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packet.py
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packet.py
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## This file is part of Scapy
## See http://www.secdev.org/projects/scapy for more informations
## Copyright (C) Philippe Biondi <phil@secdev.org>
## This program is published under a GPLv2 license
"""
Packet class. Binding mechanism. fuzz() method.
"""
import time,itertools,os
import copy
from fields import StrField,ConditionalField,Emph,PacketListField
from config import conf
from base_classes import BasePacket,Gen,SetGen,Packet_metaclass,NewDefaultValues
from volatile import VolatileValue
from utils import import_hexcap,tex_escape,colgen,get_temp_file
from error import Scapy_Exception,log_runtime
try:
import pyx
except ImportError:
pass
class RawVal:
def __init__(self, val=""):
self.val = val
def __str__(self):
return str(self.val)
def __repr__(self):
return "<RawVal [%r]>" % self.val
class Packet(BasePacket):
__metaclass__ = Packet_metaclass
name=None
fields_desc = []
aliastypes = []
overload_fields = {}
underlayer = None
payload_guess = []
initialized = 0
show_indent=1
explicit = 0
@classmethod
def from_hexcap(cls):
return cls(import_hexcap())
@classmethod
def upper_bonds(self):
for fval,upper in self.payload_guess:
print "%-20s %s" % (upper.__name__, ", ".join("%-12s" % ("%s=%r"%i) for i in fval.iteritems()))
@classmethod
def lower_bonds(self):
for lower,fval in self.overload_fields.iteritems():
print "%-20s %s" % (lower.__name__, ", ".join("%-12s" % ("%s=%r"%i) for i in fval.iteritems()))
def __init__(self, _pkt="", post_transform=None, _internal=0, _underlayer=None, **fields):
self.time = time.time()
self.sent_time = 0
if self.name is None:
self.name = self.__class__.__name__
self.aliastypes = [ self.__class__ ] + self.aliastypes
self.default_fields = {}
self.overloaded_fields = {}
self.fields={}
self.fieldtype={}
self.packetfields=[]
self.__dict__["payload"] = NoPayload()
self.init_fields()
self.underlayer = _underlayer
self.initialized = 1
if _pkt:
self.dissect(_pkt)
if not _internal:
self.dissection_done(self)
for f in fields.keys():
self.fields[f] = self.get_field(f).any2i(self,fields[f])
if type(post_transform) is list:
self.post_transforms = post_transform
elif post_transform is None:
self.post_transforms = []
else:
self.post_transforms = [post_transform]
def init_fields(self):
self.do_init_fields(self.fields_desc)
def do_init_fields(self, flist):
for f in flist:
self.default_fields[f.name] = copy.deepcopy(f.default)
self.fieldtype[f.name] = f
if f.holds_packets:
self.packetfields.append(f)
def dissection_done(self,pkt):
"""DEV: will be called after a dissection is completed"""
self.post_dissection(pkt)
self.payload.dissection_done(pkt)
def post_dissection(self, pkt):
"""DEV: is called after the dissection of the whole packet"""
pass
def get_field(self, fld):
"""DEV: returns the field instance from the name of the field"""
return self.fieldtype[fld]
def add_payload(self, payload):
if payload is None:
return
elif not isinstance(self.payload, NoPayload):
self.payload.add_payload(payload)
else:
if isinstance(payload, Packet):
self.__dict__["payload"] = payload
payload.add_underlayer(self)
for t in self.aliastypes:
if payload.overload_fields.has_key(t):
self.overloaded_fields = payload.overload_fields[t]
break
elif type(payload) is str:
self.__dict__["payload"] = conf.raw_layer(load=payload)
else:
raise TypeError("payload must be either 'Packet' or 'str', not [%s]" % repr(payload))
def remove_payload(self):
self.payload.remove_underlayer(self)
self.__dict__["payload"] = NoPayload()
self.overloaded_fields = {}
def add_underlayer(self, underlayer):
self.underlayer = underlayer
def remove_underlayer(self,other):
self.underlayer = None
def copy(self):
"""Returns a deep copy of the instance."""
