mdw@git.distorted.org.uk Git - hippotat/blob - hippotatlib/slip.py

   1 # -*- python -*-
   2 #
   3 # Hippotat - Asinine IP Over HTTP program
   4 # hippotatlib/slip.py - SLIP handling
   5 #
   6 # Copyright 2017 Ian Jackson
   7 #
   8 # GPLv3+
   9 #
  10 #    This program is free software: you can redistribute it and/or modify
  11 #    it under the terms of the GNU General Public License as published by
  12 #    the Free Software Foundation, either version 3 of the License, or
  13 #    (at your option) any later version.
  14 #
  15 #    This program is distributed in the hope that it will be useful,
  16 #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 #    GNU General Public License for more details.
  19 #
  20 #    You should have received a copy of the GNU General Public License
  21 #    along with this program, in the file GPLv3.  If not,
  22 #    see <http://www.gnu.org/licenses/>.
  23
  24
  25 end = b'\300'
  26 esc = b'\333'
  27 esc_end = b'\334'
  28 esc_esc = b'\335'
  29 delimiter = end
  30
  31 def encode(packet):
  32   return (packet
  33           .replace(esc, esc + esc_esc)
  34           .replace(end, esc + esc_end))
  35
  36 def decode(data, keep_tail=False):
  37   #print('DECODE ', repr(data))
  38   out = []
  39   inp = data.split(end)
  40   tail = []
  41   if keep_tail:
  42     tail.append(inp.pop())
  43   for packet in inp:
  44     pdata = b''
  45     while True:
  46       eix = packet.find(esc)
  47       if eix == -1:
  48         pdata += packet
  49         break
  50       #print('ESC ', repr((pdata, packet, eix)))
  51       pdata += packet[0 : eix]
  52       ck = packet[eix+1]
  53       #print('ESC... %o' % ck)
  54       if   ck == esc_esc[0]: pdata += esc
  55       elif ck == esc_end[0]: pdata += end
  56       else: raise ValueError('invalid SLIP escape 0%o %#x' % (ck, ck))
  57       packet = packet[eix+2 : ]
  58     out.append(pdata)
  59   #print('DECODED ', repr(out))
  60   out += tail
  61   return out
  62 # -*- python -*-
  63