/
pkt.py
executable file
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/
pkt.py
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# $Id$
"""Simple packet creation and parsing."""
import copy, itertools, socket, struct
class Error(Exception): pass
class UnpackError(Error): pass
class NeedData(UnpackError): pass
class PackError(Error): pass
class _MetaPacket(type):
def __new__(cls, clsname, clsbases, clsdict):
t = type.__new__(cls, clsname, clsbases, clsdict)
st = getattr(t, '__hdr__', None)
if st is not None:
# XXX - __slots__ only created in __new__()
clsdict['__slots__'] = [ x[0] for x in st ] + [ 'data' ]
t = type.__new__(cls, clsname, clsbases, clsdict)
t.__hdr_fields__ = [ x[0] for x in st ]
t.__hdr_fmt__ = getattr(t, '__byte_order__', '>') + \
''.join([ x[1] for x in st ])
t.__hdr_len__ = struct.calcsize(t.__hdr_fmt__)
t.__hdr_defaults__ = dict(zip(
t.__hdr_fields__, [ x[2] for x in st ]))
t.__hdr_names__ = [ x[3] for x in st ]
return t
class Packet(object):
"""Base packet class, with metaclass magic to generate members from
self.__hdr__.
__hdr__ should be defined as a list of (name, structfmt, default) tuples
__byte_order__ can be set to override the default ('>')
Example::
>>> class Foo(Packet):
... __hdr__ = (('foo', 'I', 1), ('bar', 'H', 2), ('baz', '4s', 'quux'))
...
>>> foo = Foo(bar=3)
>>> foo
Foo(bar=3)
>>> str(foo)
'\x00\x00\x00\x01\x00\x03quux'
>>> foo.bar
3
>>> foo.baz
'quux'
>>> foo.foo = 7
>>> foo.baz = 'whee'
>>> foo
Foo(baz='whee', foo=7, bar=3)
>>> Foo('hello, world!')
Foo(baz=' wor', foo=1751477356L, bar=28460, data='ld!')
"""
__metaclass__ = _MetaPacket
def __init__(self, *args, **kwargs):
"""Packet constructor with ([buf], [field=val,...]) prototype.
Arguments:
buf -- optional packet buffer to unpack
Optional keyword arguments correspond to members to set
(matching fields in self.__hdr__, or 'data').
"""
self.data = ''
if args:
try:
self.unpack(args[0])
except struct.error:
if len(args[0]) < self.__hdr_len__:
raise NeedData
raise UnpackError('invalid %s: %r' %
(self.__class__.__name__, args[0]))
else:
for k in self.__hdr_fields__:
setattr(self, k, copy.copy(self.__hdr_defaults__[k]))
for k, v in kwargs.iteritems():
setattr(self, k, v)
def __len__(self):
return self.__hdr_len__ + len(self.data)
def __getitem__(self, k):
try: return getattr(self, k)
except AttributeError: raise KeyError
def __repr__(self):
l = [ '%s=%r' % (k, getattr(self, k))
for k in self.__hdr_defaults__
if getattr(self, k) != self.__hdr_defaults__[k] ]
if self.data:
l.append('data=%r' % self.data)
return '%s(%s)' % (self.__class__.__name__, ', '.join(l))
def __str__(self):
return self.pack_hdr() + str(self.data)
def pack_hdr(self):
"""Return packed header string."""
try:
return struct.pack(self.__hdr_fmt__,
*[ getattr(self, k) for k in self.__hdr_fields__ ])
except struct.error:
vals = []
for k in self.__hdr_fields__:
v = getattr(self, k)
if isinstance(v, tuple):
vals.extend(v)
else:
vals.append(v)
try:
return struct.pack(self.__hdr_fmt__, *vals)
except struct.error, e:
raise PackError(str(e))
def pack(self):
"""Return packed header + self.data string."""
return str(self)
def unpack(self, buf):
"""Unpack packet header fields from buf, and set self.data."""
for k, v in itertools.izip(self.__hdr_fields__,
struct.unpack(self.__hdr_fmt__, buf[:self.__hdr_len__])):
setattr(self, k, v)
for k, v in itertools.izip(self.__hdr_fields__,self.__hdr_names__):
setattr(self, k +'_name', v)
self.data = buf[self.__hdr_len__:]