NAME
    IO::Event - Tied Filehandles for Nonblocking IO with Object Callbacks

SYNOPSIS
     use IO::Event;
     use IO::Event 'emulate_Event';
     use IO::Event 'AnyEvent';

     my $ioe = IO::Event->new($filehandle);

     my $ioe = IO::Event::Socket::INET->new( [ARGS] )

     my $ioe = IO::Event::Socket::UNIX->new( [ARGS] )

     my $timer = IO::Event->timer(
            [after => $seconds],
            interval => $seconds,
            cb => CODE);

     my $idler = IO::Event->idle(
            [min => $seconds], 
            [max => $seconds],
            [reentrant => 0],
            cb => CODE);

     IO::Event::loop();

     IO::Event::unloop_all();

DESCRIPTION
    IO::Event provides a object-based callback system for handling
    nonblocking IO. The design goal is to provide a system that just does
    the right thing w/o the user needing to think about it much.

    All APIs are kept as simple as possible yet at the same time, all
    functionality is accesible if needed. Simple things are easy. Hard
    things are possible.

    Most of the time file handling syntax will work fine: "<$filehandle>"
    and "print $filehandle 'stuff'".

    IO::Event provides automatic buffering of output (with a callback to
    throttle). It provides automatic line-at-a-time input.

    After initial setup, call "IO::Event::loop()".

    IO::Event was originally written to use Event. IO::Event still defaults
    to using Event but it can now use AnyEvent or its own event loop.

CHOOSING AN EVENT HANDLER
    Until you create your first IO::Event object, you can choose which
    underlying event handler to use. The default is Event. To choose an
    event handler, use one of the following lines, import
    "no_emulate_Event", "emulate_Event", or "AnyEvent".

     use IO::Event 'no_emulate_Event'
     use IO::Event 'emulate_Event'
     use IO::Event 'AnyEvent'

    The "no_emulate_Event" option means: use Event. The "emulate_Event"
    option means IO::Event should use its own event loop.

    Why?

    You should use AnyEvent if you want to have compatibility with other
    event loops. You should use "emulate_Event" if you don't need
    compatibility with other event loops and you have missing-event bugs
    when using Event. You should use Event if it works for you.

    The APIs are a bit different depending on which event loop you're using.

  Event
    To use Event's event loop:

     use IO::Event 'no_emulate_Event';

    or just:

     use IO::Event

    IO::Event's definition for "loop()", "timer()", "idle()" and
    "unloop_all()" all default to the Event version unless "emulate_Event"
    or "AnyEvent" have been imported. This allows you to easily switch back
    and forth between Event's API and the others.

  AnyEvent
    To use AnyEvent's select loop, import "AnyEvent".

     use IO::Event 'AnyEvent';

    You can use AnyEvent's API directly or you can use IO::Event's emulated
    APIs: "IO::Event::loop()", "IO::Event::unloop()", "IO::Event::timer()",
    and "IO::Event::idle()". These behave like Event's routines of the same
    name but use AnyEvent underneath.

    During testing, using the pure-perl event loop of AnyEvent::Impl::Perl
    from AnyEvent version 5.271, some read events were dropped. To work
    around this, a synthetic read-ready event is dispatched for all
    connected read filehandles every two seconds. Turn this off or adjust
    its frequency by changing $IO::Event::AnyEvent::lost_event_hack. A
    numeric value is the time (in seconds) between dispatching read events.
    A false value turns off this performance-sapping hack.

    AnyEvent only provides basic support for idle() events: it promises to
    invoke them "every now and then".

  "emulate_Event"
    To use IO::Event's own select loop, import "emulate_Event".

     use IO::Event 'emulate_Event';

    IO::Event does not provide a complete emulation of everything that Event
    does. It provides the full timer API:

     my $timer = IO::Event::timer( [ARGS] )

    instead of

     my $timer = Event::timer( [ARGS] )

    However it does not provide timer events on filehandles, nor does it
    provide events for signals, or variable accesses.

    Use "IO::Event::loop()" instead of "Event::loop()". Use
    "IO::Event::unloop_all()" instead of "Event::unloop_all()". Use
    "IO::Event::idle()" instead of "Event::idle()". It does not provide any
    other methods or functions from Event. If you need them, please send a
    patch.

