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RESOLVER(3)		   Linux Programmer's Manual		   RESOLVER(3)

       res_init,    res_query,	 res_search,   res_querydomain,	  res_mkquery,
       res_send, dn_comp, dn_expand - resolver routines

       #include	<netinet/in.h>
       #include	<arpa/nameser.h>
       #include	<resolv.h>
       extern struct state _res;

       int res_init(void);

       int res_query(const char	*dname,	int class, int type,
	      unsigned char *answer, int anslen);

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

       int res_querydomain(const char *name, const char	*domain,
	      int class, int type, unsigned char *answer,
	      int anslen);

       int res_mkquery(int op, const char *dname, int class,
	      int type,	char *data, int	datalen, struct	rrec *newrr,
	      char *buf, int buflen);

       int res_send(const char *msg, int msglen, char *answer,
	      int anslen);

       int dn_comp(unsigned char *exp_dn, unsigned char	*comp_dn,
	      int length, unsigned char	**dnptrs, unsigned char	*exp_dn,
	      unsigned char **lastdnptr);

       int dn_expand(unsigned char *msg, unsigned char *eomorig,
	      unsigned char *comp_dn, unsigned char *exp_dn,
	      int length);

       These functions make queries to and interpret the responses from	Inter-
       net domain name servers.

       The  res_init() function	reads the configuration	files (see resolv+(8))
       to get the default domain  name,	 search	 order	and  name  server  ad-
       dress(es).   If no server is given, the local host is tried.  If	no do-
       main is given, that associated with the local host is used.  It can  be
       overridden  with	 the  environment variable LOCALDOMAIN.	 res_init() is
       normally	executed by the	first call to one of the other functions.

       The res_query() function	queries	the name server	for  the  fully-quali-
       fied  domain  name name of specified type and class.  The reply is left
       in the buffer answer of length anslen supplied by the caller.

       The res_search()	function makes a query and waits for the response like
       res_query(),  but  in  addition implements the default and search rules
       controlled by RES_DEFNAMES and RES_DNSRCH (see description of _res  op-
       tions below).

       The  res_querydomain()  function	makes a	query using res_query()	on the
       concatenation of	name and domain.

       The following functions are lower-level routines	used by	res_query().

       The res_mkquery() function constructs a query message in	buf of	length
       buflen  for the domain name dname.  The query type op is	usually	QUERY,
       but can be any of the types defined in _arpa/nameser.h_.	 newrr is cur-
       rently unused.

       The  res_send()	function  sends	 a pre-formatted query given in	msg of
       length msglen and returns the answer  in	 answer	 which	is  of	length
       anslen.	It will	call res_init(), if it has not already been called.

       The  dn_comp() function compresses the domain name exp_dn and stores it
       in the buffer comp_dn of	length length.	The compression	uses an	 array
       of  pointers  dnptrs to previously compressed names in the current mes-
       sage.  The first	pointer	points to the beginning	of the message and the
       list ends with NULL.  The limit of the array is specified by lastdnptr.
       if dnptr	is NULL, domain	names are not  compressed.   If	 lastdnptr  is
       NULL, the list of labels	is not updated.

       The  dn_expand()	function expands the compressed	domain name comp_dn to
       a full domain name, which is  placed  in	 the  buffer  exp_dn  of  size
       length.	 The compressed	name is	contained in a query or	reply message,
       and msg points to the beginning of the message.

       The resolver routines use global	configuration  and  state  information
       contained  in  the structure _res, which	is defined in _resolv.h_.  The
       only field that is normally manipulated by the  user  is	 _res.options.
       This field can contain the bitwise ``or'' of the	following options:

	      True if res_init() has been called.

	      Print debugging messages.

	      Accept  authoritative  answers only.  res_send() continues until
	      it fins an authoritative answer or returns an error.  [Not  cur-
	      rently implemented].

	      Use TCP connections for queries rather than UDP datagrams.

	      Query primary domain name	server only.

	      Ignore truncation	errors.	 Don't retry with TCP.	[Not currently

	      Set the recursion	desired	bit in queries.	 Recursion is  carried
	      out  by  the domain name server, not by res_send().  [Enabled by

	      If set, res_search() will	append the default domain name to sin-
	      gle  component names, ie.	those that do not contain a dot.  [En-
	      abled by default].

	      Used with	RES_USEVC to keep  the	TCP  connection	 open  between

	      If  set,	res_search() will search for host names	in the current
	      domain and in parent domains.  This option is used by gethostby-
	      name(3).	[Enabled by default].

       The res_init() function returns 0 on success, or	-1 if an error occurs.

       The  res_query(),  res_search(),	 res_querydomain(),  res_mkquery() and
       res_send() functions return the length of the response, or -1 if	an er-
       ror occurs.

       The  dn_comp()  and dn_expand() functions return	the length of the com-
       pressed name, or	-1 if an error occurs.

       /etc/resolv.conf		 resolver configuration	file
       /etc/host.conf		 resolver configuration	file

       BSD 4.3

       gethostbyname(3), hostname(7), named(8),	resolv+(8)

BSD				  1993-05-21			   RESOLVER(3)


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