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+NAME="NET-COMMON-TCPIP-MANPAGES-RESOLVER">resolver</H1
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+>RESOLVER(3) System Library Functions Manual RESOLVER(3)
+
+NAME
+ res_query, res_search, res_mkquery, res_send, res_init, dn_comp,
+ dn_expand - resolver routines
+
+SYNOPSIS
+ #include <sys/types.h>
+ #include <netinet/in.h>
+ #include <arpa/nameser.h>
+ #include <resolv.h>
+
+ int
+ res_query(char *dname, int class, int type, u_char *answer, int anslen);
+
+ int
+ res_search(char *dname, int class, int type, u_char *answer, int anslen);
+
+ int
+ res_mkquery(int op, char *dname, int class, int type, char *data,
+ int datalen, struct rrec *newrr, char *buf, int buflen);
+
+ int
+ res_send(char *msg, int msglen, char *answer, int anslen);
+
+ int
+ res_init(void);
+
+ int
+ dn_comp(char *exp_dn, char *comp_dn, int length, char **dnptrs,
+ char **lastdnptr);
+
+ int
+ 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
+ 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_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 imple-
+ mented.
+
+ 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 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
+ 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, 10.1.1.1 will be returned as ::ffff:10.1.1.1.
+ The option is not meaningful on OpenBSD.
+
+ The res_init() routine reads 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 config-
+ ured, 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 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 resolv.conf(5).
+ Initialization normally 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
+ response, and makes preliminary checks on the reply. The query requests
+ information of the specified type and class for the specified fully qual-
+ ified 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
+ update 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
+ local name server, and handle timeouts 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 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 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
+ error.
+
+FILES
+ /etc/resolv.conf configuration file see resolv.conf(5).
+
+SEE ALSO
+ gethostbyname(3), resolv.conf(5), hostname(7), named(8)
+
+ RFC1032, RFC1033, RFC1034, RFC1035, RFC1535, RFC974
+
+ Name Server Operations Guide for BIND.
+
+HISTORY
+ The res_query function appeared in 4.3BSD.
+
+BSD June 4, 1993 BSD
+ </PRE
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