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Minix/CD-ROM-2.0/MINIX/MANUALS/CAT3/RESOLVER.3
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Minix/CD-ROM-2.0/MINIX/MANUALS/CAT3/RESOLVER.3
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RESOLVER(3) Minix Programmer's Manual RESOLVER(3)
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NAME
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resolver, res_query, res_search, res_mkquery, res_send, res_init,
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dn_comp, dn_expand - resolver routines
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SYNOPSIS
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#include <sys/types.h>
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#include <net/gen/in.h>
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#include <net/gen/nameser.h>
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#include <net/gen/resolv.h>
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res_query(dname, class, type, answer, anslen)
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char *dname;
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int class, type;
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u_char *answer;
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int anslen;
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res_search(dname, class, type, answer, anslen)
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char *dname;
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int class, type;
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u_char *answer;
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int anslen;
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res_mkquery(op, dname, class, type, data, datalen, newrr, buf, buflen)
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int op;
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char *dname;
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int class, type;
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char *data;
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int datalen;
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struct rrec *newrr;
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char *buf;
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int buflen;
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res_send(msg, msglen, answer, anslen)
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char *msg;
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int msglen;
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char *answer;
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int anslen;
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res_init()
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dn_comp(exp_dn, comp_dn, length, dnptrs, lastdnptr)
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char *exp_dn, *comp_dn;
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int length;
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char **dnptrs, **lastdnptr;
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dn_expand(msg, eomorig, comp_dn, exp_dn, length)
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char *msg, *eomorig, *comp_dn, exp_dn;
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int length;
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4BSD June 23, 1990 1
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RESOLVER(3) Minix Programmer's Manual RESOLVER(3)
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DESCRIPTION
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These routines are used for making, sending and interpreting query and
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reply messages with Internet domain name servers.
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Global configuration and state information that is used by the resolver
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routines is kept in the structure _res. Most of the values have
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reasonable defaults and can be ignored. Options stored in _res.options
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are defined in resolv.h and are as follows. Options are stored as a
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simple bit mask containing the bitwise ``or'' of the options enabled.
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RES_INIT
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True if the initial name server address and default domain name are
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initialized (i.e., res_init has been called).
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RES_DEBUG
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Print debugging messages.
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RES_AAONLY
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Accept authoritative answers only. With this option, res_send
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should continue until it finds an authoritative answer or finds an
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error. Currently this is not implemented.
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RES_USEVC
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Use TCP connections for queries instead of UDP datagrams.
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RES_STAYOPEN
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Used with RES_USEVC to keep the TCP connection open between queries.
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This is useful only in programs that regularly do many queries. UDP
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should be the normal mode used.
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RES_IGNTC
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Unused currently (ignore truncation errors, i.e., don't retry with
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TCP).
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RES_RECURSE
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Set the recursion-desired bit in queries. This is the default.
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(res_send does not do iterative queries and expects the name server
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to handle recursion.)
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RES_DEFNAMES
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If set, res_search will append the default domain name to single-
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component names (those that do not contain a dot). This option is
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enabled by default.
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RES_DNSRCH
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If this option is set, res_search will search for host names in the
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current domain and in parent domains; see hostname(7). This is used
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by the standard host lookup routine gethostbyname(3). This option
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is enabled by default.
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4BSD June 23, 1990 2
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RESOLVER(3) Minix Programmer's Manual RESOLVER(3)
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The res_init routine reads the configuration file (if any; see
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resolver(5)) to get the default domain name, search list and the Internet
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address of the local name server(s). If no server is configured, the
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host running the resolver is tried. The current domain name is defined
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by the hostname if not specified in the configuration file; it can be
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overridden by the environment variable LOCALDOMAIN. Initialization
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normally occurs on the first call to one of the following routines.
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The res_query function provides an interface to the server query
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mechanism. It constructs a query, sends it to the local server, awaits a
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response, and makes preliminary checks on the reply. The query requests
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information of the specified type and class for the specified fully-
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qualified domain name dname . The reply message is left in the answer
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buffer with length anslen supplied by the caller.
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The res_search routine makes a query and awaits a response like
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res_query, but in addition, it implements the default and search rules
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controlled by the RES_DEFNAMES and RES_DNSRCH options. It returns the
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first successful reply.
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The remaining routines are lower-level routines used by res_query. The
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res_mkquery function constructs a standard query message and places it in
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buf. It returns the size of the query, or -1 if the query is larger than
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buflen. The query type op is usually QUERY, but can be any of the query
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types defined in <arpa/nameser.h>. The domain name for the query is
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given by dname. Newrr is currently unused but is intended for making
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update messages.
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The res_send routine sends a pre-formatted query and returns an answer.
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It will call res_init if RES_INIT is not set, send the query to the local
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name server, and handle timeouts and retries. The length of the reply
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message is returned, or -1 if there were errors.
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The dn_comp function compresses the domain name exp_dn and stores it in
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comp_dn. The size of the compressed name is returned or -1 if there were
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errors. The size of the array pointed to by comp_dn is given by length.
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The compression uses an array of pointers dnptrs to previously-compressed
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names in the current message. The first pointer points to to the
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beginning of the message and the list ends with NULL. The limit to the
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array is specified by lastdnptr. A side effect of dn_comp is to update
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the list of pointers for labels inserted into the message as the name is
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compressed. If dnptr is NULL, names are not compressed. If lastdnptr is
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NULL, the list of labels is not updated.
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The dn_expand entry expands the compressed domain name comp_dn to a full
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domain name The compressed name is contained in a query or reply message;
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msg is a pointer to the beginning of the message. The uncompressed name
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is placed in the buffer indicated by exp_dn which is of size length. The
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size of compressed name is returned or -1 if there was an error.
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4BSD June 23, 1990 3
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RESOLVER(3) Minix Programmer's Manual RESOLVER(3)
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FILES
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/etc/resolv.conf see resolver(5)
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SEE ALSO
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gethostbyname(3), named(8), resolver(5), hostname(7),
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RFC1032, RFC1033, RFC1034, RFC1035, RFC974,
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SMM:11 Name Server Operations Guide for BIND
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4BSD June 23, 1990 4
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