path: root/usr.sbin/named/man/resolver.3

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.\"	@(#)resolver.3	6.5 (Berkeley) 6/23/90
.\"	$From: resolver.3,v 8.4 1996/05/09 05:59:10 vixie Exp $
.\"
.TH RESOLVER 3 "December 11, 1995
.UC 4
.SH NAME
res_query, res_search, res_mkquery, res_send, res_init, dn_comp, dn_expand \- resolver routines
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <netinet/in.h>
.br
.B #include <arpa/nameser.h>
.br
.B #include <resolv.h>
.PP
.B "res_query(dname, class, type, answer, anslen)"
.br
.B const char *dname;
.br
.B int class, type;
.br
.B u_char *answer;
.br
.B int anslen;
.PP
.B "res_search(dname, class, type, answer, anslen)"
.br
.B const char *dname;
.br
.B int class, type;
.br
.B u_char *answer;
.br
.B int anslen;
.PP
.B "res_mkquery(op, dname, class, type, data, datalen, newrr, buf, buflen)"
.br
.B int op;
.br
.B const char *dname;
.br
.B int class, type;
.br
.B const char *data;
.br
.B int datalen;
.br
.B struct rrec *newrr;
.br
.B u_char *buf;
.br
.B int buflen;
.PP
.B res_send(msg, msglen, answer, anslen)
.br
.B const u_char *msg;
.br
.B int msglen;
.br
.B u_char *answer;
.br
.B int anslen;
.PP
.B res_init()
.PP
.B dn_comp(exp_dn, comp_dn, length, dnptrs, lastdnptr)
.br
.B const char *exp_dn;
.br
.B u_char *comp_dn;
.br
.B int length;
.br
.B u_char **dnptrs, **lastdnptr;
.PP
.B dn_expand(msg, eomorig, comp_dn, exp_dn, length)
.br
.B const u_char *msg, *eomorig, *comp_dn;
.br
.B char *exp_dn;
.br
.B int  length;
.PP
.B herror(const char *s)
.PP
.B hstrerror(int err)
.SH DESCRIPTION
These routines are used for making, sending and interpreting
query and reply messages with Internet domain name servers.
.PP
Global configuration and state information that is used by the
resolver routines is kept in the structure
.IR _res .
Most of the values have reasonable defaults and can be ignored.
Options
stored in
.I _res.options
are defined in
.I resolv.h
and are as follows.
Options are stored as a simple bit mask containing the bitwise ``or''
of the options enabled.
.IP RES_INIT
True if the initial name server address and default domain name are
initialized (i.e.,
.I res_init
has been called).
.IP RES_DEBUG
Print debugging messages.
.IP RES_AAONLY
Accept authoritative answers only.
With this option,
.I res_send
should continue until it finds an authoritative answer or finds an error.
Currently this is not implemented.
.IP RES_USEVC
Use TCP connections for queries instead of UDP datagrams.
.IP 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.
.IP RES_IGNTC
Unused currently (ignore truncation errors, i.e., don't retry with TCP).
.IP RES_RECURSE
Set the recursion-desired bit in queries.
This is the default.
(\c
.I res_send
does not do iterative queries and expects the name server
to handle recursion.)
.IP RES_DEFNAMES
If set,
.I 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.
.IP RES_DNSRCH
If this option is set,
.I res_search
will search for host names in the current domain and in parent domains; see
.IR hostname (7).
This is used by the standard host lookup routine
.IR gethostbyname (3).
This option is enabled by default.
.IP RES_NOALIASES
This option turns off the user level aliasing feature controlled by
the HOSTALIASES environment variable.  Network daemons should set this option.
.PP
The
.I res_init
routine
reads the configuration file (if any; see
.IR resolver (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
.I "search list"
on a per-process basis.  This is similar to the
.I 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
.I _res
structure or are inherited from the configuration file's
.I options
command.  The syntax of the ``RES_OPTIONS'' environment variable
is explained in
.IR resolver (5).
Initialization normally occurs on the first call
to one of the other resolver routines.
.PP
The
.I 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
.I type
and
.I class
for the specified fully-qualified domain name
.I dname .
The reply message is left in the
.I answer
buffer with length
.I anslen
supplied by the caller.
.PP
The
.I res_search
routine makes a query and awaits a response like
.IR 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.
.PP
The remaining routines are lower-level routines used by
.IR res_query .
The
.I res_mkquery
function
constructs a standard query message and places it in
.IR buf .
It returns the size of the query, or \-1 if the query is
larger than
.IR buflen .
The query type
.I op
is usually QUERY, but can be any of the query types defined in
.IR <arpa/nameser.h> .
The domain name for the query is given by
.IR dname .
.I Newrr
is currently unused but is intended for making update messages.
.PP
The
.I res_send
routine
sends a pre-formatted query and returns an answer.
It will call
.I 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.
.PP
The
.I dn_comp
function
compresses the domain name
.I exp_dn
and stores it in
.IR comp_dn .
The size of the compressed name is returned or \-1 if there were errors.
The size of the array pointed to by
.I comp_dn
is given by
.IR length .
The compression uses
an array of pointers
.I dnptrs
to previously-compressed names in the current message.
The first pointer points to
to the beginning of the message and the list ends with NULL.
The limit to the array is specified by
.IR lastdnptr .
A side effect of
.I dn_comp
is to update the list of pointers for
labels inserted into the message
as the name is compressed.
If
.I dnptr
is NULL, names are not compressed.
If
.I lastdnptr
is NULL, the list of labels is not updated.
.PP
The
.I dn_expand
entry
expands the compressed domain name
.I comp_dn
to a full domain name
The compressed name is contained in a query or reply message;
.I msg
is a pointer to the beginning of the message.
The uncompressed name is placed in the buffer indicated by
.I exp_dn
which is of size
.IR length .
The size of compressed name is returned or \-1 if there was an error.
.PP
The external variable
.B h_errno
is set whenever an error occurs during resolver operation.  The following
definitions are given in
.BR <netdb.h> :
.PP
.nf
#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-Authoritive not found, or SERVFAIL */
#define NO_RECOVERY    3   /* Nonrecoverable: FORMERR, REFUSED, NOTIMP */
#define NO_DATA        4   /* Valid name, no data for requested type */
.ft R
.ad
.fi
.PP
The
.B herror
function writes a message to the diagnostic output consisting of the string
parameter
.BR s ,
the constant string ": ", and a message corresponding to the value of
.BR h_errno .
.PP
The
.B hstrerror
function returns a string which is the message text corresponding to the
value of the
.B err
parameter.
.SH FILES
/etc/resolv.conf	see resolver(5)
.SH "SEE ALSO"
gethostbyname(3), named(8), resolver(5), hostname(7),
.br
RFC1032, RFC1033, RFC1034, RFC1035, RFC974, 
.br
SMM:11 Name Server Operations Guide for BIND