CONSTRUCTORS
    IO::Event->new($filehandle, [ $handler, [ $options ]])
        The basic "new" constructor takes a filehandle and returns a
        psuedo-filehandle. Treat the IO::Event object as a filehandle. Do
        not use the original filehandle without good reason (let us know if
        you find a good reason so we can fix the problem).

        The handler is the class or object where you provide callback
        functions to handle IO events. It defaults to the package of the
        calling context.

        If present, $options is a hash reference with the following possible
        keys:

        description  A text description of this filehandle. Used for
                     debugging and error messages.

        read_only    Set to true if this is a read-only filehandle. Do not
                     accept output.

        write_only   Set to true if this is a write-only filehandle. Do not
                     attept to read.

        autoread     Set to 0 if this should not be an auto-read filehandle.

    IO::Event::Socket::INET->new( [ARGS] )
        This constructor uses IO::Socket::INET->new() to create a socket
        using the ARGS provided. It returns an IO::Event object.

        The handler defaults as above or can be set with an additional
        pseudo-parameter for IO::Socket::UNIX->new(): "Handler". A
        description for the socket can be provided with an additional
        psuedo-parameter: "Description".

    IO::Event::Socket::UNIX->new( [ARGS] )
        This constructor uses IO::Socket::UNIX->new() to create a socket
        using the ARGS provided. It returns an IO::Event object.

        The handler defaults as above or can be set with an additional
        pseudo-parameter for IO::Socket::UNIX->new(): "Handler". A
        description for the socket can be provided with an additional
        psuedo-parameter: "Description".

MANDATORY HANDLERS
    These handler methods must be available in the handler object/class if
    the situation in which they would be called arises.

    ie_input($handler, $ioe, $input_buffer_reference)
        Invoked when there is fresh data in the input buffer. The input can
        be retreived via directly reading it from $$input_buffer_reference
        or via "read()" from the $ioe filehandle, or by using a variety of
        standard methods for getting data:

                <$ioe>                  like IO::Handle
                $ioe->get()             like Data::LineBuffer
                $ioe->read()            like IO::Handle
                $ioe->sysread()         like IO::Handle
                $ioe->getline()         like IO::Handle
                $ioe->getlines()        like IO::Handle
                $ioe->getsome()         see below
                $ioe->ungets()          like FileHandle::Unget

        At end-of-file, ie_input will only be invoked once. There may or may
        not be data in the input buffer.

    ie_connection($handler, $ioe)
        Invoked when a listen()ing socket is ready to accept(). It should
        call accept:

                sub ie_connection
                {
                        my ($pkg, $ioe) = @_;
                        my $newfh = $ioe->accept()
                }

    ie_read_ready($handler, $ioe, $underlying_file_handle)
        If autoreading is turned off then this will be invoked.

    ie_werror($handler, $ioe, $output_buffer_reference)
        A write error has occured when trying to drain the write buffer.
        Provide an empty subroutine if you don't care.

OPTIONAL HANDLERS
    These handler methods will be called if they are defined but it is not
    required that they be defined.

    ie_eof($handler, $ioe, $input_buffer_reference)
        This is invoked when the read-side of the filehandle has been closed
        by its source.

    ie_output
        This is invoked when data has just been written to the underlying
        filehandle.

    ie_outputdone
        This is invoked when all pending data has just been written to the
        underlying filehandle.

    ie_connected
        This is invoked when a "connect()" completes.

    ie_connect_failed($handler, $ioe, $error_code)
        This is invoked when a "connect()" fails. For a timeout, the error
        code will be ETIMEOUT.

    ie_died($handler, $ioe, $method, $@)
        If another handler calls "die" then ie_died will be called with the
        IO::Event object, the name of the method just invoked, and the die
        string. If no ie_died() callback exists then execution will
        terminate.

    ie_timer
        This is invoked for timer events.

    ie_exception
        Invoked when an exceptional condition arises on the underlying
        filehandle

    ie_outputoverflow($handler, $ioe, $overflowing,
    $output_buffer_reference)
        Invoked when there is too much output data and the output buffers
        are overflowing. You can take some action to generate less output.
        This will be invoked exactly once (with $overflowing == 1) when
        there is too much data in the buffer and then exactly once again
        (with $overflowing == 0) when there is no longer too much data in
        the buffer.

