Provided by: libpoe-component-resolver-perl_0.921-1_all 
NAME
POE::Component::Resolver - A non-blocking getaddrinfo() resolver
VERSION
version 0.921
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() 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 getaddrinfo()
returns them. These defaults can be overridden with constructor parameters. getaddrinfo() delegates to
the operating system's resolver, which may be reconfigured according to the usual conventions.
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 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 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. 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'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.
perl v5.26.1 2018-04-08 POE::Component::Resolver(3pm)