File Coverage

blib/lib/Danga/Socket/AnyEvent.pm

Criterion	Covered	Total	%
statement	135	409	33.0
branch	18	168	10.7
condition	5	56	8.9
subroutine	34	74	45.9
pod	0	39	0.0
total	192	746	25.7

###########################################################################

=head1 NAME

Danga::Socket::AnyEvent - Danga::Socket reimplemented in terms of AnyEvent

=head1 SYNOPSIS

  # This will clobber the Danga::Socket namespace
  # with the new implementation.
  use Danga::Socket::AnyEvent;

  # Then just use Danga::Socket as normal.

=head1 DESCRIPTION

This is an alternative implementation of L that is
implemented in terms of L, an abstraction layer for
event loops. This allows Danga::Socket applications to run
in any event loop supported by AnyEvent, and allows Danga::Socket
applications to make use of AnyEvent-based libraries.

Loading this module will install a workalike set of functions
into the Danga::Socket package. It must therefore be loaded before
anything loads the real L. If you try to load
this module after Danga::Socket has been loaded then it will
die.

=head1 DIFFERENCES FROM Danga::Socket

Although this module aims to be a faithful recreation of the
features and interface of Danga::Socket, there are some known
differences:

=over

=item * The C feature will only work if the caller
runs the event loop via CEventLoop>; if a caller
runs the AnyEvent event loop directly, or if some other library
runs it, then the timeout will not take effect.

=item * The C feature behaves in a slightly
different way than in the stock Danga::Socket. It's currently
implemented via an AnyEvent idlewatcher that runs whenever
the event loop goes idle after running a Danga::Socket event.
This means that it will probably run at different times than
it would have in Danga::Socket's own event loops.

=item * The C method will always return true, regardless
of what backend is actually implementing the event loop. Make
sure to use AnyEvent's L backend if you would like to use
Epoll/KQueue/etc rather than other, less efficient mechanisms.

=back

=cut

###########################################################################

package Danga::Socket::AnyEvent;

use vars qw{$VERSION};
$VERSION = "0.04";
use Carp;

BEGIN {
    # Detect if someone's already loaded Danga::Socket and bail out.
    if ($INC{"Danga/Socket.pm"}) {
        Carp::croak("Can't load Danga::Socket::AnyEvent: the real Danga::Socket was already loaded from ".$INC{"Danga/Socket.pm"});
    }
}

package # hidden from PAUSE
    Danga::Socket;

our $VERSION = "1.61";

use strict;
use bytes;
use POSIX ();
use Time::HiRes ();
use AnyEvent;

my $opt_bsd_resource = eval "use BSD::Resource; 1;";

use warnings;
no  warnings qw(deprecated);

use Sys::Syscall qw(:epoll);

use fields ('sock',              # underlying socket
            'fd',                # numeric file descriptor
            'write_buf',         # arrayref of scalars, scalarrefs, or coderefs to write
            'write_buf_offset',  # offset into first array of write_buf to start writing at
            'write_buf_size',    # total length of data in all write_buf items
            'write_set_watch',   # bool: true if we internally set watch_write rather than by a subclass
            'read_push_back',    # arrayref of "pushed-back" read data the application didn't want
            'closed',            # bool: socket is closed
            'corked',            # bool: socket is corked
            'event_watch',       # bitmask of events the client is interested in (POLLIN,OUT,etc.)
            'peer_v6',           # bool: cached; if peer is an IPv6 address
            'peer_ip',           # cached stringified IP address of $sock
            'peer_port',         # cached port number of $sock
            'local_ip',          # cached stringified IP address of local end of $sock
            'local_port',        # cached port number of local end of $sock
            'writer_func',       # subref which does writing.  must return bytes written (or undef) and set $! on errors
            );

use Errno  qw(EINPROGRESS EWOULDBLOCK EISCONN ENOTSOCK
              EPIPE EAGAIN EBADF ECONNRESET ENOPROTOOPT);
use Socket qw(IPPROTO_TCP);
use Carp   qw(croak confess);

