NAME¶
dns - Tcl Domain Name Service Client
SYNOPSIS¶
package require
Tcl 8.2
package require
dns ?1.3.3?
::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
::dns::nameservers
DESCRIPTION¶
The dns package provides a Tcl only Domain Name Service client. You should refer
to (1) and (2) 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 (4) of 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 have the
tcludp package installed and have
a version that correctly handles binary data (> 1.0.4). This is available
at
http://tcludp.sourceforge.net/. If the
udp package is present
then UDP will be used by default.
COMMANDS¶
- ::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, SPF, SRV, AAAA, AXFR, MAILB, MAILA and *. See RFC1035 for
details about the return values. See http://spf.pobox.com/ about
SPF. See (3) about AAAA records and RFC2782 for details of SRV
records.
- -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. Default is
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. Default is
30 seconds.
- -loglevel level
- Set the log level used for emitting diagnostic messages
from this package. The default is warn. See the log package
for details of the available levels.
- ::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
completion.
- ::dns::cleanup token
- Remove all state variables associated with the request.
- ::dns::nameservers
- Attempts to return a list of the nameservers currently
configured for the users system. On a unix machine this parses the
/etc/resolv.conf file for nameservers (if it exists) and on Windows
systems we examine certain parts of the registry. If no nameserver can be
found then the loopback address (127.0.0.1) is used as a default.
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:
Reverse address lookup:
% set tok [dns::resolve 127.0.0.1]
::dns::1
% dns::name $tok
localhost
% dns::cleanup $tok
REFERENCES¶
- [1]
- Mockapetris, P., "Domain Names - Concepts and
Facilities", RFC 1034, November 1987. (
http://www.ietf.org/rfc/rfc1034.txt)
- [2]
- Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, November 1087. (
http://www.ietf.org/rfc/rfc1035.txt)
- [3]
- Thompson, S. and Huitema, C., "DNS Extensions to
support IP version 6", RFC 1886, December 1995. (
http://www.ietf.org/rfc/rfc1886.txt)
- [4]
- Josefsson, S., "Domain Name System Uniform Resource
Identifiers", Internet-Draft, October 2003, (
http://www.ietf.org/internet-drafts/draft-josefsson-dns-url-09.txt)
- [5]
- Gulbrandsen, A., Vixie, P. and Esibov, L., "A DNS RR
for specifying the location of services (DNS SRV)", RFC 2782,
February 2000, ( http://www.ietf.org/rfc/rfc2782.txt)
- [6]
- Ohta, M. "Incremental Zone Transfer in DNS", RFC
1995, August 1996, ( http://www.ietf.org/rfc/rfc1995.txt)
AUTHORS¶
Pat Thoyts
BUGS, IDEAS, FEEDBACK¶
This document, and the package it describes, will undoubtedly contain bugs and
other problems. Please report such in the category
dns of the
Tcllib
SF Trackers [
http://sourceforge.net/tracker/?group_id=12883]. Please also
report any ideas for enhancements you may have for either package and/or
documentation.
SEE ALSO¶
resolver(5)
KEYWORDS¶
DNS, domain name service, resolver, rfc 1034, rfc 1035, rfc 1886
CATEGORY¶
Networking
COPYRIGHT¶
Copyright (c) 2002, Pat Thoyts