\" Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
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\" acknowledgement:  ``This product includes software developed by the
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\"      @(#)resolver.3  6.5 (Berkeley) 6/23/90
\"      Id: resolver.man3,v 1.2 2009/01/21 00:12:34 each Exp
\"
Dd July 4, 2000
Dt RESOLVER 3
Os BSD 4
Sh NAME
Nm res_ninit ,
Nm res_ourserver_p ,
Nm fp_resstat ,
Nm res_hostalias ,
Nm res_pquery ,
Nm res_nquery ,
Nm res_nsearch ,
Nm res_nquerydomain ,
Nm res_nmkquery ,
Nm res_nsend ,
Nm res_nupdate ,
Nm res_nmkupdate ,
Nm res_nclose ,
Nm res_nsendsigned ,
Nm res_findzonecut ,
Nm res_getservers ,
Nm res_setservers ,
Nm res_ndestroy ,
Nm dn_comp ,
Nm dn_expand ,
Nm hstrerror ,
Nm res_init ,
Nm res_isourserver ,
Nm fp_nquery ,
Nm p_query ,
Nm hostalias ,
Nm res_query ,
Nm res_search ,
Nm res_querydomain ,
Nm res_mkquery ,
Nm res_send ,
Nm res_update ,
Nm res_close ,
Nm herror
Nd resolver routines
Sh SYNOPSIS
Fd #include <sys/types.h>
Fd #include <netinet/in.h>
Fd #include <arpa/nameser.h>
Fd #include <resolv.h>
Fd #include <res_update.h>
Vt typedef struct __res_state *res_state ;
Pp
Ft int
Fn res_ninit "res_state statp"
Ft int
Fn res_ourserver_p "const res_state statp" "const struct sockaddr_in *addr"
Ft void
Fn fp_resstat "const res_state statp" "FILE *fp"
Ft "const char *"
Fn res_hostalias "const res_state statp" "const char *name" "char *buf" "size_t buflen"
Ft int
Fn res_pquery "const res_state statp" "const u_char *msg" "int msglen" "FILE *fp"
Ft int
Fn res_nquery "res_state statp" "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
Ft int
Fn res_nsearch "res_state statp" "const char *dname" "int class" "int type" "u_char * answer" "int anslen"
Ft int
Fn res_nquerydomain "res_state statp" "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
Ft int
Fo res_nmkquery
Fa "res_state statp"
Fa "int op"
Fa "const char *dname"
Fa "int class"
Fa "int type"
Fa "const u_char *data"
Fa "int datalen"
Fa "const u_char *newrr"
Fa "u_char *buf"
Fa "int buflen"
Fc
Ft int
Fn res_nsend "res_state statp" "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
Ft int
Fn res_nupdate "res_state statp" "ns_updrec *rrecp_in"
Ft int
Fn res_nmkupdate "res_state statp" "ns_updrec *rrecp_in" "u_char *buf" "int buflen"
Ft void
Fn res_nclose "res_state statp"
Ft int
Fn res_nsendsigned "res_state statp" "const u_char *msg" "int msglen" "ns_tsig_key *key" "u_char *answer" "int anslen"
Ft int
Fn res_findzonecut "res_state statp" "const char *dname" "ns_class class" "int options" "char *zname" "size_t zsize" "struct in_addr *addrs" "int naddrs"
Ft int
Fn res_getservers "res_state statp" "union res_sockaddr_union *set" "int cnt"
Ft void
Fn res_setservers "res_state statp" "const union res_sockaddr_union *set" "int cnt"
Ft void
Fn res_ndestroy "res_state statp"
Ft int
Fn dn_comp "const char *exp_dn" "u_char *comp_dn" "int length" "u_char **dnptrs" "u_char **lastdnptr"
Ft int
Fn dn_expand "const u_char *msg" "const u_char *eomorig" "const u_char *comp_dn" "char *exp_dn" "int  length"
Ft "const char *"
Fn hstrerror "int err"
Ss DEPRECATED
Fd #include <sys/types.h>
Fd #include <netinet/in.h>
Fd #include <arpa/nameser.h>
Fd #include <resolv.h>
Fd #include <res_update.h>
Ft int
Fn res_init "void"
Ft int
Fn res_isourserver "const struct sockaddr_in *addr"
Ft int
Fn fp_nquery "const u_char *msg" "int msglen" "FILE *fp"
Ft void
Fn p_query "const u_char *msg" "FILE *fp"
Ft "const char *"
Fn hostalias "const char *name"
Ft int
Fn res_query "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
Ft int
Fn res_search "const char *dname" "int class" "int type" "u_char *answer" "int anslen"
Ft int
Fn res_querydomain "const char *name" "const char *domain" "int class" "int type" "u_char *answer" "int anslen"
Ft int
Fo res_mkquery
Fa "int op"
Fa "const char *dname"
Fa "int class"
Fa "int type"
Fa "const char *data"
Fa "int datalen"
Fa "struct rrec *newrr"
Fa "u_char *buf"
Fa "int buflen"
Fc
Ft int
Fn res_send "const u_char *msg" "int msglen" "u_char *answer" "int anslen"
Ft int
Fn res_update "ns_updrec *rrecp_in"
Ft void
Fn res_close "void"
Ft void
Fn herror "const char *s"
Sh DESCRIPTION
These routines are used for making, sending and interpreting
query and reply messages with Internet domain name servers.
