1# Copyright 2012, Google Inc.
2# All rights reserved.
3#
4# Redistribution and use in source and binary forms, with or without
5# modification, are permitted provided that the following conditions are
6# met:
7#
8#     * Redistributions of source code must retain the above copyright
9# notice, this list of conditions and the following disclaimer.
10#     * Redistributions in binary form must reproduce the above
11# copyright notice, this list of conditions and the following disclaimer
12# in the documentation and/or other materials provided with the
13# distribution.
14#     * Neither the name of Google Inc. nor the names of its
15# contributors may be used to endorse or promote products derived from
16# this software without specific prior written permission.
17#
18# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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21# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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24# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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28# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29"""This file provides the opening handshake processor for the WebSocket
30protocol (RFC 6455).
31
32Specification:
33http://tools.ietf.org/html/rfc6455
34"""
35
36from __future__ import absolute_import
37import base64
38import logging
39import os
40import re
41from hashlib import sha1
42
43from mod_pywebsocket import common
44from mod_pywebsocket.extensions import get_extension_processor
45from mod_pywebsocket.handshake._base import check_request_line
46from mod_pywebsocket.handshake._base import format_header
47from mod_pywebsocket.handshake._base import get_mandatory_header
48from mod_pywebsocket.handshake._base import HandshakeException
49from mod_pywebsocket.handshake._base import parse_token_list
50from mod_pywebsocket.handshake._base import validate_mandatory_header
51from mod_pywebsocket.handshake._base import validate_subprotocol
52from mod_pywebsocket.handshake._base import VersionException
53from mod_pywebsocket.stream import Stream
54from mod_pywebsocket.stream import StreamOptions
55from mod_pywebsocket import util
56from six.moves import map
57from six.moves import range
58
59# Used to validate the value in the Sec-WebSocket-Key header strictly. RFC 4648
60# disallows non-zero padding, so the character right before == must be any of
61# A, Q, g and w.
62_SEC_WEBSOCKET_KEY_REGEX = re.compile('^[+/0-9A-Za-z]{21}[AQgw]==$')
63
64# Defining aliases for values used frequently.
65_VERSION_LATEST = common.VERSION_HYBI_LATEST
66_VERSION_LATEST_STRING = str(_VERSION_LATEST)
67_SUPPORTED_VERSIONS = [
68    _VERSION_LATEST,
69]
70
71
72def compute_accept(key):
73    """Computes value for the Sec-WebSocket-Accept header from value of the
74    Sec-WebSocket-Key header.
75    """
76
77    accept_binary = sha1(key + common.WEBSOCKET_ACCEPT_UUID).digest()
78    accept = base64.b64encode(accept_binary)
79
80    return accept
81
82
83def compute_accept_from_unicode(unicode_key):
84    """A wrapper function for compute_accept which takes a unicode string as an
85    argument, and encodes it to byte string. It then passes it on to
86    compute_accept.
87    """
88
89    key = unicode_key.encode('UTF-8')
90    return compute_accept(key)
91
92
93class Handshaker(object):
94    """Opening handshake processor for the WebSocket protocol (RFC 6455)."""
95    def __init__(self, request, dispatcher):
96        """Construct an instance.
97
98        Args:
99            request: mod_python request.
100            dispatcher: Dispatcher (dispatch.Dispatcher).
101
102        Handshaker will add attributes such as ws_resource during handshake.
103        """
104
105        self._logger = util.get_class_logger(self)
106
107        self._request = request
108        self._dispatcher = dispatcher
109
110    def _validate_connection_header(self):
111        connection = get_mandatory_header(self._request,
112                                          common.CONNECTION_HEADER)
113
114        try:
115            connection_tokens = parse_token_list(connection)
116        except HandshakeException as e:
117            raise HandshakeException('Failed to parse %s: %s' %
118                                     (common.CONNECTION_HEADER, e))
119
120        connection_is_valid = False
121        for token in connection_tokens:
122            if token.lower() == common.UPGRADE_CONNECTION_TYPE.lower():
123                connection_is_valid = True
124                break
125        if not connection_is_valid:
126            raise HandshakeException(
127                '%s header doesn\'t contain "%s"' %
128                (common.CONNECTION_HEADER, common.UPGRADE_CONNECTION_TYPE))
129
130    def do_handshake(self):
131        self._request.ws_close_code = None
132        self._request.ws_close_reason = None
133
134        # Parsing.
