
RESOLVER(3)            FreeBSD 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,
     dn_comp, dn_expand, hstrerror, res_init, res_isourserver, fp_nquery,
     p_query, hostalias, res_query, res_search, res_querydomain, res_mkquery,
     res_send, res_update, res_close, herror - resolver routines

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

     typedef struct __res_state *res_state;

     res_ninit(res_state statp)

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

     fp_resstat(const res_state statp, FILE *fp)

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

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

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

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

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

     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)

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

     res_nupdate(res_state statp, ns_updrec *rrecp_in)

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

     res_nclose(res_state statp)

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

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

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


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

     hstrerror(int err)

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

     res_init(void)

     res_isourserver(const struct sockaddr_in *addr)

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

     p_query(const u_char *msg, FILE *fp)

     hostalias(const char *name)

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

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

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

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

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

     res_update(ns_updrec *rrecp_in)

     res_close(void)

     herror(const char *s)

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() and herror() are deprecated and are
     supplied for compatability with old source code.  They use global config-
     uration 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.  Op-
     tions 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 initialized (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 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
              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 ex-
              pects the name server to handle recursion.)

     RES_DEFNAMES
              If set, res_nsearch() / res_search() will append the default do-
              main 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_NOALIASES
              This option turns off the user level aliasing feature controlled
              by the HOSTALIASES environment variable.  Network daemons should
              set this option.

     RES_USE_INET6
              This option causes gethostbyname(3) to look for AAAA records be-
              fore looking for A records if none are found.

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

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

     The res_ninit() / res_init() routine reads the configuration file (if
     any; see resolver(5))  to get the default domain name, search list and
     the Internet address of the local name server(s).  If no server is con-
     figured, 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 environ-
     ment 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 vari-
     able (``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
     resolver(5).  Initialization normally occurs on the first call to one of
     the other resolver routines.

     The res_nquery() / res_query() functions provides interfaces to the serv-
     er query mechanism.  They constructs a query, sends it to the local serv-
     er, awaits a response, and makes preliminary checks on the reply.  The
     query requests information of the specified type and class for the speci-
     fied 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 re-
     sponse like res_nquery() / res_query(), but in addition, it implements
     the default and search rules controlled by the RES_DEFNAMES and
     RES_DNSRCH options.  It returns the length of the first successful 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 serv-
     er, 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 buffer 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 not found or an error occurred.  res_hostalias() uses buf to store
     the result in, hostalias() uses a static buffer.

     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 section 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 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 to the begin-
     ning 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 com-
     pressed.  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 er-
     ror.

     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 */

     The herror() function writes a message to the diagnostic output consist-
     ing of the string parameter s, the constant string ": ", and a message
     corresponding to the value of h_errno .

     The hstrerror() function returns a string which is the message text cor-
     responding to the value of the err parameter.

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

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