res_search Subroutine

Communications Technical Reference, Volume 2

res_search Subroutine

Purpose

Makes a query and awaits a response.

Library

Standard C Library (libc.a)

Syntax

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

int res_search (DomName, Class, Type, Answer, AnswerLength)
char *DomName;
int Class;
int Type;
u_char *Answer;
int AnswerLength;

Description

The res_search subroutine makes a query and awaits a response like the res_query subroutine. However, it also implements the default and search rules controlled by the RES_DEFNAMES and RES_DNSRCH options.

The res_search subroutine is one of a set of subroutines that form the resolver, a set of functions that resolve domain names. The _res data structure contains global information used by the resolver subroutines. The /usr/include/resolv.h file contains the _res structure definition.

Parameters

DomName

Points to the name of the domain. If the DomName parameter points to a single-component name and the RES_DEFNAMES structure is set, as it is by default, the subroutine appends the default domain name to the single-component name. The current domain name is defined by the name server in use or is specified in the /etc/resolv.conf file.

If the RES_DNSRCH bit is set, as it is by default, the res_search subroutine searches for host names in both the current domain and in parent domains.

Class

Specifies one of the following values:

C_IN	Specifies the ARPA Internet.
C_CHAOS	Specifies the Chaos network at MIT.

Type

Requires one of the following values:

T_A	Host address
T_NS	Authoritative server
T_MD	Mail destination
T_MF	Mail forwarder
T_CNAME	Canonical name
T_SOA	Start-of-authority zone
T_MB	Mailbox-domain name
T_MG	Mail-group member
T_MR	Mail-rename name
T_NULL	Null resource record
T_WKS	Well-known service
T_PTR	Domain name pointer
T_HINFO	Host information
T_MINFO	Mailbox information
T_MX	Mail-routing information
T_UINFO	User (finger command) information
T_UID	User ID
T_GID	Group ID

Answer

Points to an address where the response is stored.

AnswerLength

Specifies the size of the answer buffer.

Return Values

Upon successful completion, the res_search subroutine returns the size of the response. Upon unsuccessful completion, the res_search subroutine returns a value of -1 and sets the h_errno value to the appropriate error.

Implementation Specifics

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

All applications containing the res_search 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

/etc/resolv.conf
	Contains the name server and domain name.

Related Information

The finger command.

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

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