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# $Id: gre.py 75 2010-08-03 14:42:19Z jon.oberheide $
"""Generic Routing Encapsulation."""
import struct
import dpkt
GRE_CP = 0x8000 # Checksum Present
GRE_RP = 0x4000 # Routing Present
GRE_KP = 0x2000 # Key Present
GRE_SP = 0x1000 # Sequence Present
GRE_SS = 0x0800 # Strict Source Route
GRE_AP = 0x0080 # Acknowledgment Present
GRE_opt_fields = (
(GRE_CP|GRE_RP, 'sum', 'H'), (GRE_CP|GRE_RP, 'off', 'H'),
(GRE_KP, 'key', 'I'), (GRE_SP, 'seq', 'I'), (GRE_AP, 'ack', 'I')
)
class GRE(dpkt.Packet):
__hdr__ = (
('flags', 'H', 0),
('p', 'H', 0x0800), # ETH_TYPE_IP
)
_protosw = {}
sre = ()
def get_v(self):
return self.flags & 0x7
def set_v(self, v):
self.flags = (self.flags & ~0x7) | (v & 0x7)
v = property(get_v, set_v)
def get_recur(self):
return (self.flags >> 5) & 0x7
def set_recur(self, v):
self.flags = (self.flags & ~0xe0) | ((v & 0x7) << 5)
recur = property(get_recur, set_recur)
class SRE(dpkt.Packet):
__hdr__ = [
('family', 'H', 0),
('off', 'B', 0),
('len', 'B', 0)
]
def unpack(self, buf):
dpkt.Packet.unpack(self, buf)
self.data = self.data[:self.len]
def opt_fields_fmts(self):
if self.v == 0:
fields, fmts = [], []
opt_fields = GRE_opt_fields
else:
fields, fmts = [ 'len', 'callid' ], [ 'H', 'H' ]
opt_fields = GRE_opt_fields[-2:]
for flags, field, fmt in opt_fields:
if self.flags & flags:
fields.append(field)
fmts.append(fmt)
return fields, fmts
def unpack(self, buf):
dpkt.Packet.unpack(self, buf)
fields, fmts = self.opt_fields_fmts()
if fields:
fmt = ''.join(fmts)
fmtlen = struct.calcsize(fmt)
vals = struct.unpack(fmt, self.data[:fmtlen])
self.data = self.data[fmtlen:]
self.__dict__.update(dict(zip(fields, vals)))
if self.flags & GRE_RP:
l = []
while True:
sre = self.SRE(self.data)
self.data = self.data[len(sre):]
l.append(sre)
if not sre.len:
break
self.sre = l
self.data = ethernet.Ethernet._typesw[self.p](self.data)
setattr(self, self.data.__class__.__name__.lower(), self.data)
def __len__(self):
opt_fmtlen = struct.calcsize(''.join(self.opt_fields_fmts()[1]))
return self.__hdr_len__ + opt_fmtlen + \
sum(map(len, self.sre)) + len(self.data)
# XXX - need to fix up repr to display optional fields...
def __str__(self):
fields, fmts = self.opt_fields_fmts()
if fields:
vals = []
for f in fields:
vals.append(getattr(self, f))
opt_s = struct.pack(''.join(fmts), *vals)
else:
opt_s = ''
return self.pack_hdr() + opt_s + ''.join(map(str, self.sre)) + \
str(self.data)
# XXX - auto-load GRE dispatch table from Ethernet dispatch table
import ethernet
GRE._protosw.update(ethernet.Ethernet._typesw)
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