METHODS
    In addition to methods described in detail below, the following methods
    behave like their "IO" (mostly "IO::Socket") counterparts (except for
    being mostly non-blocking...):

            connect
            listen
            open
            read
            sysread
            syswrite
            print
            eof
            shutdown

    Through AUTOLOAD (see the SUBSTITUTED METHODS section) methods are
    passed to underlying "Event" objects:

            loop
            unloop
            and many more...

    Through AUTOLOAD (see the SUBSTITUTED METHODS section) methods are
    passed to underlying "IO" objects:

            fileno
            stat
            truncate
            error
            opened
            untaint
            and many more...

    IO::Event defines its own methods too:

    ->accept($handler, %options)
        accept() is nearly identical to the normal IO::Socket::accept()
        method except that instead of optionally passing a class specifier
        for the new socket, you optionally pass a handler object or class.
        The returned filehandle is an IO::Event object.

        Supported options:

        description
            Sets the description for the new socket

        autoread
            Set to 0 if you do not want auto-read

    ->can_read($amount)
        Returns true if $amount bytes worth of input is available for
        reading. Note: this does not return true at EOF so be careful not to
        hang forever at EOF.

    ->getsome($amount)
        Returns $amount bytes worth of input or undef if the request can't
        be filled. Returns what it can at EOF.

    ->get()
        get() is like getline() except that it pre-chomp()s the results and
        assumes the input_record_separator is "\n". This is like get() from
        Data::LineBuffer.

    ->unget()
        Push chomp()ed lines back into the input buffer. This is like
        unget() from Data::LineBuffer.

    ->ungetline(), ->xungetc(), ->ungets()
        This is what ungetc() should be: it pushes a string back into the
        input buffer. This is unlike IO::Handle->ungetc which takes an
        ordinal and pushes one character back into the the input buffer.
        This is like FileHandle::Unget.

    ->handler($new_handler)
        Sets the handler object/class if $new_handler is provided. Returns
        the old handler.

    ->filehandle()
        Returns the underlying "IO::Handle".

    ->event()
        Returns the underling "Event".

    ->listener($listening)
        Used to note that a filehandle is being used to listen for
        connections (instead of receiving data). A passed parameter of 0
        does the opposite. Returns the old value. This is mostly used
        internally in IO::Event.

    ->input_record_separator($new_sep)
        IO::Handle doesn't allow input_record_separator's on a per
        filehandle basis. IO::Event does. If you don't ever set a
        filehandle's input record separator, then it contineously defaults
        to the current value of $/. If you set it, then it will use your
        value and never look at $/ again.

    ->readevents($readevents)
        Get/set listening for read-ready events on the underlying
        filehandle. This could be used by ie_outputoverflow to control input
        flows.

    ->output_bufsize($output_bufsize)
        Get/set the size of the output buffer.

    ->autoread($autoread)
        Get/set automatic reading if data when data can be read. Without
        autoread turned on, the input buffer ins't filled and none of the
        read methods will work. The point of this is for working with
        non-data filehandles. This is an experts-only method that kinda
        defeats the purpose of this module. This would be necessary using
        recv() to get data.

    ->drain()
        Used to start looking for write-ready events on the underlying
        filehandle. In normal operation this is handled automatically.
        Deprecated: use writeevents(1) instead.

    ->reentrant($reentrant)
        Get/set reentrant callbacks. By default, IO::Event avoids making
        reentrant callbacks. This is good because your code is less likely
        to break. This is bad because you won't learn about things right
        away. For example, you will not learn the the output buffer is
        overflowing during print(). You'll have to wait for the output
        buffer to begin draining to find out. This could be a problem.

    ->close()
        If there is output buffered, close will be delayed until the output
        buffer drains.

    ->forceclose
        Close close immediately, even if there is output buffered.

    ->ie_desc([new description])
        Returns (and sets) the text description of the filehandle. For
        debugging.

TIMER API
    The following timer construction arguments are supported by IO::Event's
    emulated event loop and IO::Event's API on top of AnyEvent:

    cb  A callback to invoke when the timer goes off. The callback can
        either be a CODE reference or an array reference. If it's an array
        reference, the array should be a two element tuple: the first
        element is an object and the second object is a method to invoke on
        the object. The only argument to the method call a reference to the
        timer object:

         my ($object, $method) = @{$timer->{cb}}
         $object->$method($timer)

    at  A time at which to invoke the callback.

    interval
        An interval, in seconds between repeat invocations of the callback.

    after
        The interval until the first invocation of the callback. After that,
        invoke every *interval*.

