# -*- coding: utf-8 -*-
"""
wsproto/frame_protocol
~~~~~~~~~~~~~~~~~~~~~~
WebSocket frame protocol implementation.
"""
import os
import struct
from codecs import getincrementaldecoder, IncrementalDecoder
from enum import IntEnum
from typing import Generator, List, NamedTuple, Optional, Tuple, TYPE_CHECKING, Union
if TYPE_CHECKING:
from .extensions import Extension # noqa
_XOR_TABLE = [bytes(a ^ b for a in range(256)) for b in range(256)]
class XorMaskerSimple:
def __init__(self, masking_key: bytes) -> None:
self._masking_key = masking_key
def process(self, data: bytes) -> bytes:
if data: # pylint:disable=no-else-return
data_array = bytearray(data)
a, b, c, d = (_XOR_TABLE[n] for n in self._masking_key)
data_array[::4] = data_array[::4].translate(a)
data_array[1::4] = data_array[1::4].translate(b)
data_array[2::4] = data_array[2::4].translate(c)
data_array[3::4] = data_array[3::4].translate(d)
# Rotate the maksing key so that the next usage continues
# with the next key element, rather than restarting.
key_rotation = len(data) % 4
self._masking_key = (
self._masking_key[key_rotation:] + self._masking_key[:key_rotation]
)
return bytes(data_array)
else:
return data
class XorMaskerNull:
def process(self, data: bytes) -> bytes:
return data
# RFC6455, Section 5.2 - Base Framing Protocol
# Payload length constants
PAYLOAD_LENGTH_TWO_BYTE = 126
PAYLOAD_LENGTH_EIGHT_BYTE = 127
MAX_PAYLOAD_NORMAL = 125
MAX_PAYLOAD_TWO_BYTE = 2 ** 16 - 1
MAX_PAYLOAD_EIGHT_BYTE = 2 ** 64 - 1
MAX_FRAME_PAYLOAD = MAX_PAYLOAD_EIGHT_BYTE
# MASK and PAYLOAD LEN are packed into a byte
MASK_MASK = 0x80
PAYLOAD_LEN_MASK = 0x7F
# FIN, RSV[123] and OPCODE are packed into a single byte
FIN_MASK = 0x80
RSV1_MASK = 0x40
RSV2_MASK = 0x20
RSV3_MASK = 0x10
OPCODE_MASK = 0x0F
[docs]class Opcode(IntEnum):
"""
RFC 6455, Section 5.2 - Base Framing Protocol
"""
#: Contiuation frame
CONTINUATION = 0x0
#: Text message
TEXT = 0x1
#: Binary message
BINARY = 0x2
#: Close frame
CLOSE = 0x8
#: Ping frame
PING = 0x9
#: Pong frame
PONG = 0xA
def iscontrol(self) -> bool:
return bool(self & 0x08)
[docs]class CloseReason(IntEnum):
"""
RFC 6455, Section 7.4.1 - Defined Status Codes
"""
#: indicates a normal closure, meaning that the purpose for
#: which the connection was established has been fulfilled.
NORMAL_CLOSURE = 1000
#: indicates that an endpoint is "going away", such as a server
#: going down or a browser having navigated away from a page.
GOING_AWAY = 1001
#: indicates that an endpoint is terminating the connection due
#: to a protocol error.
PROTOCOL_ERROR = 1002
#: indicates that an endpoint is terminating the connection
#: because it has received a type of data it cannot accept (e.g., an
#: endpoint that understands only text data MAY send this if it
#: receives a binary message).
UNSUPPORTED_DATA = 1003
#: Reserved. The specific meaning might be defined in the future.
# DON'T DEFINE THIS: RESERVED_1004 = 1004
#: is a reserved value and MUST NOT be set as a status code in a
#: Close control frame by an endpoint. It is designated for use in
#: applications expecting a status code to indicate that no status
#: code was actually present.
NO_STATUS_RCVD = 1005
#: is a reserved value and MUST NOT be set as a status code in a
#: Close control frame by an endpoint. It is designated for use in
#: applications expecting a status code to indicate that the
#: connection was closed abnormally, e.g., without sending or
#: receiving a Close control frame.
ABNORMAL_CLOSURE = 1006
#: indicates that an endpoint is terminating the connection
#: because it has received data within a message that was not
#: consistent with the type of the message (e.g., non-UTF-8 [RFC3629]
#: data within a text message).