clone = self.__class__()
clone.fields = self.fields.copy()
for k in clone.fields:
clone.fields[k]=self.get_field(k).do_copy(clone.fields[k])
clone.default_fields = self.default_fields.copy()
clone.overloaded_fields = self.overloaded_fields.copy()
clone.overload_fields = self.overload_fields.copy()
clone.underlayer=self.underlayer
clone.explicit=self.explicit
clone.post_transforms=self.post_transforms[:]
clone.__dict__["payload"] = self.payload.copy()
clone.payload.add_underlayer(clone)
return clone
def getfieldval(self, attr):
if attr in self.fields:
return self.fields[attr]
if attr in self.overloaded_fields:
return self.overloaded_fields[attr]
if attr in self.default_fields:
return self.default_fields[attr]
return self.payload.getfieldval(attr)
def getfield_and_val(self, attr):
if attr in self.fields:
return self.get_field(attr),self.fields[attr]
if attr in self.overloaded_fields:
return self.get_field(attr),self.overloaded_fields[attr]
if attr in self.default_fields:
return self.get_field(attr),self.default_fields[attr]
return self.payload.getfield_and_val(attr)
def __getattr__(self, attr):
if self.initialized:
fld,v = self.getfield_and_val(attr)
if fld is not None:
return fld.i2h(self, v)
return v
raise AttributeError(attr)
def setfieldval(self, attr, val):
if self.default_fields.has_key(attr):
fld = self.get_field(attr)
if fld is None:
any2i = lambda x,y: y
else:
any2i = fld.any2i
self.fields[attr] = any2i(self, val)
self.explicit=0
elif attr == "payload":
self.remove_payload()
self.add_payload(val)
else:
self.payload.setfieldval(attr,val)
def __setattr__(self, attr, val):
if self.initialized:
try:
self.setfieldval(attr,val)
except AttributeError:
pass
else:
return
self.__dict__[attr] = val
def delfieldval(self, attr):
if self.fields.has_key(attr):
del(self.fields[attr])
self.explicit=0 # in case a default value must be explicited
elif self.default_fields.has_key(attr):
pass
elif attr == "payload":
self.remove_payload()
else:
self.payload.delfieldval(attr)
def __delattr__(self, attr):
if self.initialized:
try:
self.delfieldval(attr)
except AttributeError:
pass
else:
return
if self.__dict__.has_key(attr):
del(self.__dict__[attr])
else:
raise AttributeError(attr)
def __repr__(self):
s = ""
ct = conf.color_theme
for f in self.fields_desc:
if isinstance(f, ConditionalField) and not f._evalcond(self):
continue
if f.name in self.fields:
val = f.i2repr(self, self.fields[f.name])
elif f.name in self.overloaded_fields:
val = f.i2repr(self, self.overloaded_fields[f.name])
else:
continue
if isinstance(f, Emph) or f in conf.emph:
ncol = ct.emph_field_name
vcol = ct.emph_field_value
else:
ncol = ct.field_name
vcol = ct.field_value
s += " %s%s%s" % (ncol(f.name),
ct.punct("="),
vcol(val))
return "%s%s %s %s%s%s"% (ct.punct("<"),
ct.layer_name(self.__class__.__name__),
s,
ct.punct("|"),
repr(self.payload),
ct.punct(">"))
def __str__(self):
return self.build()
def __div__(self, other):
if isinstance(other, Packet):
cloneA = self.copy()
cloneB = other.copy()
cloneA.add_payload(cloneB)
return cloneA
elif type(other) is str:
return self/conf.raw_layer(load=other)
else:
return other.__rdiv__(self)
def __rdiv__(self, other):
if type(other) is str:
return conf.raw_layer(load=other)/self
else:
raise TypeError
def __mul__(self, other):
if type(other) is int:
return [self]*other
else:
raise TypeError
def __rmul__(self,other):
return self.__mul__(other)
def __nonzero__(self):
return True
def __len__(self):
return len(self.__str__())
def self_build(self, field_pos_list=None):
p=""
for f in self.fields_desc:
val = self.getfieldval(f.name)
if isinstance(val, RawVal):
sval = str(val)
p += sval
if field_pos_list is not None:
field_pos_list.append( (f.name, sval.encode("string_escape"), len(p), len(sval) ) )
else:
p = f.addfield(self, p, val)
return p
def do_build_payload(self):
return self.payload.do_build()
def do_build(self):
if not self.explicit:
self = self.__iter__().next()
pkt = self.self_build()
for t in self.post_transforms:
pkt = t(pkt)
pay = self.do_build_payload()
p = self.post_build(pkt,pay)
return p
def build_padding(self):
return self.payload.build_padding()
def build(self):
p = self.do_build()
p += self.build_padding()
p = self.build_done(p)
return p
def post_build(self, pkt, pay):
"""DEV: called right after the current layer is build."""
