# Copyright 2012, Google Inc.
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# 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.
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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"""Common functions and exceptions used by WebSocket opening handshake
processors.
"""

from __future__ import absolute_import

from mod_pywebsocket import common
from mod_pywebsocket import http_header_util
from mod_pywebsocket.extensions import get_extension_processor
from mod_pywebsocket.stream import StreamOptions
from mod_pywebsocket.stream import Stream
from mod_pywebsocket import util

from six.moves import map
from six.moves import range

# Defining aliases for values used frequently.
_VERSION_LATEST = common.VERSION_HYBI_LATEST
_VERSION_LATEST_STRING = str(_VERSION_LATEST)
_SUPPORTED_VERSIONS = [
    _VERSION_LATEST,
]


class AbortedByUserException(Exception):
    """Exception for aborting a connection intentionally.

    If this exception is raised in do_extra_handshake handler, the connection
    will be abandoned. No other WebSocket or HTTP(S) handler will be invoked.

    If this exception is raised in transfer_data_handler, the connection will
    be closed without closing handshake. No other WebSocket or HTTP(S) handler
    will be invoked.
    """

    pass


class HandshakeException(Exception):
    """This exception will be raised when an error occurred while processing
    WebSocket initial handshake.
    """
    def __init__(self, name, status=None):
        super(HandshakeException, self).__init__(name)
        self.status = status


class VersionException(Exception):
    """This exception will be raised when a version of client request does not
    match with version the server supports.
    """
    def __init__(self, name, supported_versions=''):
        """Construct an instance.

        Args:
            supported_version: a str object to show supported hybi versions.
                               (e.g. '13')
        """
        super(VersionException, self).__init__(name)
        self.supported_versions = supported_versions


def get_default_port(is_secure):
    if is_secure:
        return common.DEFAULT_WEB_SOCKET_SECURE_PORT
    else:
        return common.DEFAULT_WEB_SOCKET_PORT


def validate_subprotocol(subprotocol):
    """Validate a value in the Sec-WebSocket-Protocol field.

    See the Section 4.1., 4.2.2., and 4.3. of RFC 6455.
    """

    if not subprotocol:
        raise HandshakeException('Invalid subprotocol name: empty')

    # Parameter should be encoded HTTP token.
    state = http_header_util.ParsingState(subprotocol)
    token = http_header_util.consume_token(state)
    rest = http_header_util.peek(state)
    # If |rest| is not None, |subprotocol| is not one token or invalid. If
    # |rest| is None, |token| must not be None because |subprotocol| is
    # concatenation of |token| and |rest| and is not None.
    if rest is not None:
        raise HandshakeException('Invalid non-token string in subprotocol '
                                 'name: %r' % rest)


def parse_host_header(request):
    fields = request.headers_in[common.HOST_HEADER].split(':', 1)
    if len(fields) == 1:
        return fields[0], get_default_port(request.is_https())
    try:
        return fields[0], int(fields[1])
    except ValueError as e:
        raise HandshakeException('Invalid port number format: %r' % e)


def get_mandatory_header(request, key):
    value = request.headers_in.get(key)
    if value is None:
        raise HandshakeException('Header %s is not defined' % key)
    return value


def validate_mandatory_header(request, key, expected_value, fail_status=None):
    value = get_mandatory_header(request, key)

    if value.lower() != expected_value.lower():
        raise HandshakeException(
            'Expected %r for header %s but found %r (case-insensitive)' %
            (expected_value, key, value),
            status=fail_status)


def parse_token_list(data):
    """Parses a header value which follows 1#token and returns parsed elements
    as a list of strings.

    Leading LWSes must be trimmed.
    """

    state = http_header_util.ParsingState(data)

    token_list = []

    while True:
        token = http_header_util.consume_token(state)
        if token is not None:
            token_list.append(token)

        http_header_util.consume_lwses(state)

        if http_header_util.peek(state) is None:
            break

        if not http_header_util.consume_string(state, ','):
            raise HandshakeException('Expected a comma but found %r' %
                                     http_header_util.peek(state))

        http_header_util.consume_lwses(state)

    if len(token_list) == 0:
        raise HandshakeException('No valid token found')

    return token_list


class HandshakerBase(object):
    def __init__(self, request, dispatcher):
        self._logger = util.get_class_logger(self)
        self._request = request
        self._dispatcher = dispatcher

    """ subclasses must implement the five following methods """

    def _protocol_rfc(self):
        """ Return the name of the RFC that the handshake class is implementing.
        """

        raise AssertionError("subclasses should implement this method")

    def _transform_header(self, header):
        """
        :param header: header name

        transform the header name if needed. For example, HTTP/2 subclass will
        return the name of the header in lower case.
        """

        raise AssertionError("subclasses should implement this method")

    def _validate_request(self):
        """ validate that all the mandatory fields are set """

        raise AssertionError("subclasses should implement this method")

    def _set_accept(self):
        """ Computes accept value based on Sec-WebSocket-Accept if needed. """

        raise AssertionError("subclasses should implement this method")

    def _send_handshake(self):
        """ Prepare and send the response after it has been parsed and processed.
        """

        raise AssertionError("subclasses should implement this method")

    def do_handshake(self):
        self._request.ws_close_code = None
        self._request.ws_close_reason = None

