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RESOLVER(3)			   BSD Library Functions Manual 		      RESOLVER(3)

NAME
     res_ninit, res_ourserver_p, fp_resstat, res_hostalias, res_pquery, res_nquery, res_nsearch,
     res_nquerydomain, res_nmkquery, res_nsend, res_nupdate, res_nmkupdate, res_nclose,
     res_nsendsigned, res_findzonecut, res_getservers, res_setservers, res_ndestroy, dn_comp,
     dn_expand, res_init, res_isourserver, fp_nquery, p_query, hostalias, res_query, res_search,
     res_querydomain, res_mkquery, res_send, res_update, res_close, -- resolver routines

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <netinet/in.h>
     #include <arpa/nameser.h>
     #include <resolv.h>
     #include <res_update.h>

     typedef struct __res_state *res_state;

     int
     res_ninit(res_state statp);

     int
     res_ourserver_p(const res_state statp, const struct sockaddr_in *addr);

     void
     fp_resstat(const res_state statp, FILE *fp);

     const char *
     res_hostalias(const res_state statp, const char *name, char *buf, size_t buflen);

     int
     res_pquery(const res_state statp, const u_char *msg, int msglen, FILE *fp);

     int
     res_nquery(res_state statp, const char *dname, int class, int type, u_char *answer,
	 int anslen);

     int
     res_nsearch(res_state statp, const char *dname, int class, int type, u_char * answer,
	 int anslen);

     int
     res_nquerydomain(res_state statp, const char *name, const char *domain, int class, int type,
	 u_char *answer, int anslen);

     int
     res_nmkquery(res_state statp, int op, const char *dname, int class, int type,
	 const u_char *data, int datalen, const u_char *newrr, u_char *buf, int buflen);

     int
     res_nsend(res_state statp, const u_char *msg, int msglen, u_char *answer, int anslen);

     int
     res_nupdate(res_state statp, ns_updrec *rrecp_in);

     int
     res_nmkupdate(res_state statp, ns_updrec *rrecp_in, u_char *buf, int buflen);

     void
     res_nclose(res_state statp);

     int
     res_nsendsigned(res_state statp, const u_char *msg, int msglen, ns_tsig_key *key,
	 u_char *answer, int anslen);

     int
     res_findzonecut(res_state statp, const char *dname, ns_class class, int options,
	 char *zname, size_t zsize, struct in_addr *addrs, int naddrs);

     int
     res_getservers(res_state statp, union res_sockaddr_union *set, int cnt);

     void
     res_setservers(res_state statp, const union res_sockaddr_union *set, int cnt);

     void
     res_ndestroy(res_state statp);

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

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

   DEPRECATED
     #include <sys/types.h>
     #include <netinet/in.h>
     #include <arpa/nameser.h>
     #include <resolv.h>
     #include <res_update.h>

     int
     res_init(void);

     int
     res_isourserver(const struct sockaddr_in *addr);

     int
     fp_nquery(const u_char *msg, int msglen, FILE *fp);

     void
     p_query(const u_char *msg, FILE *fp);

     const char *
     hostalias(const char *name);

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

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

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

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

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

     int
     res_update(ns_updrec *rrecp_in);

     void
     res_close(void);

DESCRIPTION
     These routines are used for making, sending and interpreting query and reply messages with
     Internet domain name servers.

     State information is kept in statp and is used to control the behavior of these functions.
     statp should be set to all zeros prior to the first call to any of these functions.

     The functions res_init(), res_isourserver(), fp_nquery(), p_query(), hostalias(),
     res_query(), res_search(), res_querydomain(), res_mkquery(), res_send(), res_update(),
     res_close() are deprecated and are supplied for compatability with old source code.  They
     use global configuration and state information that is kept in the structure _res rather
     than that referenced through statp.

     Most of the values in statp and _res are initialized on the first call to res_ninit() /
     res_init() to reasonable defaults and can be ignored.  Options stored in statp->options /
     _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 initial-
		    ized (i.e., res_ninit() / res_init() has been called).

     RES_DEBUG	    Print debugging messages.

     RES_AAONLY     Accept authoritative answers only.	Should continue until it finds an author-
		    itative 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	    Ignore truncation errors, i.e., don't retry with TCP.

     RES_RECURSE    Set the recursion-desired bit in queries.  This is the default.  (res_nsend()
		    / res_send() does not do iterative queries and expects the name server to
		    handle recursion.)

     RES_DEFNAMES   If set, res_nsearch() / res_search() will append the default domain name to
		    single-component names (those that do not contain a dot).  This option is
		    enabled by default.

     RES_DNSRCH     If this option is set, res_nsearch() / 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.

     RES_USE_INET6  Enables support for IPv6-only applications.  This causes IPv4 addresses to be
		    returned as an IPv4 mapped address.  For example, 10.1.1.1 will be returned
		    as ::ffff:10.1.1.1.  The option is meaningful with certain kernel configura-
		    tion only.

     RES_USE_EDNS0  Enables support for OPT pseudo-RR for EDNS0 extension.  With the option,
		    resolver code will attach OPT pseudo-RR into DNS queries, to inform of our
		    receive buffer size.  The option will allow DNS servers to take advantage of
		    non-default receive buffer size, and to send larger replies.  DNS query pack-
		    ets with EDNS0 extension is not compatible with non-EDNS0 DNS servers.

     RES_NOALIASES  This option turns off the user level aliasing feature controlled by the
		    HOSTALIASES environment variable.  Network daemons should set this option.

     RES_ROTATE     This options causes the res_nsend() / res_send() to rotate the list of name-
		    servers in statp->nsaddr_list / _res.nsaddr_list.

     RES_KEEPTSIG   This option causes res_nsendsigned() to leave the message unchanged after
		    TSIG verification; otherwise the TSIG record would be removed and the header
		    updated.

