Logo Search packages:      
Sourcecode: ldaptor version File versions

pureber.py

# Twisted, the Framework of Your Internet
# Copyright (C) 2001 Matthew W. Lefkowitz
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of version 2.1 of the GNU Lesser General Public
# License as published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

"""Pure, simple, BER encoding and decoding"""

# This BER library is currently aimed at supporting LDAP, thus
# the following restrictions from RFC2251 apply:
#
# (1) Only the definite form of length encoding will be used.
#
# (2) OCTET STRING values will be encoded in the primitive form
#     only.
#
# (3) If the value of a BOOLEAN type is true, the encoding MUST have
#     its contents octets set to hex "FF".
#
# (4) If a value of a type is its default value, it MUST be absent.
#     Only some BOOLEAN and INTEGER types have default values in
#     this protocol definition.


import string

# xxxxxxxx
# |/|\.../
# | | |
# | | tag
# | |
# | primitive (0) or structured (1)
# |
# class

CLASS_MASK        = 0xc0
CLASS_UNIVERSAL   = 0x00
CLASS_APPLICATION = 0x40
CLASS_CONTEXT           = 0x80
CLASS_PRIVATE           = 0xc0

STRUCTURED_MASK         = 0x20
STRUCTURED        = 0x20
NOT_STRUCTURED          = 0x00

TAG_MASK          = 0x1f

# LENGTH
# 0xxxxxxx = 0..127
# 1xxxxxxx = len is stored in the next 0xxxxxxx octets
# indefinite form not supported

class UnknownBERTag(Exception):
    def __init__(self, tag, context):
        Exception.__init__(self)
        self.tag = tag
        self.context = context

    def __str__(self):
        return "BERDecoderContext has no tag 0x%02x: %s" \
               % (self.tag, self.context)

import UserList

def berDecodeLength(m, offset=0):
    """
    Return a tuple of (length, lengthLength).
    m must be atleast one byte long.
    """
    l=ber2int(m[offset+0])
    ll=1
    if l&0x80:
      ll=1+(l&0x7F)
      need(m, offset+ll)
      l=ber2int(m[offset+1:offset+ll], signed=0)
    return (l, ll)

def int2berlen(i):
    assert i>=0
    e=int2ber(i, signed=False)
    if i <= 127:
        return e
    else:
        l=len(e)
        assert l>0
        assert l<=127
        return chr(0x80|l) + e

def int2ber(i, signed=True):
    encoded=''
    while ((signed and (i>127 or i<-128))
           or (not signed and (i>255))):
      encoded=chr(i%256)+encoded
      i=i>>8
    encoded=chr(i%256)+encoded
    return encoded

def ber2int(e, signed=True):
    need(e, 1)
    v=0L+ord(e[0])
    if v&0x80 and signed:
      v=v-256
    for i in range(1, len(e)):
      v=(v<<8) | ord(e[i])
    return v

class BERBase:
    tag = None

    def identification(self):
      return self.tag

    def __init__(self, tag=None):
      if tag is not None:
          self.tag=tag

    def __len__(self):
      return len(str(self))

    def __cmp__(self, other):
      if isinstance(other, BERBase):
          return cmp(str(self), str(other))
      else:
          return -1

    def __eq__(self, other):
      if isinstance(other, BERBase):
          return str(self) == str(other)
      else:
          return False

    def __ne__(self, other):
      if isinstance(other, BERBase):
          return str(self) != str(other)
      else:
          return False

class BERStructured(BERBase):
    def identification(self):
      return STRUCTURED|self.tag

class BERException(Exception): pass

class BERExceptionInsufficientData(Exception): pass

def need(buf, n):
    d=n-len(buf)
    if d>0:
      raise BERExceptionInsufficientData, d

class BERInteger(BERBase):
    tag = 0x02
    value = None

    def fromBER(klass, tag, content, berdecoder=None):
      assert len(content)>0
      value=ber2int(content)
        r = klass(value=value, tag=tag)
        return r
    fromBER = classmethod(fromBER)

    def __init__(self, value=None, tag=None):
      """Create a new BERInteger object.
      value is an integer.
      """
      BERBase.__init__(self, tag)
      assert value is not None
        self.value=value

    def __str__(self):
      encoded=int2ber(self.value)
      return chr(self.identification()) \
             +int2berlen(len(encoded)) \
             +encoded

    def __repr__(self):
      if self.tag==self.__class__.tag:
          return self.__class__.__name__+"(value=%r)"%self.value
      else:
          return self.__class__.__name__+"(value=%r, tag=%d)" \
               %(self.value, self.tag)

class BEROctetString(BERBase):
    tag = 0x04

    value = None

    def fromBER(klass, tag, content, berdecoder=None):
      assert len(content)>=0
        r = klass(value=content, tag=tag)
        return r
    fromBER = classmethod(fromBER)

    def __init__(self, value=None, tag=None):
      BERBase.__init__(self, tag)
      assert value is not None
        self.value=value

    def __str__(self):
      return chr(self.identification()) \
             +int2berlen(len(self.value)) \
             +self.value

    def __repr__(self):
      if self.tag==self.__class__.tag:
          return self.__class__.__name__+"(value=%s)" \
               %repr(self.value)
      else:
          return self.__class__.__name__ \
               +"(value=%s, tag=%d)" \
               %(repr(self.value), self.tag)