Pp
State information is kept in
Fa statp
and is used to control the behavior of these functions.
Fa statp
should be set to all zeros prior to the first call to any of these functions.
Pp
The functions
Fn res_init ,
Fn res_isourserver ,
Fn fp_nquery ,
Fn p_query ,
Fn hostalias ,
Fn res_query ,
Fn res_search ,
Fn res_querydomain ,
Fn res_mkquery ,
Fn res_send ,
Fn res_update ,
Fn res_close
and
Fn herror
are deprecated and are supplied for compatability with old source
code.
They use global configuration and state information that is
kept in the structure
Ft _res
rather than that referenced through
Ft statp .
Pp
Most of the values in
Ft statp
and
Ft _res
are initialized on the first call to
Fn res_ninit
/
Fn res_init
to reasonable defaults and can be ignored.
Options
stored in
Ft statp->options
/
Ft _res.options
are defined in
Pa resolv.h
and are as follows.
Options are stored as a simple bit mask containing the bitwise
Dq OR
of the options enabled.
Bl -tag -width "RES_DEB"
It Dv RES_INIT
True if the initial name server address and default domain name are
initialized (i.e.,
Fn res_ninit
/
Fn res_init
has been called).
It Dv RES_DEBUG
Print debugging messages.
It Dv RES_AAONLY
Accept authoritative answers only.
Should continue until it finds an authoritative answer or finds an error.
Currently this is not implemented.
It Dv RES_USEVC
Use TCP connections for queries instead of UDP datagrams.
It Dv RES_STAYOPEN
Used with
Dv 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.
It Dv RES_IGNTC
Ignore truncation errors, i.e., don't retry with TCP.
It Dv RES_RECURSE
Set the recursion-desired bit in queries.
This is the default.
(\c
Fn res_nsend
/
Fn res_send
does not do iterative queries and expects the name server
to handle recursion.)
It Dv RES_DEFNAMES
If set,
Fn res_nsearch
/
Fn 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.
It Dv RES_DNSRCH
If this option is set,
Fn res_nsearch
/
Fn res_search
will search for host names in the current domain and in parent domains; see
Xr hostname 7 .
This is used by the standard host lookup routine
Xr gethostbyname 3 .
This option is enabled by default.
It Dv RES_NOALIASES
This option turns off the user level aliasing feature controlled by
the
Ev HOSTALIASES
environment variable.
Network daemons should set this option.
It Dv RES_USE_INET6
This option causes
Xr gethostbyname 3
to look for AAAA records before looking for A records if none are found.
It Dv RES_ROTATE
This options causes the
Fn res_nsend
/
Fn res_send
to rotate the list of nameservers in
Fa statp->nsaddr_list
/
Fa _res.nsaddr_list .
It Dv RES_KEEPTSIG
This option causes
Fn res_nsendsigned
to leave the message unchanged after TSIG verification; otherwise the TSIG
record would be removed and the header updated.
