dn_comp Subroutine

Purpose

Compresses a domain name.

Library

Standard C Library (libc.a)

Syntax

#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>

int dn_comp (ExpDomNam, CompDomNam, Length, DomNamPtr, LastDomNamPtr)
u_char *ExpDomNam, *CompDomNam;
int Length;
u_char **DomNamPtr, **LastDomNamPtr;

Description

The dn_comp subroutine compresses a domain name to conserve space. When compressing names, the client process must keep a record of suffixes that have appeared previously. The dn_comp subroutine compresses a full domain name by comparing suffixes to a list of previously used suffixes and removing the longest possible suffix.

The dn_comp subroutine compresses the domain name pointed to by the ExpDomNam parameter and stores it in the area pointed to by the CompDomNam parameter. The dn_comp subroutine inserts labels into the message as the name is compressed. The dn_comp subroutine also maintains a list of pointers to the message labels and updates the list of label pointers.

• If the value of the DomNamPtr parameter is null, the dn_comp subroutine does not compress any names. The dn_comp subroutine translates a domain name from ASCII to internal format without removing suffixes (compressing). Otherwise, the DomNamPtr parameter is the address of pointers to previously compressed suffixes.
• If the LastDomNamPtr parameter is null, the dn_comp subroutine does not update the list of label pointers.

The dn_comp subroutine is one of a set of subroutines that form the resolver. The resolver is a set of functions that perform a translation between domain names and network addresses. Global information used by the resolver subroutines resides in the _res data structure. The /usr/include/resolv.h file contains the _res data structure definition.

Parameters

Return Values

Upon successful completion, the dn_comp subroutine returns the size of the compressed domain name.

If unsuccessful, the dn_comp subroutine returns a value of -1 to the calling program.

Implementation Specifics

The dn_comp subroutine is part of Base Operating System (BOS) Runtime.

All applications containing the dn_comp subroutine must be compiled with _BSD set to a specific value. Acceptable values are 43 and 44. In addition, all socket applications must include the BSD libbsd.a library.

Files

Related Information

The named daemon.

The dn_expand subroutine, _getlong subroutine, _getshort subroutine, putlong subroutine, putshort subroutine, res_init subroutine, res_mkquery subroutine, res_query subroutine, res_search subroutine, res_send subroutine.

TCP/IP Name Resolution in AIX Version 4.3 System Management Guide: Communications and Networks.

Sockets Overview, and Understanding Domain Name Resolution in AIX Version 4.3 Communications Programming Concepts