INVALID_FRAME_PAYLOAD_DATA = 1007
#: indicates that an endpoint is terminating the connection
#: because it has received a message that violates its policy. This
#: is a generic status code that can be returned when there is no
#: other more suitable status code (e.g., 1003 or 1009) or if there
#: is a need to hide specific details about the policy.
POLICY_VIOLATION = 1008
#: indicates that an endpoint is terminating the connection
#: because it has received a message that is too big for it to
#: process.
MESSAGE_TOO_BIG = 1009
#: indicates that an endpoint (client) is terminating the
#: connection because it has expected the server to negotiate one or
#: more extension, but the server didn't return them in the response
#: message of the WebSocket handshake. The list of extensions that
#: are needed SHOULD appear in the /reason/ part of the Close frame.
#: Note that this status code is not used by the server, because it
#: can fail the WebSocket handshake instead.
MANDATORY_EXT = 1010
#: indicates that a server is terminating the connection because
#: it encountered an unexpected condition that prevented it from
#: fulfilling the request.
INTERNAL_ERROR = 1011
#: Server/service is restarting
#: (not part of RFC6455)
SERVICE_RESTART = 1012
#: Temporary server condition forced blocking client's request
#: (not part of RFC6455)
TRY_AGAIN_LATER = 1013
#: is a reserved value and MUST NOT be set as a status code in a
#: Close control frame by an endpoint. It is designated for use in
#: applications expecting a status code to indicate that the
#: connection was closed due to a failure to perform a TLS handshake
#: (e.g., the server certificate can't be verified).
TLS_HANDSHAKE_FAILED = 1015
# RFC 6455, Section 7.4.1 - Defined Status Codes
LOCAL_ONLY_CLOSE_REASONS = (
CloseReason.NO_STATUS_RCVD,
CloseReason.ABNORMAL_CLOSURE,
CloseReason.TLS_HANDSHAKE_FAILED,
)
# RFC 6455, Section 7.4.2 - Status Code Ranges
MIN_CLOSE_REASON = 1000
MIN_PROTOCOL_CLOSE_REASON = 1000
MAX_PROTOCOL_CLOSE_REASON = 2999
MIN_LIBRARY_CLOSE_REASON = 3000
MAX_LIBRARY_CLOSE_REASON = 3999
MIN_PRIVATE_CLOSE_REASON = 4000
MAX_PRIVATE_CLOSE_REASON = 4999
MAX_CLOSE_REASON = 4999
NULL_MASK = struct.pack("!I", 0)
class ParseFailed(Exception):
def __init__(
self, msg: str, code: CloseReason = CloseReason.PROTOCOL_ERROR
) -> None:
super().__init__(msg)
self.code = code
class RsvBits(NamedTuple):
rsv1: bool
rsv2: bool
rsv3: bool
class Header(NamedTuple):
fin: bool
rsv: RsvBits
opcode: Opcode
payload_len: int
masking_key: Optional[bytes]
class Frame(NamedTuple):
opcode: Opcode
payload: Union[bytes, str, Tuple[int, str]]
frame_finished: bool
message_finished: bool
def _truncate_utf8(data: bytes, nbytes: int) -> bytes:
if len(data) <= nbytes:
return data
# Truncate
data = data[:nbytes]