class BERNull(BERBase):
    tag = 0x05

    def fromBER(klass, tag, content, berdecoder=None):
      assert len(content) == 0
        r = klass(tag=tag)
        return r
    fromBER = classmethod(fromBER)

    def __init__(self, tag=None):
      BERBase.__init__(self, tag)

    def __str__(self):
      return chr(self.identification())+chr(0)

    def __repr__(self):
      if self.tag==self.__class__.tag:
          return self.__class__.__name__+"()"
      else:
          return self.__class__.__name__+"(tag=%d)"%self.tag

class BERBoolean(BERBase):
    tag = 0x01

    def fromBER(klass, tag, content, berdecoder=None):
      assert len(content) > 0
      value = ber2int(content)
        r = klass(value=value, tag=tag)
        return r
    fromBER = classmethod(fromBER)

    def __init__(self, value=None, tag=None):
      """Create a new BERInteger object.
      value is an integer.
      """
      BERBase.__init__(self, tag)
      assert value is not None
        if value:
            value=0xFF
        self.value=value

    def __str__(self):
      assert self.value==0 or self.value==0xFF
      return chr(self.identification()) \
             +int2berlen(1) \
             +chr(self.value)

    def __repr__(self):
      if self.tag==self.__class__.tag:
          return self.__class__.__name__+"(value=%d)"%self.value
      else:
          return self.__class__.__name__+"(value=%d, tag=%d)" \
               %(self.value, self.tag)


class BEREnumerated(BERInteger):
    tag = 0x0a

class BERSequence(BERStructured, UserList.UserList):
    # TODO __getslice__ calls __init__ with no args.
    tag = 0x10

    def fromBER(klass, tag, content, berdecoder=None):
        l = berDecodeMultiple(content, berdecoder)
        r = klass(l, tag=tag)
        return r
    fromBER = classmethod(fromBER)

    def __init__(self, value=None, tag=None):
      BERStructured.__init__(self, tag)
      UserList.UserList.__init__(self)
      assert value is not None
        self[:]=value

    def __str__(self):
      r=string.join(map(str, self.data), '')
      return chr(self.identification())+int2berlen(len(r))+r

    def __repr__(self):
      if self.tag==self.__class__.tag:
          return self.__class__.__name__+"(value=%s)"%repr(self.data)
      else:
          return self.__class__.__name__+"(value=%s, tag=%d)" \
               %(repr(self.data), self.tag)


class BERSequenceOf(BERSequence):
    pass

class BERSet(BERSequence):
    tag = 0x11
    pass



class BERDecoderContext:
    Identities = {
      BERInteger.tag: BERInteger,
      BEROctetString.tag: BEROctetString,
      BERNull.tag: BERNull,
      BERBoolean.tag: BERBoolean,
      BEREnumerated.tag: BEREnumerated,
      BERSequence.tag: BERSequence,
      BERSet.tag: BERSet,
      }

    def __init__(self, fallback=None, inherit=None):
      self.fallback=fallback
      self.inherit_context=inherit

    def lookup_id(self, id):
      try:
          return self.Identities[id]
      except KeyError:
          if self.fallback:
            return self.fallback.lookup_id(id)
          else:
            return None

    def inherit(self):
      return self.inherit_context or self

    def __repr__(self):
        identities = []
        for tag, class_ in self.Identities.items():
            identities.append('0x%02x: %s' % (tag, class_.__name__))
      return "<"+self.__class__.__name__ \
             +" identities={%s}" % ', '.join(identities) \
             +" fallback="+repr(self.fallback) \
             +" inherit="+repr(self.inherit_context) \
             +">"

def berDecodeObject(context, m):
    """berDecodeObject(context, string) -> (berobject, bytesUsed)
    berobject may be None.
    """
    while m:
      need(m, 2)
      i=ber2int(m[0], signed=0)&(CLASS_MASK|TAG_MASK)

        length, lenlen = berDecodeLength(m, offset=1)
        need(m, 1+lenlen+length)
        m2 = m[1+lenlen:1+lenlen+length]

      berclass=context.lookup_id(i)
      if berclass:
          inh=context.inherit()
          assert inh
            r = berclass.fromBER(tag=i,
                                 content=m2,
                                 berdecoder=inh)
            return (r, 1+lenlen+length)
      else:
          #raise UnknownBERTag, (i, context)
            print str(UnknownBERTag(i, context)) #TODO
            return (None, 1+lenlen+length)
    return (None, 0)

def berDecodeMultiple(content, berdecoder):
    """berDecodeMultiple(content, berdecoder) -> [objects]

    Decodes everything in content and returns a list of decoded
    objects.

    All of content will be decoded, and content must contain complete
    BER objects.
    """
    l = []
    while content:
        n, bytes = berDecodeObject(berdecoder, content)
        if n is not None:
            l.append(n)
        assert bytes <= len(content)
        content = content[bytes:]
    return l

#TODO unimplemented classes are below:

#class BERObjectIdentifier(BERBase):
#    tag = 0x06
#    pass

#class BERIA5String(BERBase):
#    tag = 0x16
#    pass

#class BERPrintableString(BERBase):
#    tag = 0x13
#    pass

#class BERT61String(BERBase):
#    tag = 0x14
#    pass

#class BERUTCTime(BERBase):
#    tag = 0x17
#    pass

#class BERBitString(BERBase):
#    tag = 0x03
#    pass

Generated by  Doxygen 1.6.0   Back to index