return pkt+pay
def build_done(self, p):
return self.payload.build_done(p)
def do_build_ps(self):
p=""
pl = []
q=""
for f in self.fields_desc:
p = f.addfield(self, p, self.getfieldval(f.name) )
if type(p) is str:
r = p[len(q):]
q = p
else:
r = ""
pl.append( (f, f.i2repr(self,self.getfieldval(f.name)), r) )
pkt,lst = self.payload.build_ps(internal=1)
p += pkt
lst.append( (self, pl) )
return p,lst
def build_ps(self,internal=0):
p,lst = self.do_build_ps()
# if not internal:
# pkt = self
# while pkt.haslayer(Padding):
# pkt = pkt.getlayer(Padding)
# lst.append( (pkt, [ ("loakjkjd", pkt.load, pkt.load) ] ) )
# p += pkt.load
# pkt = pkt.payload
return p,lst
def psdump(self, filename=None, **kargs):
"""psdump(filename=None, layer_shift=0, rebuild=1)
Creates an EPS file describing a packet. If filename is not provided a temporary file is created and gs is called."""
canvas = self.canvas_dump(**kargs)
if filename is None:
fname = get_temp_file(autoext=".eps")
canvas.writeEPSfile(fname)
subprocess.Popen([conf.prog.psreader, fname+".eps"])
else:
canvas.writeEPSfile(filename)
def pdfdump(self, filename=None, **kargs):
"""pdfdump(filename=None, layer_shift=0, rebuild=1)
Creates a PDF file describing a packet. If filename is not provided a temporary file is created and xpdf is called."""
canvas = self.canvas_dump(**kargs)
if filename is None:
fname = get_temp_file(autoext=".pdf")
canvas.writePDFfile(fname)
subprocess.Popen([conf.prog.pdfreader, fname+".pdf"])
else:
canvas.writePDFfile(filename)
def canvas_dump(self, layer_shift=0, rebuild=1):
canvas = pyx.canvas.canvas()
if rebuild:
p,t = self.__class__(str(self)).build_ps()
else:
p,t = self.build_ps()
YTXT=len(t)
for n,l in t:
YTXT += len(l)
YTXT = float(YTXT)
YDUMP=YTXT
XSTART = 1
XDSTART = 10
y = 0.0
yd = 0.0
xd = 0
XMUL= 0.55
YMUL = 0.4
backcolor=colgen(0.6, 0.8, 1.0, trans=pyx.color.rgb)
forecolor=colgen(0.2, 0.5, 0.8, trans=pyx.color.rgb)
# backcolor=makecol(0.376, 0.729, 0.525, 1.0)
def hexstr(x):
s = []
for c in x:
s.append("%02x" % ord(c))
return " ".join(s)
def make_dump_txt(x,y,txt):
return pyx.text.text(XDSTART+x*XMUL, (YDUMP-y)*YMUL, r"\tt{%s}"%hexstr(txt), [pyx.text.size.Large])
def make_box(o):
return pyx.box.rect(o.left(), o.bottom(), o.width(), o.height(), relcenter=(0.5,0.5))
def make_frame(lst):
if len(lst) == 1:
b = lst[0].bbox()
b.enlarge(pyx.unit.u_pt)
return b.path()
else:
fb = lst[0].bbox()
fb.enlarge(pyx.unit.u_pt)
lb = lst[-1].bbox()
lb.enlarge(pyx.unit.u_pt)
if len(lst) == 2 and fb.left() > lb.right():
return pyx.path.path(pyx.path.moveto(fb.right(), fb.top()),
pyx.path.lineto(fb.left(), fb.top()),
pyx.path.lineto(fb.left(), fb.bottom()),
pyx.path.lineto(fb.right(), fb.bottom()),
pyx.path.moveto(lb.left(), lb.top()),
pyx.path.lineto(lb.right(), lb.top()),
pyx.path.lineto(lb.right(), lb.bottom()),
pyx.path.lineto(lb.left(), lb.bottom()))
else:
# XXX
gb = lst[1].bbox()
if gb != lb:
gb.enlarge(pyx.unit.u_pt)
kb = lst[-2].bbox()
if kb != gb and kb != lb:
kb.enlarge(pyx.unit.u_pt)
return pyx.path.path(pyx.path.moveto(fb.left(), fb.top()),
pyx.path.lineto(fb.right(), fb.top()),
pyx.path.lineto(fb.right(), kb.bottom()),
pyx.path.lineto(lb.right(), kb.bottom()),
pyx.path.lineto(lb.right(), lb.bottom()),
pyx.path.lineto(lb.left(), lb.bottom()),
