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# -*- coding: utf-8 -*-
"""
DNSLabel/DNSBuffer - DNS label handling & encoding/decoding
"""
from __future__ import print_function
import fnmatch
from dnslib.bit import get_bits,set_bits
from dnslib.buffer import Buffer, BufferError
class DNSLabelError(Exception):
pass
class DNSLabel(object):
"""
Container for DNS label
Supports IDNA encoding for unicode domain names
>>> l1 = DNSLabel("aaa.bbb.ccc.")
>>> l2 = DNSLabel([b"aaa",b"bbb",b"ccc"])
>>> l1 == l2
True
>>> l3 = DNSLabel("AAA.BBB.CCC")
>>> l1 == l3
True
>>> l1 == 'AAA.BBB.CCC'
True
>>> x = { l1 : 1 }
>>> x[l1]
1
>>> l1
<DNSLabel: 'aaa.bbb.ccc.'>
>>> str(l1)
'aaa.bbb.ccc.'
>>> l3 = l1.add("xxx.yyy")
>>> l3
<DNSLabel: 'xxx.yyy.aaa.bbb.ccc.'>
>>> l3.matchSuffix(l1)
True
>>> l3.matchSuffix("xxx.yyy.")
False
>>> l3.stripSuffix("bbb.ccc.")
<DNSLabel: 'xxx.yyy.aaa.'>
>>> l3.matchGlob("*.[abc]aa.BBB.ccc")
True
>>> l3.matchGlob("*.[abc]xx.bbb.ccc")
False
# Too hard to get unicode doctests to work on Python 3.2
# (works on 3.3)
# >>> u1 = DNSLabel(u'\u2295.com')
# >>> u1.__str__() == u'\u2295.com.'
# True
# >>> u1.label == ( b"xn--keh", b"com" )
# True
"""
def __init__(self,label):
"""
Create DNS label instance
Label can be specified as:
- a list/tuple of byte strings
- a byte string (split into components separated by b'.')
- a unicode string which will be encoded according to RFC3490/IDNA
"""
if type(label) == DNSLabel:
self.label = label.label
elif type(label) in (list,tuple):
self.label = tuple(label)
else:
if not label or label in (b'.','.'):
self.label = ()
elif type(label) is not bytes:
self.label = tuple(label.encode("idna").\
rstrip(b".").split(b"."))
else:
self.label = tuple(label.rstrip(b".").split(b"."))
def add(self,name):
"""
Prepend name to label
"""
new = DNSLabel(name)
if self.label:
new.label += self.label
return new
def matchGlob(self,pattern):
if type(pattern) != DNSLabel:
pattern = DNSLabel(pattern)
return fnmatch.fnmatch(str(self).lower(),str(pattern).lower())
def matchSuffix(self,suffix):
"""
Return True if label suffix matches
"""
suffix = DNSLabel(suffix)
return self.label[-len(suffix.label):] == suffix.label
def stripSuffix(self,suffix):
"""
Strip suffix from label
"""
suffix = DNSLabel(suffix)
if self.label[-len(suffix.label):] == suffix.label:
return DNSLabel(self.label[:-len(suffix.label)])
else:
return self
def idna(self):
return ".".join([ s.decode("idna") for s in self.label ]) + "."
def __str__(self):
return ".".join([ s.decode() for s in self.label ]) + "."
def __repr__(self):
return "<DNSLabel: '%s'>" % str(self)
def __hash__(self):
return hash(self.label)
def __ne__(self,other):
return not self == other
def __eq__(self,other):
if type(other) != DNSLabel:
return self.__eq__(DNSLabel(other))
else:
return [ l.lower() for l in self.label ] == \
[ l.lower() for l in other.label ]
def __len__(self):
return len(b'.'.join(self.label))
class DNSBuffer(Buffer):
"""
Extends Buffer to provide DNS name encoding/decoding (with caching)
# Needed for Python 2/3 doctest compatibility
>>> def p(s):
... if not isinstance(s,str):
... return s.decode()
... return s
>>> b = DNSBuffer()
>>> b.encode_name(b'aaa.bbb.ccc.')
