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RESOLVER(3)                Library Functions Manual                RESOLVER(3)

     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

     Standard C Library (libc, -lc)
     DNS Resolver Library (libresolv, -lresolv)

     #include <resolv.h>
     #include <res_update.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);

     const char *
     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);

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

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

     res_ndestroy(res_state statp);

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

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

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


     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);

     const char *
     hostalias(const char *name);

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

     res_search(const char *dname, int class, int 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, int 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);


     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
     compatibility 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 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

     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, will be returned as ::ffff:
                    The option is meaningful with certain kernel configuration

     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 packets 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 res_nsend() / res_send() to rotate the
                    list of nameservers in statp->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.

                    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 are set.

     The res_ninit() / res_init() routines read 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 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 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.

     In NetBSD the initialization code also sets up a kqueue(2) and creates a
     kevent(2) watching a file descriptor that points to the resolver file.
     Every resolver function calls the internal function __res_check() which
     checks for a new kevent(2) related to the resolv.conf(5) file, and
     reloads the file if necessary.  This does not work if the file is
     accessed through a symlink and the symlink changes to point to a
     different file.  To fix the symlink issue one could add a system call per
     resolver call to get the current time, and reload every so often.  This
     is not done currently, but it is under consideration.

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

     The res_nquery() / res_query() functions provide interfaces to the server
     query mechanism.  They construct a query, send it to the local server,
     await a response, and make 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.  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, they implement
     the default and search rules controlled by the RES_DEFNAMES and
     RES_DNSRCH options.  They return 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 construct a
     standard query message and place it in buf.  They return 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 send a pre-
     formatted query and return an answer.  They 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 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

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

     The functions res_hostalias() / hostalias() look up name in the file
     referred to by the HOSTALIASES files and 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.  They identify the containing zone for each record and group
     the records according to containing zone maintaining in zone order then
     send an 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

     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 an 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 socket file
     descriptors referenced through statp / _res.  These functions were
     designed to be used to emulate endhostent(3), and don't release other
     resources held in res_state; to free all_resources, call res_ndestroy().

     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 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.  eomorig is a
     pointer to the first location after the message.  The uncompressed 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 are 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 following functions are only in libresolv: res_findzonecut(),
     res_nmkupdate(), res_nsendsigned(), and res_nupdate().  All the rest are
     in both libc and libresolv.

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

     getaddrinfo(3), gethostbyaddr(3), gethostbyname(3), getnameinfo(3),
     resolv.conf(5), hostname(7), named(8)

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

     Name Server Operations Guide for BIND.

     The res_ninit function appeared in 4.3BSD.

NetBSD 10.99                   February 7, 2018                   NetBSD 10.99