Author: Pedro Vicente Fernandez

Proyect structure
==============================

The proyect has the following file tree:

|-- Makefile
|-- src
|   |-- DNSDatabase.cpp
|   |-- DNSQuery.cpp
|   |-- DNSRegister.cpp
|   |-- DNSRequest.cpp
|   |-- DNSResponse.cpp
|   |-- DNSServer.cpp
|   |-- FlatFile.cpp
|   |-- HashTable.cpp
|   |-- include
|   |   |-- DNSDatabase.hpp
|   |   |-- DNSDefine.hpp
|   |   |-- DNSError.hpp
|   |   |-- DNSHeader.hpp
|   |   |-- DNSQuery.hpp
|   |   |-- DNSRegister.hpp
|   |   |-- DNSRequest.hpp
|   |   |-- DNSResponse.hpp
|   |   |-- DNSServer.hpp
|   |   |-- FlatFile.hpp
|   |   |-- HashTable.hpp
|   |   |-- LogSystem.hpp
|   |   |-- NonCopyable.hpp
|   |   |-- String.hpp
|   |   |-- StringList.hpp
|   |   |-- Tokenizer.hpp
|   |   `-- Utils.hpp
|   |-- LogSystem.cpp
|   |-- main.cpp
|   |-- Makefile
|   |-- String.cpp
|   |-- StringList.cpp
|   |-- Tokenizer.cpp
|   `-- Utils.cpp
`-- tests
    |-- Main.hpp
    |-- Makefile
    |-- TSDNSDatabase.cpp
    |-- TSDNSServer.cpp
    |-- TSFlatFile.cpp
    |-- TSHash.cpp
    |-- TSString.cpp
    |-- TSStringList.cpp
    |-- TSTokenizer.cpp
    `-- TSUtils.cpp


To make the binary you only type 'make' in the shell and a binary name 'dns' is created in the
base directory.

The tests folder has a set of unitary tests for each class in the proyect. To make unitary tests
is necessary libcppunit-dev package.

Parameters:
=============================================

'dns' bynary accepts the following parameters:

Usage:
        -p      UDP port number
        -h      Hosts file path

Deafault values are:

Port: 53
File: /etc/hosts

Application uses syslog to show error and warning messages and it can be consulted in /var/log/syslog.
Error messages also are shown in stderr.

Application exit with errors when cannot do bind over any configured interface in the system.
Application needs root privileges when port is minor than 1024.

DNS service is listening for each configured interface in the system.

An error while is loading host file don't make that application exit.

Program structure
=============================
We have the following requeriments, don't use of STL libraries and c++ templates.
Classes are located in 2 namespaces:

- namespace utils: utilities in the program
	include/HashTable.hpp (HasTable of Strings Nodes)
	include/LogSystem.hpp (SystemLog messages)
	include/NonCopyable.hpp (Noncopyable objects interface)
	include/String.hpp (String implementation with stl interface and deep copy)
	include/StringList.hpp (String List implementation with stl interface)
	include/Tokenizer.hpp (String tokenizer with concurrency support)
	include/Utils.hpp (utility functions in the program)

- namespace dns: contains the dns classes
	DNSDatabase.hpp (Contains all dns registers in a hash table)
	DNSDefine.hpp (Static definitions and enumerated types)
	DNSError.hpp (Error codes)
	DNSHeader.hpp (DNSHeader handler)
	DNSQuery.hpp (dns query objects and parsing dns requests)
	DNSRegister.hpp (Contains a dns register in database with all ips associated with a host)
	DNSRequest.hpp (dns request abstraction)
	DNSResponse.hpp (dns response abastraction)
	DNSServer.hpp (instance of dns server)

Functionality ends:
Basic dns service, supporting single queries of A type. If the query is not supported and response code not supported is returned.

- Support for IPV4 and A registers. The hosts file is loaded wlike names associated with ips and don't exists alias for names. Therefore CNAME response has not been implemented.

- Support for A and ANY types. With other type response code not implemented is returned.

- Support por single queries. For multiple queries a response code not implemented is returned.

- If dns request has format errors a response code format error is returned.

- Server doesn't support TCP protocol for large requests and recursion. 

- If queried name is not in database, not found error is returned.

- Single process and single thread application. To support multithread applications minimal changes are needed.

- Host file reload is not supported.


Documentation
========================

All header files contains doxygen documentation format.

Soporte Multiplataforma
============================
Compiled with g++(4.4 and 4.1) in ubuntu 32 and 64 bits.

Don't compiled in Solaris and HP-UX platform.

Data Structure
=======================
Hash Table, due to simplicity and fast development.
Hash with open dispersion (String Lists) nodes and case insensitive compares.

Some hash string algorithms has been tested.

RS Hash Function
JS Hash Function
PJW Hash Function
ELF Hash Function
BKDR Hash Function
SDBM Hash Function
DJB Hash Function
DEK Hash Function
AP Hash Function

Hash string algorithm from boost library has been selected. Results are similar than AP, DEK, SDBM and complexity is minor.

seed ^= tolower(str[i]) + 0x9e3779b9 + (seed<<6) + (seed>>2);

Load charge is 0.8, to make rehasing of all elements.

Complexity search is O(1) if not collissions occurs.

Future work
==============================
Support of CNAMES, Recursion, TCP protocol and IPV6.

Multithread support: Concurrent server with preforked threads and pthread_conditions.

Performance comparision with balanced binary tree (Red/Black Trees and AVL) who are most efficient in storage, with Bloom Filters (don't have false positives in search) with O(1) and the following AVL/RBT wiht O(log n).

Performance comparision with patricia tries who has complexity search O(1) and are more efficient in storage.