import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

testing/mochitest/pywebsocket/mod_pywebsocket/extensions.py

@@ -0,0 +1,764 @@
+# Copyright 2012, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+from mod_pywebsocket import common
+from mod_pywebsocket import util
+from mod_pywebsocket.http_header_util import quote_if_necessary
+
+
+# The list of available server side extension processor classes.
+_available_processors = {}
+_compression_extension_names = []
+
+
+class ExtensionProcessorInterface(object):
+
+    def __init__(self, request):
+        self._logger = util.get_class_logger(self)
+
+        self._request = request
+        self._active = True
+
+    def request(self):
+        return self._request
+
+    def name(self):
+        return None
+
+    def check_consistency_with_other_processors(self, processors):
+        pass
+
+    def set_active(self, active):
+        self._active = active
+
+    def is_active(self):
+        return self._active
+
+    def _get_extension_response_internal(self):
+        return None
+
+    def get_extension_response(self):
+        if not self._active:
+            self._logger.debug('Extension %s is deactivated', self.name())
+            return None
+
+        response = self._get_extension_response_internal()
+        if response is None:
+            self._active = False
+        return response
+
+    def _setup_stream_options_internal(self, stream_options):
+        pass
+
+    def setup_stream_options(self, stream_options):
+        if self._active:
+            self._setup_stream_options_internal(stream_options)
+
+
+def _log_outgoing_compression_ratio(
+        logger, original_bytes, filtered_bytes, average_ratio):
+    # Print inf when ratio is not available.
+    ratio = float('inf')
+    if original_bytes != 0:
+        ratio = float(filtered_bytes) / original_bytes
+
+    logger.debug('Outgoing compression ratio: %f (average: %f)' %
+            (ratio, average_ratio))
+
+
+def _log_incoming_compression_ratio(
+        logger, received_bytes, filtered_bytes, average_ratio):
+    # Print inf when ratio is not available.
+    ratio = float('inf')
+    if filtered_bytes != 0:
+        ratio = float(received_bytes) / filtered_bytes
+
+    logger.debug('Incoming compression ratio: %f (average: %f)' %
+            (ratio, average_ratio))
+
+
+def _parse_window_bits(bits):
+    """Return parsed integer value iff the given string conforms to the
+    grammar of the window bits extension parameters.
+    """
+
+    if bits is None:
+        raise ValueError('Value is required')
+
+    # For non integer values such as "10.0", ValueError will be raised.
+    int_bits = int(bits)
+
+    # First condition is to drop leading zero case e.g. "08".
+    if bits != str(int_bits) or int_bits < 8 or int_bits > 15:
+        raise ValueError('Invalid value: %r' % bits)
+
+    return int_bits
+
+
+class _AverageRatioCalculator(object):
+    """Stores total bytes of original and result data, and calculates average
+    result / original ratio.
+    """
+
+    def __init__(self):
+        self._total_original_bytes = 0
+        self._total_result_bytes = 0
+
+    def add_original_bytes(self, value):
+        self._total_original_bytes += value
+
+    def add_result_bytes(self, value):
+        self._total_result_bytes += value
+
+    def get_average_ratio(self):
+        if self._total_original_bytes != 0:
+            return (float(self._total_result_bytes) /
+                    self._total_original_bytes)
+        else:
+            return float('inf')
+
+
+class DeflateFrameExtensionProcessor(ExtensionProcessorInterface):
+    """deflate-frame extension processor.
+
+    Specification:
+    http://tools.ietf.org/html/draft-tyoshino-hybi-websocket-perframe-deflate
+    """
+
+    _WINDOW_BITS_PARAM = 'max_window_bits'
+    _NO_CONTEXT_TAKEOVER_PARAM = 'no_context_takeover'
+
+    def __init__(self, request):
+        ExtensionProcessorInterface.__init__(self, request)
+        self._logger = util.get_class_logger(self)
+
+        self._response_window_bits = None
+        self._response_no_context_takeover = False
+        self._bfinal = False
+
+        # Calculates
+        #     (Total outgoing bytes supplied to this filter) /
+        #     (Total bytes sent to the network after applying this filter)
+        self._outgoing_average_ratio_calculator = _AverageRatioCalculator()
+
+        # Calculates
+        #     (Total bytes received from the network) /
+        #     (Total incoming bytes obtained after applying this filter)
+        self._incoming_average_ratio_calculator = _AverageRatioCalculator()
+
+    def name(self):
+        return common.DEFLATE_FRAME_EXTENSION
+
+    def _get_extension_response_internal(self):
+        # Any unknown parameter will be just ignored.