use constant TCP_CORK => ($^O eq "linux" ? 3 : 0); # FIXME: not hard-coded (Linux-specific too)
use constant DebugLevel => 0;

use constant POLLIN        => 1;
use constant POLLOUT       => 4;
use constant POLLERR       => 8;
use constant POLLHUP       => 16;
use constant POLLNVAL      => 32;

our (
     %Timers,                    # timers
     %FdWatchers,                # fd (num) -> [ AnyEvent read watcher, AnyEvent write watcher ]
     %DescriptorMap,             # fd (num) -> Danga::Socket object that owns it
     %OtherFds,                  # fd (num) -> sub to run when that fd is ready to read or write
     %PushBackSet,               # fd (num) -> Danga::Socket (fds with pushed back read data)
     $PostLoopCallback,          # subref to call at the end of each loop, if defined (global)
     %PLCMap,                    # fd (num) -> PostLoopCallback (per-object)
     $IdleWatcher,               # an AnyEvent idle watcher that'll run PostEventLoop and then delete itself.
     $MainLoopCondVar,           # When EventLoop is running this contains the AnyEvent condvar that
                                 # will cause the main loop to exit if you call ->send() on it.
     @ToClose,                   # sockets to close when event loop is done
     $DoProfile,                 # if on, enable profiling
     %Profiling,                 # what => [ utime, stime, calls ]
     $DoneInit,                  # if we've done the one-time module init yet
     $LoopTimeout,               # timeout of event loop in milliseconds

     );

Reset();

=head1 METHODS

=cut

#####################################################################
### C L A S S   M E T H O D S
#####################################################################

=head2 C<< CLASS->Reset() >>

Reset all state

=cut
sub Reset {
    %Timers = ();
    %FdWatchers = ();
    %DescriptorMap = ();
    %OtherFds = ();
}

=head2 C<< CLASS->HaveEpoll() >>

Returns a true value if this class will use IO::Epoll for async IO.

=cut
sub HaveEpoll {
    return 1;
}

=head2 C<< CLASS->WatchedSockets() >>

Returns the number of file descriptors for which we have watchers installed.

=cut
sub WatchedSockets {
    return scalar(keys(%FdWatchers));
}
*watched_sockets = *WatchedSockets;

=head2 C<< CLASS->EnableProfiling() >>

Turns profiling on, clearing current profiling data.

=cut
sub EnableProfiling {
    if ($opt_bsd_resource) {
        %Profiling = ();
        $DoProfile = 1;
        return 1;
    }
    return 0;
}

=head2 C<< CLASS->DisableProfiling() >>

Turns off profiling, but retains data up to this point

=cut
sub DisableProfiling {
    $DoProfile = 0;
}

=head2 C<< CLASS->ProfilingData() >>

Returns reference to a hash of data in format:

  ITEM => [ utime, stime, #calls ]

=cut
sub ProfilingData {
    return \%Profiling;
}

=head2 C<< CLASS->ToClose() >>

Return the list of sockets that are awaiting close() at the end of the
current event loop.

=cut
sub ToClose { return @ToClose; }

=head2 C<< CLASS->OtherFds( [%fdmap] ) >>

Get/set the hash of file descriptors that need processing in parallel with
the registered Danga::Socket objects.

Callers must not modify the returned hash.

=cut
sub OtherFds {
    my $class = shift;
    if ( @_ ) {
        # Clean up any watchers that we no longer need.
        foreach my $fd (keys %OtherFds) {
            delete $FdWatchers{$fd};
        }
        %OtherFds = ();
        $class->AddOtherFds(@_);
    }
    return wantarray ? %OtherFds : \%OtherFds;
}

=head2 C<< CLASS->AddOtherFds( [%fdmap] ) >>

Add fds to the OtherFds hash for processing.

