RESOLVER(3)                          BSD                           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 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 stored in _res.options
     are defined in <resolv.h> and are as follows. Options are a simple bit
     mask and are ORed in to enable.

     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 many queries.  UDP should be the normal mode
                    used.

     RES_IGNTC      Unused currently (ignore truncation errors, that is, 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   Append the default domain name to single label queries.
                    This is the default.

     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),
     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 uppercase.  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 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, we don't
     try to compress names. If lastdnptr is NULL, we don't update the list.

FILES
     /etc/resolv.conf    see resolver(5)

SEE ALSO
     named(8), resolver(5), RFC882, RFC883, RFC973, RFC974