res_query Subroutine

Communications Technical Reference, Volume 2

res_query Subroutine

Purpose

Provides an interface to the server query mechanism.

Library

Standard C Library (libc.a)

Syntax

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

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

Description

The res_query subroutine provides an interface to the server query mechanism. It constructs a query, sends it to the local server, awaits a response, and makes preliminary checks on the reply. The query requests information of the specified type and class for the fully-qualified domain name specified in the DomName parameter. The reply message is left in the answer buffer whose size is specified by the AnswerLength parameter, which is supplied by the caller.

The res_query 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.

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

Implementation Specifics

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

All applications containing the res_query 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_search subroutine, res_send subroutine.

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