# But we might have cut a codepoint in half, in which case we want to
# discard the partial character so the data is at least
# well-formed. This is a little inefficient since it processes the
# whole message twice when in theory we could just peek at the last
# few characters, but since this is only used for close messages (max
# length = 125 bytes) it really doesn't matter.
data = data.decode("utf-8", errors="ignore").encode("utf-8")
return data
class Buffer:
def __init__(self, initial_bytes: Optional[bytes] = None) -> None:
self.buffer = bytearray()
self.bytes_used = 0
if initial_bytes:
self.feed(initial_bytes)
def feed(self, new_bytes: bytes) -> None:
self.buffer += new_bytes
def consume_at_most(self, nbytes: int) -> bytes:
if not nbytes:
return bytearray()
data = self.buffer[self.bytes_used : self.bytes_used + nbytes]
self.bytes_used += len(data)
return data
def consume_exactly(self, nbytes: int) -> Optional[bytes]:
if len(self.buffer) - self.bytes_used < nbytes:
return None
return self.consume_at_most(nbytes)
def commit(self) -> None:
# In CPython 3.4+, del[:n] is amortized O(n), *not* quadratic
del self.buffer[: self.bytes_used]
self.bytes_used = 0
def rollback(self) -> None:
self.bytes_used = 0
def __len__(self) -> int:
return len(self.buffer)
class MessageDecoder:
def __init__(self) -> None:
self.opcode: Optional[Opcode] = None
self.decoder: Optional[IncrementalDecoder] = None
def process_frame(self, frame: Frame) -> Frame:
assert not frame.opcode.iscontrol()
if self.opcode is None:
if frame.opcode is Opcode.CONTINUATION:
raise ParseFailed("unexpected CONTINUATION")
self.opcode = frame.opcode
elif frame.opcode is not Opcode.CONTINUATION:
raise ParseFailed("expected CONTINUATION, got %r" % frame.opcode)
if frame.opcode is Opcode.TEXT:
self.decoder = getincrementaldecoder("utf-8")()
finished = frame.frame_finished and frame.message_finished
if self.decoder is None:
data = frame.payload
else:
assert isinstance(frame.payload, (bytes, bytearray))
try:
data = self.decoder.decode(frame.payload, finished)
except UnicodeDecodeError as exc:
raise ParseFailed(str(exc), CloseReason.INVALID_FRAME_PAYLOAD_DATA)
frame = Frame(self.opcode, data, frame.frame_finished, finished)
if finished:
self.opcode = None
self.decoder = None
return frame
class FrameDecoder:
def __init__(
self, client: bool, extensions: Optional[List["Extension"]] = None
) -> None:
self.client = client
self.extensions = extensions or []
self.buffer = Buffer()
self.header: Optional[Header] = None
self.effective_opcode: Optional[Opcode] = None
self.masker: Union[None, XorMaskerNull, XorMaskerSimple] = None
self.payload_required = 0
self.payload_consumed = 0
def receive_bytes(self, data: bytes) -> None:
self.buffer.feed(data)
def process_buffer(self) -> Optional[Frame]:
if not self.header:
if not self.parse_header():
return None
# parse_header() sets these.
assert self.header is not None
assert self.masker is not None
assert self.effective_opcode is not None
if len(self.buffer) < self.payload_required:
return None
payload_remaining = self.header.payload_len - self.payload_consumed
payload = self.buffer.consume_at_most(payload_remaining)
if not payload and self.header.payload_len > 0:
return None
self.buffer.commit()
self.payload_consumed += len(payload)
finished = self.payload_consumed == self.header.payload_len
payload = self.masker.process(payload)
for extension in self.extensions:
payload_ = extension.frame_inbound_payload_data(self, payload)
if isinstance(payload_, CloseReason):
raise ParseFailed("error in extension", payload_)
payload = payload_
if finished:
final = bytearray()
for extension in self.extensions:
result = extension.frame_inbound_complete(self, self.header.fin)
if isinstance(result, CloseReason):
raise ParseFailed("error in extension", result)
if result is not None:
final += result
payload += final
frame = Frame(self.effective_opcode, payload, finished, self.header.fin)
if finished:
self.header = None
self.effective_opcode = None
self.masker = None
else:
self.effective_opcode = Opcode.CONTINUATION
return frame
def parse_header(self) -> bool:
data = self.buffer.consume_exactly(2)
if data is None:
self.buffer.rollback()
return False
fin = bool(data[0] & FIN_MASK)
