NAME
    AnyEvent::Net::Curl::Queued - Any::Moose wrapper for queued downloads
    via Net::Curl & AnyEvent

VERSION
    version 0.024

SYNOPSIS
        #!/usr/bin/env perl

        package CrawlApache;
        use strict;
        use utf8;
        use warnings qw(all);

        use HTML::LinkExtor;
        use Any::Moose;

        extends 'AnyEvent::Net::Curl::Queued::Easy';

        after finish => sub {
            my ($self, $result) = @_;

            say $result . "\t" . $self->final_url;

            if (
                not $self->has_error
                and $self->getinfo('content_type') =~ m{^text/html}
            ) {
                my @links;

                HTML::LinkExtor->new(sub {
                    my ($tag, %links) = @_;
                    push @links,
                        grep { $_->scheme eq 'http' and $_->host eq 'localhost' }
                        values %links;
                }, $self->final_url)->parse(${$self->data});

                for my $link (@links) {
                    $self->queue->prepend(sub {
                        CrawlApache->new({ initial_url => $link });
                    });
                }
            }
        };

        no Any::Moose;
        __PACKAGE__->meta->make_immutable;

        1;

        package main;
        use strict;
        use utf8;
        use warnings qw(all);

        use AnyEvent::Net::Curl::Queued;

        my $q = AnyEvent::Net::Curl::Queued->new;
        $q->append(sub {
            CrawlApache->new({ initial_url => 'http://localhost/manual/' })
        });
        $q->wait;

DESCRIPTION
    Efficient and flexible batch downloader with a straight-forward
    interface:

    *   create a queue;

    *   append/prepend URLs;

    *   wait for downloads to end (retry on errors).

    Download init/finish/error handling is defined through Moose's method
    modifiers.

  MOTIVATION
    I am very unhappy with the performance of LWP. It's almost perfect for
    properly handling HTTP headers, cookies & stuff, but it comes at the
    cost of *speed*. While this doesn't matter when you make single
    downloads, batch downloading becomes a real pain.

    When I download large batch of documents, I don't care about cookies or
    headers, only content and proper redirection matters. And, as it is
    clearly an I/O bottleneck operation, I want to make as many parallel
    requests as possible.

    So, this is what CPAN offers to fulfill my needs:

    *   Net::Curl: Perl interface to the all-mighty libcurl
        <http://curl.haxx.se/libcurl/>, is well-documented (opposite to
        WWW::Curl);

    *   AnyEvent: the DBI of event loops. Net::Curl also provides a nice and
        well-documented example of AnyEvent usage (03-multi-event.pl);

    *   MooseX::NonMoose: Net::Curl uses a Pure-Perl object implementation,
        which is lightweight, but a bit messy for my Moose-based projects.
        MooseX::NonMoose patches this gap.

    AnyEvent::Net::Curl::Queued is a glue module to wrap it all together. It
    offers no callbacks and (almost) no default handlers. It's up to you to
    extend the base class AnyEvent::Net::Curl::Queued::Easy so it will
    actually download something and store it somewhere.

  ALTERNATIVES
    As there's more than one way to do it, I'll list the alternatives which
    can be used to implement batch downloads:

    *   WWW::Mechanize: no (builtin) parallelism, no (builtin) queueing.
        Slow, but very powerful for site traversal;

    *   LWP::UserAgent: no parallelism, no queueing. WWW::Mechanize is built
        on top of LWP, by the way;

    *   LWP::Curl: LWP::UserAgent-alike interface for WWW::Curl. No
        parallelism, no queueing. Fast and simple to use;

    *   HTTP::Tiny: no parallelism, no queueing. Fast and part of CORE since
        Perl v5.13.9;

    *   HTTP::Lite: no parallelism, no queueing. Also fast;

    *   AnyEvent::Curl::Multi: queued parallel downloads via WWW::Curl.
        Queues are non-lazy, thus large ones can use many RAM;

    *   Parallel::Downloader: queued parallel downloads via AnyEvent::HTTP.
        Very fast and is pure-Perl (compiling event driver is optional). You
        only access results when the whole batch is done; so huge batches
        will require lots of RAM to store contents.

ATTRIBUTES
  allow_dups
    Allow duplicate requests (default: false). By default, requests to the
    same URL (more precisely, requests with the same signature are issued
    only once. To seed POST parameters, you must extend the
    AnyEvent::Net::Curl::Queued::Easy class. Setting "allow_dups" to true
    value disables request checks.

  completed
    Count completed requests.

  cv
    AnyEvent condition variable. Initialized automatically, unless you
    specify your own. Also reset automatically after "wait", so keep your
    own reference if you really need it!

  max
    Maximum number of parallel connections (default: 4; minimum value: 1).

  multi
    Net::Curl::Multi instance.

  queue
    "ArrayRef" to the queue. Has the following helper methods:

    *   queue_push: append item at the end of the queue;

    *   queue_unshift: prepend item at the top of the queue;

    *   dequeue: shift item from the top of the queue;

    *   count: number of items in queue.

  share
    Net::Curl::Share instance.

  stats
    AnyEvent::Net::Curl::Queued::Stats instance.

  timeout
    Timeout (default: 60 seconds).

  unique
    Signature cache.

  watchdog
    The last resort against the non-deterministic chaos of evil lurking
    sockets.

METHODS
  start()
    Populate empty request slots with workers from the queue.

  empty()
    Check if there are active requests or requests in queue.

  add($worker)
    Activate a worker.

  append($worker)
    Put the worker (instance of AnyEvent::Net::Curl::Queued::Easy) at the
    end of the queue. For lazy initialization, wrap the worker in a "sub {
    ... }", the same way you do with the Moose "default => sub { ... }":

        $queue->append(sub {
            AnyEvent::Net::Curl::Queued::Easy->new({ initial_url => 'http://.../' })
        });

  prepend($worker)
    Put the worker (instance of AnyEvent::Net::Curl::Queued::Easy) at the
    beginning of the queue. For lazy initialization, wrap the worker in a
    "sub { ... }", the same way you do with the Moose "default => sub { ...
    }":

        $queue->prepend(sub {
            AnyEvent::Net::Curl::Queued::Easy->new({ initial_url => 'http://.../' })
        });

  wait()
    Process queue.

CAVEAT
    The *"Attempt to free unreferenced scalar: SV 0xdeadbeef during global
    destruction."* message on finalization is mostly harmless.

SEE ALSO
    *   AnyEvent

    *   Any::Moose

    *   Net::Curl

    *   WWW::Curl

    *   AnyEvent::Curl::Multi

AUTHOR
    Stanislaw Pusep <stas@sysd.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2012 by Stanislaw Pusep.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.