mirror of
https://github.com/Grasscutters/mitmproxy.git
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371 lines
13 KiB
Python
371 lines
13 KiB
Python
from __future__ import absolute_import
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import base64
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import hashlib
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import os
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import struct
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import io
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from . import utils, odict
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# Colleciton of utility functions that implement small portions of the RFC6455
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# WebSockets Protocol Useful for building WebSocket clients and servers.
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#
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# Emphassis is on readabilty, simplicity and modularity, not performance or
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# completeness
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#
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# This is a work in progress and does not yet contain all the utilites need to
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# create fully complient client/servers #
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# Spec: https://tools.ietf.org/html/rfc6455
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# The magic sha that websocket servers must know to prove they understand
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# RFC6455
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websockets_magic = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
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VERSION = "13"
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MAX_16_BIT_INT = (1 << 16)
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MAX_64_BIT_INT = (1 << 64)
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class OPCODE:
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CONTINUE = 0x00
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TEXT = 0x01
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BINARY = 0x02
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CLOSE = 0x08
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PING = 0x09
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PONG = 0x0a
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class Frame(object):
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"""
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Represents one websockets frame.
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Constructor takes human readable forms of the frame components
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from_bytes() is also avaliable.
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WebSockets Frame as defined in RFC6455
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-------+-+-------------+-------------------------------+
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|F|R|R|R| opcode|M| Payload len | Extended payload length |
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|I|S|S|S| (4) |A| (7) | (16/64) |
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|N|V|V|V| |S| | (if payload len==126/127) |
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| |1|2|3| |K| | |
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+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
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| Extended payload length continued, if payload len == 127 |
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+ - - - - - - - - - - - - - - - +-------------------------------+
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| |Masking-key, if MASK set to 1 |
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+-------------------------------+-------------------------------+
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| Masking-key (continued) | Payload Data |
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+-------------------------------- - - - - - - - - - - - - - - - +
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: Payload Data continued ... :
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+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
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| Payload Data continued ... |
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+---------------------------------------------------------------+
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"""
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def __init__(
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self,
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fin, # decmial integer 1 or 0
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opcode, # decmial integer 1 - 4
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mask_bit, # decimal integer 1 or 0
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payload_length_code, # decimal integer 1 - 127
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decoded_payload, # bytestring
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rsv1 = 0, # decimal integer 1 or 0
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rsv2 = 0, # decimal integer 1 or 0
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rsv3 = 0, # decimal integer 1 or 0
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payload = None, # bytestring
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masking_key = None, # 32 bit byte string
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actual_payload_length = None, # any decimal integer
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):
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self.fin = fin
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self.rsv1 = rsv1
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self.rsv2 = rsv2
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self.rsv3 = rsv3
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self.opcode = opcode
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self.mask_bit = mask_bit
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self.payload_length_code = payload_length_code
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self.masking_key = masking_key
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self.payload = payload
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self.decoded_payload = decoded_payload
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self.actual_payload_length = actual_payload_length
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@classmethod
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def default(cls, message, from_client = False):
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"""
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Construct a basic websocket frame from some default values.
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Creates a non-fragmented text frame.
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"""
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length_code, actual_length = get_payload_length_pair(message)
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if from_client:
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mask_bit = 1
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# Random masking key
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masking_key = os.urandom(4)
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payload = apply_mask(message, masking_key)
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else:
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mask_bit = 0
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masking_key = None
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payload = message
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return cls(
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fin = 1, # final frame
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opcode = OPCODE.TEXT, # text
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mask_bit = mask_bit,
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payload_length_code = length_code,
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payload = payload,
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masking_key = masking_key,
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decoded_payload = message,
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actual_payload_length = actual_length
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)
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def is_valid(self):
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"""
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Validate websocket frame invariants, call at anytime to ensure the
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Frame has not been corrupted.
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"""
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constraints = [
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0 <= self.fin <= 1,
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0 <= self.rsv1 <= 1,
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0 <= self.rsv2 <= 1,
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0 <= self.rsv3 <= 1,
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1 <= self.opcode <= 4,
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0 <= self.mask_bit <= 1,
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1 <= self.payload_length_code <= 127,
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self.actual_payload_length == len(self.payload)
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]
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if not all(constraints):
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return False
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elif self.mask_bit == 1 and not 1 <= len(self.masking_key) <= 4:
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return False
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elif self.mask_bit == 0 and self.masking_key is not None:
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return False
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elif self.payload and self.masking_key:
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decoded = apply_mask(self.payload, self.masking_key)
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if decoded != self.decoded_payload:
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return False
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return True
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def human_readable(self): # pragma: nocover
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return "\n".join([
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("fin - " + str(self.fin)),
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("rsv1 - " + str(self.rsv1)),
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("rsv2 - " + str(self.rsv2)),
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("rsv3 - " + str(self.rsv3)),
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("opcode - " + str(self.opcode)),
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("mask_bit - " + str(self.mask_bit)),
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("payload_length_code - " + str(self.payload_length_code)),
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("masking_key - " + repr(str(self.masking_key))),
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("payload - " + repr(str(self.payload))),
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("decoded_payload - " + repr(str(self.decoded_payload))),
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("actual_payload_length - " + str(self.actual_payload_length))
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])
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@classmethod
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def from_bytes(cls, bytestring):
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"""
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Construct a websocket frame from an in-memory bytestring
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to construct a frame from a stream of bytes, use from_file() directly
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"""
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return cls.from_file(io.BytesIO(bytestring))
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def to_bytes(self):
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"""
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Serialize the frame back into the wire format, returns a bytestring
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If you haven't checked is_valid_frame() then there's no guarentees
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that the serialized bytes will be correct. see safe_to_bytes()
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"""
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# break down of the bit-math used to construct the first byte from the
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# frame's integer values first shift the significant bit into the
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# correct position
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# 00000001 << 7 = 10000000
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# ...