rsv = RsvBits(
bool(data[0] & RSV1_MASK),
bool(data[0] & RSV2_MASK),
bool(data[0] & RSV3_MASK),
)
opcode = data[0] & OPCODE_MASK
try:
opcode = Opcode(opcode)
except ValueError:
raise ParseFailed("Invalid opcode {:#x}".format(opcode))
if opcode.iscontrol() and not fin:
raise ParseFailed("Invalid attempt to fragment control frame")
has_mask = bool(data[1] & MASK_MASK)
payload_len_short = data[1] & PAYLOAD_LEN_MASK
payload_len = self.parse_extended_payload_length(opcode, payload_len_short)
if payload_len is None:
self.buffer.rollback()
return False
self.extension_processing(opcode, rsv, payload_len)
if has_mask and self.client:
raise ParseFailed("client received unexpected masked frame")
if not has_mask and not self.client:
raise ParseFailed("server received unexpected unmasked frame")
if has_mask:
masking_key = self.buffer.consume_exactly(4)
if masking_key is None:
self.buffer.rollback()
return False
self.masker = XorMaskerSimple(masking_key)
else:
self.masker = XorMaskerNull()
self.buffer.commit()
self.header = Header(fin, rsv, opcode, payload_len, None)
self.effective_opcode = self.header.opcode
if self.header.opcode.iscontrol():
self.payload_required = payload_len
else:
self.payload_required = 0
self.payload_consumed = 0
return True
def parse_extended_payload_length(
self, opcode: Opcode, payload_len: int
) -> Optional[int]:
if opcode.iscontrol() and payload_len > MAX_PAYLOAD_NORMAL:
raise ParseFailed("Control frame with payload len > 125")
if payload_len == PAYLOAD_LENGTH_TWO_BYTE:
data = self.buffer.consume_exactly(2)
if data is None:
return None
(payload_len,) = struct.unpack("!H", data)
if payload_len <= MAX_PAYLOAD_NORMAL:
raise ParseFailed(
"Payload length used 2 bytes when 1 would have sufficed"
)
elif payload_len == PAYLOAD_LENGTH_EIGHT_BYTE:
data = self.buffer.consume_exactly(8)
if data is None:
return None
(payload_len,) = struct.unpack("!Q", data)
if payload_len <= MAX_PAYLOAD_TWO_BYTE:
raise ParseFailed(
"Payload length used 8 bytes when 2 would have sufficed"
)
if payload_len >> 63:
# I'm not sure why this is illegal, but that's what the RFC
# says, so...
raise ParseFailed("8-byte payload length with non-zero MSB")
return payload_len
def extension_processing(
self, opcode: Opcode, rsv: RsvBits, payload_len: int
) -> None:
rsv_used = [False, False, False]
for extension in self.extensions:
result = extension.frame_inbound_header(self, opcode, rsv, payload_len)
if isinstance(result, CloseReason):
raise ParseFailed("error in extension", result)
for bit, used in enumerate(result):
if used:
rsv_used[bit] = True
for expected, found in zip(rsv_used, rsv):
if found and not expected:
raise ParseFailed("Reserved bit set unexpectedly")
class FrameProtocol:
def __init__(self, client: bool, extensions: List["Extension"]) -> None:
self.client = client
self.extensions = [ext for ext in extensions if ext.enabled()]
# Global state
self._frame_decoder = FrameDecoder(self.client, self.extensions)
self._message_decoder = MessageDecoder()
self._parse_more = self._parse_more_gen()
self._outbound_opcode: Optional[Opcode] = None
def _process_close(self, frame: Frame) -> Frame:
data = frame.payload
assert isinstance(data, (bytes, bytearray))
if not data:
# "If this Close control frame contains no status code, _The
# WebSocket Connection Close Code_ is considered to be 1005"
data = (CloseReason.NO_STATUS_RCVD, "")
elif len(data) == 1:
raise ParseFailed("CLOSE with 1 byte payload")
else:
(code,) = struct.unpack("!H", data[:2])
if code < MIN_CLOSE_REASON or code > MAX_CLOSE_REASON:
raise ParseFailed("CLOSE with invalid code")
try:
code = CloseReason(code)
except ValueError:
pass
if code in LOCAL_ONLY_CLOSE_REASONS:
raise ParseFailed("remote CLOSE with local-only reason")
if not isinstance(code, CloseReason) and code <= MAX_PROTOCOL_CLOSE_REASON:
raise ParseFailed("CLOSE with unknown reserved code")
try:
reason = data[2:].decode("utf-8")
except UnicodeDecodeError as exc:
raise ParseFailed(
"Error decoding CLOSE reason: " + str(exc),
CloseReason.INVALID_FRAME_PAYLOAD_DATA,
)
data = (code, reason)
return Frame(frame.opcode, data, frame.frame_finished, frame.message_finished)
def _parse_more_gen(self) -> Generator[Optional[Frame], None, None]:
