153 lines
5 KiB
Python
153 lines
5 KiB
Python
"""
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The :mod:`websockets.handshake` module deals with the WebSocket opening
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handshake according to `section 4 of RFC 6455`_.
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.. _section 4 of RFC 6455: http://tools.ietf.org/html/rfc6455#section-4
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Functions defined in this module manipulate HTTP headers. The ``headers``
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argument must implement ``get`` and ``__setitem__`` and ``get`` — a small
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subset of the :class:`~collections.abc.MutableMapping` abstract base class.
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Headers names and values are :class:`str` objects containing only ASCII
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characters.
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Some checks cannot be performed because they depend too much on the
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context; instead, they're documented below.
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To accept a connection, a server must:
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- Read the request, check that the method is GET, and check the headers with
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:func:`check_request`,
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- Send a 101 response to the client with the headers created by
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:func:`build_response` if the request is valid; otherwise, send an
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appropriate HTTP error code.
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To open a connection, a client must:
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- Send a GET request to the server with the headers created by
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:func:`build_request`,
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- Read the response, check that the status code is 101, and check the headers
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with :func:`check_response`.
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"""
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import base64
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import binascii
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import hashlib
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import random
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from .exceptions import InvalidHeaderValue, InvalidUpgrade
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from .headers import parse_connection, parse_upgrade
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__all__ = [
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'build_request', 'check_request',
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'build_response', 'check_response',
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]
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GUID = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
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def build_request(headers):
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"""
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Build a handshake request to send to the server.
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Return the ``key`` which must be passed to :func:`check_response`.
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"""
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raw_key = bytes(random.getrandbits(8) for _ in range(16))
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key = base64.b64encode(raw_key).decode()
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headers['Upgrade'] = 'websocket'
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headers['Connection'] = 'Upgrade'
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headers['Sec-WebSocket-Key'] = key
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headers['Sec-WebSocket-Version'] = '13'
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return key
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def check_request(headers):
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"""
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Check a handshake request received from the client.
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If the handshake is valid, this function returns the ``key`` which must be
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passed to :func:`build_response`.
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Otherwise it raises an :exc:`~websockets.exceptions.InvalidHandshake`
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exception and the server must return an error like 400 Bad Request.
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This function doesn't verify that the request is an HTTP/1.1 or higher GET
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request and doesn't perform Host and Origin checks. These controls are
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usually performed earlier in the HTTP request handling code. They're the
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responsibility of the caller.
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"""
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connection = parse_connection(headers.get('Connection', ''))
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if not any(value.lower() == 'upgrade' for value in connection):
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raise InvalidUpgrade('Connection', headers.get('Connection', ''))
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upgrade = parse_upgrade(headers.get('Upgrade', ''))
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# For compatibility with non-strict implementations, ignore case when
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# checking the Upgrade header. It's supposed to be 'WebSocket'.
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if not (len(upgrade) == 1 and upgrade[0].lower() == 'websocket'):
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raise InvalidUpgrade('Upgrade', headers.get('Upgrade', ''))
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key = headers.get('Sec-WebSocket-Key', '')
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try:
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raw_key = base64.b64decode(key.encode(), validate=True)
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except binascii.Error:
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raise InvalidHeaderValue('Sec-WebSocket-Key', key)
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if len(raw_key) != 16:
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raise InvalidHeaderValue('Sec-WebSocket-Key', key)
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version = headers.get('Sec-WebSocket-Version', '')
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if version != '13':
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raise InvalidHeaderValue('Sec-WebSocket-Version', version)
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return key
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def build_response(headers, key):
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"""
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Build a handshake response to send to the client.
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``key`` comes from :func:`check_request`.
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"""
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headers['Upgrade'] = 'websocket'
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headers['Connection'] = 'Upgrade'
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headers['Sec-WebSocket-Accept'] = accept(key)
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def check_response(headers, key):
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"""
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Check a handshake response received from the server.
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``key`` comes from :func:`build_request`.
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If the handshake is valid, this function returns ``None``.
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Otherwise it raises an :exc:`~websockets.exceptions.InvalidHandshake`
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exception.
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This function doesn't verify that the response is an HTTP/1.1 or higher
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response with a 101 status code. These controls are the responsibility of
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the caller.
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"""
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connection = parse_connection(headers.get('Connection', ''))
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if not any(value.lower() == 'upgrade' for value in connection):
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raise InvalidUpgrade('Connection', headers.get('Connection', ''))
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upgrade = parse_upgrade(headers.get('Upgrade', ''))
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# For compatibility with non-strict implementations, ignore case when
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# checking the Upgrade header. It's supposed to be 'WebSocket'.
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if not (len(upgrade) == 1 and upgrade[0].lower() == 'websocket'):
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raise InvalidUpgrade('Upgrade', headers.get('Upgrade', ''))
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if headers.get('Sec-WebSocket-Accept', '') != accept(key):
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raise InvalidHeaderValue(
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'Sec-WebSocket-Accept', headers.get('Sec-WebSocket-Accept', ''))
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def accept(key):
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sha1 = hashlib.sha1((key + GUID).encode()).digest()
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return base64.b64encode(sha1).decode()
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