pyx.path.lineto(lb.left(), gb.top()),
pyx.path.lineto(fb.left(), gb.top()),
pyx.path.closepath(),)
def make_dump(s, shift=0, y=0, col=None, bkcol=None, larg=16):
c = pyx.canvas.canvas()
tlist = []
while s:
dmp,s = s[:larg-shift],s[larg-shift:]
txt = make_dump_txt(shift, y, dmp)
tlist.append(txt)
shift += len(dmp)
if shift >= 16:
shift = 0
y += 1
if col is None:
col = pyx.color.rgb.red
if bkcol is None:
col = pyx.color.rgb.white
c.stroke(make_frame(tlist),[col,pyx.deco.filled([bkcol]),pyx.style.linewidth.Thick])
for txt in tlist:
c.insert(txt)
return c, tlist[-1].bbox(), shift, y
last_shift,last_y=0,0.0
while t:
bkcol = backcolor.next()
proto,fields = t.pop()
y += 0.5
pt = pyx.text.text(XSTART, (YTXT-y)*YMUL, r"\font\cmssfont=cmss10\cmssfont{%s}" % proto.name, [ pyx.text.size.Large])
y += 1
ptbb=pt.bbox()
ptbb.enlarge(pyx.unit.u_pt*2)
canvas.stroke(ptbb.path(),[pyx.color.rgb.black, pyx.deco.filled([bkcol])])
canvas.insert(pt)
for fname, fval, fdump in fields:
col = forecolor.next()
ft = pyx.text.text(XSTART, (YTXT-y)*YMUL, r"\font\cmssfont=cmss10\cmssfont{%s}" % tex_escape(fname.name))
if isinstance(fval, str):
if len(fval) > 18:
fval = fval[:18]+"[...]"
else:
fval=""
vt = pyx.text.text(XSTART+3, (YTXT-y)*YMUL, r"\font\cmssfont=cmss10\cmssfont{%s}" % tex_escape(fval))
y += 1.0
if fdump:
dt,target,last_shift,last_y = make_dump(fdump, last_shift, last_y, col, bkcol)
dtb = dt.bbox()
dtb=target
vtb = vt.bbox()
bxvt = make_box(vtb)
bxdt = make_box(dtb)
dtb.enlarge(pyx.unit.u_pt)
try:
if yd < 0:
cnx = pyx.connector.curve(bxvt,bxdt,absangle1=0, absangle2=-90)
else:
cnx = pyx.connector.curve(bxvt,bxdt,absangle1=0, absangle2=90)
except:
pass
else:
canvas.stroke(cnx,[pyx.style.linewidth.thin,pyx.deco.earrow.small,col])
canvas.insert(dt)
canvas.insert(ft)
canvas.insert(vt)
last_y += layer_shift
return canvas
def extract_padding(self, s):
"""DEV: to be overloaded to extract current layer's padding. Return a couple of strings (actual layer, padding)"""
return s,None
def post_dissect(self, s):
"""DEV: is called right after the current layer has been dissected"""
return s
def pre_dissect(self, s):
"""DEV: is called right before the current layer is dissected"""
return s
def do_dissect(self, s):
flist = self.fields_desc[:]
flist.reverse()
while s and flist:
f = flist.pop()
s,fval = f.getfield(self, s)
self.fields[f.name] = fval
return s
def do_dissect_payload(self, s):
if s:
cls = self.guess_payload_class(s)
try:
p = cls(s, _internal=1, _underlayer=self)
except KeyboardInterrupt:
raise
except:
if conf.debug_dissector:
if isinstance(cls,type) and issubclass(cls,Packet):
log_runtime.error("%s dissector failed" % cls.name)
else:
log_runtime.error("%s.guess_payload_class() returned [%s]" % (self.__class__.__name__,repr(cls)))
if cls is not None:
raise
p = conf.raw_layer(s, _internal=1, _underlayer=self)
self.add_payload(p)
def dissect(self, s):
s = self.pre_dissect(s)
s = self.do_dissect(s)
s = self.post_dissect(s)
payl,pad = self.extract_padding(s)
self.do_dissect_payload(payl)
if pad and conf.padding:
self.add_payload(Padding(pad))
def guess_payload_class(self, payload):
"""DEV: Guesses the next payload class from layer bonds. Can be overloaded to use a different mechanism."""
