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RESOLVER(3)							   RESOLVER(3)

NAME
       res_query,   res_search,	  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_query(dname, class, type, answer, anslen)
       char *dname;
       int class, type;
       u_char *answer;
       int anslen;

       res_search(dname, class, type, answer, anslen)
       char *dname;
       int class, type;
       u_char *answer;
       int anslen;

       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 query  and
       reply messages with Internet domain name servers.

       Global configuration and state information that is used by the resolver
       routines is kept in the structure _res.	Most of the values  have  rea‐
       sonable	defaults  and  can be ignored.	Options stored in _res.options
       are defined in resolv.h and are as follows.  Options are	 stored	 as  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_search will append the default domain name to sin‐
	      gle-component names (those that do not  contain  a  dot).	  This
	      option is enabled by default.

       RES_DNSRCH
	      If  this option is set, res_search will search for host names in
	      the current domain and in parent domains; see hostname(7).  This
	      is  used	by  the standard host lookup routine gethostbyname(3).
	      This option is enabled by default.

       The  res_init  routine  reads  the  configuration  file	(if  any;  see
       resolver(5)) to get the default domain name, search list and the Inter‐
       net address of the local name server(s).	 If no server  is  configured,
       the  host  running  the	resolver is tried.  The current domain name is
       defined by the hostname if not specified in the configuration file;  it
       can  be overridden by the environment variable LOCALDOMAIN.  This envi‐
       ronment variable may contain several blank-separated tokens if you wish
       to override the search list on a per-process basis.  This is similar to
       the search command in  the  configuration  file.	  Another  environment
       variable	 (``RES_OPTIONS'')  can	 be  set  to override certain internal
       resolver options which are otherwise set by changing fields in the _res
       structure  or  are inherited from the configuration file's options com‐
       mand.  The  syntax  of  the  ``RES_OPTIONS''  environment  variable  is
       explained  in resolver(5).  Initialization normally occurs on the first
       call to one of the other resolver routines.

       The res_query function provides an interface to the server query mecha‐
       nism.   It  constructs  a query, sends it to the local server, awaits a
       response, and  makes  preliminary  checks  on  the  reply.   The	 query
       requests	 information of the specified type and class for the specified
       fully-qualified domain name dname .  The reply message is left  in  the
       answer buffer with length anslen supplied by the caller.

       The  res_search	routine	 makes	a  query  and  awaits  a response like
       res_query, but in addition, it implements the default and search	 rules
       controlled  by the RES_DEFNAMES and RES_DNSRCH options.	It returns the
       first successful reply.

       The remaining routines are lower-level routines used by res_query.  The
       res_mkquery  function constructs a standard query message and places it
       in buf.	It returns the size of the query, or -1 if the query is larger
       than buflen.  The query type op is usually QUERY, but can be any of the
       query types defined in <arpa/nameser.h>.	 The domain name for the query
       is  given by dname.  Newrr is currently unused but is intended for mak‐
       ing update messages.

       The res_send routine sends a pre-formatted query 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
       reply message is returned, or -1 if there were errors.

       The dn_comp function 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.   The size of the array pointed to by comp_dn is given by
       length.	The compression uses an array of  pointers  dnptrs  to	previ‐
       ously-compressed	 names	in  the	 current  message.   The first pointer
       points to to the beginning of the message and the list ends with	 NULL.
       The  limit  to  the  array is specified by lastdnptr.  A side effect of
       dn_comp is to update the list of pointers for labels inserted into  the
       message	as  the	 name  is compressed.  If dnptr is NULL, names are not
       compressed.  If lastdnptr is NULL, the list of labels is not updated.

       The dn_expand entry expands the compressed domain  name	comp_dn	 to  a
       full  domain  name The compressed name is contained in a query or reply
       message; msg is a pointer to the beginning of the message.  The	uncom‐
       pressed	name  is  placed in the buffer indicated by exp_dn which is of
       size length.  The size of compressed name is returned or	 -1  if	 there
       was an error.

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

SEE ALSO
       gethostbyname(3), named(8), resolver(5), hostname(7),
       RFC1032, RFC1033, RFC1034, RFC1035, RFC974,
       SMM:11 Name Server Operations Guide for BIND

4th Berkeley Distribution      November 11, 1993		   RESOLVER(3)
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