1# Copyright 2012, Google Inc.
2# All rights reserved.
3#
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5# modification, are permitted provided that the following conditions are
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17#
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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 re
39from hashlib import sha1
40
41from mod_pywebsocket import common
42from mod_pywebsocket.handshake.base import get_mandatory_header
43from mod_pywebsocket.handshake.base import HandshakeException
44from mod_pywebsocket.handshake.base import parse_token_list
45from mod_pywebsocket.handshake.base import validate_mandatory_header
46from mod_pywebsocket.handshake.base import HandshakerBase
47from mod_pywebsocket import util
48
49# Used to validate the value in the Sec-WebSocket-Key header strictly. RFC 4648
50# disallows non-zero padding, so the character right before == must be any of
51# A, Q, g and w.
52_SEC_WEBSOCKET_KEY_REGEX = re.compile('^[+/0-9A-Za-z]{21}[AQgw]==$')
53
54
55def check_request_line(request):
56    # 5.1 1. The three character UTF-8 string "GET".
57    # 5.1 2. A UTF-8-encoded U+0020 SPACE character (0x20 byte).
58    if request.method != u'GET':
59        raise HandshakeException('Method is not GET: %r' % request.method)
60
61    if request.protocol != u'HTTP/1.1':
62        raise HandshakeException('Version is not HTTP/1.1: %r' %
63                                 request.protocol)
64
65
66def compute_accept(key):
67    """Computes value for the Sec-WebSocket-Accept header from value of the
68    Sec-WebSocket-Key header.
69    """
70
71    accept_binary = sha1(key + common.WEBSOCKET_ACCEPT_UUID).digest()
72    accept = base64.b64encode(accept_binary)
73
74    return accept
75
76
77def compute_accept_from_unicode(unicode_key):
78    """A wrapper function for compute_accept which takes a unicode string as an
79    argument, and encodes it to byte string. It then passes it on to
80    compute_accept.
81    """
82
83    key = unicode_key.encode('UTF-8')
84    return compute_accept(key)
85
86
87def format_header(name, value):
88    return u'%s: %s\r\n' % (name, value)
89
90
91class Handshaker(HandshakerBase):
92    """Opening handshake processor for the WebSocket protocol (RFC 6455)."""
93    def __init__(self, request, dispatcher):
94        """Construct an instance.
95
96        Args:
97            request: mod_python request.
98            dispatcher: Dispatcher (dispatch.Dispatcher).
99
100        Handshaker will add attributes such as ws_resource during handshake.
101        """
102        super(Handshaker, self).__init__(request, dispatcher)
103
104    def _transform_header(self, header):
105        return header
106
107    def _protocol_rfc(self):
108        return 'RFC 6455'
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 _validate_request(self):
131        check_request_line(self._request)
132        validate_mandatory_header(self._request, common.UPGRADE_HEADER,
133                                  common.WEBSOCKET_UPGRADE_TYPE)
134        self._validate_connection_header()
135        unused_host = get_mandatory_header(self._request, common.HOST_HEADER)
136
137    def _set_accept(self):
138        # Key validation, response generation.
139        key = self._get_key()
140        accept = compute_accept(key)
141        self._logger.debug('%s: %r (%s)', common.SEC_WEBSOCKET_ACCEPT_HEADER,
142                           accept, util.hexify(base64.b64decode(accept)))
143        self._request._accept = accept
144
145    def _validate_key(self, key):
146        if key.find(',') >= 0:
147            raise HandshakeException('Request has multiple %s header lines or '
148                                     'contains illegal character \',\': %r' %
149                                     (common.SEC_WEBSOCKET_KEY_HEADER, key))
150
151        # Validate
152        key_is_valid = False
153        try:
154            # Validate key by quick regex match before parsing by base64
155            # module. Because base64 module skips invalid characters, we have
156            # to do this in advance to make this server strictly reject illegal
157            # keys.
158            if _SEC_WEBSOCKET_KEY_REGEX.match(key):
159                decoded_key = base64.b64decode(key)
160                if len(decoded_key) == 16:
161                    key_is_valid = True
162        except TypeError as e:
163            pass
164
165        if not key_is_valid:
166            raise HandshakeException('Illegal value for header %s: %r' %
167                                     (common.SEC_WEBSOCKET_KEY_HEADER, key))
168
169        return decoded_key
170
171    def _get_key(self):
172        key = get_mandatory_header(self._request,
173                                   common.SEC_WEBSOCKET_KEY_HEADER)
174
175        decoded_key = self._validate_key(key)
176
177        self._logger.debug('%s: %r (%s)', common.SEC_WEBSOCKET_KEY_HEADER, key,
178                           util.hexify(decoded_key))
179
180        return key.encode('UTF-8')
181
182    def _create_handshake_response(self, accept):
183        response = []
184
185        response.append(u'HTTP/1.1 101 Switching Protocols\r\n')
186
187        # WebSocket headers
188        response.append(
189            format_header(common.UPGRADE_HEADER,
190                          common.WEBSOCKET_UPGRADE_TYPE))
191        response.append(
192            format_header(common.CONNECTION_HEADER,
193                          common.UPGRADE_CONNECTION_TYPE))
194        response.append(
195            format_header(common.SEC_WEBSOCKET_ACCEPT_HEADER,
196                          accept.decode('UTF-8')))
197        if self._request.ws_protocol is not None:
198            response.append(
199                format_header(common.SEC_WEBSOCKET_PROTOCOL_HEADER,
200                              self._request.ws_protocol))
201        if (self._request.ws_extensions is not None
202                and len(self._request.ws_extensions) != 0):
203            response.append(
204                format_header(
205                    common.SEC_WEBSOCKET_EXTENSIONS_HEADER,
206                    common.format_extensions(self._request.ws_extensions)))
207
208        # Headers not specific for WebSocket
209        for name, value in self._request.extra_headers:
210            response.append(format_header(name, value))
211
212        response.append(u'\r\n')
213
214        return u''.join(response)
215
216    def _send_handshake(self):
217        raw_response = self._create_handshake_response(self._request._accept)
218        self._request.connection.write(raw_response.encode('UTF-8'))
219        self._logger.debug('Sent server\'s opening handshake: %r',
220                           raw_response)
221
222
223# vi:sts=4 sw=4 et
224