for t in self.aliastypes:
for fval, cls in t.payload_guess:
ok = 1
for k in fval.keys():
if not hasattr(self, k) or fval[k] != self.getfieldval(k):
ok = 0
break
if ok:
return cls
return self.default_payload_class(payload)
def default_payload_class(self, payload):
"""DEV: Returns the default payload class if nothing has been found by the guess_payload_class() method."""
return conf.raw_layer
def hide_defaults(self):
"""Removes fields' values that are the same as default values."""
for k in self.fields.keys():
if self.default_fields.has_key(k):
if self.default_fields[k] == self.fields[k]:
del(self.fields[k])
self.payload.hide_defaults()
def clone_with(self, payload=None, **kargs):
pkt = self.__class__()
pkt.explicit = 1
pkt.fields = kargs
pkt.time = self.time
pkt.underlayer = self.underlayer
pkt.overload_fields = self.overload_fields.copy()
pkt.post_transforms = self.post_transforms
if payload is not None:
pkt.add_payload(payload)
return pkt
def __iter__(self):
def loop(todo, done, self=self):
if todo:
eltname = todo.pop()
elt = self.getfieldval(eltname)
if not isinstance(elt, Gen):
if self.get_field(eltname).islist:
elt = SetGen([elt])
else:
elt = SetGen(elt)
for e in elt:
done[eltname]=e
for x in loop(todo[:], done):
yield x
else:
if isinstance(self.payload,NoPayload):
payloads = [None]
else:
payloads = self.payload
for payl in payloads:
done2=done.copy()
for k in done2:
if isinstance(done2[k], VolatileValue):
done2[k] = done2[k]._fix()
pkt = self.clone_with(payload=payl, **done2)
yield pkt
if self.explicit:
todo = []
done = self.fields
else:
todo = [ k for (k,v) in itertools.chain(self.default_fields.iteritems(),
self.overloaded_fields.iteritems())
if isinstance(v, VolatileValue) ] + self.fields.keys()
done = {}
return loop(todo, done)
def __gt__(self, other):
"""True if other is an answer from self (self ==> other)."""
if isinstance(other, Packet):
return other < self
elif type(other) is str:
return 1
else:
raise TypeError((self, other))
def __lt__(self, other):
"""True if self is an answer from other (other ==> self)."""
if isinstance(other, Packet):
return self.answers(other)
elif type(other) is str:
return 1
else:
raise TypeError((self, other))
def __eq__(self, other):
if not isinstance(other, self.__class__):
return False
for f in self.fields_desc:
if f not in other.fields_desc:
return False
if self.getfieldval(f.name) != other.getfieldval(f.name):
return False
return self.payload == other.payload
def __ne__(self, other):
return not self.__eq__(other)
def hashret(self):
"""DEV: returns a string that has the same value for a request and its answer."""
return self.payload.hashret()
def answers(self, other):
"""DEV: true if self is an answer from other"""
if other.__class__ == self.__class__:
return self.payload.answers(other.payload)
return 0
def haslayer(self, cls):
"""true if self has a layer that is an instance of cls. Superseded by "cls in self" syntax."""
if self.__class__ == cls or self.__class__.__name__ == cls:
return 1
for f in self.packetfields:
fvalue_gen = self.getfieldval(f.name)
if fvalue_gen is None:
continue
if not f.islist:
fvalue_gen = SetGen(fvalue_gen,_iterpacket=0)
for fvalue in fvalue_gen:
if isinstance(fvalue, Packet):
ret = fvalue.haslayer(cls)
if ret:
return ret
return self.payload.haslayer(cls)
def getlayer(self, cls, nb=1, _track=None):
"""Return the nb^th layer that is an instance of cls."""