135
136        check_request_line(self._request)
137
138        validate_mandatory_header(self._request, common.UPGRADE_HEADER,
139                                  common.WEBSOCKET_UPGRADE_TYPE)
140
141        self._validate_connection_header()
142
143        self._request.ws_resource = self._request.uri
144
145        unused_host = get_mandatory_header(self._request, common.HOST_HEADER)
146
147        self._request.ws_version = self._check_version()
148
149        try:
150            self._get_origin()
151            self._set_protocol()
152            self._parse_extensions()
153
154            # Key validation, response generation.
155
156            key = self._get_key()
157            accept = compute_accept(key)
158            self._logger.debug('%s: %r (%s)',
159                               common.SEC_WEBSOCKET_ACCEPT_HEADER, accept,
160                               util.hexify(base64.b64decode(accept)))
161
162            self._logger.debug('Protocol version is RFC 6455')
163
164            # Setup extension processors.
165
166            processors = []
167            if self._request.ws_requested_extensions is not None:
168                for extension_request in self._request.ws_requested_extensions:
169                    processor = get_extension_processor(extension_request)
170                    # Unknown extension requests are just ignored.
171                    if processor is not None:
172                        processors.append(processor)
173            self._request.ws_extension_processors = processors
174
175            # List of extra headers. The extra handshake handler may add header
176            # data as name/value pairs to this list and pywebsocket appends
177            # them to the WebSocket handshake.
178            self._request.extra_headers = []
179
180            # Extra handshake handler may modify/remove processors.
181            self._dispatcher.do_extra_handshake(self._request)
182            processors = [
183                processor
184                for processor in self._request.ws_extension_processors
185                if processor is not None
186            ]
187
188            # Ask each processor if there are extensions on the request which
189            # cannot co-exist. When processor decided other processors cannot
190            # co-exist with it, the processor marks them (or itself) as
191            # "inactive". The first extension processor has the right to
192            # make the final call.
193            for processor in reversed(processors):
194                if processor.is_active():
195                    processor.check_consistency_with_other_processors(
196                        processors)
197            processors = [
198                processor for processor in processors if processor.is_active()
199            ]
200
201            accepted_extensions = []
202
203            stream_options = StreamOptions()
204
205            for index, processor in enumerate(processors):
206                if not processor.is_active():
207                    continue
208
209                extension_response = processor.get_extension_response()
210                if extension_response is None:
211                    # Rejected.
212                    continue
213
214                accepted_extensions.append(extension_response)
215
216                processor.setup_stream_options(stream_options)
217
218                # Inactivate all of the following compression extensions.
219                for j in range(index + 1, len(processors)):
220                    processors[j].set_active(False)
221
222            if len(accepted_extensions) > 0:
223                self._request.ws_extensions = accepted_extensions
224                self._logger.debug(
225                    'Extensions accepted: %r',
226                    list(
227                        map(common.ExtensionParameter.name,
228                            accepted_extensions)))
229            else:
230                self._request.ws_extensions = None
231
232            self._request.ws_stream = self._create_stream(stream_options)
233
234            if self._request.ws_requested_protocols is not None:
235                if self._request.ws_protocol is None:
236                    raise HandshakeException(
237                        'do_extra_handshake must choose one subprotocol from '
238                        'ws_requested_protocols and set it to ws_protocol')
239                validate_subprotocol(self._request.ws_protocol)
240
241                self._logger.debug('Subprotocol accepted: %r',
242                                   self._request.ws_protocol)
243            else:
244                if self._request.ws_protocol is not None:
245                    raise HandshakeException(
246                        'ws_protocol must be None when the client didn\'t '
247                        'request any subprotocol')
248
249            self._send_handshake(accept)
250        except HandshakeException as e:
251            if not e.status:
252                # Fallback to 400 bad request by default.
