NAME
    POE::Component::Resolver - A non-blocking getaddrinfo() resolver

VERSION
    version 0.918

SYNOPSIS
            #!/usr/bin/perl

            use warnings;
            use strict;

            use POE;
            use POE::Component::Resolver qw(AF_INET AF_INET6);

            my $r = POE::Component::Resolver->new(
                    max_resolvers => 8,
                    idle_timeout  => 5,
                    af_order      => [ AF_INET6, AF_INET ],
                    # sidecar_program => $path_to_program,
            );

            my @hosts = qw( ipv6-test.com );
            my $tcp   = getprotobyname("tcp");

            POE::Session->create(
                    inline_states => {
                            _start => sub {
                                    foreach my $host (@hosts) {
                                            $r->resolve(
                                                    host    => $host,
                                                    service => "http",
                                                    event   => "got_response",
                                                    hints   => { protocol => $tcp },
                                            ) or die $!;
                                    }
                            },

                            _stop => sub { print "client session stopped\n" },

                            got_response => sub {
                                    my ($error, $addresses, $request) = @_[ARG0..ARG2];
                                    use YAML; print YAML::Dump(
                                            {
                                                    error => $error,
                                                    addr => $addresses,
                                                    req => $request,
                                            }
                                    );
                            },
                    }
            );

            POE::Kernel->run();

DESCRIPTION
    POE::Component::Resolver performs Socket::GetAddrInfo::getaddrinfo()
    calls in subprocesses where they're permitted to block as long as
    necessary.

    By default it will run eight subprocesses and prefer address families in
    whatever order Socket::GetAddrInfo returns them. These defaults can be
    overridden with constructor parameters.

  PUBLIC METHODS
   new
    Create a new resolver. Returns an object that must be held and used to
    make requests. See the synopsis.

    Accepts up to four optional named parameters.

    "af_order" may contain an arrayref with the address families to permit,
    in the order in which they're preferred. Without "af_order", the
    component will prefer IPv4 addresses over IPv6 for legacy compatibility.
    This may change in the future as IPv6 gains more widespread acceptance.
    See "ENVIRONMENT VARIABLES" for a way to override the default without
    hacking modules.

            # Prefer IPv6 addresses, but also return IPv4 ones.
            my $r1 = POE::Component::Resolver->new(
                    af_order => [ AF_INET6, AF_INET ]
            );

            # Only return IPv6 addresses,
            # or nothing in cases where only IPv4 addresses exist.
            my $r2 = POE::Component::Resolver->new(
                    af_order => [ AF_INET6 ]
            );

    "idle_timeout" determines how long to keep idle resolver subprocesses
    before cleaning them up, in seconds. It defaults to 15.0 seconds.

    "max_resolvers" controls the component's parallelism by defining the
    maximum number of sidecar processes to manage. It defaults to 8, but
    fewer or more processes can be configured depending on the resources you
    have available and the amount of parallelism you require.

            # One at a time, but without the pesky blocking.
            my $r3 = POE::Component::Resolver->new( max_resolvers => 1 );

    "sidecar_program" contains the disk location of a program that will
    perform blocking lookups on standard input and print the results on
    standard output. The sidecar program is needed only in special
    environments where the bundling and execution of extra utilities is
    tricky. PAR is one such environment.

    The sidecar program needs to contain at least two statements:

            use POE::Component::Resolver::Sidecar;
            POE::Component::Resover::Sidecar->main();

   resolve
    resolve() begins a new request to resolve a domain. The request will be
    enqueued in the component until a sidecar process can service it.
    resolve() returns a request ID that may be used to cancel() a request
    before it has completed (or undef if the request couldn't begin, such as
    during shutdown). Resolve requires two parameters and accepts some
    additional optional ones.

    "host" and "service" are required and contain the host (name or Internet
    address) and service (name or numeric port) that will be passed verbatim
    to getaddrinfo(). See Socket::GetAddrInfo for details.

    "event" is optional; it contains the name of the event that will contain
    the resolver response. If omitted, it will default to
    "resolver_response"; you may want to specify a shorter event name.

    "hints" is optional. If specified, it must contain a hashref of hints
    exactly as getaddrinfo() expects them. See Socket::GetAddrInfo for
    details.

    "misc" is optional continuation data that will be passed back in the
    response. It may contain any type of data the application requires.

   cancel
    Cancel a request, given the request's ID.

            my $request_id = $resolver->resolve("poe.dyndns.org", "http");
            $resolver->cancel($request_id);

   shutdown
    Shut down the resolver. POE::Component::Resolver retains resources
    including child processes for up to "idle_timeout" seconds. This may
    keep programs running up to "idle_timeout" seconds longer than they
    should.