+
+        window_bits = None
+        if self._request.has_parameter(self._WINDOW_BITS_PARAM):
+            window_bits = self._request.get_parameter_value(
+                self._WINDOW_BITS_PARAM)
+            try:
+                window_bits = _parse_window_bits(window_bits)
+            except ValueError, e:
+                return None
+
+        no_context_takeover = self._request.has_parameter(
+            self._NO_CONTEXT_TAKEOVER_PARAM)
+        if (no_context_takeover and
+            self._request.get_parameter_value(
+                self._NO_CONTEXT_TAKEOVER_PARAM) is not None):
+            return None
+
+        self._rfc1979_deflater = util._RFC1979Deflater(
+            window_bits, no_context_takeover)
+
+        self._rfc1979_inflater = util._RFC1979Inflater()
+
+        self._compress_outgoing = True
+
+        response = common.ExtensionParameter(self._request.name())
+
+        if self._response_window_bits is not None:
+            response.add_parameter(
+                self._WINDOW_BITS_PARAM, str(self._response_window_bits))
+        if self._response_no_context_takeover:
+            response.add_parameter(
+                self._NO_CONTEXT_TAKEOVER_PARAM, None)
+
+        self._logger.debug(
+            'Enable %s extension ('
+            'request: window_bits=%s; no_context_takeover=%r, '
+            'response: window_wbits=%s; no_context_takeover=%r)' %
+            (self._request.name(),
+             window_bits,
+             no_context_takeover,
+             self._response_window_bits,
+             self._response_no_context_takeover))
+
+        return response
+
+    def _setup_stream_options_internal(self, stream_options):
+
+        class _OutgoingFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+
+            def filter(self, frame):
+                self._parent._outgoing_filter(frame)
+
+        class _IncomingFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+
+            def filter(self, frame):
+                self._parent._incoming_filter(frame)
+
+        stream_options.outgoing_frame_filters.append(
+            _OutgoingFilter(self))
+        stream_options.incoming_frame_filters.insert(
+            0, _IncomingFilter(self))
+
+    def set_response_window_bits(self, value):
+        self._response_window_bits = value
+
+    def set_response_no_context_takeover(self, value):
+        self._response_no_context_takeover = value
+
+    def set_bfinal(self, value):
+        self._bfinal = value
+
+    def enable_outgoing_compression(self):
+        self._compress_outgoing = True
+
+    def disable_outgoing_compression(self):
+        self._compress_outgoing = False
+
+    def _outgoing_filter(self, frame):
+        """Transform outgoing frames. This method is called only by
+        an _OutgoingFilter instance.
+        """
+
+        original_payload_size = len(frame.payload)
+        self._outgoing_average_ratio_calculator.add_original_bytes(
+                original_payload_size)
+
+        if (not self._compress_outgoing or
+            common.is_control_opcode(frame.opcode)):
+            self._outgoing_average_ratio_calculator.add_result_bytes(
+                    original_payload_size)
+            return
+
+        frame.payload = self._rfc1979_deflater.filter(
+            frame.payload, bfinal=self._bfinal)
+        frame.rsv1 = 1
+
+        filtered_payload_size = len(frame.payload)
+        self._outgoing_average_ratio_calculator.add_result_bytes(
+                filtered_payload_size)
+
+        _log_outgoing_compression_ratio(
+                self._logger,
+                original_payload_size,
+                filtered_payload_size,
+                self._outgoing_average_ratio_calculator.get_average_ratio())
+
+    def _incoming_filter(self, frame):
+        """Transform incoming frames. This method is called only by
+        an _IncomingFilter instance.
