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dns(n) 1.0.4 "dns"
dns - Tcl Domain Name Service Client
package require Tcl 8.2
package require dns ?1.0.4?
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
information 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 substitute for the C library
resolver - it does however implement name resolution over DNS.
The package also extends the package uri to support DNS URIs
or the form dns:what.host.com or
dns://my.nameserver/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 version that correctly handles binary
data. This should be publicly available shortly.
- ::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
qualified domain name or a DNS URI.
- -nameserver hostname or -server hostname
-
Specify an alternative name server for this request.
- -protocol tcp|udp
-
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, NULL, WKS, PTR, HINFO, MINFO, MX, TXT, AXFR, MAILB,
MAILA and *. See RFC1035 for details about the return values.
- -class CLASS
-
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 recursively 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 tcp|udp
-
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::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 completion.
- ::dns::cleanup token
-
Remove all state variables associated with the request.
| |
% 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"]
|
Pat Thoyts
resolver(5)
DNS , domain name service , resolver , rfc 1034 , rfc 1035
Copyright © 2002, Pat Thoyts