253                e.status = common.HTTP_STATUS_BAD_REQUEST
254            raise e
255
256    def _get_origin(self):
257        origin_header = common.ORIGIN_HEADER
258        origin = self._request.headers_in.get(origin_header)
259        if origin is None:
260            self._logger.debug('Client request does not have origin header')
261        self._request.ws_origin = origin
262
263    def _check_version(self):
264        version = get_mandatory_header(self._request,
265                                       common.SEC_WEBSOCKET_VERSION_HEADER)
266        if version == _VERSION_LATEST_STRING:
267            return _VERSION_LATEST
268
269        if version.find(',') >= 0:
270            raise HandshakeException(
271                'Multiple versions (%r) are not allowed for header %s' %
272                (version, common.SEC_WEBSOCKET_VERSION_HEADER),
273                status=common.HTTP_STATUS_BAD_REQUEST)
274        raise VersionException('Unsupported version %r for header %s' %
275                               (version, common.SEC_WEBSOCKET_VERSION_HEADER),
276                               supported_versions=', '.join(
277                                   map(str, _SUPPORTED_VERSIONS)))
278
279    def _set_protocol(self):
280        self._request.ws_protocol = None
281        # MOZILLA
282        self._request.sts = None
283        # /MOZILLA
284
285        protocol_header = self._request.headers_in.get(
286            common.SEC_WEBSOCKET_PROTOCOL_HEADER)
287
288        if protocol_header is None:
289            self._request.ws_requested_protocols = None
290            return
291
292        self._request.ws_requested_protocols = parse_token_list(
293            protocol_header)
294        self._logger.debug('Subprotocols requested: %r',
295                           self._request.ws_requested_protocols)
296
297    def _parse_extensions(self):
298        extensions_header = self._request.headers_in.get(
299            common.SEC_WEBSOCKET_EXTENSIONS_HEADER)
300        if not extensions_header:
301            self._request.ws_requested_extensions = None
302            return
303
304        try:
305            self._request.ws_requested_extensions = common.parse_extensions(
306                extensions_header)
307        except common.ExtensionParsingException as e:
308            raise HandshakeException(
309                'Failed to parse Sec-WebSocket-Extensions header: %r' % e)
310
311        self._logger.debug(
312            'Extensions requested: %r',
313            list(
314                map(common.ExtensionParameter.name,
315                    self._request.ws_requested_extensions)))
316
317    def _validate_key(self, key):
318        if key.find(',') >= 0:
319            raise HandshakeException('Request has multiple %s header lines or '
320                                     'contains illegal character \',\': %r' %
321                                     (common.SEC_WEBSOCKET_KEY_HEADER, key))
322
323        # Validate
324        key_is_valid = False
325        try:
326            # Validate key by quick regex match before parsing by base64
327            # module. Because base64 module skips invalid characters, we have
328            # to do this in advance to make this server strictly reject illegal
329            # keys.
330            if _SEC_WEBSOCKET_KEY_REGEX.match(key):
331                decoded_key = base64.b64decode(key)
332                if len(decoded_key) == 16:
333                    key_is_valid = True
334        except TypeError as e:
335            pass
336
337        if not key_is_valid:
338            raise HandshakeException('Illegal value for header %s: %r' %
339                                     (common.SEC_WEBSOCKET_KEY_HEADER, key))
340
341        return decoded_key
342
343    def _get_key(self):
344        key = get_mandatory_header(self._request,
345                                   common.SEC_WEBSOCKET_KEY_HEADER)
346
347        decoded_key = self._validate_key(key)
348
349        self._logger.debug('%s: %r (%s)', common.SEC_WEBSOCKET_KEY_HEADER, key,
350                           util.hexify(decoded_key))
351
352        return key.encode('UTF-8')
353
354    def _create_stream(self, stream_options):
355        return Stream(self._request, stream_options)
356
357    def _create_handshake_response(self, accept):
358        response = []
359
360        response.append(u'HTTP/1.1 101 Switching Protocols\r\n')
361
362        # WebSocket headers
363        response.append(
364            format_header(common.UPGRADE_HEADER,
365                          common.WEBSOCKET_UPGRADE_TYPE))
366        response.append(
367            format_header(common.CONNECTION_HEADER,
368                          common.UPGRADE_CONNECTION_TYPE))
369        response.append(
370            format_header(common.SEC_WEBSOCKET_ACCEPT_HEADER,
371                          accept.decode('UTF-8')))
372        if self._request.ws_protocol is not None:
373            response.append(
374                format_header(common.SEC_WEBSOCKET_PROTOCOL_HEADER,
375                              self._request.ws_protocol))
376        if (self._request.ws_extensions is not None
377                and len(self._request.ws_extensions) != 0):
378            response.append(
379                format_header(
380                    common.SEC_WEBSOCKET_EXTENSIONS_HEADER,
381                    common.format_extensions(self._request.ws_extensions)))
382        # MOZILLA
383        if self._request.sts is not None:
384            response.append(format_header("Strict-Transport-Security",
385                                          self._request.sts))
386        # /MOZILLA
387
388        # Headers not specific for WebSocket
389        for name, value in self._request.extra_headers:
390            response.append(format_header(name, value))
391
392        response.append(u'\r\n')
393
394        return u''.join(response)
395
396    def _send_handshake(self, accept):
397        raw_response = self._create_handshake_response(accept)
398        self._request.connection.write(raw_response.encode('UTF-8'))
399        self._logger.debug('Sent server\'s opening handshake: %r',
400                           raw_response)
401
402
403# vi:sts=4 sw=4 et
404