=cut
sub AddOtherFds {
    my ($class, %fdmap) = @_;

    foreach my $fd (keys %fdmap) {
        my $coderef = $fdmap{$fd};
        $OtherFds{$fd} = $coderef;

        # The OtherFds interface uses the same callback for both read and write events,
        # so create two AnyEvent watchers that differ only in their mode.
        $FdWatchers{$fd} = [ map {
            my $mode = $_;
            AnyEvent->io(
                fh => $fd,
                poll => $mode,
                cb => _wrap_watcher_cb($coderef),
            )
        } qw(r w) ];
    }
}

=head2 C<< CLASS->SetLoopTimeout( $timeout ) >>

Set the loop timeout for the event loop to some value in milliseconds.

A timeout of 0 (zero) means poll forever. A timeout of -1 means poll and return
immediately.

=cut
sub SetLoopTimeout {
    return $LoopTimeout = $_[1] + 0;
}

=head2 C<< CLASS->DebugMsg( $format, @args ) >>

Print the debugging message specified by the C-style I and
I

=cut
sub DebugMsg {
    my ( $class, $fmt, @args ) = @_;
    chomp $fmt;
    printf STDERR ">>> $fmt\n", @args;
}

=head2 C<< CLASS->AddTimer( $seconds, $coderef ) >>

Add a timer to occur $seconds from now. $seconds may be fractional, but timers
are not guaranteed to fire at the exact time you ask for.

Returns a timer object which you can call C<< $timer->cancel >> on if you need to.

=cut
sub AddTimer {
    my $class = shift;
    my ($secs, $coderef) = @_;

    my $timer = [ undef ];

    my $key = "$timer"; # Just stringify the timer array to get our hash key

    my $cancel = sub {
        delete $Timers{$key};
    };

    my $cb = sub {
        $coderef->();
        $cancel->();
    };

    $timer->[0] = $cancel;

    # We save the watcher in $Timers to keep it alive until it runs,
    # or until $cancel above overwrites it with undef to cause it to
    # get collected.
    $Timers{$key} = AnyEvent->timer(
        after => $secs,
        cb => _wrap_watcher_cb($cb),
    );

    return bless $timer, 'Danga::Socket::Timer';
}

=head2 C<< CLASS->DescriptorMap() >>

Get the hash of Danga::Socket objects keyed by the file descriptor (fileno) they
are wrapping.

Returns a hash in list context or a hashref in scalar context.

=cut
sub DescriptorMap {
    return wantarray ? %DescriptorMap : \%DescriptorMap;
}
*descriptor_map = *DescriptorMap;
*get_sock_ref = *DescriptorMap;

=head2 C<< CLASS->EventLoop() >>

Start processing IO events. In most daemon programs this never exits. See
C below for how to exit the loop.

=cut

sub EventLoop {
    my $class = shift;

    my $timeout_watcher;
    if ($LoopTimeout && $LoopTimeout != -1) {
        # Return after the given amount of milliseconds (which we must of, of course, convert to seconds)
        my $timeout = $LoopTimeout * 0.001;
        $timeout_watcher = AnyEvent->timer(
            cb => sub { PostEventLoop() },
            after => $timeout,
            interval => $timeout,
        );
    }

    $MainLoopCondVar = AnyEvent->condvar;
    $MainLoopCondVar->recv(); # Blocks until $MainLoopCondVar->send is called

    # Always run PostLoopCallback before we return, even if we timed out before we completed an event.
    PostEventLoop();

    $MainLoopCondVar = undef;
}

## profiling-related data/functions
our ($Prof_utime0, $Prof_stime0);
sub _pre_profile {
    ($Prof_utime0, $Prof_stime0) = getrusage();
}

sub _post_profile {
    # get post information
    my ($autime, $astime) = getrusage();

    # calculate differences
    my $utime = $autime - $Prof_utime0;
    my $stime = $astime - $Prof_stime0;

    foreach my $k (@_) {
        $Profiling{$k} ||= [ 0.0, 0.0, 0 ];
        $Profiling{$k}->[0] += $utime;
        $Profiling{$k}->[1] += $stime;
        $Profiling{$k}->[2]++;
    }
}

=head2 C<< CLASS->SetPostLoopCallback( CODEREF ) >>

Sets post loop callback function.  Pass a subref and it will be
called every time the event loop finishes.

