Use DN objects instead of strings

* Convert every string specifying a DN into a DN object

* Every place a dn was manipulated in some fashion it was replaced by
  the use of DN operators

* Add new DNParam parameter type for parameters which are DN's

* DN objects are used 100% of the time throughout the entire data
  pipeline whenever something is logically a dn.

* Many classes now enforce DN usage for their attributes which are
  dn's. This is implmented via ipautil.dn_attribute_property(). The
  only permitted types for a class attribute specified to be a DN are
  either None or a DN object.

* Require that every place a dn is used it must be a DN object.
  This translates into lot of::

    assert isinstance(dn, DN)

  sprinkled through out the code. Maintaining these asserts is
  valuable to preserve DN type enforcement. The asserts can be
  disabled in production.

  The goal of 100% DN usage 100% of the time has been realized, these
  asserts are meant to preserve that.

  The asserts also proved valuable in detecting functions which did
  not obey their function signatures, such as the baseldap pre and
  post callbacks.

* Moved ipalib.dn to ipapython.dn because DN class is shared with all
  components, not just the server which uses ipalib.

* All API's now accept DN's natively, no need to convert to str (or
  unicode).

* Removed ipalib.encoder and encode/decode decorators. Type conversion
  is now explicitly performed in each IPASimpleLDAPObject method which
  emulates a ldap.SimpleLDAPObject method.

* Entity & Entry classes now utilize DN's

* Removed __getattr__ in Entity & Entity clases. There were two
  problems with it. It presented synthetic Python object attributes
  based on the current LDAP data it contained. There is no way to
  validate synthetic attributes using code checkers, you can't search
  the code to find LDAP attribute accesses (because synthetic
  attriutes look like Python attributes instead of LDAP data) and
  error handling is circumscribed. Secondly __getattr__ was hiding
  Python internal methods which broke class semantics.

* Replace use of methods inherited from ldap.SimpleLDAPObject via
  IPAdmin class with IPAdmin methods. Directly using inherited methods
  was causing us to bypass IPA logic. Mostly this meant replacing the
  use of search_s() with getEntry() or getList(). Similarly direct
  access of the LDAP data in classes using IPAdmin were replaced with
  calls to getValue() or getValues().

* Objects returned by ldap2.find_entries() are now compatible with
  either the python-ldap access methodology or the Entity/Entry access
  methodology.

* All ldap operations now funnel through the common
  IPASimpleLDAPObject giving us a single location where we interface
  to python-ldap and perform conversions.

* The above 4 modifications means we've greatly reduced the
  proliferation of multiple inconsistent ways to perform LDAP
  operations. We are well on the way to having a single API in IPA for
  doing LDAP (a long range goal).

* All certificate subject bases are now DN's

* DN objects were enhanced thusly:
  - find, rfind, index, rindex, replace and insert methods were added
  - AVA, RDN and DN classes were refactored in immutable and mutable
    variants, the mutable variants are EditableAVA, EditableRDN and
    EditableDN. By default we use the immutable variants preserving
    important semantics. To edit a DN cast it to an EditableDN and
    cast it back to DN when done editing. These issues are fully
    described in other documentation.
  - first_key_match was removed
  - DN equalty comparison permits comparison to a basestring

* Fixed ldapupdate to work with DN's. This work included:
  - Enhance test_updates.py to do more checking after applying
    update. Add test for update_from_dict(). Convert code to use
    unittest classes.
  - Consolidated duplicate code.
  - Moved code which should have been in the class into the class.
  - Fix the handling of the 'deleteentry' update action. It's no longer
    necessary to supply fake attributes to make it work. Detect case
    where subsequent update applies a change to entry previously marked
    for deletetion. General clean-up and simplification of the
    'deleteentry' logic.
  - Rewrote a couple of functions to be clearer and more Pythonic.
  - Added documentation on the data structure being used.
  - Simplfy the use of update_from_dict()

* Removed all usage of get_schema() which was being called prior to
  accessing the .schema attribute of an object. If a class is using
  internal lazy loading as an optimization it's not right to require
  users of the interface to be aware of internal
  optimization's. schema is now a property and when the schema
  property is accessed it calls a private internal method to perform
  the lazy loading.

* Added SchemaCache class to cache the schema's from individual
  servers. This was done because of the observation we talk to
  different LDAP servers, each of which may have it's own
  schema. Previously we globally cached the schema from the first
  server we connected to and returned that schema in all contexts. The
  cache includes controls to invalidate it thus forcing a schema
  refresh.

* Schema caching is now senstive to the run time context. During
  install and upgrade the schema can change leading to errors due to
  out-of-date cached schema. The schema cache is refreshed in these
  contexts.

* We are aware of the LDAP syntax of all LDAP attributes. Every
  attribute returned from an LDAP operation is passed through a
  central table look-up based on it's LDAP syntax. The table key is
  the LDAP syntax it's value is a Python callable that returns a
  Python object matching the LDAP syntax. There are a handful of LDAP
  attributes whose syntax is historically incorrect
  (e.g. DistguishedNames that are defined as DirectoryStrings). The
  table driven conversion mechanism is augmented with a table of
  hard coded exceptions.

  Currently only the following conversions occur via the table:

  - dn's are converted to DN objects

  - binary objects are converted to Python str objects (IPA
    convention).

  - everything else is converted to unicode using UTF-8 decoding (IPA
    convention).

  However, now that the table driven conversion mechanism is in place
  it would be trivial to do things such as converting attributes
  which have LDAP integer syntax into a Python integer, etc.

* Expected values in the unit tests which are a DN no longer need to
  use lambda expressions to promote the returned value to a DN for
  equality comparison. The return value is automatically promoted to
  a DN. The lambda expressions have been removed making the code much
  simpler and easier to read.

* Add class level logging to a number of classes which did not support
  logging, less need for use of root_logger.

* Remove ipaserver/conn.py, it was unused.

* Consolidated duplicate code wherever it was found.

* Fixed many places that used string concatenation to form a new
  string rather than string formatting operators. This is necessary
  because string formatting converts it's arguments to a string prior
  to building the result string. You can't concatenate a string and a
  non-string.

* Simplify logic in rename_managed plugin. Use DN operators to edit
  dn's.

* The live version of ipa-ldap-updater did not generate a log file.
  The offline version did, now both do.

https://fedorahosted.org/freeipa/ticket/1670
https://fedorahosted.org/freeipa/ticket/1671
https://fedorahosted.org/freeipa/ticket/1672
https://fedorahosted.org/freeipa/ticket/1673
https://fedorahosted.org/freeipa/ticket/1674
https://fedorahosted.org/freeipa/ticket/1392
https://fedorahosted.org/freeipa/ticket/2872

