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.

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

Parameters

Item Description
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.

Files

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