POE::Component::Client::DNS(3)

NAME
POE::Component::Client::DNS - non-blocking, concurrent DNS requests

SYNOPSIS
  use POE qw(Component::Client::DNS);

  my $named = POE::Component::Client::DNS->spawn(
    Alias => "named"
  );

  POE::Session->create(
    inline_states  => {
      _start   => \&start_tests,
      response => \&got_response,
    }
  );

  POE::Kernel->run();
  exit;

  sub start_tests {
    my $response = $named->resolve(
      event   => "response",
      host    => "localhost",
      context => { },
    );
    if ($response) {
      $_[KERNEL]->yield(response => $response);
    }
  }

  sub got_response {
    my $response = $_[ARG0];
    my @answers = $response->{response}->answer();

    foreach my $answer (@answers) {
      print(
        "$response->{host} = ",
        $answer->type(), " ",
        $answer->rdatastr(), "\n"
      );
    }
  }

DESCRIPTION
POE::Component::Client::DNS provides a facility for non-blocking, concurrent DNS requests. Using POE, it allows other tasks to run while waiting for name servers to respond.

PUBLIC METHODS

spawn
    A program must spawn at least one POE::Component::Client::DNS instance before it can perform background DNS lookups. Each instance represents a connection to a name server, or a pool of them. If a program only needs to request DNS lookups from one server, then you only need one POE::Component::Client::DNS instance.

    As of version 0.98 you can override the default timeout per request. From this point forward there is no need to spawn multiple instances o affect different timeouts for each request.

    PoCo::Client::DNS's "spawn" method takes a few named parameters:

    Alias sets the component's alias. Requests will be posted to this alias. The component's alias defaults to "resolver" if one is not provided. Programs spawning more than one DNS client component must specify aliases for N-1 of them, otherwise alias collisions will occur.

      Alias => $session_alias,  # defaults to "resolver"

    Timeout sets the component's default timeout. The timeout may be overridden per request. See the "request" event, later on. If no Timeout is set, the component will wait 90 seconds per request by default.

    Timeouts may be set to real numbers. Timeouts are more accurate if you have Time::HiRes installed. POE (and thus this component) will use Time::HiRes automatically if it's available.

      Timeout => $seconds_to_wait,  # defaults to 90

    Nameservers holds a reference to a list of name servers to try. The list is passed directly to Net::DNS::Resolver's nameservers() method. By default, POE::Component::Client::DNS will query the name servers that appear in /etc/resolv.conf or its equivalent.

      Nameservers => \@name_servers,  # defaults to /etc/resolv.conf's

    HostsFile (optional) holds the name of a specific hosts file to use for resolving hardcoded addresses. By default, it looks for a file named /etc/hosts.

    On Windows systems, it may look in the following other places:

      $ENV{SystemRoot}\System32\Drivers\Etc\hosts
      $ENV{SystemRoot}\System\Drivers\Etc\hosts
      $ENV{SystemRoot}\hosts

resolve
    resolve() requests the component to resolve a host name. It will return a hash reference (described in RESPONSE MESSAGES, below) if it can honor the request immediately (perhaps from a cache). Otherwise it returns undef if a resolver must be consulted asynchronously.

    Requests are passed as a list of named fields.

      $resolver->resolve(
        class   => $dns_record_class,  # defaults to "IN"
        type    => $dns_record_type,   # defaults to "A"
        host    => $request_host,      # required
        context => $request_context,   # required
        event   => $response_event,    # required
        timeout => $request_timeout,   # defaults to spawn()'s Timeout
      );

    The "class" and "type" fields specify what kind of information to return about a host. Most of the time internet addresses are requested for host names, so the class and type default to "IN" (internet) and "A" (address), respectively.

    The "host" field designates the host to look up. It is required.

    The "event" field tells the component which event to send back when a response is available. It is required, but it will not be used if resolve() can immediately return a cached response.

    "timeout" tells the component how long to wait for a response to this request. It defaults to the "Timeout" given at spawn() time.

    "context" includes some external data that links responses back to their requests. The context data is provided by the program that uses POE::Component::Client::DNS. The component will pass the context back to the program without modification. The "context" parameter is required, and may contain anything that fits in a scalar.

shutdown
    shutdown() causes the component to terminate gracefully. It will finish serving pending requests then close down.

get_resolver
    POE::Component::Client::DNS uses a Net::DNS::Resolver object internally. get_resolver() returns that object so it may be interrogated or modified. See Net::DNS::Resolver for options.

    Set the resolver to check on nonstandard port 1153:

      $poco_client_dns->resolver()->port(1153);

RESPONSE MESSAGES
POE::Component::Client::DNS responds in one of two ways. Its resolve() method will return a response immediately if it can be found in the component's cache. Otherwise the component posts the response back in $_[ARG0]. In either case, the response is a hash reference containing the same fields:

  host     => $request_host,
  type     => $request_type,
  class    => $request_class,
  context  => $request_context,
  response => $net_dns_packet,
  error    => $net_dns_error,

The "host", "type", "class", and "context" response fields are identical to those given in the request message.

"response" contains a Net::DNS::Packet object on success or undef if the lookup failed. The Net::DNS::Packet object describes the response to the program's request. It may contain several DNS records. Please consult Net::DNS and Net::DNS::Packet for more information.

"error" contains a description of any error that has occurred. It is only valid if "response" is undefined.

SEE ALSO
POE - POE::Component::Client::DNS builds heavily on POE.

Net::DNS - This module uses Net::DNS internally.

Net::DNS::Packet - Responses are returned as Net::DNS::Packet objects.

DEPRECATIONS
The older, list-based interfaces are no longer documented as of version 0.98. They are being phased out. The method-based interface, first implementedin version 0.98, will replace the deprecated interfaces after a six-month phase-out period.

Version 0.98 was released in October of 2004. The deprecated interfaces will continue to work without warnings until January 2005.

As of January 2005, programs that use the deprecated interfaces will continue to work, but they will generate mandatory warnings. Those warnings will persist until April 2005.

As of April 2005 the mandatory warnings will be upgraded to mandatory errors. Support for the deprecated interfaces will be removed entirely.

BUG TRACKER
https://rt.cpan.org/Dist/Display.html?Queue=POE-Component-Client-DNS

REPOSITORY
http://github.com/rcaputo/poe-component-client-dns

OTHER RESOURCES
http://search.cpan.org/dist/POE-Component-Client-DNS/

AUTHOR & COPYRIGHTS
POE::Component::Client::DNS is Copyright 1999-2009 by Rocco Caputo. All rights are reserved. POE::Component::Client::DNS is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

Postback arguments were contributed by tag.

POD ERRORS
Hey! The above document had some coding errors, which are explained below:

Around line 716:
    You forgot a '=back' before '=head1'