4 files changed, 1698 insertions, 24 deletions

diff --git a/ipapython/dn.py b/ipapython/dn.py
new file mode 100644
index 00000000..6cce40e2
--- /dev/null
+++ b/ipapython/dn.py
@@ -0,0 +1,1643 @@
+# Authors:
+#   John Dennis <jdennis@redhat.com>
+#
+# Copyright (C) 2011  Red Hat
+# see file 'COPYING' for use and warranty information
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+'''
+
+Goal
+----
+
+To allow a Python programmer the ability to operate on DN's
+(Distinguished Names) in a simple intuitive manner supporting all the
+Pythonic mechanisms for manipulating objects such that the simple
+majority case remains simple with simple code, yet the corner cases
+are fully supported. With the result both simple and complex cases are
+100% correct.
+
+This is achieved with a fair of amount of syntax sugar which is best
+described as "Do What I Mean" (i.e. DWIM). The class implementations
+take simple expressions and internally convert them to their more
+complex full definitions hiding much of the complexity from the
+programmer.
+
+Anatomy of a DN
+---------------
+
+Some definitions:
+
+AVA
+    An AVA is an Attribute Value Assertion. In more simple terms it's
+    an attribute value pair typically expressed as attr=value
+    (e.g. cn=Bob). Both the attr and value in an AVA when expressed in
+    a string representation are subject to encoding rules.
+
+RDN
+    A RDN is a Relative Distinguished Name. A RDN is a non-empty set of
+    AVA's. In the common case a RDN is single valued consisting of 1
+    AVA (e.g. cn=Bob). But a RDN may be multi-valued consisting of
+    more than one AVA. Because the RDN is a set of AVA's the AVA's are
+    unordered when they appear in a multi-valued RDN. In the string
+    representation of a RDN AVA's are separated by the plus sign (+).
+
+DN
+    A DN is a ordered sequence of 1 or more RDN's. In the string
+    representation of a DN each RDN is separated by a comma (,)
+
+Thus a DN is:
+
+Sequence of set of <encoded attr, encoded value> pairs
+
+The following are valid DN's
+
+# 1 RDN with 1 AVA (e.g. cn=Bob)
+RDN(AVA)
+
+# 2 RDN's each with 1 AVA (e.g. cn=Bob,dc=redhat.com)
+RDN(AVA),RDN(AVA)
+
+# 2 RDN's the first RDN is multi-valued with 2 AVA's
+# the second RDN is singled valued with 1 AVA
+# (e.g. cn=Bob+ou=people,dc=redhat.com
+RDN({AVA,AVA}),RDN(AVA)
+
+Common programming mistakes
+---------------------------
+
+DN's present a pernicious problem for programmers. They appear to have
+a very simple string format in the majority case, a sequence of
+attr=value pairs separated by commas. For example:
+
+dn='cn=Bob,ou=people,dc=redhat,dc=com'
+
+As such there is a tendency to believe you can form DN's by simple
+string manipulations such as:
+
+dn='%s=%s' % ('cn','Bob') + ',ou=people,dc=redhat,dc=com'
+
+Or to extract a attr & value by searching the string, for example:
+
+attr=dn[0 : dn.find('=')]
+value=dn[dn.find('=')+1 : dn.find(',')]
+
+Or compare a value returned by an LDAP query to a known value:
+
+if value == 'Bob'
+
+All of these simple coding assumptions are WRONG and will FAIL when a
+DN is not one of the simple DN's (simple DN's are probably the 95% of
+all DN's). This is what makes DN handling pernicious. What works in
+95% of the cases and is simple, fails for the 5% of DN's which are not
+simple.
+
+Examples of where the simple assumptions fail are:
+
+* A RDN may be multi-valued
+
+* A multi-valued RDN has no ordering on it's components
+
+* Attr's and values must be UTF-8 encoded
+
+* String representations of AVA's, RDN's and DN's must be completely UTF-8
+
+* An attr or value may have reserved characters which must be escaped.
+
+* Whitespace needs special handling
+
+To complicate matters a bit more the RFC for the string representation
+of DN's (RFC 4514) permits a variety of different syntax's each of
+which can evaluate to exactly the same DN but have different string
+representations. For example, the attr "r,w" which contains a reserved
+character (the comma) can be encoded as a string in these different
+ways:
+
+'r\,w'          # backslash escape
+'r\2cw'         # hexadecimal ascii escape
+'#722C77'       # binary encoded
+
+It should be clear a DN string may NOT be a simple string, rather a DN
+string is ENCODED. For simple strings the encoding of the DN is
+identical to the simple string value (this common case leads to
+erroneous assumptions and bugs because it does not account for
+encodings).
+
+The openldap library we use at the client level uses the backslash
+escape form. The LDAP server we use uses the hexadecimal ascii escape
+form. Thus 'r,w' appears as 'r\,w' when sent from the client to the
+LDAP server as part of a DN. But when it's returned as a DN from the
+server in an LDAP search it's returned as 'r\2cw'. Any attempt to
+compare 'r\,w' to 'r\2cw' for equality will fail despite the fact they
+are indeed equal once decoded. Such a test fails because you're
+comparing two different encodings of the same value. In MIME you
+wouldn't expect the base64 encoding of a string to be equal to the
+same string encoded as quoted-printable would you?
+
+When you are comparing attrs or values which are part of a DN and
+other string you MUST:
+
+* Know if either of the strings have been encoded and make sure you're
+  comparing only decoded components component-wise.
+
+* Extract the component from the DN and decode it. You CANNOT decode
+  the entire DN as a string and operate on it. Why? Consider a value
+  with a comma embedded in it. For example:
+
+  cn=r\2cw,cn=privilege
+
+  Is a DN with 2 RDN components: cn=r,w followed by "cn=privilege"
+
+  But if you decode the entire DN string as a whole you would get:
+
+  cn=r,w,cn=privilege
+
+  Which is a malformed DN with 3 RDN's, the 2nd RDN is invalid.
+
+* Determine if a RDN is multi-valued, if so you must account
+  for the fact each AVA component in the multi-valued RDN can appear
+  in any order and still be equivalent. For example the following two
+  RDN's are equal:
+
+  cn=Bob+ou=people
+  ou=people+cn=Bob
+
+  In addition each AVA (cn=Bob & ou=people) needs to be
+  INDEPENDENTLY decoded prior to comparing the unordered set of AVA's
+  in the multi-valued RDN.
+
+If you are trying to form a new DN or RDN from a raw string you cannot
+simply do string concatenation or string formatting unless you ESCAPE
+the components independently prior to concatenation, for example:
+
+  base = 'dc=redhat,dc=com'
+  value = 'r,w'
+  dn = 'cn=%s,%s' % (value, base)
+
+Will result in the malformed DN 'cn=r,w,dc=redhat,dc=com'
+
+Syntax Sugar
+------------
+
+The majority of DN's have a simple string form:
+
+attr=value,attr=value
+
+We want the programmer to be able to create DN's, compare them, and
+operate on their components as simply and concisely as possible so
+the classes are implemented to provide a lot of syntax sugar.
+
+The classes automatically handle UTF-8 <-> Unicode conversions. Every
+attr and value which is returned from a class will be Unicode. Every
+attr and value assigned into an object will be promoted to
+Unicode. All string representations in RFC 4514 format will be UTF-8
+and properly escaped. Thus at the "user" or "API" level every string
+is Unicode with the single exception that the str() method returns RFC
+compliant escaped UTF-8.
+
+RDN's are assumed to be single-valued. If you need a multi-valued RDN
+(an exception) you must explicitly create a multi-valued RDN.
+
+Thus DN's are assumed to be a sequence of attr, value pairs, which is
+equivalent to a sequence of RDN's. The attr and value in the pair MUST
+be strings.
+
+The DN and RDN constructors take a sequence, the constructor parses
+the sequence to find items it knows about.
+
+The DN constructor will accept in it's sequence:
+  * tuple of 2 strings, converting it to an RDN
+  * list of 2 strings, converting it to an RDN
+  * a RDN object
+  * a DN syntax string (e.g. 'cn=Bob,dc=redhat.com')
+
+Note DN syntax strings should be avoided if possible when passing to a
+constructor because they run afoul of the problems outlined above
+which the DN, RDN & AVA classes are meant to overcome. But sometimes a
+DN syntax string is all you have to work with. DN strings which come
+from a LDAP library or server will be properly formed and it's safe to
+use those. However DN strings provided via user input should be
+treated suspiciously as they may be improperly formed. You can test
+for this by passing the string to the DN constructor and see if it
+throws an exception.
+
+The sequence passed to the DN constructor takes each item in order,
+produces one or more RDN's from it and appends those RDN in order to
+its internal RDN sequence.
+
+For example:
+
+   DN(('cn', 'Bob'), ('dc', 'redhat.com'))
+
+This is equivalent to the DN string:
+
+    cn=Bob,dc=redhat.com
+
+And is exactly equal to:
+
+    DN(RDN(AVA('cn','Bob')),RDN(AVA('dc','redhat.com')))
+
+The following are alternative syntax's which are all exactly
+equivalent to the above example.
+
+   DN(['cn', 'Bob'], ['dc', 'redhat.com'])
+   DN(RDN('cn', 'Bob'), RDN('dc', 'redhat.com'))
+
+You can provide a properly escaped string representation.
+
+   DN('cn=Bob,dc=redhat.com')
+
+You can mix and match any of the forms in the constructor parameter
+list.
+
+   DN(('cn', 'Bob'), 'dc=redhat.com')
+   DN(('cn', 'Bob'), RDN('dc', 'redhat.com'))
+
+AVA's have an attr and value property, thus if you have an AVA
+
+# Get the attr and value
+ava.attr  -> u'cn'
+ava.value -> u'Bob'
+
+# Set the attr and value
+ava.attr  = 'cn'
+ava.value = 'Bob'
+
+Since RDN's are assumed to be single valued, exactly the same
+behavior applies to an RDN. If the RDN is multi-valued then the attr
+property returns the attr of the first AVA, likewise for the value.
+
+# Get the attr and value
+rdn.attr  -> u'cn'
+rdn.value -> u'Bob'
+
+# Set the attr and value
+rdn.attr  = 'cn'