# Consume as much as we can from self._buffer, yielding events, and
# then yield None when we need more data. Or raise ParseFailed.
# XX FIXME this should probably be refactored so that we never see
# disabled extensions in the first place...
self.extensions = [ext for ext in self.extensions if ext.enabled()]
closed = False
while not closed:
frame = self._frame_decoder.process_buffer()
if frame is not None:
if not frame.opcode.iscontrol():
frame = self._message_decoder.process_frame(frame)
elif frame.opcode == Opcode.CLOSE:
frame = self._process_close(frame)
closed = True
yield frame
def receive_bytes(self, data: bytes) -> None:
self._frame_decoder.receive_bytes(data)
def received_frames(self) -> Generator[Frame, None, None]:
for event in self._parse_more:
if event is None:
break
else:
yield event
def close(self, code: Optional[int] = None, reason: Optional[str] = None) -> bytes:
payload = bytearray()
if code is None and reason is not None:
raise TypeError("cannot specify a reason without a code")
if code in LOCAL_ONLY_CLOSE_REASONS:
code = CloseReason.NORMAL_CLOSURE
if code is not None:
payload += bytearray(struct.pack("!H", code))
if reason is not None:
payload += _truncate_utf8(
reason.encode("utf-8"), MAX_PAYLOAD_NORMAL - 2
)
return self._serialize_frame(Opcode.CLOSE, payload)
def ping(self, payload: bytes = b"") -> bytes:
return self._serialize_frame(Opcode.PING, payload)
def pong(self, payload: bytes = b"") -> bytes:
return self._serialize_frame(Opcode.PONG, payload)
def send_data(
self, payload: Union[bytes, bytearray, str] = b"", fin: bool = True
) -> bytes:
if isinstance(payload, (bytes, bytearray, memoryview)):
opcode = Opcode.BINARY
elif isinstance(payload, str):
opcode = Opcode.TEXT
payload = payload.encode("utf-8")
else:
raise ValueError("Must provide bytes or text")
if self._outbound_opcode is None:
self._outbound_opcode = opcode
elif self._outbound_opcode is not opcode:
raise TypeError("Data type mismatch inside message")
else:
opcode = Opcode.CONTINUATION
if fin:
self._outbound_opcode = None
return self._serialize_frame(opcode, payload, fin)
def _make_fin_rsv_opcode(self, fin: bool, rsv: RsvBits, opcode: Opcode) -> int:
fin_bits = int(fin) << 7
rsv_bits = (int(rsv.rsv1) << 6) + (int(rsv.rsv2) << 5) + (int(rsv.rsv3) << 4)
opcode_bits = int(opcode)
return fin_bits | rsv_bits | opcode_bits
def _serialize_frame(
self, opcode: Opcode, payload: bytes = b"", fin: bool = True
) -> bytes:
rsv = RsvBits(False, False, False)
for extension in reversed(self.extensions):
rsv, payload = extension.frame_outbound(self, opcode, rsv, payload, fin)
fin_rsv_opcode = self._make_fin_rsv_opcode(fin, rsv, opcode)
payload_length = len(payload)
quad_payload = False
if payload_length <= MAX_PAYLOAD_NORMAL:
first_payload = payload_length
second_payload = None
elif payload_length <= MAX_PAYLOAD_TWO_BYTE:
first_payload = PAYLOAD_LENGTH_TWO_BYTE
second_payload = payload_length
else:
first_payload = PAYLOAD_LENGTH_EIGHT_BYTE
second_payload = payload_length
quad_payload = True
if self.client:
first_payload |= 1 << 7
header = bytearray([fin_rsv_opcode, first_payload])
if second_payload is not None:
if opcode.iscontrol():
raise ValueError("payload too long for control frame")
if quad_payload:
header += bytearray(struct.pack("!Q", second_payload))
else:
header += bytearray(struct.pack("!H", second_payload))
if self.client:
# "The masking key is a 32-bit value chosen at random by the
# client. When preparing a masked frame, the client MUST pick a
# fresh masking key from the set of allowed 32-bit values. The
# masking key needs to be unpredictable; thus, the masking key
# MUST be derived from a strong source of entropy, and the masking
# key for a given frame MUST NOT make it simple for a server/proxy
# to predict the masking key for a subsequent frame. The
# unpredictability of the masking key is essential to prevent
# authors of malicious applications from selecting the bytes that
# appear on the wire."
# -- https://tools.ietf.org/html/rfc6455#section-5.3
masking_key = os.urandom(4)
masker = XorMaskerSimple(masking_key)
return header + masking_key + masker.process(payload)
return header + payload