| 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 | |