        # Parsing.
        self._validate_request()
        self._request.ws_resource = self._request.uri
        self._request.ws_version = self._check_version()

        try:
            self._get_origin()
            self._set_protocol()
            self._parse_extensions()

            self._set_accept()

            self._logger.debug('Protocol version is ' + self._protocol_rfc())

            # Setup extension processors.
            self._request.ws_extension_processors = self._get_extension_processors_requested(
            )

            # List of extra headers. The extra handshake handler may add header
            # data as name/value pairs to this list and pywebsocket appends
            # them to the WebSocket handshake.
            self._request.extra_headers = []

            # Extra handshake handler may modify/remove processors.
            self._dispatcher.do_extra_handshake(self._request)

            stream_options = StreamOptions()
            self._process_extensions(stream_options)

            self._request.ws_stream = Stream(self._request, stream_options)

            if self._request.ws_requested_protocols is not None:
                if self._request.ws_protocol is None:
                    raise HandshakeException(
                        'do_extra_handshake must choose one subprotocol from '
                        'ws_requested_protocols and set it to ws_protocol')
                validate_subprotocol(self._request.ws_protocol)

                self._logger.debug('Subprotocol accepted: %r',
                                   self._request.ws_protocol)
            else:
                if self._request.ws_protocol is not None:
                    raise HandshakeException(
                        'ws_protocol must be None when the client didn\'t '
                        'request any subprotocol')

            self._send_handshake()
        except HandshakeException as e:
            if not e.status:
                # Fallback to 400 bad request by default.
                e.status = common.HTTP_STATUS_BAD_REQUEST
            raise e

    def _check_version(self):
        sec_websocket_version_header = self._transform_header(
            common.SEC_WEBSOCKET_VERSION_HEADER)
        version = get_mandatory_header(self._request,
                                       sec_websocket_version_header)
        if version == _VERSION_LATEST_STRING:
            return _VERSION_LATEST

        if version.find(',') >= 0:
            raise HandshakeException(
                'Multiple versions (%r) are not allowed for header %s' %
                (version, sec_websocket_version_header),
                status=common.HTTP_STATUS_BAD_REQUEST)
        raise VersionException('Unsupported version %r for header %s' %
                               (version, sec_websocket_version_header),
                               supported_versions=', '.join(
                                   map(str, _SUPPORTED_VERSIONS)))

    def _get_origin(self):
        origin_header = self._transform_header(common.ORIGIN_HEADER)
        origin = self._request.headers_in.get(origin_header)
        if origin is None:
            self._logger.debug('Client request does not have origin header')
        self._request.ws_origin = origin

    def _set_protocol(self):
        self._request.ws_protocol = None

        sec_websocket_protocol_header = self._transform_header(
            common.SEC_WEBSOCKET_PROTOCOL_HEADER)
        protocol_header = self._request.headers_in.get(
            sec_websocket_protocol_header)

        if protocol_header is None:
            self._request.ws_requested_protocols = None
            return

        self._request.ws_requested_protocols = parse_token_list(
            protocol_header)
        self._logger.debug('Subprotocols requested: %r',
                           self._request.ws_requested_protocols)

    def _parse_extensions(self):
        sec_websocket_extensions_header = self._transform_header(
            common.SEC_WEBSOCKET_EXTENSIONS_HEADER)
        extensions_header = self._request.headers_in.get(
            sec_websocket_extensions_header)
        if not extensions_header:
            self._request.ws_requested_extensions = None
            return

        try:
            self._request.ws_requested_extensions = common.parse_extensions(
                extensions_header)
        except common.ExtensionParsingException as e:
            raise HandshakeException(
                'Failed to parse sec-websocket-extensions header: %r' % e)

        self._logger.debug(
            'Extensions requested: %r',
            list(
                map(common.ExtensionParameter.name,
                    self._request.ws_requested_extensions)))

    def _get_extension_processors_requested(self):
        processors = []
        if self._request.ws_requested_extensions is not None:
            for extension_request in self._request.ws_requested_extensions:
                processor = get_extension_processor(extension_request)
                # Unknown extension requests are just ignored.
                if processor is not None:
                    processors.append(processor)
        return processors

    def _process_extensions(self, stream_options):
        processors = [
            processor for processor in self._request.ws_extension_processors
            if processor is not None
        ]

        # Ask each processor if there are extensions on the request which
        # cannot co-exist. When processor decided other processors cannot
        # co-exist with it, the processor marks them (or itself) as
        # "inactive". The first extension processor has the right to
        # make the final call.
        for processor in reversed(processors):
            if processor.is_active():
                processor.check_consistency_with_other_processors(processors)
        processors = [
            processor for processor in processors if processor.is_active()
        ]

        accepted_extensions = []

        for index, processor in enumerate(processors):
            if not processor.is_active():
                continue

            extension_response = processor.get_extension_response()
            if extension_response is None:
                # Rejected.
                continue

            accepted_extensions.append(extension_response)

            processor.setup_stream_options(stream_options)

            # Inactivate all of the following compression extensions.
            for j in range(index + 1, len(processors)):
                processors[j].set_active(False)

        if len(accepted_extensions) > 0:
            self._request.ws_extensions = accepted_extensions
            self._logger.debug(
                'Extensions accepted: %r',
                list(map(common.ExtensionParameter.name, accepted_extensions)))
        else:
            self._request.ws_extensions = None


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