Return 1 (or any true value) from the sub to make the loop continue, 0 or false
and it will exit.

The callback function will be passed two parameters: \%DescriptorMap, \%OtherFds.

=cut
sub SetPostLoopCallback {
    my ($class, $ref) = @_;

    if (ref $class) {
        # per-object callback
        my Danga::Socket $self = $class;
        if (defined $ref && ref $ref eq 'CODE') {
            $PLCMap{$self->{fd}} = $ref;
        } else {
            delete $PLCMap{$self->{fd}};
        }
    } else {
        # global callback
        $PostLoopCallback = (defined $ref && ref $ref eq 'CODE') ? $ref : undef;
    }
}

# Internal function: run the post-event callback, send read events
# for pushed-back data, and close pending connections.  returns 1
# if event loop should continue, or 0 to shut it all down.
sub PostEventLoop {
    # fire read events for objects with pushed-back read data
    my $loop = 1;
    while ($loop) {
        $loop = 0;
        foreach my $fd (keys %PushBackSet) {
            my Danga::Socket $pob = $PushBackSet{$fd};

            # a previous event_read invocation could've closed a
            # connection that we already evaluated in "keys
            # %PushBackSet", so skip ones that seem to have
            # disappeared.  this is expected.
            next unless $pob;

            die "ASSERT: the $pob socket has no read_push_back" unless @{$pob->{read_push_back}};
            next unless (! $pob->{closed} &&
                         $pob->{event_watch} & POLLIN);
            $loop = 1;
            $pob->event_read;
        }
    }

    # now we can close sockets that wanted to close during our event processing.
    # (we didn't want to close them during the loop, as we didn't want fd numbers
    #  being reused and confused during the event loop)
    while (my $sock = shift @ToClose) {
        my $fd = fileno($sock);

        # close the socket.  (not a Danga::Socket close)
        $sock->close;

        # and now we can finally remove the fd from the map.  see
        # comment above in _cleanup.
        delete $DescriptorMap{$fd};
    }


    # by default we keep running, unless a postloop callback (either per-object
    # or global) cancels it
    my $keep_running = 1;

    # per-object post-loop-callbacks
    for my $plc (values %PLCMap) {
        $keep_running &&= $plc->(\%DescriptorMap, \%OtherFds);
    }

    # now we're at the very end, call callback if defined
    if (defined $PostLoopCallback) {
        $keep_running &&= $PostLoopCallback->(\%DescriptorMap, \%OtherFds);
    }

    return $keep_running;
}

# Internal method to decorate a watcher callback with extra code to install
# the IdleWatcher necessary to run PostEventLoop.
sub _wrap_watcher_cb {
    my ($cb) = @_;

    return sub {
        my $ret = $cb->(@_);
        $IdleWatcher = AnyEvent->idle(
            cb => sub {
                my $keep_running = PostEventLoop();
                $IdleWatcher = undef; # Free this watcher
                $MainLoopCondVar->send unless $keep_running;
            },
        );
        return $ret;
    };
}

#####################################################################
### Danga::Socket-the-object code
#####################################################################

=head2 OBJECT METHODS

=head2 C<< CLASS->new( $socket ) >>

Create a new Danga::Socket subclass object for the given I which will
react to events on it during the C.

