PREPARE/prepare/pypacker/layer567/telnet.py

"""Telnet."""

from pypacker import pypacker, triggerlist
import struct

IAC	= 255		# interpret as command:
DONT	= 254		# you are not to use option
DO	= 253		# please, you use option
WONT	= 252		# I won"t use option
WILL	= 251		# I will use option
SB	= 250		# interpret as subnegotiation
GA	= 249		# you may reverse the line
EL	= 248		# erase the current line
EC	= 247		# erase the current character
AYT	= 246		# are you there
AO	= 245		# abort output--but let prog finish
IP	= 244		# interrupt process--permanently
BREAK	= 243		# break
DM	= 242		# data mark--for connect. cleaning
NOP	= 241		# nop
SE	= 240		# end sub negotiation
EOR	= 239		# end of record (transparent mode)
ABORT	= 238		# Abort process
SUSP	= 237		# Suspend process
xEOF	= 236		# End of file: EOF is already used...

SYNCH	= 242		# for telfunc calls


class TelnetTriggerList(triggerlist.TriggerList):
	def _pack(self):
		return b"".join(self)

TELNET_OPTION_START	= b"\xff\xaa"
TELNET_OPTION_END	= b"\xff\x00"


class Telnet(pypacker.Packet):
	__hdr__ = (
		("telnet_data", None, TelnetTriggerList),
	)

	def _dissect(self, buf):
		self._init_triggerlist("telnet_data", buf, self._parse_data)
		return len(buf)

	@staticmethod
	def _parse_data(buf):

		off = 0
		t_data = []
		t_len = len(buf)

		# parse telnet data:
		# fffaXX = start of options
		# fff0 = end of options
		while off < t_len:
			if buf[off: off + 2] == TELNET_OPTION_START:
				# add start marker
				t_data.append(buf[off: off + 3])
				off += 3
				# find end of option
				idx_end = buf.find(TELNET_OPTION_END, off)
				# add option data
				t_data.append(buf[off: idx_end + 1])
				# add end marker
				t_data.append(TELNET_OPTION_END)
				off = idx_end + 2
			else:
				# add command
				t_data.append(buf[off: off + 3])
				off += 3
		return t_data


def strip_options(buf):
	"""Return a list of lines and dict of options from telnet data."""
	l = buf.split(struct.pack("B", IAC))
	b = []
	d = {}
	subopt = False
	for w in l:
		if not w:
			continue
		o = w[0]
		if o > SB:
			# print("WILL/WONT/DO/DONT/IAC", "w")
			w = w[2:]
		elif o == SE:
			# print("SE", "w")
			w = w[1:]
			subopt = False
		elif o == SB:
			# print("SB", "w")
			subopt = True
			for opt in (b"USER", b"DISPLAY", b"TERM"):
				p = w.find(opt + b"\x01")
				if p != -1:
					d[opt] = w[p + len(opt) + 1:].split(b"\x00", 1)[0]
			w = None
		elif subopt:
			w = None
		if w:
			w = w.replace(b"\x00", b"\n").splitlines()
			if not w[-1]:
				w.pop()
			b.extend(w)
	return b, d