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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  Internet  domain  name

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

       The  res_query() function queries the name server for the fully-qualified domain name name
       of specified type and class.  The reply is left in the buffer answer of length anslen sup-
       plied 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 options 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 currently 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 message.  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  manipu-
       lated  by the user is _res.options.  This field can contain the bitwise ``or'' of the fol-
       lowing options:

	      True if res_init() has been called.

	      Print debugging messages.

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

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

	      If set, res_search() will append the default domain name to single component names,
	      ie. those that do not contain a dot.  [Enabled by default].

	      Used with RES_USEVC to keep the TCP connection open between queries.

	      If set, res_search() will search for host names in the current domain and in parent
	      domains.	This option is used by gethostbyname(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 error occurs.

       The dn_comp() and dn_expand() functions return the length of the compressed 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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