+rdn.value = 'Bob'
+
+Also RDN's can be indexed by name or position (see the RDN class doc
+for details).
+
+rdn['cn'] -> u'Bob'
+rdn[0] -> AVA('cn', 'Bob')
+
+A DN is a sequence of RDN's, as such any of Python's container
+operators can be applied to a DN in a intuitive way.
+
+# How many RDN's in a DN?
+len(dn)
+
+# WARNING, this a count of RDN's not how characters there are in the
+# string representation the dn, instead that would be:
+len(str(dn))
+
+# Iterate over each RDN in a DN
+for rdn in dn:
+
+# Get the first RDN in a DN
+dn[0] -> RDN('cn', 'Bob')
+
+# Get the value of the first RDN in a DN
+dn[0].value -> u'Bob'
+
+# Get the value of the first RDN by indexing by attr name
+dn['cn'] -> u'Bob'
+
+# WARNING, when a string is used as an index key the FIRST RDN's value
+# in the sequence whose attr matches the key is returned. Thus if you
+# have a DN like this "cn=foo,cn=bar" then dn['cn'] will always return
+# 'foo' even though there is another attr with the name 'cn'. This is
+# almost always what the programmer wants. See the class doc for how
+# you can override this default behavior and get a list of every value
+# whose attr matches the key.
+
+# Set the first RDN in the DN (all are equivalent)
+dn[0] = ('cn', 'Bob')
+dn[0] = ['cn', 'Bob']
+dn[0] = RDN('cn', 'Bob')
+
+dn[0].attr = 'cn'
+dn[0].value = 'Bob'
+
+# Get the first two RDN's using slices
+dn[0:2]
+
+# Get the last two RDN's using slices
+dn[-2:]
+
+# Get a list of all RDN's using slices
+dn[:]
+
+# Set the 2nd and 3rd RDN using slices (all are equivalent)
+dn[1:3] = ('cn', 'Bob), ('dc', 'redhat.com')
+dn[1:3] = RDN('cn', 'Bob), RDN('dc', 'redhat.com')
+
+String representations and escapes:
+
+# To get an RFC compliant string representation of a DN, RDN or AVA
+# simply call str() on it or evaluate it in a string context.
+str(dn) -> 'cn=Bob,dc=redhat.com'
+
+# When working with attr's and values you do not have to worry about
+# escapes, simply use the raw unescaped string in a natural fashion.
+
+rdn = RDN('cn', 'r,w')
+
+# Thus:
+rdn.value == 'r,w' -> True
+
+# But:
+str(rdn) == 'cn=r,w' -> False
+# Because:
+str(rdn) -> 'cn=r\2cw' or 'cn='r\,w' # depending on the underlying LDAP library
+
+Equality and Comparing:
+
+# All DN's, RDN's and AVA's support equality testing in an intuitive
+# manner.
+dn1 = DN(('cn', 'Bob'))
+dn2 = DN(RDN('cn', 'Bob'))
+dn1 == dn2 -> True
+dn1[0] == dn2[0] -> True
+dn1[0].value = 'Bobby'
+dn1 == dn2 -> False
+
+DN objects implement startswith(), endswith() and the "in" membership
+operator. You may pass a DN or RDN object to these. Examples:
+
+if dn.endswith(base_dn):
+if dn.startswith(rdn1):
+if container_dn in dn:
+
+# See the class doc for how DN's, RDN's and AVA's compare
+# (e.g. cmp()). The general rule is for objects supporting multiple
+# values first their lengths are compared, then if the lengths match
+# the respective components of each are pair-wise compared until one
+# is discovered to be  non-equal. The comparision is case insensitive.
+
+Cloning (Object Copy):
+
+All the class types are capable of cloning by passing an object of the
+same type (or subclass) to the constructor. The new object is a copy
+of the object passed as input to the constructor. One place this is
+useful is when you want to coerce between immutable and mutable
+versions in order to modify an object.
+
+Concatenation, In-Place Addition, Insertion:
+
+# DN's and RDN's can be concatenated.
+# Return a new DN by appending the RDN's of dn2 to dn1
+dn3 = dn1 + dn2
+
+# Append a RDN to DN's RDN sequence (all are equivalent)
+dn += ('cn', 'Bob')
+dn += RDN('cn', 'Bob')
+
+# Append a DN to an existing DN
+dn1 += dn2
+
+# Prepend a RDN to an existing DN
+dn1.insert(0, RDN('cn', 'Bob'))
+
+Finally see the unittest for a more complete set of ways you can
+manipulate these objects.
+
+Mutability
+----------
+
+Python makes a clear distinction between mutable and immutable
+objects. Examples of immutable Python objects are strings, integers
+and floats. Examples of mutable Python objects are lists, dicts, and
+sets. Immutable objects cannot be modified, mutable objects can be
+modified. An object's mutability affects how the object behaves when
+passed to a function or method, this is because it's the object's
+reference which is always passed, thus immutable objects behave as if
+it were "call by value" and mutable objects behave as if it were "call
+by reference" (mutable objects can be modifed inside the
+function/method and that modification will be visible to the
+caller. On object's mutability also affects how an object will behave
+when used as a key in a dict or as a member of a set.
+
+The following discussion applies equally to AVA, RDN and DN object
+class variants.
+
+The AVA, RDN and DN classes have both immutable and mutable
+variants. The base classes (AVA, RDN, DN) are immutable. Each of the
+immutable base classes have a mutable subclass whose name begins with
+'Editable'. Thus the DN class is immutable, instances of that class
+cannot be modified, there is a mutable class EditableDN derived from
+DN whose instances can be modified. The primary difference between the
+immutable and mutable variants is:
+
+* Immutable variants are preferred.
+
+* Mutable variants are exactly identical in behavior to their
+  immutable parent class (except for supporting assignment, etc.)
+
+* Immutable objects that test as equal will be the same as dict keys
+  and set members even if they are different objects. Mutable variants
+  are not hashable and thus cannot be used as a dict key nor inserted
+  into a set.
+
+* Only mutable variants support modification via assignment, insert or
+  in-place addition (e.g. +=).
+
+* In-place addtion (e.g. +=) works for both immutable and mutable
+  variants. The distinction is for immutable objects the lhs is
+  replaced with a new immutable result while a mutable object will be
+  modfied in place and lhs object remains the same object.
+
+It is trival to coerce between an mutable and immutable AVA, RDN and
+DN types. These classes can clone their objects by passing an object
+of the same type to the constructor. For example:
+
+  dn1 = DN(('cn', 'Bob')) # dn1 is immutable
+  dn2 = EditableDN(dn1)   # dn2 is mutable copy of dn1,
+                          # equal to dn1 until it's modified
+
+  and visa-versa
+
+  dn1 = EditableDN(('cn', 'Bob')) # dn1 is mutable
+  dn2 = DN(dn1)                   # dn2 is immutable copy of dn1, equal to dn1
+
+'''
+
+from ldap.dn import str2dn, dn2str
+from ldap import DECODING_ERROR
+import sys
+
+__all__ = ['AVA', 'EditableAVA', 'RDN', 'EditableRDN', 'DN', 'EditableDN']
+
+def _adjust_indices(start, end, length):
+    'helper to fixup start/end slice values'
+
+    if end > length:
+        end = length
+    elif end < 0:
+        end += length
+        if end < 0:
+            end = 0
+
+    if start < 0:
+        start += length
+        if start < 0:
+            start = 0
+
+    return start, end
+
+class AVA(object):
+    '''
+    AVA(arg0, ...)
+
+    An AVA is an LDAP Attribute Value Assertion. It is convenient to think of
+    AVA's as a <attr,value> pair. AVA's are members of RDN's (Relative
+    Distinguished Name).
+
+    The AVA constructor is passed a sequence of args and a set of
+    keyword parameters used for configuration.
+
+    The arg sequence may be:
+
+    1) With 2 arguments, the first argument will be the attr, the 2nd
+    the value. Each argument must be scalar convertable to unicode.
+
+    2) With a sigle list or tuple argument containing exactly 2 items.
+    Each item must be scalar convertable to unicode.
+
+    3) With a single string (or unicode) argument, in this case the string will
+    be interpretted using the DN syntax described in RFC 4514 to yield a AVA
+    <attr,value> pair. The parsing recognizes the DN syntax escaping rules.
+
+    For example:
+
+    ava = AVA('cn', 'Bob')	# case 1: two strings
+    ava = AVA(('cn', 'Bob'))    # case 2: 2-valued tuple
+    ava = AVA(['cn', 'Bob'])    # case 2: 2-valued list
+    ava = AVA('cn=Bob')         # case 3: DN syntax
+
+    AVA object have two properties for accessing their data:
+
+    attr:  the attribute name, cn in our exmaple
+    value: the attribute's value, Bob in our example
+
+    When attr and value are returned they will always be unicode. When
+    attr or value are set they will be promoted to unicode.
+
+    AVA objects support indexing by name, e.g.
+
+    ava['cn']
+
+    returns the value (Bob in our example). If the index does key does not match
+    the attr then a KeyError will be raised.
+
+    AVA objects support equality testing and comparsion (e.g. cmp()). When they
+    are compared the attr is compared first, if the 2 attr's are equal then the
+    values are compared. The comparision is case insensitive (because attr's map
+    to numeric OID's and their values derive from from the 'name' atribute type
+    (OID 2.5.4.41) whose EQUALITY MATCH RULE is caseIgnoreMatch.
+
+    The str method of an AVA returns the string representation in RFC 4514 DN
+    syntax with proper escaping.
+    '''
+    is_mutable = False
+    flags = 0
+
+    def __init__(self, *args, **kwds):
+        if len(args) == 1:
+            arg = args[0]
+            if isinstance(arg, AVA):
+                ava = (arg.attr, arg.value)
+            elif isinstance(arg, basestring):
+                try:
+                    rdns = str2dn(arg.encode('utf-8'))
+                except DECODING_ERROR:
+                    raise ValueError("malformed AVA string = \"%s\"" % arg)
+                if len(rdns) != 1:
+                    raise ValueError("multiple RDN's specified by \"%s\"" % (arg))
+                rdn = rdns[0]
+                if len(rdn) != 1:
+                    raise ValueError("multiple AVA's specified by \"%s\"" % (arg))
+                ava = rdn[0]