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# then combine:
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#
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# 10000000 fin
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# 01000000 res1
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# 00100000 res2
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# 00010000 res3
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# 00000001 opcode
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# -------- OR
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# 11110001 = first_byte
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first_byte = (self.fin << 7) | (self.rsv1 << 6) |\
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(self.rsv2 << 4) | (self.rsv3 << 4) | self.opcode
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second_byte = (self.mask_bit << 7) | self.payload_length_code
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b = chr(first_byte) + chr(second_byte)
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if self.actual_payload_length < 126:
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pass
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elif self.actual_payload_length < MAX_16_BIT_INT:
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# '!H' pack as 16 bit unsigned short
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# add 2 byte extended payload length
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b += struct.pack('!H', self.actual_payload_length)
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elif self.actual_payload_length < MAX_64_BIT_INT:
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# '!Q' = pack as 64 bit unsigned long long
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# add 8 bytes extended payload length
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b += struct.pack('!Q', self.actual_payload_length)
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if self.masking_key is not None:
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b += self.masking_key
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b += self.payload # already will be encoded if neccessary
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return b
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def to_file(self, writer):
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writer.write(self.to_bytes())
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writer.flush()
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@classmethod
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def from_file(cls, fp):
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"""
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read a websockets frame sent by a server or client
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fp is a "file like" object that could be backed by a network
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stream or a disk or an in memory stream reader
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"""
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first_byte = utils.bytes_to_int(fp.read(1))
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second_byte = utils.bytes_to_int(fp.read(1))
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# grab the left most bit
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fin = first_byte >> 7
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# grab right most 4 bits by and-ing with 00001111
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opcode = first_byte & 15
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# grab left most bit
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mask_bit = second_byte >> 7
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# grab the next 7 bits
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payload_length = second_byte & 127
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# payload_lengthy > 125 indicates you need to read more bytes
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# to get the actual payload length
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if payload_length <= 125:
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actual_payload_length = payload_length
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elif payload_length == 126:
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actual_payload_length = utils.bytes_to_int(fp.read(2))
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elif payload_length == 127:
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actual_payload_length = utils.bytes_to_int(fp.read(8))
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# masking key only present if mask bit set
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if mask_bit == 1:
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masking_key = fp.read(4)
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else:
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masking_key = None
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payload = fp.read(actual_payload_length)
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if mask_bit == 1:
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decoded_payload = apply_mask(payload, masking_key)
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else:
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decoded_payload = payload
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return cls(
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fin = fin,
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opcode = opcode,
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mask_bit = mask_bit,
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payload_length_code = payload_length,
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payload = payload,
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masking_key = masking_key,
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decoded_payload = decoded_payload,
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actual_payload_length = actual_payload_length
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)
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def __eq__(self, other):
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return (
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self.fin == other.fin and
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self.rsv1 == other.rsv1 and
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self.rsv2 == other.rsv2 and
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self.rsv3 == other.rsv3 and
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self.opcode == other.opcode and
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self.mask_bit == other.mask_bit and
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self.payload_length_code == other.payload_length_code and
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self.masking_key == other.masking_key and
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self.payload == other.payload and
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self.decoded_payload == other.decoded_payload and
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self.actual_payload_length == other.actual_payload_length
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)
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def apply_mask(message, masking_key):
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"""
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Data sent from the server must be masked to prevent malicious clients
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from sending data over the wire in predictable patterns
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This method both encodes and decodes strings with the provided mask
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Servers do not have to mask data they send to the client.
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https://tools.ietf.org/html/rfc6455#section-5.3
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"""
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masks = [utils.bytes_to_int(byte) for byte in masking_key]
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result = ""
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for char in message:
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result += chr(ord(char) ^ masks[len(result) % 4])
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return result
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def client_handshake_headers(key=None, version=VERSION):
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"""
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Create the headers for a valid HTTP upgrade request. If Key is not
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specified, it is generated, and can be found in sec-websocket-key in
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the returned header set.
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Returns an instance of ODictCaseless
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"""
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if not key:
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key = base64.b64encode(os.urandom(16)).decode('utf-8')
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return odict.ODictCaseless([
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('Connection', 'Upgrade'),
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('Upgrade', 'websocket'),
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('Sec-WebSocket-Key', key),
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('Sec-WebSocket-Version', version)
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])
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def server_handshake_headers(key):
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"""
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The server response is a valid HTTP 101 response.
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"""
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return odict.ODictCaseless(
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[
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('Connection', 'Upgrade'),
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('Upgrade', 'websocket'),
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('Sec-WebSocket-Accept', create_server_nonce(key))
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]
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)
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def get_payload_length_pair(payload_bytestring):
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"""
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A websockets frame contains an initial length_code, and an optional
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extended length code to represent the actual length if length code is
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larger than 125
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"""
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actual_length = len(payload_bytestring)
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if actual_length <= 125:
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length_code = actual_length
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elif actual_length >= 126 and actual_length <= 65535:
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length_code = 126
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else:
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length_code = 127
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return (length_code, actual_length)
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def check_client_handshake(req):
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if req.headers.get_first("upgrade", None) != "websocket":
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return
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return req.headers.get_first('sec-websocket-key')
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def check_server_handshake(resp):
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if resp.headers.get_first("upgrade", None) != "websocket":
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return
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return resp.headers.get_first('sec-websocket-accept')
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def create_server_nonce(client_nonce):
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return base64.b64encode(
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hashlib.sha1(client_nonce + websockets_magic).hexdigest().decode('hex')
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)
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