>>> len(b)
13
>>> b.encode_name(b'aaa.bbb.ccc.')
>>> len(b)
15
>>> b.encode_name(b'xxx.yyy.zzz')
>>> len(b)
28
>>> b.encode_name(b'zzz.xxx.bbb.ccc.')
>>> len(b)
38
>>> b.encode_name(b'aaa.xxx.bbb.ccc')
>>> len(b)
44
>>> b.offset = 0
>>> print(b.decode_name())
aaa.bbb.ccc.
>>> print(b.decode_name())
aaa.bbb.ccc.
>>> print(b.decode_name())
xxx.yyy.zzz.
>>> print(b.decode_name())
zzz.xxx.bbb.ccc.
>>> print(b.decode_name())
aaa.xxx.bbb.ccc.
>>> b = DNSBuffer()
>>> b.encode_name([b'a.aa',b'b.bb',b'c.cc'])
>>> b.offset = 0
>>> len(b.decode_name().label)
3
>>> b = DNSBuffer()
>>> b.encode_name_nocompress(b'aaa.bbb.ccc.')
>>> len(b)
13
>>> b.encode_name_nocompress(b'aaa.bbb.ccc.')
>>> len(b)
26
>>> b.offset = 0
>>> print(b.decode_name())
aaa.bbb.ccc.
>>> print(b.decode_name())
aaa.bbb.ccc.
"""
def __init__(self,data=b''):
"""
Add 'names' dict to cache stored labels
"""
super(DNSBuffer,self).__init__(data)
self.names = {}
def decode_name(self,last=-1):
"""
Decode label at current offset in buffer (following pointers
to cached elements where necessary)
"""
label = []
done = False
while not done:
(length,) = self.unpack("!B")
if get_bits(length,6,2) == 3:
# Pointer
self.offset -= 1
pointer = get_bits(self.unpack("!H")[0],0,14)
save = self.offset
if last == save:
raise BufferError("Recursive pointer in DNSLabel [offset=%d,pointer=%d,length=%d]" %
(self.offset,pointer,len(self.data)))
if pointer < self.offset:
self.offset = pointer
else:
# Pointer can't point forwards
raise BufferError("Invalid pointer in DNSLabel [offset=%d,pointer=%d,length=%d]" %
(self.offset,pointer,len(self.data)))
label.extend(self.decode_name(save).label)
self.offset = save
done = True
else:
if length > 0:
l = self.get(length)
try:
l.decode()
except UnicodeDecodeError:
raise BufferError("Invalid label <%s>" % l)
label.append(l)
else:
done = True
return DNSLabel(label)
def encode_name(self,name):
"""
Encode label and store at end of buffer (compressing
cached elements where needed) and store elements
in 'names' dict
"""
if not isinstance(name,DNSLabel):
name = DNSLabel(name)
if len(name) > 253:
raise DNSLabelError("Domain label too long: %r" % name)
name = list(name.label)
while name:
if tuple(name) in self.names:
# Cached - set pointer
pointer = self.names[tuple(name)]
pointer = set_bits(pointer,3,14,2)
self.pack("!H",pointer)
return
else:
self.names[tuple(name)] = self.offset
element = name.pop(0)
if len(element) > 63:
raise DNSLabelError("Label component too long: %r" % element)
self.pack("!B",len(element))
self.append(element)
self.append(b'\x00')
def encode_name_nocompress(self,name):
"""
Encode and store label with no compression
(needed for RRSIG)
"""
if not isinstance(name,DNSLabel):
name = DNSLabel(name)
if len(name) > 253:
raise DNSLabelError("Domain label too long: %r" % name)
name = list(name.label)
while name:
element = name.pop(0)
if len(element) > 63:
raise DNSLabelError("Label component too long: %r" % element)
self.pack("!B",len(element))
self.append(element)
self.append(b'\x00')
if __name__ == '__main__':
import doctest
doctest.testmod()
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