+            elif isinstance(arg, (tuple, list)):
+                ava = arg
+                if len(ava) != 2:
+                    raise ValueError("tuple or list must be 2-valued, not \"%s\"" % (ava))
+            else:
+                raise TypeError("with 1 argument, argument must be str,unicode,tuple or list, got %s instead" % \
+                                arg.__class__.__name__)
+
+            attr  = ava[0]
+            value = ava[1]
+        elif len(args) == 2:
+            attr  = args[0]
+            value = args[1]
+        else:
+            raise TypeError("takes 1 or 2 arguments (%d given)" % (len(args)))
+
+        self._set_attr(attr)
+        self._set_value(value)
+
+    def _get_attr(self):
+        return self._attr_unicode
+
+    def _set_attr(self, new_attr):
+        # Scalars only
+        if isinstance(new_attr, (tuple, list)):
+            raise TypeError("attr must be scalar, got %s" % type(new_attr))
+
+        try:
+            if isinstance(new_attr, unicode):
+                self._attr_unicode = new_attr
+            elif isinstance(new_attr, str):
+                self._attr_unicode = new_attr.decode('utf-8')
+            else:
+                self._attr_unicode = unicode(new_attr)
+        except Exception, e:
+            raise ValueError('unable to convert attr "%s" to unicode: %s' % (new_attr, e))
+
+    attr  = property(_get_attr)
+
+    def _get_value(self):
+        return self._value_unicode
+
+    def _set_value(self, new_value):
+        # Scalars only
+        if isinstance(new_value, (tuple, list)):
+            raise TypeError("value must be scalar, got %s" % type(new_value))
+
+        try:
+            if isinstance(new_value, unicode):
+                self._value_unicode  = new_value
+            elif isinstance(new_value, str):
+                self._value_unicode  = new_value.decode('utf-8')
+            else:
+                self._value_unicode  = unicode(new_value)
+        except Exception, e:
+            raise ValueError('unable to convert value "%s" to unicode: %s' % (new_value, e))
+
+    value = property(_get_value)
+
+    def _to_openldap(self):
+        return [[(self._attr_unicode.encode('utf-8'), self._value_unicode.encode('utf-8'), self.flags)]]
+
+    def __str__(self):
+        return dn2str(self._to_openldap())
+
+    def __repr__(self):
+        return "%s.%s('%s')" % (self.__module__, self.__class__.__name__, self.__str__())
+
+    def __getitem__(self, key):
+        if isinstance(key, basestring):
+            if key == self._attr_unicode:
+                return self._value_unicode
+            raise KeyError("\"%s\" not found in %s" % (key, self.__str__()))
+        else:
+            raise TypeError("unsupported type for AVA indexing, must be basestring; not %s" % \
+                                (key.__class__.__name__))
+
+    def __hash__(self):
+        # Hash is computed from AVA's string representation because it's immutable
+        return hash(str(self))
+
+    def __eq__(self, other):
+        '''
+        The attr comparison is case insensitive because attr is
+        really an LDAP attribute type which means it's specified with
+        an OID (dotted number) and not a string. Since OID's are
+        numeric the human readable name which maps to the OID is not
+        significant in case.
+
+        The value comparison is also case insensitive because the all
+        attribute types used in a DN are derived from the 'name'
+        atribute type (OID 2.5.4.41) whose EQUALITY MATCH RULE is
+        caseIgnoreMatch.
+        '''
+        # Try coercing string to AVA, if successful compare to coerced object
+        if isinstance(other, basestring):
+            try:
+                other_ava = AVA(other)
+                return self.__eq__(other_ava)
+            except Exception:
+                return False
+
+        # If it's not an AVA it can't be equal
+        if not isinstance(other, AVA):
+            return False
+
+        # Perform comparision between objects of same type
+        return self._attr_unicode.lower() == other.attr.lower() and \
+            self._value_unicode.lower() == other.value.lower()
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __cmp__(self, other):
+        'comparision is case insensitive, see __eq__ doc for explanation'
+
+        if not isinstance(other, AVA):
+            raise TypeError("expected AVA but got %s" % (other.__class__.__name__))
+
+        result = cmp(self._attr_unicode.lower(), other.attr.lower())
+        if result != 0:
+            return result
+        result = cmp(self._value_unicode.lower(), other.value.lower())
+        return result
+
+class EditableAVA(AVA):
+    '''
+    Exactly identical to the AVA class except
+
+    * Hash value is based on object identity, not object
+      value. Objects that test as equal will be non-unique when
+      used as a dict key or member of a set.
+
+    * The attr and value properties may be modified after object creation.
+
+    '''
+    is_mutable = True
+    __hash__ = None
+
+    attr  = property(AVA._get_attr, AVA._set_attr)
+    value = property(AVA._get_value, AVA._set_value)
+
+
+
+class RDN(object):
+    '''
+    RDN(arg0, ...)
+
+    An RDN is a LDAP Relative Distinguished Name. RDN's are members of DN's
+    (Distinguished Name). An RDN contains 1 or more AVA's. If the RDN contains
+    more than one AVA it is said to be a multi-valued RDN. When an RDN is
+    multi-valued the AVA's are unorderd comprising a set. However this
+    implementation orders the AVA's according to the AVA comparison function to
+    make equality and comparison testing easier. Think of this a canonical
+    normalization (however LDAP does not impose any ordering on multiple AVA's
+    within an RDN). Single valued RDN's are the norm and thus the RDN
+    constructor has simple syntax for them.
+
+    The RDN constructor is passed a sequence of args and a set of
+    keyword parameters used for configuration.
+
+    The constructor iterates though the sequence and adds AVA's to the RDN.
+
+    The arg sequence may be:
+
+    * A 2-valued tuple or list denotes the <attr,value> pair of an AVA. The
+    first member is the attr and the second member is the value, both members
+    must be strings (or unicode). The tuple or list is passed to the AVA
+    constructor and the resulting AVA is added to the RDN. Multiple tuples or
+    lists may appear in the argument list, each adds one additional AVA to the
+    RDN.
+
+    * A single string (or unicode) argument, in this case the string will
+    be interpretted using the DN syntax described in RFC 4514 to yield one or
+    more AVA <attr,value> pairs. The parsing recognizes the DN syntax escaping
+    rules.
+
+    * A AVA object, the AVA will be copied into the new RDN respecting
+      the constructors keyword configuration parameters.
+
+    * A RDN object, the AVA's in the RDN are copied into the new RDN
+      respecting the constructors keyword configuration parameters.
+
+    Single AVA Examples:
+
+    RDN(('cn', 'Bob'))                  # tuple yields 1 AVA
+    RDN('cn=Bob')                       # DN syntax with 1 AVA
+    RDN(AVA('cn', 'Bob'))               # AVA object adds 1 AVA
+
+    Multiple AVA Examples:
+
+    RDN(('cn', 'Bob'),('ou', 'people')) # 2 tuples yields 2 AVA's
+    RDN('cn=Bob+ou=people')             # DN syntax with 2 AVA's
+    RDN(AVA('cn', 'Bob'),AVA('ou', 'people')) # 2 AVA objects adds 2 AVA's
+    RDN(('cn', 'Bob'), 'ou=people')     # 2 args, 1st tuple forms 1 AVA,
+                                        # 2nd DN syntax string adds 1 AVA,
+                                        # 2 AVA's in total
+
+    Note: The RHS of a slice assignment is interpreted exactly in the
+    same manner as the constructor argument list (see above examples).
+
+    RDN objects support iteration over their AVA members. You can iterate all
+    AVA members via any Python iteration syntax. RDN objects support full Python
+    indexing using bracket [] notation. Examples:
+
+    len(rdn)            # return the number of AVA's
+    rdn[0]              # indexing the first AVA
+    rdn['cn']           # index by AVA attr, returns AVA value
+    for ava in rdn:     # iterate over each AVA
+    rdn[:]              # a slice, in this case a copy of each AVA
+
+    WARNING: When indexing by attr (e.g. rdn['cn']) there is a possibility more
+    than one AVA has the same attr name as the index key. The default behavior
+    is to return the value of the first AVA whose attr matches the index
+    key.
+
+    RDN objects support the AVA attr and value properties as another programmer
+    convenience because the vast majority of RDN's are single valued. The attr
+    and value properties return the attr and value properties of the first AVA
+    in the RDN, for example:
+
+    rdn = RDN(('cn', 'Bob')) # rdn has 1 AVA whose attr == 'cn' and value == 'Bob'
+    len(rdn) -> 1
+    rdn.attr -> u'cn'      # exactly equivalent to rdn[0].attr
+    rdn.value -> u'Bob'    # exactly equivalent to rdn[0].value
+
+    When attr and value are returned they will always be unicode. When
+    attr or value are set they will be promoted to unicode.
+
+    If an RDN is multi-valued the attr and value properties still return only
+    the first AVA's properties, programmer beware! Recall the AVA's in the RDN
+    are sorted according the to AVA collating semantics.
+
+    RDN objects support equality testing and comparision. See AVA for the
+    definition of the comparision method.
+
+    RDN objects support concatenation and addition with other RDN's or AVA's
+
+    rdn1 + rdn2 # yields a new RDN object with the contents of each RDN.
+    rdn1 + ava1 # yields a new RDN object with the contents of rdn1 and ava1
+
+    RDN objects can add AVA's objects via in-place addition.
+