if type(cls) is int:
nb = cls+1
cls = None
if type(cls) is str and "." in cls:
ccls,fld = cls.split(".",1)
else:
ccls,fld = cls,None
if cls is None or self.__class__ == cls or self.__class__.name == ccls:
if nb == 1:
if fld is None:
return self
else:
return self.getfieldval(fld)
else:
nb -=1
for f in self.packetfields:
fvalue_gen = self.getfieldval(f.name)
if fvalue_gen is None:
continue
if not f.islist:
fvalue_gen = SetGen(fvalue_gen,_iterpacket=0)
for fvalue in fvalue_gen:
if isinstance(fvalue, Packet):
track=[]
ret = fvalue.getlayer(cls, nb, _track=track)
if ret is not None:
return ret
nb = track[0]
return self.payload.getlayer(cls,nb,_track=_track)
def firstlayer(self):
q = self
while q.underlayer is not None:
q = q.underlayer
return q
def __getitem__(self, cls):
if type(cls) is slice:
lname = cls.start
if cls.stop:
ret = self.getlayer(cls.start, cls.stop)
else:
ret = self.getlayer(cls.start)
if ret is None and cls.step is not None:
ret = cls.step
else:
lname=cls
ret = self.getlayer(cls)
if ret is None:
if type(lname) is Packet_metaclass:
lname = lname.__name__
elif type(lname) is not str:
lname = repr(lname)
raise IndexError("Layer [%s] not found" % lname)
return ret
def __delitem__(self, cls):
del(self[cls].underlayer.payload)
def __setitem__(self, cls, val):
self[cls].underlayer.payload = val
def __contains__(self, cls):
""""cls in self" returns true if self has a layer which is an instance of cls."""
return self.haslayer(cls)
def route(self):
return (None,None,None)
def fragment(self, *args, **kargs):
return self.payload.fragment(*args, **kargs)
def display(self,*args,**kargs): # Deprecated. Use show()
"""Deprecated. Use show() method."""
self.show(*args,**kargs)
def show(self, indent=3, lvl="", label_lvl=""):
"""Prints a hierarchical view of the packet. "indent" gives the size of indentation for each layer."""
ct = conf.color_theme
print "%s%s %s %s" % (label_lvl,
ct.punct("###["),
ct.layer_name(self.name),
ct.punct("]###"))
for f in self.fields_desc:
if isinstance(f, ConditionalField) and not f._evalcond(self):
continue
if isinstance(f, Emph) or f in conf.emph:
ncol = ct.emph_field_name
vcol = ct.emph_field_value
else:
ncol = ct.field_name
vcol = ct.field_value
fvalue = self.getfieldval(f.name)
if isinstance(fvalue, Packet) or (f.islist and f.holds_packets and type(fvalue) is list):
print "%s \\%-10s\\" % (label_lvl+lvl, ncol(f.name))
fvalue_gen = SetGen(fvalue,_iterpacket=0)
for fvalue in fvalue_gen:
fvalue.show(indent=indent, label_lvl=label_lvl+lvl+" |")
else:
begn = "%s %-10s%s " % (label_lvl+lvl,
ncol(f.name),
ct.punct("="),)
reprval = f.i2repr(self,fvalue)
if type(reprval) is str:
reprval = reprval.replace("\n", "\n"+" "*(len(label_lvl)
+len(lvl)
+len(f.name)
+4))
print "%s%s" % (begn,vcol(reprval))
self.payload.show(indent=indent, lvl=lvl+(" "*indent*self.show_indent), label_lvl=label_lvl)
def show2(self):
"""Prints a hierarchical view of an assembled version of the packet, so that automatic fields are calculated (checksums, etc.)"""
self.__class__(str(self)).show()
def sprintf(self, fmt, relax=1):
"""sprintf(format, [relax=1]) -> str
where format is a string that can include directives. A directive begins and
ends by % and has the following format %[fmt[r],][cls[:nb].]field%.
fmt is a classic printf directive, "r" can be appended for raw substitution
(ex: IP.flags=0x18 instead of SA), nb is the number of the layer we want
(ex: for IP/IP packets, IP:2.src is the src of the upper IP layer).
Special case : "%.time%" is the creation time.
Ex : p.sprintf("%.time% %-15s,IP.src% -> %-15s,IP.dst% %IP.chksum% "
"%03xr,IP.proto% %r,TCP.flags%")
Moreover, the format string can include conditionnal statements. A conditionnal
statement looks like : {layer:string} where layer is a layer name, and string
is the string to insert in place of the condition if it is true, i.e. if layer
is present. If layer is preceded by a "!", the result si inverted. Conditions
can be imbricated. A valid statement can be :
p.sprintf("This is a{TCP: TCP}{UDP: UDP}{ICMP:n ICMP} packet")
p.sprintf("{IP:%IP.dst% {ICMP:%ICMP.type%}{TCP:%TCP.dport%}}")
A side effect is that, to obtain "{" and "}" characters, you must use
"%(" and "%)".
