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This document tries to describe the software layout and design of the library.
It should provide some help for contributing code to this package.
CONTRIBUTING TO NSS-LDAPD
=========================
Contributions to nss-ldapd are most welcome. However not all contributions
will be automatically integrated. Some notes:
* for enhancements it is a good idea to send an email first
* send your patches in unified diff (diff -u) format
* try to use the svn version of the software to develop the patch
* clearly state which problem you're trying to solve and how this is
accomplished
* please follow the existing coding conventions
* patches will be integrated on a best-effort bases
* please test the patch and include information on testing with the patch
(platforms tested, etc)
* include a copyright statement in the patched code if you feel the
contribution is significant enough (e.g. more than a few lines)
* when including third-party code, retain copyright information (copyright
holder and license) and ensure that the license is LGPL compatible
* contributions will be acknowledged in the AUTHORS file
THE COMMUNICATIONS PROTOCOL
===========================
The protocol used for communicating between the NSS library and the nslcd
daemon is very simple and almost fully described in the nslcd.h header file.
The nslcd-common.h header file defines some macros that are used for reading
and writing protocol entities (strings, 32-bit integers, etc).
Some of the protocol handling code is automatically generated from the macros
defined in nslcd.h. This cannot be done automatically in every case though so
changing the protocol requires manual checking in the relevant source files in
both the nss and the nslcd directories.
If the protocol is changed in an incompatible way the protocol version should
be incremented in nslcd.h. There is currently no versioning schema available
for this.
RELEASE VERSIONING
==================
A new versioning schema was chosen over the nss_ldap release schema. The
schema is a simple major.minor numbering starting with 0.1. Until a 1.0
release is made the code will be considered work in progress. The interfaces
may change and features may be added and removed.
GENERAL DESIGN
==============
The basic design splits the functionality in two parts. The NSS part
interfaces with libc and translates the NSS requests into simple generic
requests (e.g. "get user with name test", "get group with gid 101" or "get all
shadow entries"). Translating these requests into LDAP requests is then the
job of the daemon so that the NSS part won't have to know anything about LDAP
(in fact replacing it with another lookup method is very simple).
nslcd -> OpenLDAP -> LDAP server
^
libc NSS -> libnss_ldap.so
design goals
------------
* make it as simple as possible (focus on simplicity)
* design as specified above
* simpler configuration and semantics
* simpler, clearer and completer documentation
* split source code into directories (src, src/hacks, src/aix, src/irs, etc)
* get rid of unneeded code and complexity
* split complexity in two parts (LDAP interface in server, NSS interface in
library)
NSS PART
========
all requests go:
_nss_ldap_FUNCTION_r(...)
This function opens the connection to the nslcd (with some timeout and retry
mechanism) builds the correct data structures and does a request (write())
to the nslcd waiting for an answer (again with a timeout and retry
mechanism) [some helper functions should be available for opening the socket
and performing the write/read combo]
http://mirrors.usc.edu/pub/gnu/Manuals/glibc-2.2.3/html_chapter/libc_28.html#SEC596
http://www.gnu.org/software/libc/manual/html_node/index.html
SERVER PART
===========
At the server end a dispatcher picks up the request and delegates it to one of
the database specific functions.
nslcd_FUNCION(...)
This functions fills in the correct parameters from the request. This
function should generate a response object [TODO: response objects can be
large]
SECURITY NOTES
==============
This design does open up the system to more potential security issues as there
is now a local interface to a daemon with privileges. Before processes could
only potentially exploit bugs in the library and gain the privileges of the
process that was doing the name lookups. In this case the privileges of the
daemon are potentially exposed.
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