View Source: resolver(3) - Waikato Linux Users Group

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RESOLVER
!!!RESOLVER
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
FILES
CONFORMING TO
SEE ALSO
----
!!NAME


res_init, res_query, res_search, res_querydomain, res_mkquery, res_send, dn_comp, dn_expand - resolver routines
!!SYNOPSIS


__#include
__''dname''__, int__ ''class''__, int__ ''type''__,
unsigned char *__''answer''__, int__ ''anslen''__);
int res_search(const char *__''dname''__, int__ ''class''__, int__ ''type''__,
unsigned char *__''answer''__, int__ ''anslen''__);
int res_querydomain(const char *__''name''__, const char *__''domain''__,
int__ ''class''__, int__ ''type''__, unsigned char *__''answer''__,
int__ ''anslen''__);
int res_mkquery(int__ ''op''__, const char *__''dname''__, int__ ''class''__,
int__ ''type''__, char *__''data''__, int__ ''datalen''__, struct rrec *__''newrr''__,
char *__''buf''__, int__ ''buflen''__);
int res_send(const char *__''msg''__, int__ ''msglen''__, char *__''answer''__,
int__ ''anslen''__);
int dn_comp(unsigned char *__''exp_dn''__, unsigned char *__''comp_dn''__,
int__ ''length''__, unsigned char **__''dnptrs''__, unsigned char *__''exp_dn''__,
unsigned char **__''lastdnptr''__);
int dn_expand(unsigned char *__''msg''__, unsigned char *__''eomorig''__,
unsigned char *__''comp_dn''__, unsigned char *__''exp_dn''__,
int__ ''length''__);
__
!!DESCRIPTION


These functions make queries to and interpret the responses
from Internet domain name servers.


The __res_init()__ function reads the configuration files
(see resolv+(8)) to get the default domain name, search
order and name server address(es). If no server is given,
the local host is tried. If no domain is given, that
associated with the local host is used. It can be overridden
with the environment variable LOCALDOMAIN. __res_init()__
is normally executed by the first call to one of the other
functions.


The __res_query()__ function queries the name server for
the fully-qualified domain name ''name'' of specified
''type'' and ''class''. The reply is left in the
buffer ''answer'' of length ''anslen'' supplied by the
caller.


The __res_search()__ function makes a query and waits for
the response like __res_query()__, but in addition
implements the default and search rules controlled by
RES_DEFNAMES and RES_DNSRCH (see description of ''_res''
options below).


The __res_querydomain()__ function makes a query using
__res_query()__ on the concatenation of ''name'' and
''domain''.


The following functions are lower-level routines used by
__res_query()__.


The __res_mkquery()__ function constructs a query message
in ''buf'' of length ''buflen'' for the domain name
''dname''. The query type ''op'' is usually QUERY, but
can be any of the types defined in
''''. ''newrr'' is currently
unused.


The __res_send()__ function sends a pre-formatted query
given in ''msg'' of length ''msglen'' and returns the
answer in ''answer'' which is of length ''anslen''. It
will call __res_init()__, if it has not already been
called.


The __dn_comp()__ function compresses the domain name
''exp_dn'' and stores it in the buffer ''comp_dn'' of
length ''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 of the
array is specified by ''lastdnptr''. if ''dnptr'' is
NULL, domain names are not compressed. If ''lastdnptr''
is NULL, the list of labels is not updated.


The dn_expand() function expands the compressed domain name
''comp_dn'' to a full domain name, which is placed in the
buffer ''exp_dn'' of size ''length''. The compressed
name is contained in a query or reply message, and
''msg'' points to the beginning of the
message.


The resolver routines use global configuration and state
information contained in the structure ''_res'', which is
defined in ''''. The only field that is
normally manipulated by the user is ''_res.options''.
This field can contain the bitwise ``or'' of the following
options:


__RES_INIT__


True if __res_init()__ has been called.


__RES_DEBUG__


Print debugging messages.


__RES_AAONLY__


Accept authoritative answers only. __res_send()__
continues until it fins an authoritative answer or returns
an error. [[Not currently implemented].


__RES_USEVC__


Use TCP connections for queries rather than UDP
datagrams.


__RES_PRIMARY__


Query primary domain name server only.


__RES_IGNTC__


Ignore truncation errors. Don't retry with TCP. [[Not
currently implemented].


__RES_RECURSE__


Set the recursion desired bit in queries. Recursion is
carried out by the domain name server, not by
__res_send()__. [[Enabled by default].


__RES_DEFNAMES__


If set, __res_search()__ will append the default domain
name to single component names, ie. those that do not
contain a dot. [[Enabled by default].


__RES_STAYOPEN__


Used with RES_USEVC to keep the TCP connection open between
queries.


__RES_DNSRCH__


If set, __res_search()__ will search for host names in
the current domain and in parent domains. This option is
used by gethostbyname(3). [[Enabled by
default].
!!RETURN VALUE


The __res_init()__ function returns 0 on success, or -1
if an error occurs.


The __res_query()__, __res_search()__,
__res_querydomain()__, __res_mkquery()__ and
__res_send()__ functions return the length of the
response, or -1 if an error occurs.


The __dn_comp()__ and __dn_expand()__ functions return
the length of the compressed name, or -1 if an error
occurs.
!!FILES


/etc/resolv.conf          resolver configuration file
/etc/host.conf            resolver configuration file
!!CONFORMING TO


BSD 4.3
!!SEE ALSO


gethostbyname(3), hostname(7),
named(8), resolv+(8)
----
22 pages link to resolver(3):
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Last edited on Tuesday, June 4, 2002 12:24:32 am by "perry"
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