+        """
+
+        received_payload_size = len(frame.payload)
+        self._incoming_average_ratio_calculator.add_result_bytes(
+                received_payload_size)
+
+        if frame.rsv1 != 1 or common.is_control_opcode(frame.opcode):
+            self._incoming_average_ratio_calculator.add_original_bytes(
+                    received_payload_size)
+            return
+
+        frame.payload = self._rfc1979_inflater.filter(frame.payload)
+        frame.rsv1 = 0
+
+        filtered_payload_size = len(frame.payload)
+        self._incoming_average_ratio_calculator.add_original_bytes(
+                filtered_payload_size)
+
+        _log_incoming_compression_ratio(
+                self._logger,
+                received_payload_size,
+                filtered_payload_size,
+                self._incoming_average_ratio_calculator.get_average_ratio())
+
+
+_available_processors[common.DEFLATE_FRAME_EXTENSION] = (
+    DeflateFrameExtensionProcessor)
+_compression_extension_names.append(common.DEFLATE_FRAME_EXTENSION)
+
+_available_processors[common.X_WEBKIT_DEFLATE_FRAME_EXTENSION] = (
+    DeflateFrameExtensionProcessor)
+_compression_extension_names.append(common.X_WEBKIT_DEFLATE_FRAME_EXTENSION)
+
+
+class PerMessageDeflateExtensionProcessor(ExtensionProcessorInterface):
+    """permessage-deflate extension processor.
+
+    Specification:
+    http://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-08
+    """
+
+    _SERVER_MAX_WINDOW_BITS_PARAM = 'server_max_window_bits'
+    _SERVER_NO_CONTEXT_TAKEOVER_PARAM = 'server_no_context_takeover'
+    _CLIENT_MAX_WINDOW_BITS_PARAM = 'client_max_window_bits'
+    _CLIENT_NO_CONTEXT_TAKEOVER_PARAM = 'client_no_context_takeover'
+
+    def __init__(self, request, draft08=True):
+        """Construct PerMessageDeflateExtensionProcessor
+
+        Args:
+            draft08: Follow the constraints on the parameters that were not
+                specified for permessage-compress but are specified for
+                permessage-deflate as on
+                draft-ietf-hybi-permessage-compression-08.
+        """
+
+        ExtensionProcessorInterface.__init__(self, request)
+        self._logger = util.get_class_logger(self)
+
+        self._preferred_client_max_window_bits = None
+        self._client_no_context_takeover = False
+
+        self._draft08 = draft08
+
+    def name(self):
+        # This method returns "deflate" (not "permessage-deflate") for
+        # compatibility.
+        return 'deflate'
+
+    def _get_extension_response_internal(self):
+        if self._draft08:
+            for name in self._request.get_parameter_names():
+                if name not in [self._SERVER_MAX_WINDOW_BITS_PARAM,
+                                self._SERVER_NO_CONTEXT_TAKEOVER_PARAM,
+                                self._CLIENT_MAX_WINDOW_BITS_PARAM]:
+                    self._logger.debug('Unknown parameter: %r', name)
+                    return None
+        else:
+            # Any unknown parameter will be just ignored.
+            pass
+
+        server_max_window_bits = None
+        if self._request.has_parameter(self._SERVER_MAX_WINDOW_BITS_PARAM):
+            server_max_window_bits = self._request.get_parameter_value(
+                    self._SERVER_MAX_WINDOW_BITS_PARAM)
+            try:
+                server_max_window_bits = _parse_window_bits(
+                    server_max_window_bits)
+            except ValueError, e:
+                self._logger.debug('Bad %s parameter: %r',
+                                   self._SERVER_MAX_WINDOW_BITS_PARAM,
+                                   e)
+                return None
+
+        server_no_context_takeover = self._request.has_parameter(
+            self._SERVER_NO_CONTEXT_TAKEOVER_PARAM)
+        if (server_no_context_takeover and
+            self._request.get_parameter_value(
+                self._SERVER_NO_CONTEXT_TAKEOVER_PARAM) is not None):
+            self._logger.debug('%s parameter must not have a value: %r',
+                               self._SERVER_NO_CONTEXT_TAKEOVER_PARAM,
+                               server_no_context_takeover)
+            return None
+
+        # client_max_window_bits from a client indicates whether the client can
+        # accept client_max_window_bits from a server or not.