+    rdn1 += rdn2 # rdn1 now contains the sum of rdn1 and rdn2
+    rdn1 += ava1 # rdn1 has ava1 added to it.
+
+    The str method of an RDN returns the string representation in RFC 4514 DN
+    syntax with proper escaping.
+    '''
+
+    is_mutable = False
+    flags = 0
+    AVA_type = AVA
+
+    def __init__(self, *args, **kwds):
+        self.avas = self._avas_from_sequence(args)
+        self.avas.sort()
+
+    def _ava_from_value(self, value):
+        if isinstance(value, AVA):
+            return self.AVA_type(value.attr, value.value)
+        elif isinstance(value, RDN):
+            avas = []
+            for ava in value.avas:
+                avas.append(self.AVA_type(ava.attr, ava.value))
+            if len(avas) == 1:
+                return avas[0]
+            else:
+                return avas
+        elif isinstance(value, basestring):
+            try:
+                rdns = str2dn(value.encode('utf-8'))
+                if len(rdns) != 1:
+                    raise ValueError("multiple RDN's specified by \"%s\"" % (value))
+                rdn = rdns[0]
+                if len(rdn) == 1:
+                    return self.AVA_type(rdn[0][0], rdn[0][1])
+                else:
+                    avas = []
+                    for ava_tuple in rdn:
+                        avas.append(self.AVA_type(ava_tuple[0], ava_tuple[1]))
+                    return avas
+            except DECODING_ERROR:
+                raise ValueError("malformed RDN string = \"%s\"" % value)
+        elif isinstance(value, (tuple, list)):
+            if len(value) != 2:
+                raise ValueError("tuple or list must be 2-valued, not \"%s\"" % (value))
+            return self.AVA_type(value)
+        else:
+            raise TypeError("must be str,unicode,tuple, or AVA, got %s instead" % \
+                            value.__class__.__name__)
+
+
+    def _avas_from_sequence(self, seq):
+        avas = []
+
+        for item in seq:
+            ava = self._ava_from_value(item)
+            if isinstance(ava, list):
+                avas.extend(ava)
+            else:
+                avas.append(ava)
+        return avas
+
+    def _to_openldap(self):
+        return [[(ava.attr.encode('utf-8'), ava.value.encode('utf-8'), self.flags) for ava in self.avas]]
+
+    def __str__(self):
+        return dn2str(self._to_openldap())
+
+    def __repr__(self):
+        return "%s.%s('%s')" % (self.__module__, self.__class__.__name__, self.__str__())
+
+    def _next(self):
+        for ava in self.avas:
+            yield ava
+
+    def __iter__(self):
+        return self._next()
+
+    def __len__(self):
+        return len(self.avas)
+
+    def __getitem__(self, key):
+        if isinstance(key, (int, long, slice)):
+            return self.avas[key]
+        elif isinstance(key, basestring):
+            for ava in self.avas:
+                if key == ava.attr:
+                    return ava.value
+            raise KeyError("\"%s\" not found in %s" % (key, self.__str__()))
+        else:
+            raise TypeError("unsupported type for RDN indexing, must be int, basestring or slice; not %s" % \
+                                (key.__class__.__name__))
+
+    def _get_attr(self):
+        if len(self.avas) == 0:
+            raise IndexError("No AVA's in this RDN")
+        return self.avas[0].attr
+
+    def _set_attr(self, new_attr):
+        if len(self.avas) == 0:
+            raise IndexError("No AVA's in this RDN")
+
+        self.avas[0].attr = new_attr
+
+    attr  = property(_get_attr)
+
+    def _get_value(self):
+        if len(self.avas) == 0:
+            raise IndexError("No AVA's in this RDN")
+        return self.avas[0].value
+
+    def _set_value(self, new_value):
+        if len(self.avas) == 0:
+            raise IndexError("No AVA's in this RDN")
+
+        self.avas[0].value = new_value
+
+    value = property(_get_value)
+
+    def __hash__(self):
+        # Hash is computed from RDN's string representation because it's immutable
+        return hash(str(self))
+
+    def __eq__(self, other):
+        # Try coercing string to RDN, if successful compare to coerced object
+        if isinstance(other, basestring):
+            try:
+                other_rdn = RDN(other)
+                return self.__eq__(other_rdn)
+            except Exception:
+                return False
+
+        # If it's not an RDN it can't be equal
+        if not isinstance(other, RDN):
+            return False
+
+        # Perform comparision between objects of same type
+        return self.avas == other.avas
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __cmp__(self, other):
+        if not isinstance(other, RDN):
+            raise TypeError("expected RDN but got %s" % (other.__class__.__name__))
+
+        result = cmp(len(self), len(other))
+        if result != 0:
+            return result
+        i = 0
+        while i < len(self):
+            result = cmp(self[i], other[i])
+            if result != 0:
+                return result
+            i += 1
+        return 0
+
+    def __add__(self, other):
+        result = self.__class__(self)
+        if isinstance(other, RDN):
+            for ava in other.avas:
+                result.avas.append(self.AVA_type(ava.attr, ava.value))
+        elif isinstance(other, AVA):
+            result.avas.append(self.AVA_type(other.attr, other.value))
+        elif isinstance(other, basestring):
+            rdn = self.__class__(other)
+            for ava in rdn.avas:
+                result.avas.append(self.AVA_type(ava.attr, ava.value))
+        else:
+            raise TypeError("expected RDN, AVA or basestring but got %s" % (other.__class__.__name__))
+
+        result.avas.sort()
+        return result
+
+class EditableRDN(RDN):
+    '''
+    Exactly identical to the RDN class except
+
+    * Hash value is based on object identity, not object
+      value. Objects that test as equal will be non-unique when
+      used as a dict key or member of a set.
+
+    * AVA components may be assigned via assignment statements.
+
+    * In-place addition modifes the lhs object.
+
+    * The attr and value properties may be modified after object creation.
+    '''
+
+    is_mutable = True
+    __hash__ = None
+    AVA_type = EditableAVA
+
+    def __setitem__(self, key, value):
+        if isinstance(key, (int, long)):
+            new_ava = self._ava_from_value(value)
+            if isinstance(new_ava, list):
+                raise TypeError("cannot assign multiple AVA's to single entry")
+            self.avas[key] = new_ava
+        elif isinstance(key, slice):
+            avas = self._avas_from_sequence(value)
+            self.avas[key] = avas
+        elif isinstance(key, basestring):
+            new_ava = self._ava_from_value(value)
+            if isinstance(new_ava, list):
+                raise TypeError("cannot assign multiple AVA's to single entry")
+            found = False
+            i = 0
+            while i < len(self.avas):
+                if key == self.avas[i].attr:
+                    found = True
+                    self.avas[i] = new_ava
+                    break
+                i += 1
+            if not found:
+                raise KeyError("\"%s\" not found in %s" % (key, self.__str__()))
+        else:
+            raise TypeError("unsupported type for RDN indexing, must be int, basestring or slice; not %s" % \
+                                (key.__class__.__name__))
+        self.avas.sort()
+
+    attr  = property(RDN._get_attr, RDN._set_attr)
+    value = property(RDN._get_value, RDN._set_value)
+
+
+    def __iadd__(self, other):
+        # If __iadd__ is not available Python will emulate += by
+        # replacing the lhs object with the result of __add__ (if available).
+        if isinstance(other, RDN):
+            for ava in other.avas:
+                self.avas.append(self.AVA_type(ava.attr, ava.value))
+        elif isinstance(other, AVA):
+            self.avas.append(self.AVA_type(other.attr, other.value))
+        elif isinstance(other, basestring):
+            rdn = self.__class__(other)
+            for ava in rdn.avas:
+                self.avas.append(self.AVA_type(ava.attr, ava.value))
+        else:
+            raise TypeError("expected RDN, AVA or basestring but got %s" % (other.__class__.__name__))
+
+        self.avas.sort()
+        return self
+
+class DN(object):
+    '''
+    DN(arg0, ...)
+
+    A DN is a LDAP Distinguished Name. A DN is an ordered sequence of RDN's.
+
+    The DN constructor is passed a sequence of args and a set of
+    keyword parameters used for configuration. normalize means the
+    attr and value will be converted to lower case.
+
+    The constructor iterates through the sequence and adds the RDN's
+    it finds in order to the DN object. Each item in the sequence may
+    be:
+
+    * A 2-valued tuple or list. The first member is the attr and the
+      second member is the value of an RDN, both members must be
+      strings (or unicode). The tuple or list is passed to the RDN
+      constructor and the resulting RDN is appended to the
+      DN. Multiple tuples or lists may appear in the argument list,
+      each adds one additional RDN to the DN.
+
+    * A single string (or unicode) argument, in this case the string
+      will be interpretted using the DN syntax described in RFC 4514
+      to yield one or more RDN's which will be appended in order to
+      the DN. The parsing recognizes the DN syntax escaping rules.
+
+    * A RDN object, the RDN will copied respecting the constructors
+      keyword configuration parameters and appended in order.
+
+    * A DN object, the RDN's in the DN are copied respecting the
+      constructors keyword configuration parameters and appended in
+      order.
+
+    Single DN Examples:
+