     RES_NOTLDQUERY
		    This option causes res_nsearch() to not attempt to resolve an unqualified
		    name as if it were a top level domain (TLD).  This option can cause problems
		    if the site has "localhost" as a TLD rather than having localhost on one or
		    more elements of the search list.  This option has no effect if neither
		    RES_DEFNAMES or RES_DNSRCH is set.

     The res_ninit() / res_init() routine reads the configuration file (if any; see
     resolv.conf(5)) to get the default domain name, search list and the Internet 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 environment vari-
     able 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 statp / _res structure or are
     inherited from the configuration file's options command.  The syntax of the RES_OPTIONS
     environment variable is explained in resolv.conf(5).  Initialization normally occurs on the
     first call to one of the other resolver routines.

     The memory referred to by statp must be set to all zeros prior to the first call to
     res_ninit().  res_ndestroy() should be call to free memory allocated by res_ninit() after
     last use.

     The res_nquery() / res_query() functions provides interfaces to the server query mechanism.
     They constructs a query, sends it to the local server, awaits a response, and makes prelimi-
     nary 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.  res_nquery() / res_query() return
     -1 on error or the length of the answer.

     The res_nsearch() / res_search() routines make a query and awaits a response like
     res_nquery() / res_query(), but in addition, it implements the default and search rules con-
     trolled by the RES_DEFNAMES and RES_DNSRCH options.  It returns the length of the first suc-
     cessful reply which is stored in answer or -1 on error.

     The remaining routines are lower-level routines used by res_nquery() / res_query().  The
     res_nmkquery() / res_mkquery() functions 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 making update messages.

     The res_nsend() / res_send() / res_nsendsigned() routines sends a pre-formatted query and
     returns an answer.  It will call res_ninit() / res_init() if RES_INIT is not set, send the
     query to the local name server, and handle timeouts and retries.  Additionally,
     res_nsendsigned() will use TSIG signatures to add authentication to the query and verify the
     response.	In this case, only one nameserver will be contacted.  The length of the reply
     message is returned, or -1 if there were errors.

     res_nquery() / res_query(), res_nsearch() / res_search() and res_nsend() / res_send() return
     a length that may be bigger than anslen.  In that case the query should be retried with a
     bigger buffer.  NOTE the answer to the second query may be larger still so supplying a buf-
     fer that bigger that the answer returned by the previous query is recommended.

     answer MUST be big enough to receive a maximum UDP response from the server or parts of the
     answer will be silently discarded.  The default maximum UDP response size is 512 bytes.

     The function res_ourserver_p() returns true when inp is one of the servers in
     statp->nsaddr_list / _res.nsaddr_list.

     The functions fp_nquery() / p_query() print out the query and any answer in msg on fp.
     p_query() is equivalent to fp_nquery() with msglen set to 512.

     The function fp_resstat() prints out the active flag bits in statp->options preceeded by the
     text ";; res options:" on file.

     The functions res_hostalias() / hostalias() lookup up name in the file referred to by the
     HOSTALIASES files return a fully qualified hostname if found or NULL if not found or an
     error occurred.  res_hostalias() uses buf to store the result in, hostalias() uses a static
     buffer.

     The functions res_getservers() and res_setservers() are used to get and set the list of
     server to be queried.

     The functions res_nupdate() / res_update() take a list of ns_updrec rrecp_in.  Identifies
     the containing zone for each record and groups the records according to containing zone
     maintaining in zone order then sends and update request to the servers for these zones.  The
     number of zones updated is returned or -1 on error.  Note that res_nupdate() will perform
     TSIG authenticated dynamic update operations if the key is not NULL.

     The function res_findzonecut() discovers the closest enclosing zone cut for a specified
     domain name, and finds the IP addresses of the zone's master servers.

     The functions res_nmkupdate() / res_mkupdate() take a linked list of ns_updrec rrecp_in and
     construct a UPDATE message in buf.  res_nmkupdate() / res_mkupdate() return the length of
     the constructed message on no error or one of the following error values.

     -1 An error occurred parsing rrecp_in.

     -2 The buffer buf was too small.

     -3 The first record was not a zone section or there was a section order problem.  The sec-
     tion order is S_ZONE, S_PREREQ and S_UPDATE.

     -4 A number overflow occurred.

     -5 Unknown operation or no records.

     The functions res_nclose() / res_close() close any open files referenced through statp /
     _res.

     The function res_ndestroy() calls res_nclose() then frees any memory allocated by
     res_ninit().

     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 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 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 com-
     pressed.  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.  eomorig is a pointer to the first location after 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.

     The variables statp->res_h_errno / _res.res_h_errno and external variable h_errno is set
     whenever an error occurs during resolver operation.  The following definitions are given in
     <netdb.h>:

     #define NETDB_INTERNAL -1
     /* see errno */
     #define NETDB_SUCCESS  0
     /* no problem */
     #define HOST_NOT_FOUND 1
     /* Authoritative Answer Host not found */
     #define TRY_AGAIN	    2
     /* Non-Authoritative not found, or SERVFAIL */
     #define NO_RECOVERY    3
     /* Non-Recoverable: FORMERR, REFUSED, NOTIMP */
     #define NO_DATA	    4
     /* Valid name, no data for requested type */

FILES
     ~			   /etc/resolv.conf The configuration file, see resolv.conf(5).

SEE ALSO
     gethostbyname(3), hostname(7), resolv.conf(5), named(8)

     RFC 974, RFC 1032, RFC 1033, RFC 1034, RFC 1035, RFC 1535

     Name Server Operations Guide for BIND.

HISTORY
     The res_ninit function appeared in 4.3BSD.

BSD					   July 4, 2000 				      BSD
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