+        client_client_max_window_bits = self._request.has_parameter(
+            self._CLIENT_MAX_WINDOW_BITS_PARAM)
+        if (self._draft08 and
+            client_client_max_window_bits and
+            self._request.get_parameter_value(
+                self._CLIENT_MAX_WINDOW_BITS_PARAM) is not None):
+            self._logger.debug('%s parameter must not have a value in a '
+                               'client\'s opening handshake: %r',
+                               self._CLIENT_MAX_WINDOW_BITS_PARAM,
+                               client_client_max_window_bits)
+            return None
+
+        self._rfc1979_deflater = util._RFC1979Deflater(
+            server_max_window_bits, server_no_context_takeover)
+
+        # Note that we prepare for incoming messages compressed with window
+        # bits upto 15 regardless of the client_max_window_bits value to be
+        # sent to the client.
+        self._rfc1979_inflater = util._RFC1979Inflater()
+
+        self._framer = _PerMessageDeflateFramer(
+            server_max_window_bits, server_no_context_takeover)
+        self._framer.set_bfinal(False)
+        self._framer.set_compress_outgoing_enabled(True)
+
+        response = common.ExtensionParameter(self._request.name())
+
+        if server_max_window_bits is not None:
+            response.add_parameter(
+                self._SERVER_MAX_WINDOW_BITS_PARAM,
+                str(server_max_window_bits))
+
+        if server_no_context_takeover:
+            response.add_parameter(
+                self._SERVER_NO_CONTEXT_TAKEOVER_PARAM, None)
+
+        if self._preferred_client_max_window_bits is not None:
+            if self._draft08 and not client_client_max_window_bits:
+                self._logger.debug('Processor is configured to use %s but '
+                                   'the client cannot accept it',
+                                   self._CLIENT_MAX_WINDOW_BITS_PARAM)
+                return None
+            response.add_parameter(
+                self._CLIENT_MAX_WINDOW_BITS_PARAM,
+                str(self._preferred_client_max_window_bits))
+
+        if self._client_no_context_takeover:
+            response.add_parameter(
+                self._CLIENT_NO_CONTEXT_TAKEOVER_PARAM, None)
+
+        self._logger.debug(
+            'Enable %s extension ('
+            'request: server_max_window_bits=%s; '
+            'server_no_context_takeover=%r, '
+            'response: client_max_window_bits=%s; '
+            'client_no_context_takeover=%r)' %
+            (self._request.name(),
+             server_max_window_bits,
+             server_no_context_takeover,
+             self._preferred_client_max_window_bits,
+             self._client_no_context_takeover))
+
+        return response
+
+    def _setup_stream_options_internal(self, stream_options):
+        self._framer.setup_stream_options(stream_options)
+
+    def set_client_max_window_bits(self, value):
+        """If this option is specified, this class adds the
+        client_max_window_bits extension parameter to the handshake response,
+        but doesn't reduce the LZ77 sliding window size of its inflater.
+        I.e., you can use this for testing client implementation but cannot
+        reduce memory usage of this class.
+
+        If this method has been called with True and an offer without the
+        client_max_window_bits extension parameter is received,
+        - (When processing the permessage-deflate extension) this processor
+          declines the request.
+        - (When processing the permessage-compress extension) this processor
+          accepts the request.
+        """
+
+        self._preferred_client_max_window_bits = value
+
+    def set_client_no_context_takeover(self, value):
+        """If this option is specified, this class adds the
+        client_no_context_takeover extension parameter to the handshake
+        response, but doesn't reset inflater for each message. I.e., you can
+        use this for testing client implementation but cannot reduce memory
+        usage of this class.