+    DN(('cn', 'Bob'))                   # tuple yields 1 RDN
+    DN(['cn', 'Bob'])                   # list yields 1 RDN
+    DN('cn=Bob')                        # DN syntax with 1 RDN
+    DN(RDN('cn', 'Bob'))                # RDN object adds 1 RDN
+
+    Multiple RDN Examples:
+
+    DN(('cn', 'Bob'),('ou', 'people'))  # 2 tuples yields 2 RDN's
+                                        # 2 RDN's total
+    DN('cn=Bob,ou=people')              # DN syntax with 2 RDN's
+                                        # 2 RDN's total
+    DN(RDN('cn', 'Bob'),RDN('ou', 'people')) # 2 RDN objects
+                                        # 2 RDN's total
+    DN(('cn', 'Bob'), "ou=people')      # 1st tuple adds 1 RDN
+                                        # 2nd DN syntax string adds 1 RDN
+                                        # 2 RDN's total
+    base_dn = DN('dc=redhat,dc=com')
+    container_dn = DN('cn=sudorules,cn=sudo')
+    DN(('cn', 'Bob'), container_dn, base_dn)
+                                        # 1st arg adds 1 RDN, cn=Bob
+                                        # 2nd arg adds 2 RDN's, cn=sudorules,cn=sudo
+                                        # 3rd arg adds 2 RDN's, dc=redhat,dc=com
+                                        # 5 RDN's total
+
+
+    Note: The RHS of a slice assignment is interpreted exactly in the
+    same manner as the constructor argument list (see above examples).
+
+    DN objects support iteration over their RDN members. You can iterate all
+    RDN members via any Python iteration syntax. DN objects support full Python
+    indexing using bracket [] notation. Examples:
+
+    len(rdn)            # return the number of RDN's
+    rdn[0]              # indexing the first RDN
+    rdn['cn']           # index by RDN attr, returns RDN value
+    for ava in rdn:     # iterate over each RDN
+    rdn[:]              # a slice, in this case a copy of each RDN
+
+    WARNING: When indexing by attr (e.g. dn['cn']) there is a
+    possibility more than one RDN has the same attr name as the index
+    key. The default behavior is to return the value of the first RDN
+    whose attr matches the index key. If it's important the attr
+    belong to a specific RDN (e.g. the first) then this is the
+    suggested construct:
+
+        try:
+            cn = dn[0]['cn']
+        except (IndexError, KeyError):
+            raise ValueError("dn '%s' missing expected cn as first attribute" % dn)
+
+    The IndexError catches a DN which does not have the expected
+    number of RDN's and the KeyError catches the case where the
+    indexed RDN does not have the expected attr.
+
+    DN object support slices.
+
+    # Get the first two RDN's using slices
+    dn[0:2]
+
+    # Get the last two RDN's using slices
+    dn[-2:]
+
+    # Get a list of all RDN's using slices
+    dn[:]
+
+    # Set the 2nd and 3rd RDN using slices (all are equivalent)
+    dn[1:3] = ('cn', 'Bob'), ('dc', 'redhat.com')
+    dn[1:3] = [['cn', 'Bob'], ['dc', 'redhat.com']]
+    dn[1:3] = RDN('cn', 'Bob'), RDN('dc', 'redhat.com')
+
+    DN objects support the insert operation.
+
+    dn.insert(i,x) is exactly equivalent to dn[i:i] = [x], thus the following
+    are all equivalent:
+
+    dn.insert(i, ('cn','Bob'))
+    dn.insert(i, ['cn','Bob'])
+    dn.insert(i, RDN(('cn','Bob')))
+    dn[i:i] = [('cn','Bob')]
+
+    DN objects support equality testing and comparision. See RDN for the
+    definition of the comparision method.
+
+    DN objects implement startswith(), endswith() and the "in" membership
+    operator. You may pass a DN or RDN object to these. Examples:
+
+    # Test if dn ends with the contents of base_dn
+    if dn.endswith(base_dn):
+    # Test if dn starts with a rdn
+    if dn.startswith(rdn1):
+    # Test if a container is present in a dn
+    if container_dn in dn:
+
+    DN objects support concatenation and addition with other DN's or RDN's
+    or strings (interpreted as RFC 4514 DN syntax).
+
+    # yields a new DN object with the RDN's of dn2 appended to the RDN's of dn1
+    dn1 + dn2
+
+    # yields a new DN object with the rdn1 appended to the RDN's of dn1
+    dn1 + rdn1
+
+    DN objects can add RDN's objects via in-place addition.
+
+    dn1 += dn2  # dn2 RDN's are appended to the dn1's RDN's
+    dn1 += rdn1 # dn1 has rdn appended to its RDN's
+    dn1 += "dc=redhat.com" # string is converted to DN, then appended
+
+    The str method of an DN returns the string representation in RFC 4514 DN
+    syntax with proper escaping.
+    '''
+
+    is_mutable = False
+    flags = 0
+    AVA_type = AVA
+    RDN_type = RDN
+
+    def __init__(self, *args, **kwds):
+        self.rdns = self._rdns_from_sequence(args)
+
+    def _rdn_from_value(self, value):
+        if isinstance(value, RDN):
+            return self.RDN_type(value)
+        elif isinstance(value, DN):
+            rdns = []
+            for rdn in value.rdns:
+                rdns.append(self.RDN_type(rdn))
+            if len(rdns) == 1:
+                return rdns[0]
+            else:
+                return rdns
+        elif isinstance(value, basestring):
+            rdns = []
+            try:
+                dn_list = str2dn(value.encode('utf-8'))
+                for rdn_list in dn_list:
+                    avas = []
+                    for ava_tuple in rdn_list:
+                        avas.append(self.AVA_type(ava_tuple[0], ava_tuple[1]))
+                    rdn = self.RDN_type(*avas)
+                    rdns.append(rdn)
+            except DECODING_ERROR:
+                raise ValueError("malformed RDN string = \"%s\"" % value)
+            if len(rdns) == 1:
+                return rdns[0]
+            else:
+                return rdns
+        elif isinstance(value, (tuple, list)):
+            if len(value) != 2:
+                raise ValueError("tuple or list must be 2-valued, not \"%s\"" % (value))
+            rdn = self.RDN_type(value)
+            return rdn
+        else:
+            raise TypeError("must be str,unicode,tuple, or RDN, got %s instead" % \
+                            value.__class__.__name__)
+
+    def _rdns_from_sequence(self, seq):
+        rdns = []
+
+        for item in seq:
+            rdn = self._rdn_from_value(item)
+            if isinstance(rdn, list):
+                rdns.extend(rdn)
+            else:
+                rdns.append(rdn)
+        return rdns
+
+    def _to_openldap(self):
+        return [[(ava.attr.encode('utf-8'), ava.value.encode('utf-8'), self.flags) for ava in rdn] for rdn in self.rdns]
+
+    def __str__(self):
+        return dn2str(self._to_openldap())
+
+    def __repr__(self):
+        return "%s.%s('%s')" % (self.__module__, self.__class__.__name__, self.__str__())
+
+    def _next(self):
+        for rdn in self.rdns:
+            yield rdn
+
+    def __iter__(self):
+        return self._next()
+
+    def __len__(self):
+        return len(self.rdns)
+
+    def __getitem__(self, key):
+        if isinstance(key, (int, long, slice)):
+            return self.rdns[key]
+        elif isinstance(key, basestring):
+            for rdn in self.rdns:
+                if key == rdn.attr:
+                    return rdn.value
+            raise KeyError("\"%s\" not found in %s" % (key, self.__str__()))
+        else:
+            raise TypeError("unsupported type for DN indexing, must be int, basestring or slice; not %s" % \
+                                (key.__class__.__name__))
+
+    def __hash__(self):
+        # Hash is computed from DN's string representation because it's immutable
+        return hash(str(self))
+
+    def __eq__(self, other):
+        # Try coercing string to DN, if successful compare to coerced object
+        if isinstance(other, basestring):
+            try:
+                other_dn = DN(other)
+                return self.__eq__(other_dn)
+            except Exception:
+                return False
+
+        # If it's not an DN it can't be equal
+        if not isinstance(other, DN):
+            return False
+
+        # Perform comparision between objects of same type
+        return self.rdns == other.rdns
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __cmp__(self, other):
+        if not isinstance(other, DN):
+            raise TypeError("expected DN but got %s" % (other.__class__.__name__))
+
+        result = cmp(len(self), len(other))
+        if result != 0:
+            return result
+        return self._cmp_sequence(other, 0, len(self))
+
+    def _cmp_sequence(self, pattern, self_start, pat_len):
+        self_idx = self_start
+        pat_idx = 0
+        while pat_idx < pat_len:
+            result = cmp(self[self_idx], pattern[pat_idx])
+            if result != 0:
+                return result
+            self_idx += 1
+            pat_idx += 1
+        return 0
+
+    def __add__(self, other):
+        result = self.__class__(self)
+        if isinstance(other, DN):
+            for rdn in other.rdns:
+                result.rdns.append(self.RDN_type(rdn))
+        elif isinstance(other, RDN):
+            result.rdns.append(self.RDN_type(other))
+        elif isinstance(other, basestring):
+            dn = self.__class__(other)
+            for rdn in dn.rdns:
+                result.rdns.append(rdn)
+        else:
+            raise TypeError("expected DN, RDN or basestring but got %s" % (other.__class__.__name__))
+
+        return result
+
+    # The implementation of startswith, endswith, tailmatch, adjust_indices
+    # was based on the Python's stringobject.c implementation
+
+    def startswith(self, prefix, start=0, end=sys.maxsize):
+        '''
+        Return True if the dn starts with the specified prefix (either a DN or
+        RDN object), False otherwise.  With optional start, test dn beginning at
+        that position.  With optional end, stop comparing dn at that position.