    The following methods (from Event) are supported on timer objects:
    start(), again(), now(), stop(), cancel(), is_cancelled(), is_running(),
    is_suspended(), pending.

IDLE API
    The following idle construction arguments are supported by IO::Event's
    emulated event loop and IO::Event's API on top of AnyEvent:

    cb  A callback to invoke when the event loop is idle. The callback can
        either be a CODE reference or an array reference. If it's an array
        reference, the array should be a two element tuple: the first
        element is an object and the second object is a method to invoke on
        the object.

         my ($object, $method) = @{$timer->{cb}}
         $object->$method();

    min The minimum time between invocations of the callback.

    max The maximum time between invocations of the callback.

    The following methods (from Event) are supported on idle objects:
    start(), again(), now(), stop(), cancel(), is_cancelled(), is_running(),
    is_suspended(), pending.

SUBSTITUED METHODS
    Any method invocations that fail because the method isn't defined in
    IO::Event will by tried twice more: once using trying for a method on
    the inner (hidden) filehandle and once more trying for a method on the
    Event object that's used to create the select loop for this module.

    This dispatch is now deprecated with the choice of event handlers.

EXAMPLE SERVER
            # This is a tcp line echo server

            my $listener = IO::Event::Socket::INET->new(
                    Listen => 10,
                    Proto => 'tcp',
                    LocalPort => 2821,
            );

            Event::loop();

            sub ie_connection
            {
                    my ($pkg, $lstnr) = @_;
                    my $client = $lstnr->accept();
                    printf "accepted connection from %s:%s\n",
                            $client->peerhost, $client->peerport;
            }

            sub ie_input
            {
                    my ($pkg, $client, $ibufref) = @_;
                    print $client <$client>;
            }

SYSREAD and EOF
    sysread() is incompatable with eof() because eof() uses getc(). Most of
    the time this isn't a problem. In other words, some of the time this is
    a problem: lines go missing.

    For this reason, IO::Event never uses sysread(). In fact, if you ask it
    to do a sysread() it does a read() for you instead.

    On the other hand, at the current time no problems with syswrite have
    come to light and IO::Event uses syswrite and never any other form of
    write/print etc.

DESTRUCTION
    IO::Event keeps copies of all of its registered filehandles. If you want
    to close a filehandle, you'll need to actually call close on it.

DATA STRUCTURE
    The filehandle object itself is a funny kind of hash reference. If you
    want to use it to store your own data, you can. Please don't use hash
    keys that begin "ie_" or "io_" as those are the prefixes used by
    "IO::Event" and "IO::Socket".

    The syntax is kinda funny:

            ${*$filehandle}{'your_hash_key'}

SEE ALSO
    For a different API on top of IO::Event, see IO::Event::Callback. It
    uses IO::Event but provides a simpler and perhaps easier-to-use API.

    The following perl modules do something that is kinda similar to what is
    being done here:

    AnyEvent::Handle, AnyEvent::AIO, IO::AIO, IO::Multiplex,
    IO::NonBlocking, IO::Select Event, POE, POE::Component::Server::TCP,
    Net::Socket::NonBlock, Net::Server::Multiplex, NetServer::Generic

    The API borrows most heavily from IO::Multiplex. IO::Event uses Event.pm
    and thus can be used in programs that are already using Event or POE.

    Since the original writing of IO::Event, AnyEvent has been released and
    now AnyEvent::AIO and <AnyEvent:Handle> should be considered the only
    good alternatives to IO::Event.

    For an example program using IO::Event, see IO::Event::rinetd which used
    to be included in this package.

BUGS
    The test suite only covers 40% of the code. The module is used by its
    author and seems solid.

LICENSE
    Copyright (C) 2002-2009 David Muir Sharnoff <muir@idiom.org>. Copyright
    (C) 2011 Google, Inc. This module may be used/copied/etc on the same
    terms as Perl itself.

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

    Around line 476:
        '=item' outside of any '=over'