It Dv RES_NOTLDQUERY
This option causes
Fn res_nsearch
to not attempt to resolve a unqualified name as if it were a top level
domain (TLD).
This option can cause problems if the site has "localhost" as a TLD rather
than having localhost on one or more elements of the search list.
This option has no effect if neither
Dv RES_DEFNAMES
or
Dv RES_DNSRCH
is set.
El
Pp
The
Fn res_ninit
/
Fn res_init
routine
reads the configuration file (if any; see
Xr 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
Ev LOCALDOMAIN .
This environment variable may contain several blank-separated
tokens if you wish to override the
Dq search list
on a per-process basis.  This is similar to the
Ic search
command in the configuration file.
Another environment variable
Pq Dq Ev RES_OPTIONS
can be set to override certain internal resolver options which are otherwise
set by changing fields in the
Ft statp
/
Ft _res
structure or are inherited from the configuration file's
Ic options
command.  The syntax of the
Dq Ev RES_OPTIONS
environment variable is explained in
Xr resolver 5 .
Initialization normally occurs on the first call
to one of the other resolver routines.
Pp
The memory referred to by
Ft statp
must be set to all zeros prior to the first call to
Fn res_ninit .
Fn res_ndestroy
should be call to free memory allocated by
Fn res_ninit
after last use.
Pp
The
Fn res_nquery
/
Fn res_query
functions provides interfaces to the server query mechanism.
They 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
Fa type
and
Fa class
for the specified fully-qualified domain name
Fa dname .
The reply message is left in the
Fa answer
buffer with length
Fa anslen
supplied by the caller.
Fn res_nquery
/
Fn res_query
return -1 on error or the length of the answer.
Pp
The
Fn res_nsearch
/
Fn res_search
routines make a query and awaits a response like
Fn res_nquery
/
Fn res_query ,
but in addition, it implements the default and search rules
controlled by the
Dv RES_DEFNAMES
and
Dv RES_DNSRCH
options.
It returns the length of the first successful reply which is stored in
Ft answer
or -1 on error.
Pp
The remaining routines are lower-level routines used by
Fn res_nquery
/
Fn res_query .
The
Fn res_nmkquery
/
Fn res_mkquery
functions
constructs a standard query message and places it in
Fa buf .
It returns the size of the query, or \-1 if the query is
larger than
Fa buflen .
The query type
Fa op
is usually
Dv QUERY ,
but can be any of the query types defined in
Pa <arpa/nameser.h> .
The domain name for the query is given by
Fa dname .
Fa Newrr
is currently unused but is intended for making update messages.
Pp
The
Fn res_nsend
/
Fn res_send
/
Fn res_nsendsigned
routines
sends a pre-formatted query and returns an answer.
It will call
Fn res_ninit
/
Fn res_init
if
Dv RES_INIT
is not set, send the query to the local name server, and
handle timeouts and retries.  Additionally,
Fn res_nsendsigned
will use TSIG signatures to add authentication to the query and verify the
response.  In this case, only one nameserver will be contacted.
The length of the reply message is returned, or \-1 if there were errors.
Pp
Fn res_nquery
/
Fn res_query ,
Fn res_nsearch
/
Fn res_search
and
Fn res_nsend
/
Fn res_send
return a length that may be bigger than
Fa anslen .
In that case the query should be retried with a bigger buffer.
NOTE the answer to the second query may be larger still so supplying
a buffer that bigger that the answer returned by the previous
query is recommended.
Pp
Fa answer
MUST be big enough to receive a maximum UDP response from the server or
parts of the answer will be silently discarded.
The default maximum UDP response size is 512 bytes.
Pp
The function
Fn res_ourserver_p
returns true when
Fa inp
is one of the servers in
Fa statp->nsaddr_list
/
Fa _res.nsaddr_list .
Pp
The functions
Fn fp_nquery
/
Fn p_query
print out the query and any answer in
Fa msg
on
Fa fp .
Fn p_query
is equivalent to
Fn fp_nquery
with
Fa msglen
set to 512.
Pp
The function
Fn fp_resstat
prints out the active flag bits in
Fa statp->options
preceeded by the text ";; res options:" on
Fa file .