+        prefix can also be a tuple of dn's or rdn's to try.
+        '''
+        if isinstance(prefix, tuple):
+            for pat in prefix:
+                if self._tailmatch(pat, start, end, -1):
+                    return True
+            return False
+
+        return self._tailmatch(prefix, start, end, -1)
+
+    def endswith(self, suffix, start=0, end=sys.maxsize):
+        '''
+        Return True if dn ends with the specified suffix (either a DN or RDN
+        object), False otherwise.  With optional start, test dn beginning at
+        that position.  With optional end, stop comparing dn at that position.
+        suffix can also be a tuple of dn's or rdn's to try.
+        '''
+        if isinstance(suffix, tuple):
+            for pat in suffix:
+                if self._tailmatch(pat, start, end, +1):
+                    return True
+            return False
+
+        return self._tailmatch(suffix, start, end, +1)
+
+    def _tailmatch(self, pattern, start, end, direction):
+        '''
+        Matches the end (direction >= 0) or start (direction < 0) of self
+        against pattern (either a DN or RDN), using the start and end
+        arguments. Returns 0 if not found and 1 if found.
+        '''
+
+        if isinstance(pattern, DN):
+            pat_len = len(pattern)
+        elif isinstance(pattern, RDN):
+            pat_len = 1
+        else:
+            raise TypeError("expected DN or RDN but got %s" % (pattern.__class__.__name__))
+
+        self_len = len(self)
+
+        start, end = _adjust_indices(start, end, self_len)
+
+        if direction < 0:       # starswith
+            if start+pat_len > self_len:
+                return 0
+        else:                   # endswith
+            if end-start < pat_len or start > self_len:
+                return 0
+
+            if end-pat_len >= start:
+                start = end - pat_len
+
+        if isinstance(pattern, DN):
+            if end-start >= pat_len:
+                return not self._cmp_sequence(pattern, start, pat_len)
+            return 0
+        else:
+            return self.rdns[start] == pattern
+
+    def __contains__(self, other):
+        'Return the outcome of the test other in self. Note the reversed operands.'
+
+        if isinstance(other, DN):
+            other_len = len(other)
+            end = len(self) - other_len
+            i = 0
+            while i <= end:
+                result = self._cmp_sequence(other, i, other_len)
+                if result == 0:
+                    return True
+                i += 1
+            return False
+
+        elif isinstance(other, RDN):
+            return other in self.rdns
+        else:
+            raise TypeError("expected DN or RDN but got %s" % (other.__class__.__name__))
+
+
+    def find(self, pattern, start=None, end=None):
+        '''
+        Return the lowest index in the DN where pattern DN (or RDN) is found,
+        such that pattern is contained in the range [start, end]. Optional
+        arguments start and end are interpreted as in slice notation. Return
+        -1 if pattern is not found.
+        '''
+
+        if isinstance(pattern, DN):
+            pat_len = len(pattern)
+        elif isinstance(pattern, RDN):
+            pat_len = 1
+        else:
+            raise TypeError("expected DN or RDN but got %s" % (pattern.__class__.__name__))
+
+        self_len = len(self)
+
+        if start is None:
+            start = 0
+        if end is None:
+            end = self_len
+
+        start, end = _adjust_indices(start, end, self_len)
+
+        i = start
+        stop = max(start, end - pat_len)
+        if isinstance(pattern, DN):
+            while i <= stop:
+                result = self._cmp_sequence(pattern, i, pat_len)
+                if result == 0:
+                    return i
+                i += 1
+            return -1
+        else:
+            while i <= stop:
+                if self.rdns[i] == pattern:
+                    return i
+                i += 1
+            return -1
+
+    def index(self, pattern, start=None, end=None):
+        '''
+        Like find() but raise ValueError when the pattern is not found.
+        '''
+
+        i = self.find(pattern, start, end)
+        if i == -1:
+            raise ValueError("pattern not found")
+        return i
+
+    def rfind(self, pattern, start=None, end=None):
+        '''
+        Return the highest index in the DN where pattern DN (or RDN) is found,
+        such that pattern is contained in the range [start, end]. Optional
+        arguments start and end are interpreted as in slice notation. Return
+        -1 if pattern is not found.
+        '''
+
+        if isinstance(pattern, DN):
+            pat_len = len(pattern)
+        elif isinstance(pattern, RDN):
+            pat_len = 1
+        else:
+            raise TypeError("expected DN or RDN but got %s" % (pattern.__class__.__name__))
+
+        self_len = len(self)
+
+        if start is None:
+            start = 0
+        if end is None:
+            end = self_len
+
+        start, end = _adjust_indices(start, end, self_len)
+
+        i = max(start, min(end, self_len - pat_len))
+        stop = start
+        if isinstance(pattern, DN):
+            while i >= stop:
+                result = self._cmp_sequence(pattern, i, pat_len)
+                if result == 0:
+                    return i
+                i -= 1
+            return -1
+        else:
+            while i >= stop:
+                if self.rdns[i] == pattern:
+                    return i
+                i -= 1
+            return -1
+
+    def rindex(self, pattern, start=None, end=None):
+        '''
+        Like rfind() but raise ValueError when the pattern is not found.
+        '''
+
+        i = self.rfind(pattern, start, end)
+        if i == -1:
+            raise ValueError("pattern not found")
+        return i
+
+class EditableDN(DN):
+    '''
+    Exactly identical to the DN class except
+
+    * Hash value is based on object identity, not object
+      value. Objects that test as equal will be non-unique when
+      used as a dict key or member of a set.
+
+    * RDN components may be assigned via assignment statements.
+
+    * RDN components may be inserted.
+
+    * In-place addition modifes the lhs object.
+
+    '''
+
+    is_mutable = True
+    __hash__ = None
+    AVA_type = EditableAVA
+    RDN_type = EditableRDN
+
+    def __setitem__(self, key, value):
+        if isinstance(key, (int, long)):
+            new_rdn = self._rdn_from_value(value)
+            if isinstance(new_rdn, list):
+                raise TypeError("cannot assign multiple RDN's to single entry")
+            self.rdns[key] = new_rdn
+        elif isinstance(key, slice):
+            rdns = self._rdns_from_sequence(value)
+            self.rdns[key] = rdns
+        elif isinstance(key, basestring):
+            new_rdn = self._rdn_from_value(value)
+            if isinstance(new_rdn, list):
+                raise TypeError("cannot assign multiple values to single entry")
+            found = False
+            i = 0
+            while i < len(self.rdns):
+                if key == self.rdns[i].attr:
+                    found = True
+                    self.rdns[i] = new_rdn
+                    break
+                i += 1
+            if not found:
+                raise KeyError("\"%s\" not found in %s" % (key, self.__str__()))
+        else:
+            raise TypeError("unsupported type for DN indexing, must be int, basestring or slice; not %s" % \
+                                (key.__class__.__name__))
+
+    def __iadd__(self, other):
+        # If __iadd__ is not available Python will emulate += by
+        # replacing the lhs object with the result of __add__ (if available).
+        if isinstance(other, DN):
+            for rdn in other.rdns:
+                self.rdns.append(self.RDN_type(rdn))
+        elif isinstance(other, RDN):
+            self.rdns.append(self.RDN_type(other))
+        elif isinstance(other, basestring):
+            dn = self.__class__(other)
+            self.__iadd__(dn)
+        else:
+            raise TypeError("expected DN, RDN or basestring but got %s" % (other.__class__.__name__))
+
+        return self
+
+    def insert(self, i, x):
+        '''
+        x must be a 2-value tuple or list promotable to an RDN object,
+        or a RDN object.
+
+        dn.insert(i, x) is the same as s[i:i] = [x]
+
+        When a negative index is passed as the first parameter to the
+        insert() method, the list length is added, as for slice
+        indices. If it is still negative, it is truncated to zero, as
+        for slice indices.
+        '''
+
+        self.rdns.insert(i, self._rdn_from_value(x))
+
+    def replace(self, old, new, count=sys.maxsize):
+        '''
+        Replace all occurrences of old DN (or RDN) with new DN (or
+        RDN). If the optional argument count is given, only the first
+        count occurrences are replaced.
+
+        Returns the number of replacements made.
+        '''
+
+        if not isinstance(old, (DN, RDN)):
+            raise TypeError("old must be DN or RDN but got %s" % (old.__class__.__name__))
+        if not isinstance(new, (DN, RDN)):
+            raise TypeError("new must be DN or RDN but got %s" % (new.__class__.__name__))
+
+
+        start = 0
+        pat_len = len(old)
+        n_replaced = 0
+        while n_replaced < count:
+            index = self.find(old, start)
+            if index < 0:
+                return n_replaced
+            self[index : index+pat_len] = new
+            n_replaced += 1
+            start = index + pat_len
+
+        return n_replaced
diff --git a/ipapython/entity.py b/ipapython/entity.py
index 27d51787..cb97b991 100644
--- a/ipapython/entity.py
+++ b/ipapython/entity.py
@@ -18,6 +18,7 @@
 import copy
 
