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 # This program is free software: you can redistribute it and/or modify
   9 # it under the terms of the GNU Affero General Public License as
  10 # published by the Free Software Foundation, either version 3 of the
  11 # License, or (at your option) any later version, with the "CAF Login
  12 # Exception" as published by Ian Jackson (version 2, or at your option
  13 # any later version) as an Additional Permission.
  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 Affero General Public License for more details.
  19 #
  20 # You should have received a copy of the GNU Affero General Public
  21 # License and the CAF Login Exception along with this program, in the
  22 # file AGPLv3+CAFv2.  If not, email Ian Jackson
  23 # <ijackson@chiark.greenend.org.uk>.
  24
  25
  26 end = b'\300'
  27 esc = b'\333'
  28 esc_end = b'\334'
  29 esc_esc = b'\335'
  30 delimiter = end
  31
  32 def encode(packet):
  33   return (packet
  34           .replace(esc, esc + esc_esc)
  35           .replace(end, esc + esc_end))
  36
  37 def decode(data, keep_tail=False):
  38   #print('DECODE ', repr(data))
  39   out = []
  40   inp = data.split(end)
  41   tail = []
  42   if keep_tail:
  43     tail.append(inp.pop())
  44   for packet in inp:
  45     pdata = b''
  46     while True:
  47       eix = packet.find(esc)
  48       if eix == -1:
  49         pdata += packet
  50         break
  51       #print('ESC ', repr((pdata, packet, eix)))
  52       pdata += packet[0 : eix]
  53       ck = packet[eix+1]
  54       #print('ESC... %o' % ck)
  55       if   ck == esc_esc[0]: pdata += esc
  56       elif ck == esc_end[0]: pdata += end
  57       else: raise ValueError('invalid SLIP escape 0%o %#x' % (ck, ck))
  58       packet = packet[eix+2 : ]
  59     out.append(pdata)
  60   #print('DECODED ', repr(out))
  61   out += tail
  62   return out
  63 # -*- python -*-
  64