=head1 Network Programming with AnyEvent

This is a tutorial that will explain the usage of AnyEvent for
Network programming.

=head2 Introduction

AnyEvent is first of all just a framework for multiple event loops.  It's a
thin abstraction layer above all kinds of event loops. It's main purpose is to
move the choice of the event loop (whether it should be Glib, Qt, EV or Event,
or even something else, see also L<AnyEvent>) from the module author to the
program author.

The problem was usually that modules like L<Net::IRC> came with their own
event loop, where the program author needed to start the event loop
of L<Net::IRC>. That usually meant that he couldn't integrate it easily with
a L<Gtk2> GUI for instance.

Another example is L<LWP>, it provides no event interface at all. It's a pure
blocking HTTP client library, which usually means that you either have to
start a thread or have to fork for a HTTP request, or use L<Coro::LWP>.

L<AnyEvent> now does B<not> force authors of modules, like L<Net::IRC>, to:

=over 4

=item 1. Write their own event loop.

=item 2. Choose one fixed event loop.

=back

If the module author uses L<AnyEvent> for all his event needs (IO events, timers,
signals, ...) all other modules can just use his module and don't have to choose
an event loop or adapt to his event loop. The choice of the event loop is ultimately
made by the program author who uses all the modules and writes the main
program. And even there he doesn't have to choose, he can just ask L<AnyEvent>
to choose any available event loop for him.

Read more about this in the main documentation of the L<AnyEvent> module.

=head2 Network programming

However, AnyEvent is not just a simple abstraction anymore. It comes with
some very useful utility modules like L<AnyEvent::Handle>, L<AnyEvent::DNS>
and L<AnyEvent::Socket> that make your life as non-blocking network programmer
a lot easier.

Now an introduction into these three submodules:

=head3 L<AnyEvent::Handle>

This module handles non-blocking IO on filehandles in a event based
manner. It provides a wrapper object around your filehandle that provides
queueing and buffering of incoming and outgoing data for you.

More about this later.

=head3 L<AnyEvent::Socket>

This module provides you with functions that handle internet socket creation
and IP address magic. The two main functions are C<tcp_connect> and
C<tcp_server>. The former will connect a (streaming) socket to an internet host
for you and the later will make a server socket for you, to accept connections.

This module also comes with transparent IPv6 support, this means: If you
write your programs with this module, you will be IPv6 ready.

=head3 L<AnyEvent::DNS>

This module allows fully asynchronous DNS resolution, and is used for example
by L<AnyEvent::Socket> to resolve hostnames and service ports.