dns(n) dns dns(n)
dns - Tcl Domain Name Service Client
package require Tcl 8.2
package require dns ?1.0.1?
::dns::resolve query ?options?
The dns package provides a Tcl only Domain Name Service client. You should refer to RFC
1034 and RFC 1035 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. 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: This package uses TCP to query DNS servers as the tcl core does not implement UDP
networking. This means that this module will not work if DNS over TCP is blocked by a
firewall, or not accepted by the chosen nameserver.
::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.
Specify the network protocol to use for this request. Can be one of tcp or
udp. However only tcp is currently implemented in the package.
Specify an alternative port.
Override the default timeout.
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.
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.
Set to false if you do not want the name server to recursively act upon your
request. Normally set to true.
Set a procedure to be called upon request completion. The procedure will be
passed the token as its only argument.
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
Set the default name server to be used by all queries. The default is local-
Set the default network protocol to be used. Defaults to tcp.
Set the default port to use on the name server. The default is 53.
Set the domain search list. This is currently not used.
Set the default timeout value for DNS lookups. Defaults to 30 seconds.
Returns a list of all domain names returned as an answer to your query.
Returns a list of the address records that match your query.
Returns a list of canonical names (usually just one) matching your query.
Returns the status flag. For a successfully completed query this will be ok. May be
error or timeout or eof. See also ::dns::error
Returns the error message provided for requests whose status is error. If there is
no error message then an empty string is returned.
Reset or cancel a DNS query.
Wait for a DNS query to complete and return the status upon completion.
Remove all state variables associated with the request.
% set tok [dns::resolve www.tcl.tk]
% dns::status $tok
% dns::address $tok
% dns::name $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"]
DNS, resolver, domain name service
dns 1.0.1 dns(n)