+        """
+
+        self._client_no_context_takeover = value
+
+    def set_bfinal(self, value):
+        self._framer.set_bfinal(value)
+
+    def enable_outgoing_compression(self):
+        self._framer.set_compress_outgoing_enabled(True)
+
+    def disable_outgoing_compression(self):
+        self._framer.set_compress_outgoing_enabled(False)
+
+
+class _PerMessageDeflateFramer(object):
+    """A framer for extensions with per-message DEFLATE feature."""
+
+    def __init__(self, deflate_max_window_bits, deflate_no_context_takeover):
+        self._logger = util.get_class_logger(self)
+
+        self._rfc1979_deflater = util._RFC1979Deflater(
+            deflate_max_window_bits, deflate_no_context_takeover)
+
+        self._rfc1979_inflater = util._RFC1979Inflater()
+
+        self._bfinal = False
+
+        self._compress_outgoing_enabled = False
+
+        # True if a message is fragmented and compression is ongoing.
+        self._compress_ongoing = False
+
+        # Calculates
+        #     (Total outgoing bytes supplied to this filter) /
+        #     (Total bytes sent to the network after applying this filter)
+        self._outgoing_average_ratio_calculator = _AverageRatioCalculator()
+
+        # Calculates
+        #     (Total bytes received from the network) /
+        #     (Total incoming bytes obtained after applying this filter)
+        self._incoming_average_ratio_calculator = _AverageRatioCalculator()
+
+    def set_bfinal(self, value):
+        self._bfinal = value
+
+    def set_compress_outgoing_enabled(self, value):
+        self._compress_outgoing_enabled = value
+
+    def _process_incoming_message(self, message, decompress):
+        if not decompress:
+            return message
+
+        received_payload_size = len(message)
+        self._incoming_average_ratio_calculator.add_result_bytes(
+                received_payload_size)
+
+        message = self._rfc1979_inflater.filter(message)
+
+        filtered_payload_size = len(message)
+        self._incoming_average_ratio_calculator.add_original_bytes(
+                filtered_payload_size)
+
+        _log_incoming_compression_ratio(
+                self._logger,
+                received_payload_size,
+                filtered_payload_size,
+                self._incoming_average_ratio_calculator.get_average_ratio())
+
+        return message
+
+    def _process_outgoing_message(self, message, end, binary):
+        if not binary:
+            message = message.encode('utf-8')
+
+        if not self._compress_outgoing_enabled:
+            return message
+
+        original_payload_size = len(message)
+        self._outgoing_average_ratio_calculator.add_original_bytes(
+            original_payload_size)
+
+        message = self._rfc1979_deflater.filter(
+            message, end=end, bfinal=self._bfinal)
+
+        filtered_payload_size = len(message)
+        self._outgoing_average_ratio_calculator.add_result_bytes(
+            filtered_payload_size)
+
+        _log_outgoing_compression_ratio(
+                self._logger,
+                original_payload_size,
+                filtered_payload_size,
+                self._outgoing_average_ratio_calculator.get_average_ratio())
+
+        if not self._compress_ongoing:
+            self._outgoing_frame_filter.set_compression_bit()
+        self._compress_ongoing = not end
+        return message
+
+    def _process_incoming_frame(self, frame):
+        if frame.rsv1 == 1 and not common.is_control_opcode(frame.opcode):
+            self._incoming_message_filter.decompress_next_message()
+            frame.rsv1 = 0
+
+    def _process_outgoing_frame(self, frame, compression_bit):
+        if (not compression_bit or
+            common.is_control_opcode(frame.opcode)):
+            return
+
+        frame.rsv1 = 1
+
+    def setup_stream_options(self, stream_options):
+        """Creates filters and sets them to the StreamOptions."""