This is normally (always?) called from your subclass via:

  $class->SUPER::new($socket);

=cut
sub new {
    my Danga::Socket $self = shift;
    $self = fields::new($self) unless ref $self;

    my $sock = shift;

    $self->{sock}        = $sock;
    my $fd = fileno($sock);

    Carp::cluck("undef sock and/or fd in Danga::Socket->new.  sock=" . ($sock || "") . ", fd=" . ($fd || ""))
        unless $sock && $fd;

    $self->{fd}          = $fd;
    $self->{write_buf}      = [];
    $self->{write_buf_offset} = 0;
    $self->{write_buf_size} = 0;
    $self->{closed} = 0;
    $self->{corked} = 0;
    $self->{read_push_back} = [];

    $self->{event_watch} = POLLERR|POLLHUP|POLLNVAL;

    # Create the slots where the watchers will go if the caller
    # decides to watch_read or watch_write.
    $FdWatchers{$fd} = [ undef, undef ];

    Carp::cluck("Danga::Socket::new blowing away existing descriptor map for fd=$fd ($DescriptorMap{$fd})")
        if $DescriptorMap{$fd};

    $DescriptorMap{$fd} = $self;
    return $self;
}


#####################################################################
### I N S T A N C E   M E T H O D S
#####################################################################

=head2 C<< $obj->tcp_cork( $boolean ) >>

Turn TCP_CORK on or off depending on the value of I.

=cut
sub tcp_cork {
    my Danga::Socket $self = $_[0];
    my $val = $_[1];

    # make sure we have a socket
    return unless $self->{sock};
    return if $val == $self->{corked};

    my $rv;
    if (TCP_CORK) {
        $rv = setsockopt($self->{sock}, IPPROTO_TCP, TCP_CORK,
                         pack("l", $val ? 1 : 0));
    } else {
        # FIXME: implement freebsd *PUSH sockopts
        $rv = 1;
    }

    # if we failed, close (if we're not already) and warn about the error
    if ($rv) {
        $self->{corked} = $val;
    } else {
        if ($! == EBADF || $! == ENOTSOCK) {
            # internal state is probably corrupted; warn and then close if
            # we're not closed already
            warn "setsockopt: $!";
            $self->close('tcp_cork_failed');
        } elsif ($! == ENOPROTOOPT || $!{ENOTSOCK} || $!{EOPNOTSUPP}) {
            # TCP implementation doesn't support corking, so just ignore it
            # or we're trying to tcp-cork a non-socket (like a socketpair pipe
            # which is acting like a socket, which Perlbal does for child
            # processes acting like inetd-like web servers)
        } else {
            # some other error; we should never hit here, but if we do, die
            die "setsockopt: $!";
        }
    }
}

=head2 C<< $obj->steal_socket() >>

Basically returns our socket and makes it so that we don't try to close it,
but we do remove it from epoll handlers.  THIS CLOSES $self.  It is the same
thing as calling close, except it gives you the socket to use.

=cut
sub steal_socket {
    my Danga::Socket $self = $_[0];
    return if $self->{closed};

    # cleanup does most of the work of closing this socket
    $self->_cleanup();

    # now undef our internal sock and fd structures so we don't use them
    my $sock = $self->{sock};
    $self->{sock} = undef;
    return $sock;
}

=head2 C<< $obj->close( [$reason] ) >>

Close the socket. The I argument will be used in debugging messages.

=cut
sub close {
    my Danga::Socket $self = $_[0];
    return if $self->{closed};

    # print out debugging info for this close
    if (DebugLevel) {
        my ($pkg, $filename, $line) = caller;
        my $reason = $_[1] || "";
        warn "Closing \#$self->{fd} due to $pkg/$filename/$line ($reason)\n";
    }

    # this does most of the work of closing us
    $self->_cleanup();

    # defer closing the actual socket until the event loop is done
    # processing this round of events.  (otherwise we might reuse fds)
    if ($self->{sock}) {
        push @ToClose, $self->{sock};
        $self->{sock} = undef;
    }

    return 0;
}

### METHOD: _cleanup()
### Called by our closers so we can clean internal data structures.
sub _cleanup {
    my Danga::Socket $self = $_[0];

    # we're effectively closed; we have no fd and sock when we leave here
    $self->{closed} = 1;

    # we need to flush our write buffer, as there may
    # be self-referential closures (sub { $client->close })
    # preventing the object from being destroyed
    $self->{write_buf} = [];

    # uncork so any final data gets sent.  only matters if the person closing
    # us forgot to do it, but we do it to be safe.
    $self->tcp_cork(0);