"""
escape = { "%": "%",
"(": "{",
")": "}" }
# Evaluate conditions
while "{" in fmt:
i = fmt.rindex("{")
j = fmt[i+1:].index("}")
cond = fmt[i+1:i+j+1]
k = cond.find(":")
if k < 0:
raise Scapy_Exception("Bad condition in format string: [%s] (read sprintf doc!)"%cond)
cond,format = cond[:k],cond[k+1:]
res = False
if cond[0] == "!":
res = True
cond = cond[1:]
if self.haslayer(cond):
res = not res
if not res:
format = ""
fmt = fmt[:i]+format+fmt[i+j+2:]
# Evaluate directives
s = ""
while "%" in fmt:
i = fmt.index("%")
s += fmt[:i]
fmt = fmt[i+1:]
if fmt and fmt[0] in escape:
s += escape[fmt[0]]
fmt = fmt[1:]
continue
try:
i = fmt.index("%")
sfclsfld = fmt[:i]
fclsfld = sfclsfld.split(",")
if len(fclsfld) == 1:
f = "s"
clsfld = fclsfld[0]
elif len(fclsfld) == 2:
f,clsfld = fclsfld
else:
raise Scapy_Exception
if "." in clsfld:
cls,fld = clsfld.split(".")
else:
cls = self.__class__.__name__
fld = clsfld
num = 1
if ":" in cls:
cls,num = cls.split(":")
num = int(num)
fmt = fmt[i+1:]
except:
raise Scapy_Exception("Bad format string [%%%s%s]" % (fmt[:25], fmt[25:] and "..."))
else:
if fld == "time":
val = time.strftime("%H:%M:%S.%%06i", time.localtime(self.time)) % int((self.time-int(self.time))*1000000)
elif cls == self.__class__.__name__ and hasattr(self, fld):
if num > 1:
val = self.payload.sprintf("%%%s,%s:%s.%s%%" % (f,cls,num-1,fld), relax)
f = "s"
elif f[-1] == "r": # Raw field value
val = getattr(self,fld)
f = f[:-1]
if not f:
f = "s"
else:
val = getattr(self,fld)
if fld in self.fieldtype:
val = self.fieldtype[fld].i2repr(self,val)
else:
val = self.payload.sprintf("%%%s%%" % sfclsfld, relax)
f = "s"
s += ("%"+f) % val
s += fmt
return s
def mysummary(self):
"""DEV: can be overloaded to return a string that summarizes the layer.
Only one mysummary() is used in a whole packet summary: the one of the upper layer,
except if a mysummary() also returns (as a couple) a list of layers whose
mysummary() must be called if they are present."""
return ""
def _do_summary(self):
found,s,needed = self.payload._do_summary()
if s:
s = " / "+s
ret = ""
if not found or self.__class__ in needed:
ret = self.mysummary()
if type(ret) is tuple:
ret,n = ret
needed += n
if ret or needed:
found = 1
if not ret:
ret = self.__class__.__name__
if self.__class__ in conf.emph:
impf = []
for f in self.fields_desc:
if f in conf.emph:
impf.append("%s=%s" % (f.name, f.i2repr(self, self.getfieldval(f.name))))
ret = "%s [%s]" % (ret," ".join(impf))
ret = "%s%s" % (ret,s)
return found,ret,needed
def summary(self, intern=0):
"""Prints a one line summary of a packet."""
found,s,needed = self._do_summary()
return s
def lastlayer(self,layer=None):
"""Returns the uppest layer of the packet"""
return self.payload.lastlayer(self)
def decode_payload_as(self,cls):
"""Reassembles the payload and decode it using another packet class"""
s = str(self.payload)
self.payload = cls(s, _internal=1, _underlayer=self)
pp = self
while pp.underlayer is not None:
pp = pp.underlayer
self.payload.dissection_done(pp)
def libnet(self):
"""Not ready yet. Should give the necessary C code that interfaces with libnet to recreate the packet"""
print "libnet_build_%s(" % self.__class__.name.lower()
det = self.__class__(str(self))
for f in self.fields_desc:
val = det.getfieldval(f.name)
if val is None:
val = 0
elif type(val) is int:
val = str(val)
else:
val = '"%s"' % str(val)
print "\t%s, \t\t/* %s */" % (val,f.name)
print ");"
def command(self):
"""Returns a string representing the command you have to type to obtain the same packet"""