+
+        class _OutgoingMessageFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+
+            def filter(self, message, end=True, binary=False):
+                return self._parent._process_outgoing_message(
+                    message, end, binary)
+
+        class _IncomingMessageFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+                self._decompress_next_message = False
+
+            def decompress_next_message(self):
+                self._decompress_next_message = True
+
+            def filter(self, message):
+                message = self._parent._process_incoming_message(
+                    message, self._decompress_next_message)
+                self._decompress_next_message = False
+                return message
+
+        self._outgoing_message_filter = _OutgoingMessageFilter(self)
+        self._incoming_message_filter = _IncomingMessageFilter(self)
+        stream_options.outgoing_message_filters.append(
+            self._outgoing_message_filter)
+        stream_options.incoming_message_filters.append(
+            self._incoming_message_filter)
+
+        class _OutgoingFrameFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+                self._set_compression_bit = False
+
+            def set_compression_bit(self):
+                self._set_compression_bit = True
+
+            def filter(self, frame):
+                self._parent._process_outgoing_frame(
+                    frame, self._set_compression_bit)
+                self._set_compression_bit = False
+
+        class _IncomingFrameFilter(object):
+
+            def __init__(self, parent):
+                self._parent = parent
+
+            def filter(self, frame):
+                self._parent._process_incoming_frame(frame)
+
+        self._outgoing_frame_filter = _OutgoingFrameFilter(self)
+        self._incoming_frame_filter = _IncomingFrameFilter(self)
+        stream_options.outgoing_frame_filters.append(
+            self._outgoing_frame_filter)
+        stream_options.incoming_frame_filters.append(
+            self._incoming_frame_filter)
+
+        stream_options.encode_text_message_to_utf8 = False
+
+
+_available_processors[common.PERMESSAGE_DEFLATE_EXTENSION] = (
+        PerMessageDeflateExtensionProcessor)
+# TODO(tyoshino): Reorganize class names.
+_compression_extension_names.append('deflate')
+
+
+class MuxExtensionProcessor(ExtensionProcessorInterface):
+    """WebSocket multiplexing extension processor."""
+
+    _QUOTA_PARAM = 'quota'
+
+    def __init__(self, request):
+        ExtensionProcessorInterface.__init__(self, request)
+        self._quota = 0
+        self._extensions = []
+
+    def name(self):
+        return common.MUX_EXTENSION
+
+    def check_consistency_with_other_processors(self, processors):
+        before_mux = True
+        for processor in processors:
+            name = processor.name()
+            if name == self.name():
+                before_mux = False
+                continue
+            if not processor.is_active():
+                continue
+            if before_mux:
+                # Mux extension cannot be used after extensions
+                # that depend on frame boundary, extension data field, or any
+                # reserved bits which are attributed to each frame.
+                if (name == common.DEFLATE_FRAME_EXTENSION or
+                    name == common.X_WEBKIT_DEFLATE_FRAME_EXTENSION):
+                    self.set_active(False)
+                    return
+            else:
+                # Mux extension should not be applied before any history-based
+                # compression extension.
+                if (name == 'deflate' or
+                    name == common.DEFLATE_FRAME_EXTENSION or
+                    name == common.X_WEBKIT_DEFLATE_FRAME_EXTENSION):
+                    self.set_active(False)
+                    return
+
+    def _get_extension_response_internal(self):
+        self._active = False
+        quota = self._request.get_parameter_value(self._QUOTA_PARAM)
+        if quota is not None:
+            try:
+                quota = int(quota)
+            except ValueError, e:
+                return None
+            if quota < 0 or quota >= 2 ** 32:
+                return None
+            self._quota = quota
+
+        self._active = True
+        return common.ExtensionParameter(common.MUX_EXTENSION)
+
+    def _setup_stream_options_internal(self, stream_options):
+        pass
+
+    def set_quota(self, quota):
+        self._quota = quota
+
+    def quota(self):
+        return self._quota
+
+    def set_extensions(self, extensions):
+        self._extensions = extensions
+
+    def extensions(self):
+        return self._extensions
+
+
+_available_processors[common.MUX_EXTENSION] = MuxExtensionProcessor
+
+
+def get_extension_processor(extension_request):
+    """Given an ExtensionParameter representing an extension offer received
+    from a client, configures and returns an instance of the corresponding
+    extension processor class.
+    """
+
+    processor_class = _available_processors.get(extension_request.name())
+    if processor_class is None:
+        return None
+    return processor_class(extension_request)
+
+
+def is_compression_extension(extension_name):
+    return extension_name in _compression_extension_names
+
+
+# vi:sts=4 sw=4 et