Pp
The functions
Fn res_hostalias
/
Fn hostalias
lookup up name in the file referred to by the
Ev HOSTALIASES
files return a fully qualified hostname if found or NULL if
not found or an error occurred.
Fn res_hostalias
uses
Fa buf
to store the result in,
Fn hostalias
uses a static buffer.
Pp
The functions
Fn res_getservers
and
Fn res_setservers
are used to get and set the list of server to be queried.
Pp
The functions
Fn res_nupdate
/
Fn res_update
take a list of ns_updrec
Fa rrecp_in .
Identifies the containing zone for each record and groups the records
according to containing zone maintaining in zone order then sends and update
request to the servers for these zones.  The number of zones updated is
returned or -1 on error.  Note that
Fn res_nupdate
will perform TSIG authenticated dynamic update operations if the key is not
NULL.
Pp
The function
Fn res_findzonecut
discovers the closest enclosing zone cut for a specified domain name,
and finds the IP addresses of the zone's master servers.
Pp
The functions
Fn res_nmkupdate
/
Fn res_mkupdate
take a linked list of ns_updrec
Fa rrecp_in
and construct a UPDATE message in
Fa buf .
Fn res_nmkupdate
/
Fn res_mkupdate
return the length of the constructed message on no error or one of the
following error values.
Bl -inset -width "-5"
It -1
An error occurred parsing
Fa rrecp_in .
It -2
The buffer
Fa buf
was too small.
It -3
The first record was not a zone section or there was a section order problem.
The section order is S_ZONE, S_PREREQ and S_UPDATE.
It -4
A number overflow occurred.
It -5
Unknown operation or no records.
El
Pp
The functions
Fn res_nclose
/
Fn res_close
close any open files referenced through
Fa statp
/
Fa _res .
Pp
The function
Fn res_ndestroy
calls
Fn res_nclose
then frees any memory allocated by
Fn res_ninit .
Pp
The
Fn dn_comp
function
compresses the domain name
Fa exp_dn
and stores it in
Fa comp_dn .
The size of the compressed name is returned or \-1 if there were errors.
The size of the array pointed to by
Fa comp_dn
is given by
Fa length .
The compression uses
an array of pointers
Fa 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
Dv NULL .
The limit to the array is specified by
Fa lastdnptr .
A side effect of
Fn dn_comp
is to update the list of pointers for labels inserted into the message
as the name is compressed.  If
Fa dnptr
is
Dv NULL ,
names are not compressed.  If
Fa lastdnptr
is
Dv NULL ,
the list of labels is not updated.
Pp
The
Fn dn_expand
entry
expands the compressed domain name
Fa comp_dn
to a full domain name.
The compressed name is contained in a query or reply message;
Fa msg
is a pointer to the beginning of the message.
Fa eomorig
is a pointer to the first location after the message.
The uncompressed name is placed in the buffer indicated by
Fa exp_dn
which is of size
Fa length .
The size of compressed name is returned or \-1 if there was an error.
Pp
The variables
Ft statp->res_h_errno
/
Ft _res.res_h_errno
and external variable
Ft h_errno
is set whenever an error occurs during resolver operation.  The following
definitions are given in
Pa <netdb.h> :
Bd -literal
#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-Authoritative not found, or SERVFAIL */
#define NO_RECOVERY    3   /* Non-Recoverable: FORMERR, REFUSED, NOTIMP */
#define NO_DATA        4   /* Valid name, no data for requested type */
Ed
Pp
The
Fn herror
function writes a message to the diagnostic output consisting of the string
parameter
Fa s ,
the constant string ": ", and a message corresponding to the value of
Ft h_errno .
Pp
The
Fn hstrerror
function returns a string which is the message text corresponding to the
value of the
Fa err
parameter.
Sh FILES
Bl -tag -width "/etc/resolv.conf    "
It Pa /etc/resolv.conf
See
Xr resolver 5 .
El
Sh SEE ALSO
Xr gethostbyname 3 ,
Xr hostname 7 ,
Xr resolver 5 ;
RFC1032, RFC1033, RFC1034, RFC1035, RFC974;
SMM:11,
Dq Name Server Operations Guide for BIND

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