    # now delete from mappings.  this fd no longer belongs to us, so we don't want
    # to get alerts for it if it becomes writable/readable/etc.
    delete $PushBackSet{$self->{fd}};
    delete $PLCMap{$self->{fd}};
    delete $FdWatchers{$self->{fd}};

    # we explicitly don't delete from DescriptorMap here until we
    # actually close the socket, as we might be in the middle of
    # processing an epoll_wait/etc that returned hundreds of fds, one
    # of which is not yet processed and is what we're closing.  if we
    # keep it in DescriptorMap, then the event harnesses can just
    # looked at $pob->{closed} and ignore it.  but if it's an
    # un-accounted for fd, then it (understandably) freak out a bit
    # and emit warnings, thinking their state got off.

    # and finally get rid of our fd so we can't use it anywhere else
    $self->{fd} = undef;
}

=head2 C<< $obj->sock() >>

Returns the underlying IO::Handle for the object.

=cut
sub sock {
    my Danga::Socket $self = shift;
    return $self->{sock};
}

=head2 C<< $obj->set_writer_func( CODEREF ) >>

Sets a function to use instead of C when writing data to the socket.

=cut
sub set_writer_func {
   my Danga::Socket $self = shift;
   my $wtr = shift;
   Carp::croak("Not a subref") unless !defined $wtr || UNIVERSAL::isa($wtr, "CODE");
   $self->{writer_func} = $wtr;
}

=head2 C<< $obj->write( $data ) >>

Write the specified data to the underlying handle.  I may be scalar,
scalar ref, code ref (to run when there), or undef just to kick-start.
Returns 1 if writes all went through, or 0 if there are writes in queue. If
it returns 1, caller should stop waiting for 'writable' events)

=cut
sub write {
    my Danga::Socket $self;
    my $data;
    ($self, $data) = @_;

    # nobody should be writing to closed sockets, but caller code can
    # do two writes within an event, have the first fail and
    # disconnect the other side (whose destructor then closes the
    # calling object, but it's still in a method), and then the
    # now-dead object does its second write.  that is this case.  we
    # just lie and say it worked.  it'll be dead soon and won't be
    # hurt by this lie.
    return 1 if $self->{closed};

    my $bref;

    # just queue data if there's already a wait
    my $need_queue;

    if (defined $data) {
        $bref = ref $data ? $data : \$data;
        if ($self->{write_buf_size}) {
            push @{$self->{write_buf}}, $bref;
            $self->{write_buf_size} += ref $bref eq "SCALAR" ? length($$bref) : 1;
            return 0;
        }

        # this flag says we're bypassing the queue system, knowing we're the
        # only outstanding write, and hoping we don't ever need to use it.
        # if so later, though, we'll need to queue
        $need_queue = 1;
    }

  WRITE:
    while (1) {
        return 1 unless $bref ||= $self->{write_buf}[0];

        my $len;
        eval {
            $len = length($$bref); # this will die if $bref is a code ref, caught below
        };
        if ($@) {
            if (UNIVERSAL::isa($bref, "CODE")) {
                unless ($need_queue) {
                    $self->{write_buf_size}--; # code refs are worth 1
                    shift @{$self->{write_buf}};
                }
                $bref->();

                # code refs are just run and never get reenqueued
                # (they're one-shot), so turn off the flag indicating the
                # outstanding data needs queueing.
                $need_queue = 0;

                undef $bref;
                next WRITE;
            }
            die "Write error: $@ <$bref>";
        }

        my $to_write = $len - $self->{write_buf_offset};
        my $written;
        if (my $wtr = $self->{writer_func}) {
            $written = $wtr->($bref, $to_write, $self->{write_buf_offset});
        } else {
            $written = syswrite($self->{sock}, $$bref, $to_write, $self->{write_buf_offset});
        }

        if (! defined $written) {
            if ($! == EPIPE) {
                return $self->close("EPIPE");
            } elsif ($! == EAGAIN) {
                # since connection has stuff to write, it should now be
                # interested in pending writes:
                if ($need_queue) {
                    push @{$self->{write_buf}}, $bref;
                    $self->{write_buf_size} += $len;
                }
                $self->{write_set_watch} = 1 unless $self->{event_watch} & POLLOUT;
                $self->watch_write(1);
                return 0;
            } elsif ($! == ECONNRESET) {
                return $self->close("ECONNRESET");
            }

