dns(n) dns dns(n)
NAME
dns - Tcl Domain Name Service Client
SYNOPSIS
package require Tcl 8.2
package require dns ??1.1??
::::dns::::resolve query ?options?
::::dns::::configure ?options?
::::dns::::name token
::::dns::::address token
::::dns::::cname token
::::dns::::result token
::::dns::::status token
::::dns::::error token
::::dns::::reset token
::::dns::::wait token
::::dns::::cleanup token
DESCRIPTION
The dns package provides a Tcl only Domain Name Service client. You
should refer to RFC 1034 (http://www.rfc-editor.org/rfc/rfc1034.txt)
and RFC 1035 (http://www.rfc-editor.org/rfc/rfc1035.txt) for informa-
tion about the DNS protocol or read resolver(3) to find out how the C
library resolves domain names. The intention of this package is to
insulate Tcl scripts from problems with using the system library
resolver for slow name servers. It may or may not be of practical use.
Internet name resolution is a complex business and DNS is only one part
of the resolver. You may find you are supposed to be using hosts files,
NIS or WINS to name a few other systems. This package is not a substi-
tute for the C library resolver - it does however implement name reso-
lution over DNS. The package also extends the package uri to support
DNS URIs or the form dns:what.host.com or dns://my.name-
server/what.host.com. The dns::::resolve command can handle DNS URIs or
simple domain names as a query.
Note: The package defaults to using DNS over TCP connections. If you
wish to use UDP you will need to get the tcludp package and get a ver-
sion that correctly handles binary data (> 1.0.4). This is available
at http://tcludp.sourceforge.net/. If the udp package is detected, it
will be used automatically.
COMANDS
::::dns::::resolve query ?options?
Resolve a domain name using the DNS protocol. query is the
domain name to be lookup up. This should be either a fully qual-
ified domain name or a DNS URI.
-nameserver hostname or -server hostname
Specify an alternative name server for this request.
-protocol tcpudp
Specify the network protocol to use for this request. Can
be one of tcp or udp.
-port portnum
Specify an alternative port.
-search domainlist
-timeout milliseconds
Override the default timeout.
-type TYPE
Specify the type of DNS record you are interested in.
Valid values are A, NS, MD, MF, CNAME, SOA, MB, MG, MR,
NUL, WKS, PTR, HINFO, MINFO, MX, TXT, SPF, AXFR, MAILB,
MAILA and *. See RFC1035 for details about the return
values. See http://spf.pobox.com/ about SPF.
-class CLAS
Specify the class of domain name. This is usually IN but
may be one of IN for internet domain names, CS, CH, HS or
* for any class.
-recurse boolean
Set to false if you do not want the name server to recur-
sively act upon your request. Normally set to true.
-command procname
Set a procedure to be called upon request completion. The
procedure will be passed the token as its only argument.
::::dns::::configure ?options?
The ::dns::configure command is used to setup the dns package.
The server to query, the protocol and domain search path are all
set via this command. If no arguments are provided then a list
of all the current settings is returned. If only one argument
then it must the the name of an option and the value for that
option is returned.
-nameserver hostname
Set the default name server to be used by all queries.
The default is localhost.
-protocol tcpudp
Set the default network protocol to be used. Defaults to
tcp.
-port portnum
Set the default port to use on the name server. The
default is 53.
-search domainlist
Set the domain search list. This is currently not used.
-timeout milliseconds
Set the default timeout value for DNS lookups. Defaults
to 30 seconds.
::::dns::::name token
Returns a list of all domain names returned as an answer to your
query.
::::dns::::address token
Returns a list of the address records that match your query.
::::dns::::cname token
Returns a list of canonical names (usually just one) matching
your query.
::::dns::::result token
Returns a list of all the decoded answer records provided for
your query. This permits you to extract the result for more
unusual query types.
::::dns::::status token
Returns the status flag. For a successfully completed query this
will be ok. May be error or timeout or eof. See also
::::dns::::error
::::dns::::error token
Returns the error message provided for requests whose status is
error. If there is no error message then an empty string is
returned.
::::dns::::reset token
Reset or cancel a DNS query.
::::dns::::wait token
Wait for a DNS query to complete and return the status upon com-
pletion.
::::dns::::cleanup token
Remove all state variables associated with the request.
EXAMPLES
% set tok [dns::resolve www.tcl.tk]
::dns::1
% dns::status $tok
ok
% dns::address $tok
199.175.6.239
% dns::name $tok
www.tcl.tk
% dns::cleanup $tok
Using DNS URIs as queries:
% set tok [dns::resolve "dns:tcl.tk;type=MX"]
% set tok [dns::resolve "dns:/l.root-servers.net/www.tcl.tk"]
Reverse address lookup:
% set tok [dns::resolve 127.0.0.1]
::dns::1
% dns::name $tok
localhost
% dns::cleanup $tok
AUTHORS
Pat Thoyts
SEE ALSO
resolver(5)
KEYWORDS
DNS, domain name service, resolver, rfc 1034, rfc 1035
COPYRIGHT
Copyright (c) 2002, Pat Thoyts
dns 1.1 dns(n)
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