res_mkquery Subroutine

Communications Technical Reference, Volume 2

res_mkquery Subroutine

Purpose

Makes query messages for name servers.

Library

Standard C Library (libc.a)

Syntax

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

int res_mkquery (Operation, DomName, Class, Type, Data, DataLength)
int res_mkquery (Reserved, Buffer, BufferLength)
int Operation;
char *DomName;
int Class, Type;
char *Data;
int DataLength;
struct rrec *Reserved;
char *Buffer;
int BufferLength;

Description

The res_mkquery subroutine creates packets for name servers in the Internet domain. The subroutine also creates a standard query message. The Buffer parameter determines the location of this message.

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

Parameters

Operation

Specifies a query type. The usual type is QUERY, but the parameter can be set to any of the query types defined in the arpa/nameser.h file.

DomName

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

Class

Specifies one of the following parameters:

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

Data

Points to the data that is sent to the name server as a search key. The data is stored as a character array.

DataLength

Defines the size of the array pointed to by the Data parameter.

Reserved

Specifies a reserved and currently unused parameter.

Buffer

Points to a location containing the query message.

BufferLength

Specifies the length of the message pointed to by the Buffer parameter.

Return Values

Upon successful completion, the res_mkquery subroutine returns the size of the query. If the query is larger than the value of the BufferLength parameter, the subroutine is unsuccessful and returns a value of -1.

Implementation Specifics

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

All applications containing the res_mkquery 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_query subroutine, res_search subroutine, res_send subroutine.

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