+#---------- SLIP handling ----------
+
+slip_end = b'\300'
+slip_esc = b'\333'
+slip_esc_end = b'\334'
+slip_esc_esc = b'\335'
+slip_delimiter = slip_end
+
+def slip_encode(packet):
+ return (packet
+ .replace(slip_esc, slip_esc + slip_esc_esc)
+ .replace(slip_end, slip_esc + slip_esc_end))
+
+def slip_decode(data):
+ print('DECODE ', repr(data))
+ out = []
+ for packet in data.split(slip_end):
+ pdata = b''
+ while True:
+ eix = packet.find(slip_esc)
+ if eix == -1:
+ pdata += packet
+ break
+ #print('ESC ', repr((pdata, packet, eix)))
+ pdata += packet[0 : eix]
+ ck = packet[eix+1]
+ #print('ESC... %o' % ck)
+ if ck == slip_esc_esc[0]: pdata += slip_esc
+ elif ck == slip_esc_end[0]: pdata += slip_end
+ else: raise ValueError('invalid SLIP escape')
+ packet = packet[eix+2 : ]
+ out.append(pdata)
+ print('DECODED ', repr(out))
+ return out
+
+#---------- packet parsing ----------
+
+def packet_addrs(packet):
+ version = packet[0] >> 4
+ if version == 4:
+ addrlen = 4
+ saddroff = 3*4
+ factory = ipaddress.IPv4Address
+ elif version == 6:
+ addrlen = 16
+ saddroff = 2*4
+ factory = ipaddress.IPv6Address
+ else:
+ raise ValueError('unsupported IP version %d' % version)
+ saddr = factory(packet[ saddroff : saddroff + addrlen ])
+ daddr = factory(packet[ saddroff + addrlen : saddroff + addrlen*2 ])
+ return (saddr, daddr)
+