def decompose_options(ofield):
tcpoptions = []
olen = len(ofield)
if olen == 0:
return tcpoptions
# Sequentially parse each option
idx = 0
while olen > 0:
if len(ofield[idx:idx+1]) == 0:
break
kind = struct.unpack('b', ofield[idx:idx+1])[0]
if kind == 0:
tcpoptions.append(['EOL',''])
elif kind == 1:
tcpoptions.append(['NOP',''])
if kind == 0 or kind == 1:
idx += 1
olen -= 1
continue
optlen = struct.unpack('b', ofield[idx+1: idx+2])[0]
if kind == tcplib.TO_MSS and olen >= 4:
mss = tcplib.unpack_mss(ofield[idx+2: idx+4])
tcpoptions.append(['MSS', mss])
elif kind == tcplib.TO_WSCALE and olen >= 3:
wscale = tcplib.unpack_winscale(ofield[idx+2: idx+3])
tcpoptions.append(['WSCALE', wscale])
elif kind == tcplib.TO_SACKOK and olen >= 2:
tcpoptions.append(['SACKOK', ''])
elif kind == tcplib.TO_TIMESTAMP and olen >= 10:
tsval, tsecr = tcplib.unpack_timestamp(ofield[idx+2: idx+10])
tcpoptions.append(['TIMESTAMP', tsval, tsecr])
elif kind == tcplib.TO_MP_CAPABLE and olen >= 12:
token, idsn = tcplib.unpack_mpcapable(ofield[idx+2: idx+12])
tcpoptions.append(['MP_CAPABLE', token, idsn])
elif kind == tcplib.TO_MP_DATA and olen >= 16:
dseq, dlen, sseq = tcplib.unpack_mpdata(ofield[idx+2: idx+16])
tcpoptions.append(['MP_DATA', dseq, dlen, sseq])
elif kind == tcplib.TO_MP_ACK and olen >= 10:
dack = tcplib.unpack_mpack(ofield[idx+2: idx+10])
tcpoptions.append(['MP_ACK', dack])
idx += optlen
olen -= optlen
return tcpoptions
wsoption = tcplib.create_winscale(WSval-sigval)
tcpwindow -= sigval
TSval = rcv_syntsecr
tcpsoption = mssoption + wsoption + sackokoption
tsecr = tcplib.unpack_timestamp(tcpoption[idx+2:idx+10])[0]
tcpsoption += tcplib.create_timestamp(TSval, tsecr)
elif kind == tcplib.TO_MP_CAPABLE and optlen == 12:
if datalen is 0:
mssoption = tcplib.create_mss(MSSval-2)
wsoption = tcplib.create_winscale(WSval-2)
tcpwindow -= 2
tsoption = tcplib.create_timestamp(TSval-2, tsecr)
tcpsoption = mssoption + wsoption + sackokoption + tsoption
tcpsoption += tcpoption[idx:idx+12]
elif kind == tcplib.TO_MP_DATA and optlen == 16:
dsn = tcplib.unpack_mpdata(tcpoption[idx+2:idx+16])
tcpsoption += tcplib.create_mpack(dsn[0]+dsn[1])
idx += optlen
olen -= optlen
tcpflag = tcplib.TH_ACK
if tcph.flag & tcplib.TH_SYN:
tcpflag |= tcplib.TH_SYN
datalen = 1
if tcph.flag & tcplib.TH_FIN:
datalen = 1
if tcpflag & tcplib.TH_SYN or tcpflag & tcplib.TH_FIN or datalen > 0:
if not tcpflag & tcplib.TH_SYN:
tcpseqno = tcph.ackno
tcpackno = tcph.seqno + datalen