 from ipapython import ipautil
+from ipapython.dn import DN
 
 def copy_CIDict(x):
     """Do a deep copy of a CIDict"""
@@ -45,19 +46,25 @@ class Entity:
             if isinstance(entrydata,tuple):
                 self.dn = entrydata[0]
                 self.data = ipautil.CIDict(entrydata[1])
-            elif isinstance(entrydata,str) or isinstance(entrydata,unicode):
+            elif isinstance(entrydata, DN):
                 self.dn = entrydata
                 self.data = ipautil.CIDict()
+            elif isinstance(entrydata, basestring):
+                self.dn = DN(entrydata)
+                self.data = ipautil.CIDict()
             elif isinstance(entrydata,dict):
                 self.dn = entrydata['dn']
                 del entrydata['dn']
                 self.data = ipautil.CIDict(entrydata)
         else:
-            self.dn = ''
+            self.dn = DN()
             self.data = ipautil.CIDict()
 
+        assert isinstance(self.dn, DN)
         self.orig_data = ipautil.CIDict(copy_CIDict(self.data))
 
+    dn = ipautil.dn_attribute_property('_dn')
+
     def __nonzero__(self):
         """This allows us to do tests like if entry: returns false if there is no data,
         true otherwise"""
@@ -67,23 +74,8 @@ class Entity:
         """Return True if this entry has an attribute named name, False otherwise"""
         return self.data and self.data.has_key(name)
 
-    def __setattr__(self,name,value):
-        """One should use setValue() or setValues() to set values except for
-           dn and data which are special."""
-        if name != 'dn' and name != 'data' and name != 'orig_data':
-            raise KeyError, 'use setValue() or setValues()'
-        else:
-            self.__dict__[name] = value
-
-    def __getattr__(self,name):
-        """If name is the name of an LDAP attribute, return the first value for that
-        attribute - equivalent to getValue - this allows the use of
-        entry.cn
-        instead of
-        entry.getValue('cn')
-        This also allows us to return None if an attribute is not found rather than
-        throwing an exception"""
-        return self.getValue(name)
+    def __str__(self):
+        return "dn: %s data: %s" % (self.dn, self.data)
 
     def getValues(self,name):
         """Get the list (array) of values for the attribute named name"""
@@ -150,6 +142,7 @@ class Entity:
     def toDict(self):
         """Convert the attrs and values to a dict. The dict is keyed on the
         attribute name.  The value is either single value or a list of values."""
+        assert isinstance(self.dn, DN)
         result = ipautil.CIDict(self.data)
         result['dn'] = self.dn
         return result
@@ -160,6 +153,7 @@ class Entity:
 
     def origDataDict(self):
         """Returns a dict of the original values of the user.  Used for updates."""
+        assert isinstance(self.dn, DN)
         result = ipautil.CIDict(self.orig_data)
         result['dn'] = self.dn
         return result
diff --git a/ipapython/ipa_log_manager.py b/ipapython/ipa_log_manager.py
index 8af0f79a..f2cd4d3a 100644
--- a/ipapython/ipa_log_manager.py
+++ b/ipapython/ipa_log_manager.py
@@ -101,10 +101,10 @@ class IPALogManager(LogManager):
           in the Env config must begin with "log_logger_level\_" and then be
           followed by a symbolic or numeric log level, for example::
 
-            log_logger_level_debug = ipalib\.dn\..*
+            log_logger_level_debug = ipapython\.dn\..*
             log_logger_level_35 = ipalib\.plugins\.dogtag
 
-          The first line says any logger belonging to the ipalib.dn module
+          The first line says any logger belonging to the ipapython.dn module
           will have it's level configured to debug.
 
           The second line say the ipa.plugins.dogtag logger will be
diff --git a/ipapython/ipautil.py b/ipapython/ipautil.py
index 1b059776..a212aa6e 100644
--- a/ipapython/ipautil.py
+++ b/ipapython/ipautil.py
@@ -49,6 +49,7 @@ from dns.exception import DNSException
 from ipapython.ipa_log_manager import *
 from ipapython import ipavalidate
 from ipapython import config
+from ipapython.dn import DN
 
 try:
     from subprocess import CalledProcessError
@@ -200,10 +201,16 @@ def format_netloc(host, port=None):
         return '%s:%s' % (host, str(port))
 
 def realm_to_suffix(realm_name):
-    """Convert a kerberos realm into the IPA suffix."""
+    'Convert a kerberos realm to a IPA suffix.'
     s = realm_name.split(".")
-    terms = ["dc=" + x.lower() for x in s]
-    return ",".join(terms)
+    suffix_dn = DN(*[('dc', x.lower()) for x in s])
+    return suffix_dn
+
+def suffix_to_realm(suffix_dn):
+    'Convert a IPA suffix to a kerberos realm.'
+    assert isinstance(suffix_dn, DN)
+    realm = '.'.join([x.value for x in suffix_dn])
+    return realm
 
 def template_str(txt, vars):
     val = string.Template(txt).substitute(vars)
@@ -1111,3 +1118,33 @@ def kinit_hostprincipal(keytab, ccachedir, principal):
         return ccache_file
     except krbV.Krb5Error, e:
         raise StandardError('Error initializing principal %s in %s: %s' % (principal, keytab, str(e)))
+
+def dn_attribute_property(private_name):
+    '''
+    Create a property for a dn attribute which assures the attribute
+    is a DN or None. If the value is not None the setter converts it to
+    a DN. The getter assures it's either None or a DN instance.
+
+    The private_name parameter is the class internal attribute the property
+    shadows.
+
+    For example if a class has an attribute called base_dn, then:
+
+        base_dn = dn_attribute_property('_base_dn')
+
+    Thus the class with have an attriubte called base_dn which can only
+    ever be None or a DN instance. The actual value is stored in _base_dn.
+    '''
+
+    def setter(self, value):
+        if value is not None:
+            value = DN(value)
+        setattr(self, private_name, value)
+
+    def getter(self):
+        value = getattr(self, private_name)
+        if value is not None:
+            assert isinstance(value, DN)
+        return value
+
+    return property(getter, setter)