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"""
Parser for the Telnet protocol. (Not a complete implementation of the telnet
specification, but sufficient for a command line interface.)
Inspired by `Twisted.conch.telnet`.
"""
from __future__ import annotations
import struct
from typing import Callable, Generator
from .log import logger
__all__ = [
"TelnetProtocolParser",
]
def int2byte(number: int) -> bytes:
return bytes((number,))
# Telnet constants.
NOP = int2byte(0)
SGA = int2byte(3)
IAC = int2byte(255)
DO = int2byte(253)
DONT = int2byte(254)
LINEMODE = int2byte(34)
SB = int2byte(250)
WILL = int2byte(251)
WONT = int2byte(252)
MODE = int2byte(1)
SE = int2byte(240)
ECHO = int2byte(1)
NAWS = int2byte(31)
LINEMODE = int2byte(34)
SUPPRESS_GO_AHEAD = int2byte(3)
TTYPE = int2byte(24)
SEND = int2byte(1)
IS = int2byte(0)
DM = int2byte(242)
BRK = int2byte(243)
IP = int2byte(244)
AO = int2byte(245)
AYT = int2byte(246)
EC = int2byte(247)
EL = int2byte(248)
GA = int2byte(249)
class TelnetProtocolParser:
"""
Parser for the Telnet protocol.
Usage::
def data_received(data):
print(data)
def size_received(rows, columns):
print(rows, columns)
p = TelnetProtocolParser(data_received, size_received)
p.feed(binary_data)
"""
def __init__(
self,
data_received_callback: Callable[[bytes], None],
size_received_callback: Callable[[int, int], None],
ttype_received_callback: Callable[[str], None],
) -> None:
self.data_received_callback = data_received_callback
self.size_received_callback = size_received_callback
self.ttype_received_callback = ttype_received_callback
self._parser = self._parse_coroutine()
self._parser.send(None) # type: ignore
def received_data(self, data: bytes) -> None:
self.data_received_callback(data)
def do_received(self, data: bytes) -> None:
"""Received telnet DO command."""
logger.info("DO %r", data)
def dont_received(self, data: bytes) -> None:
"""Received telnet DONT command."""
logger.info("DONT %r", data)
def will_received(self, data: bytes) -> None:
"""Received telnet WILL command."""
logger.info("WILL %r", data)
def wont_received(self, data: bytes) -> None:
"""Received telnet WONT command."""
logger.info("WONT %r", data)
def command_received(self, command: bytes, data: bytes) -> None:
if command == DO:
self.do_received(data)
elif command == DONT:
self.dont_received(data)
elif command == WILL:
self.will_received(data)
elif command == WONT:
self.wont_received(data)
else:
logger.info("command received %r %r", command, data)
def naws(self, data: bytes) -> None:
"""
Received NAWS. (Window dimensions.)
"""
if len(data) == 4:
# NOTE: the first parameter of struct.unpack should be
# a 'str' object. Both on Py2/py3. This crashes on OSX
# otherwise.
columns, rows = struct.unpack("!HH", data)
self.size_received_callback(rows, columns)
else:
logger.warning("Wrong number of NAWS bytes")
def ttype(self, data: bytes) -> None:
"""
Received terminal type.
"""
subcmd, data = data[0:1], data[1:]
if subcmd == IS:
ttype = data.decode("ascii")
self.ttype_received_callback(ttype)
else:
logger.warning("Received a non-IS terminal type Subnegotiation")
def negotiate(self, data: bytes) -> None:
"""
Got negotiate data.
"""
command, payload = data[0:1], data[1:]
if command == NAWS:
self.naws(payload)
elif command == TTYPE:
self.ttype(payload)
else:
logger.info("Negotiate (%r got bytes)", len(data))
def _parse_coroutine(self) -> Generator[None, bytes, None]:
"""
Parser state machine.
Every 'yield' expression returns the next byte.
"""
while True:
d = yield
if d == int2byte(0):
pass # NOP
# Go to state escaped.
elif d == IAC:
d2 = yield
if d2 == IAC:
self.received_data(d2)
# Handle simple commands.
elif d2 in (NOP, DM, BRK, IP, AO, AYT, EC, EL, GA):
self.command_received(d2, b"")
# Handle IAC-[DO/DONT/WILL/WONT] commands.
elif d2 in (DO, DONT, WILL, WONT):
d3 = yield
self.command_received(d2, d3)
# Subnegotiation
elif d2 == SB:
# Consume everything until next IAC-SE
data = []
while True:
d3 = yield
if d3 == IAC:
d4 = yield
if d4 == SE:
break
else:
data.append(d4)
else:
data.append(d3)
self.negotiate(b"".join(data))
else:
self.received_data(d)
def feed(self, data: bytes) -> None:
"""
Feed data to the parser.
"""
for b in data:
self._parser.send(int2byte(b))
|
