path: root/newlib/libc/sys/linux/net/resolver.3

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

NAME
     res_query, res_search, res_mkquery, res_send, res_init, dn_comp, dn_expand, dn_skipname,
     ns_get16, ns_get32, ns_put16, ns_put32 -- resolver routines

LIBRARY
     Standard C Library (libc, -lc)

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

     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_mkquery(int op, const char *dname, int class, int type, const u_char *data, int datalen,
         const u_char *newrr_in, u_char *buf, int buflen);

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

     int
     res_init();

     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);

     int
     dn_skipname(const u_char *comp_dn, const u_char *eom);

     u_int
     ns_get16(const u_char *src);

     u_long
     ns_get32(const u_char *src);

     void
     ns_put16(u_int src, u_char *dst);

     void
     ns_put32(u_long src, u_char *dst);

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 reasonable defaults and can be ignored.  Op-
     tions stored in _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_init() has been called).

     RES_DEBUG      Print debugging messages.

     RES_AAONLY     Accept authoritative answers only.  With this option, res_send() should con-
                    tinue 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      Unused currently (ignore truncation errors, i.e., don't retry with TCP).

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

     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 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  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, re-
                    solver code will attach OPT pseudo-RR into DNS queries, to inform of our re-
                    ceive 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.

     The res_init() routine reads the configuration file (if any; see resolver(5)) to get the de-
     fault 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 _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 following rou-
     tines.

     The res_query() function provides an interface to the server query mechanism.  It constructs
     a query, sends it to the local server, awaits a response, 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 addi-
     tion, 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 update mes-
     sages.

     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 local name server, and handle time-
     outs and retries.  The length of the reply 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 the be-
     ginning 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.  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 dn_skipname() function skips over a compressed domain name, which starts at a location
     pointed to by comp_dn.  The compressed name is contained in a query or reply message; eom is
     a pointer to the end of the message.  The size of compressed name is returned or -1 if there
     was an error.

     The ns_get16() function gets a 16-bit quantity from a buffer pointed to by src.

     The ns_get32() function gets a 32-bit quantity from a buffer pointed to by src.

     The ns_put16() function puts a 16-bit quantity src to a buffer pointed to by dst.

     The ns_put32() function puts a 32-bit quantity src to a buffer pointed to by dst.

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

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

     RFC1032, RFC1033, RFC1034, RFC1035, RFC974

     Name Server Operations Guide for BIND.

HISTORY
     The res_query function appeared in 4.3BSD.

BSD                                        June 4, 1993                                       BSD