RESOLVER(3)RESOLVER(3)NAME
res_mkquery, res_send, res_init, dn_comp, dn_expand - resolver routines
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
res_mkquery(op, dname, class, type, data, datalen, newrr, buf, buflen)
int op;
char *dname;
int class, type;
char *data;
int datalen;
struct rrec *newrr;
char *buf;
int buflen;
res_send(msg, msglen, answer, anslen)
char *msg;
int msglen;
char *answer;
int anslen;
res_init()
dn_comp(exp_dn, comp_dn, length, dnptrs, lastdnptr)
char *exp_dn, *comp_dn;
int length;
char **dnptrs, **lastdnptr;
dn_expand(msg, eomorig, comp_dn, exp_dn, length)
char *msg, *eomorig, *comp_dn, exp_dn;
int length;
DESCRIPTION
These routines are used for making, sending and interpreting packets
for use with 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 stored
in _res.options are defined in resolv.h and are as follows. Options
are stored a simple bit mask containing the bitwise ``or'' of the
options enabled.
RES_INIT
True if the initial name server address and default domain name
are initialized (i.e., res_init has been called).
RES_DEBUG
Print debugging messages.
RES_AAONLY
Accept authoritative answers only. With this option, res_send
should 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 datagrams.
RES_STAYOPEN
Used with RES_USEVC to keep the TCP connection open between
queries. This is useful only in programs that regularly do many
queries. UDP should be the normal mode used.
RES_IGNTC
Unused currently (ignore truncation errors, i.e., don't 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
If set, res_mkquery will append the default domain name to
single-component names (those that do not contain a dot). This
is the default.
RES_DNSRCH
If this option is set, the standard host lookup routine
gethostbyname(3) will search for host names in the current
domain and in parent domains; see hostname(7).
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_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 nameser.h. Dname is the domain name. If dname
consists of a single label and the RES_DEFNAMES flag is enabled (the
default), the current domain name will be appended to dname. The
current domain name is defined by the hostname or is specified in a
system file; it 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, exp_dn is a pointer to a buffer of size
length for the result. The size of compressed name is returned or -1
if there was an error.
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 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, names are not compressed. If lastdnptr is NULL, the
list of labels is not updated.
FILES
/etc/resolv.conf see resolver(5)SEE ALSOgethostbyname(3), named(8), resolver(5), hostname(7),
RFC882, RFC883, RFC973, RFC974,
SMM:11 Name Server Operations Guide for BIND
4th Berkeley Distribution November 21, 1987 RESOLVER(3)