    POE::Component::Resolver will release its resources (including child
    processes) when its shutdown() method is called.

   unpack_addr
    In scalar context, unpack_addr($response_addr_hashref) returns the addr
    element of $response_addr_hashref in a numeric form appropriate for the
    address family of the address.

            sub handle_resolver_response {
                    my ($error, $addresses, $request) = @_[ARG0..ARG2];

                    foreach my $a (@$addresses) {
                            my $numeric_addr = $resolver->unpack_addr($a);
                            print "$request->{host} = $numeric_addr\n";
                    }
            }

    In list context, it returns the numeric port and address.

            sub handle_resolver_response {
                    my ($error, $addresses, $request) = @_[ARG0..ARG2];

                    foreach my $a (@$addresses) {
                            my ($$numeric_addr, $port) = $resolver->unpack_addr($a);
                            print "$request->{host} = $numeric_addr\n";
                    }
            }

    unpack_addr() is a convenience wrapper around getnameinfo() from
    Socket::GetAddrInfo. You're certainly welcome to use the discrete
    function instead.

    unpack_addr() returns bleak emptiness on failure, regardless of context.
    You can check for undef return.

  PUBLIC EVENTS
   resolver_response
    The resolver response event includes three parameters.

    $_[ARG0] and $_[ARG1] contain the retrn values from
    Socket::GetAddrInfo's getaddrinfo() call. These are an error message (if
    the call failed), and an arrayref of address structures if the call
    succeeded.

    The component provides its own error message, 'component shut down'.
    This response is given for every pending request at the time the user
    shuts down the component.

    $_[ARG2] contains a hashref of information provided to the resolve()
    method. Specifically, the values of resolve()'s "host", "service" and
    "misc" parameters.

ENVIRONMENT VARIABLES
  POCO_RESOLVER_IPV
    The POCO_RESOLVER_IPV environment variable sets this component's default
    Internet Protocol Version search order. If the variable exists, it
    should contain a string with the numbers 4 and/or 6.
    POE::Component::Resolver will treate these as Internet Protocol versions
    to consider, in the order they are preferred.

    POE::Component::Resolver's new() method accepts an "af_order" parameter
    that overrides this environment variable.

    Default to IPv4 addresses only:

            export POCO_RESOLVER_IPV=4

    Default to IPv6 addresses only:

            export POCO_RESOLVER_IPV=6

    Prefer IPv6, but accept IPv4 if needed:

            export POCO_RESOLVER_IPV=64

    Prefer IPv4, but accept IPv6 if needed:

            export POCO_RESOLVER_IPV=46

COMPATIBILITY ISSUES
  Microsoft Windows
    This module requires "Microsoft TCP/IP version 6" to be installed. Steps
    for Windows XP Pro (the steps for your particular version of Windows may
    be subtly or drastically different):

    *   Open your Control Panel

    *   Open your Network Connections

    *   Select your network connection from the available one(s)

    *   In the Local Area Connection Status dialog, click the Properties
        button

    *   If "Microsoft TCP/IP version 6" is listed as an item being used, you
        are done.

    *   Otherwise click Install...

    *   Choose to add a Protocol

    *   And install "Microsoft TCP/IP version 6" from the list of network
        protocols.

BUGS
    There is no timeout on requests.

    There is no way to cancel a pending request.

TROUBLESHOOTING
  programs linger for several seconds before exiting
    Programs should shutdown() their POE::Component::Resolver objects when
    they are through needing asynchronous DNS resolution. Programs should
    additionally destroy their resolvers if they intend to run awhile and
    want to reuse the memory they consume.

    In some cases, it may be necessary to shutdown components that perform
    asynchronous DNS using POE::Component::Resolver... such as
    POE::Component::IRC, POE::Component::Client::Keepalive and
    POE::Component::Client::HTTP.

    By default, the resolver subprocesses hang around for idle_timeout,
    which defaults to 15.0 seconds. Destroying the Resolver object will
    clean up the process pool. Assuming only that is keeping the event loop
    active, the program will then exit cleanly.

    Alternatively, reduce idle_timeout to a more manageable number, such as
    5.0 seconds.

    Otherwise something else may also be keeping the event loop active.

LICENSE
    Except where otherwise noted, this distribution is Copyright 2011 by
    Rocco Caputo. All rights reserved. This distribution is free software;
    you may redistribute it and/or modify it under the same terms as Perl
    itself.