            DebugLevel >= 1 && $self->debugmsg("Closing connection ($self) due to write error: $!\n");

            return $self->close("write_error");
        } elsif ($written != $to_write) {
            DebugLevel >= 2 && $self->debugmsg("Wrote PARTIAL %d bytes to %d",
                                               $written, $self->{fd});
            if ($need_queue) {
                push @{$self->{write_buf}}, $bref;
                $self->{write_buf_size} += $len;
            }
            # since connection has stuff to write, it should now be
            # interested in pending writes:
            $self->{write_buf_offset} += $written;
            $self->{write_buf_size} -= $written;
            $self->on_incomplete_write;
            return 0;
        } elsif ($written == $to_write) {
            DebugLevel >= 2 && $self->debugmsg("Wrote ALL %d bytes to %d (nq=%d)",
                                               $written, $self->{fd}, $need_queue);
            $self->{write_buf_offset} = 0;

            if ($self->{write_set_watch}) {
                $self->watch_write(0);
                $self->{write_set_watch} = 0;
            }

            # this was our only write, so we can return immediately
            # since we avoided incrementing the buffer size or
            # putting it in the buffer.  we also know there
            # can't be anything else to write.
            return 1 if $need_queue;

            $self->{write_buf_size} -= $written;
            shift @{$self->{write_buf}};
            undef $bref;
            next WRITE;
        }
    }
}

sub on_incomplete_write {
    my Danga::Socket $self = shift;
    $self->{write_set_watch} = 1 unless $self->{event_watch} & POLLOUT;
    $self->watch_write(1);
}

=head2 C<< $obj->push_back_read( $buf ) >>

Push back I (a scalar or scalarref) into the read stream. Useful if you read
more than you need to and want to return this data on the next "read".

=cut
sub push_back_read {
    my Danga::Socket $self = shift;
    my $buf = shift;
    push @{$self->{read_push_back}}, ref $buf ? $buf : \$buf;
    $self->{event_watch} |= POLLIN;
    $PushBackSet{$self->{fd}} = $self;
}

=head2 C<< $obj->read( $bytecount ) >>

Read at most I bytes from the underlying handle; returns scalar
ref on read, or undef on connection closed.

=cut
sub read {
    my Danga::Socket $self = shift;
    return if $self->{closed};
    my $bytes = shift;
    my $buf;
    my $sock = $self->{sock};

    if (@{$self->{read_push_back}}) {
        $buf = shift @{$self->{read_push_back}};
        my $len = length($$buf);

        if ($len <= $bytes) {
            delete $PushBackSet{$self->{fd}} unless @{$self->{read_push_back}};
            return $buf;
        } else {
            # if the pushed back read is too big, we have to split it
            my $overflow = substr($$buf, $bytes);
            $buf = substr($$buf, 0, $bytes);
            unshift @{$self->{read_push_back}}, \$overflow;
            return \$buf;
        }
    }

    # if this is too high, perl quits(!!).  reports on mailing lists
    # don't seem to point to a universal answer.  5MB worked for some,
    # crashed for others.  1MB works for more people.  let's go with 1MB
    # for now.  :/
    my $req_bytes = $bytes > 1048576 ? 1048576 : $bytes;

    my $res = sysread($sock, $buf, $req_bytes, 0);
    DebugLevel >= 2 && $self->debugmsg("sysread = %d; \$! = %d", $res, $!);

    if (! $res && $! != EWOULDBLOCK) {
        # catches 0=conn closed or undef=error
        DebugLevel >= 2 && $self->debugmsg("Fd \#%d read hit the end of the road.", $self->{fd});
        return undef;
    }

    return \$buf;
}

=head2 (VIRTUAL) C<< $obj->event_read() >>

Readable event handler. Concrete deriviatives of Danga::Socket should
provide an implementation of this. The default implementation will die if
called.

