resolver(3N) resolver(3N)
NAME
resolver, res_mkquery, res_send, res_init, dn_comp, dn_expand
- resolver routines
SYNOPSIS
cc [options] file -lresolv -lsocket -lnsl
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
int res_mkquery(int op, char *dname, int class, int type,
char *data, int datalen, struct rrec *newrr, char *buf,
int buflen);
int res_send(char *buf, int buflen, char *answer, int anslen);
int res_init(void);
int dn_comp(u_char *exp_dn, u_char *comp_dn, int length, u_char **dnptrs,
u_char **lastdnptr);
int dn_expand(u_char *msg, u_char *eomorig, u_char *comp_dn,
u_char *exp_dn, int length);
DESCRIPTION
These routines are used for making, sending and interpreting
packets to Internet domain name servers. Global information
that is used by the resolver routines is kept in the variable
_res. Most of the values have reasonable defaults and can be
ignored. Options are a simple bit mask and are OR'ed in to
enable. Options stored in _res.options are defined in
resolv.h and are as follows.
RES_INIT True if the initial name server address
and default domain name are initialized
(that is, res_init has been called).
RES_DEBUG Print debugging messages.
RES_AAONLY Accept authoritative answers only.
res_send will continue until it finds an
authoritative answer or finds an error.
Currently this is not implemented.
RES_USEVC Use TCP connections for queries instead of
UDP.
RES_STAYOPEN Used with RES_USEVC to keep the TCP
connection open between queries. This is
useful only in programs that regularly do
Copyright 1994 Novell, Inc. Page 1
resolver(3N) resolver(3N)
many queries. UDP should be the normal
mode used.
RES_IGNTC Unused currently (ignore truncation
errors, that is, do not retry with TCP).
RES_RECURSE Set the recursion desired bit in queries.
This is the default. res_send does not do
iterative queries and expects the name
server to handle recursion.
RES_DEFNAMES Append the default domain name to single
label queries. This is the default.
RES_DNSRCH Allow search for a domain name up the
local hierarchical domain tree.
res_init reads the initialization file to get the default
domain name and the Internet address of the initial hosts
running the name server. If this line does not exist, the
host running the resolver is tried. res_init returns 0 for
success, and -1 for failure. res_mkquery makes a standard
query message and places it in buf. res_mkquery will return
the size of the query or -1 if the query is larger than
buflen. op is usually QUERY but can be any of the query types
defined in arpa/nameser.h. dname is the domain name. If
dname consists of a single label and the RES_DEFNAMES flag is
enabled (the default), dname will be appended with the current
domain name. The current domain name is defined in a system
file and can be overridden by the environment variable
LOCALDOMAIN. newrr is currently unused but is intended for
making update messages.
res_send sends a query to name servers and returns an answer.
It will call res_init if RES_INIT is not set, send the query
to the local name server, and handle timeouts and retries.
The length of the message is returned or -1 if there were
errors.
dn_expand expands the compressed domain name comp_dn to a full
domain name. Expanded names are converted to upper case. msg
is a pointer to the beginning of the message, eomorig is a
pointer to the first memory location after the message, exp_dn
is a pointer to a buffer of size length for the result. The
size of the compressed name is returned or -1 if there was an
error.
Copyright 1994 Novell, Inc. Page 2
resolver(3N) resolver(3N)
dn_comp compresses the domain name exp_dn and stores it in
comp_dn. The size of the compressed name is returned or -1 if
there were errors. length is the size of the array pointed to
by comp_dn. dnptrs is a list of pointers to previously
compressed names in the current message. The first pointer
points to the beginning of the message and the list ends with
NULL. lastdnptr is a pointer to the end of the array pointed
to dnptrs. A side effect is to update the list of pointers
for labels inserted into the message by dn_comp as the name is
compressed. If dnptr is NULL, do not try to compress names.
If lastdnptr is NULL, do not update the list.
Files
/etc/resolv.conf
/usr/include/arpa/nameserv.h
/usr/include/netinet/in.h
/usr/include/resolv.h
/usr/include/sys/types.h
/usr/lib/libresolv.a
/usr/lib/resolv.so
REFERENCES
named(1M), resolv.conf(4)
NOTICES
/usr/lib/libresolv.a is necessary for compiling programs.
Programs must be loaded with the option -lresolv.
Copyright 1994 Novell, Inc. Page 3