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

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

SYNOPSIS
     #include <&lt;sys/types.h>&gt;
     #include <&lt;netinet/in.h>&gt;
     #include <&lt;arpa/nameser.h>&gt;
     #include <&lt;resolv.h>&gt;

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

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

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

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

     res_init();

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

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

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

     Global configuration and state information that is used by the resolver
     routines is kept in the structure _res. Most of the values have reason-
     able defaults and can be ignored.  Options stored in _res.options are de-
     fined 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_init() has been called).

     RES_DEBUG     Print debugging messages.

     RES_AAONLY    Accept authoritative answers only.  With this option,
                   res_send() should continue until it finds an authoritative
                   answer or finds an error.  Currently this is not implement-
                   ed.

     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     Unused currently (ignore truncation errors, i.e., don't
                   retry with TCP).

     RES_RECURSE   Set the recursion-desired bit in queries.  This is the de-
                   fault.  (res_send() does not do iterative queries and ex-
                   pects the name server to handle recursion.)

     RES_DEFNAMES  If set, 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_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 rou-
                   tine gethostbyname(3).  This option is enabled by default.

     The res_init() routine reads the configuration file (if any; see
     resolver(5))  to get the default domain name, search list and the Inter-
     net 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. Initialization nor-
     mally occurs on the first call to one of the following routines.

     The res_query() function provides an interface to the server query mecha-
     nism.  It constructs a query, sends it to the local server, awaits a re-
     sponse, and makes 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.

     The res_search() routine makes a query and awaits a response like
     res_query(), but in addition, it implements the default and search rules
     controlled by the RES_DEFNAMES and RES_DNSRCH options.  It returns the
     first successful reply.

     The remaining routines are lower-level routines used by res_query().  The
     res_mkquery() function 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 up-
     date messages.

     The res_send() routine sends a pre-formatted query and returns an answer.
     It will call res_init() if RES_INIT is not set, send the query to the lo-
     cal name server, and handle timeouts and retries.  The length of the re-
     ply message is returned, or -1 if there were errors.

     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.

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

SEE ALSO
     gethostbyname(3),  named(8),  resolver(5),  hostname(7),

     RFC1032, RFC1033, RFC1034, RFC1035, RFC974


     Name Server Operations Guide for BIND.

HISTORY
     The res_query function appeared in 4.3BSD.

4.3 Berkeley Distribution        June 4, 1993                                3