: None, self._on_http_response,
              104857600, self.tcp_client, 65536, 104857600)
  
      def close(self, code=None, reason=None):
          """Closes the websocket connection.
  
          ``code`` and ``reason`` are documented under
          `WebSocketHandler.close`.
  
          .. versionadded:: 3.2
  
          .. versionchanged:: 4.0
  
             Added the ``code`` and ``reason`` arguments.
          """
          if self.protocol is not None:
              self.protocol.close(code, reason)
              self.protocol = None
  
      def on_connection_close(self):
          if not self.connect_future.done():
              self.connect_future.set_exception(StreamClosedError())
          self.on_message(None)
          self.tcp_client.close()
          super(WebSocketClientConnection, self).on_connection_close()
  
      def _on_http_response(self, response):
          if not self.connect_future.done():
              if response.error:
                  self.connect_future.set_exception(response.error)
              else:
                  self.connect_future.set_exception(WebSocketError(
                      "Non-websocket response"))
  
      def headers_received(self, start_line, headers):
          if start_line.code != 101:
              return super(WebSocketClientConnection, self).headers_received(
                  start_line, headers)
  
          self.headers = headers
          self.protocol = self.get_websocket_protocol()
          self.protocol._process_server_headers(self.key, self.headers)
          self.protocol.start_pinging()
          IOLoop.current().add_callback(self.protocol._receive_frame_loop)
  
          if self._timeout is not None:
              self.io_loop.remove_timeout(self._timeout)
              self._timeout = None
  
          self.stream = self.connection.detach()
          self.stream.set_close_callback(self.on_connection_close)
          # Once we've taken over the connection, clear the final callback
          # we set on the http request.  This deactivates the error handling
          # in simple_httpclient that would otherwise interfere with our
          # ability to see exceptions.
          self.final_callback = None
  
          future_set_result_unless_cancelled(self.connect_future, self)
  
      def write_message(self, message, binary=False):
          """Sends a message to the WebSocket server.
  
          If the stream is closed, raises `WebSocketClosedError`.
          Returns a `.Future` which can be used for flow control.
  
          .. versionchanged:: 5.0
             Exception raised on a closed stream changed from `.StreamClosedError`
             to `WebSocketClosedError`.
          """
          return self.protocol.write_message(message, binary=binary)
  
      def read_message(self, callback=None):
          """Reads a message from the WebSocket server.
  
          If on_message_callback was specified at WebSocket
          initialization, this function will never return messages
  
          Returns a future whose result is the message, or None
          if the connection is closed.  If a callback argument
          is given it will be called with the future when it is
          ready.
          """
  
          future = self.read_queue.get()
          if callback is not None:
              self.io_loop.add_future(future, callback)
          return future
  
      def on_message(self, message):
          if self._on_message_callback:
              self._on_message_callback(message)
          else:
              return self.read_queue.put(message)
  
      def ping(self, data=b''):
          """Send ping frame to the remote end.
  
          The data argument allows a small amount of data (up to 125
          bytes) to be sent as a part of the ping message. Note that not
          all websocket implementations expose this data to
          applications.
  
          Consider using the ``ping_interval`` argument to
          `websocket_connect` instead of sending pings manually.
  
          .. versionadded:: 5.1
  
          """
          data = utf8(data)
          if self.protocol is None:
              raise WebSocketClosedError()
          self.protocol.write_ping(data)
  
      def on_pong(self, data):
          pass
  
      def on_ping(self, data):
          pass
  
      def get_websocket_protocol(self):
          return WebSocketProtocol13(self, mask_outgoing=True,
                                     compression_options=self.compression_options)
  
      @property
      def selected_subprotocol(self):
          """The subprotocol selected by the server.
  
          .. versionadded:: 5.1
          """
          return self.protocol.selected_subprotocol
  
  
  def websocket_connect(url, callback=None, connect_timeout=None,
                        on_message_callback=None, compression_options=None,
                        ping_interval=None, ping_timeout=None,
                        max_message_size=_default_max_message_size, subprotocols=None):
      """Client-side websocket support.
  
      Takes a url and returns a Future whose result is a
      `WebSocketClientConnection`.
  
      ``compression_options`` is interpreted in the same way as the
      return value of `.WebSocketHandler.get_compression_options`.
  
      The connection supports two styles of operation. In the coroutine
      style, the application typically calls
      `~.WebSocketClientConnection.read_message` in a loop::
  
          conn = yield websocket_connect(url)
          while True:
              msg = yield conn.read_message()
              if msg is None: break
              # Do something with msg
  
      In the callback style, pass an ``on_message_callback`` to
      ``websocket_connect``. In both styles, a message of ``None``
      indicates that the connection has been closed.
  
      ``subprotocols`` may be a list of strings specifying proposed
      subprotocols. The selected protocol may be found on the
      ``selected_subprotocol`` attribute of the connection object
      when the connection is complete.
  
      .. versionchanged:: 3.2
         Also accepts ``HTTPRequest`` objects in place of urls.
  
      .. versionchanged:: 4.1
         Added ``compression_options`` and ``on_message_callback``.
  
      .. versionchanged:: 4.5
         Added the ``ping_interval``, ``ping_timeout``, and ``max_message_size``
         arguments, which have the same meaning as in `WebSocketHandler`.
  
      .. versionchanged:: 5.0
         The ``io_loop`` argument (deprecated since version 4.1) has been removed.
  
      .. versionchanged:: 5.1
         Added the ``subprotocols`` argument.
      """
      if isinstance(url, httpclient.HTTPRequest):
          assert connect_timeout is None
          request = url
          # Copy and convert the headers dict/object (see comments in
          # AsyncHTTPClient.fetch)
          request.headers = httputil.HTTPHeaders(request.headers)
      else:
          request = httpclient.HTTPRequest(url, connect_timeout=connect_timeout)
      request = httpclient._RequestProxy(
          request, httpclient.HTTPRequest._DEFAULTS)
      conn = WebSocketClientConnection(request,
                                       on_message_callback=on_message_callback,
                                       compression_options=compression_options,
                                       ping_interval=ping_interval,
                                       ping_timeout=ping_timeout,
                                       max_message_size=max_message_size,
                                       subprotocols=subprotocols)
      if callback is not None:
          IOLoop.current().add_future(conn.connect_future, callback)
      return conn.connect_future
  