=cut
sub event_read  { die "Base class event_read called for $_[0]\n"; }

=head2 (VIRTUAL) C<< $obj->event_err() >>

Error event handler. Concrete deriviatives of Danga::Socket should
provide an implementation of this. The default implementation will die if
called.

=cut
sub event_err   { die "Base class event_err called for $_[0]\n"; }

=head2 (VIRTUAL) C<< $obj->event_hup() >>

'Hangup' event handler. Concrete deriviatives of Danga::Socket should
provide an implementation of this. The default implementation will die if
called.

=cut
sub event_hup   { die "Base class event_hup called for $_[0]\n"; }

=head2 C<< $obj->event_write() >>

Writable event handler. Concrete deriviatives of Danga::Socket may wish to
provide an implementation of this. The default implementation calls
C with an C.

=cut
sub event_write {
    my $self = shift;
    $self->write(undef);
}

=head2 C<< $obj->watch_read( $boolean ) >>

Turn 'readable' event notification on or off.

=cut
sub watch_read {
    my Danga::Socket $self = shift;
    return if $self->{closed} || !$self->{sock};

    my $val = shift;
    my $fd = fileno($self->{sock});
    my $watchers = $FdWatchers{$fd};
    if ($val) {
        $watchers->[0] = AnyEvent->io(
            fh => $fd,
            poll => 'r',
            cb => _wrap_watcher_cb(sub {
                $self->event_read() unless $self->{closed};
            }),
        );
        if ( $PushBackSet{$fd} ) {
            $self->{event_watch} |= POLLIN;
        }
    }
    else {
        $watchers->[0] = undef;
        if ( $PushBackSet{$fd} ) {
            $self->{event_watch} &= ~POLLIN;
        }
    }
}

=head2 C<< $obj->watch_write( $boolean ) >>

Turn 'writable' event notification on or off.

=cut
sub watch_write {
    my Danga::Socket $self = shift;
    return if $self->{closed} || !$self->{sock};

    my $val = shift;
    my $fd = fileno($self->{sock});

    if ($val && caller ne __PACKAGE__) {
        # A subclass registered interest, it's now responsible for this.
        $self->{write_set_watch} = 0;
    }

    my $watchers = $FdWatchers{$fd};
    if ($val) {
        $watchers->[1] = AnyEvent->io(
            fh => $fd,
            poll => 'w',
            cb => _wrap_watcher_cb(sub {
                $self->event_write() unless $self->{closed};
            }),
        );
    }
    else {
        $watchers->[1] = undef;
    }
}

=head2 C<< $obj->dump_error( $message ) >>

Prints to STDERR a backtrace with information about this socket and what lead
up to the dump_error call.

=cut
sub dump_error {
    my $i = 0;
    my @list;
    while (my ($file, $line, $sub) = (caller($i++))[1..3]) {
        push @list, "\t$file:$line called $sub\n";
    }

    warn "ERROR: $_[1]\n" .
        "\t$_[0] = " . $_[0]->as_string . "\n" .
        join('', @list);
}

=head2 C<< $obj->debugmsg( $format, @args ) >>

Print the debugging message specified by the C-style I and
I.

=cut
sub debugmsg {
    my ( $self, $fmt, @args ) = @_;
    confess "Not an object" unless ref $self;

    chomp $fmt;
    printf STDERR ">>> $fmt\n", @args;
}


=head2 C<< $obj->peer_ip_string() >>

Returns the string describing the peer's IP

=cut
sub peer_ip_string {
    my Danga::Socket $self = shift;
    return _undef("peer_ip_string undef: no sock") unless $self->{sock};
    return $self->{peer_ip} if defined $self->{peer_ip};

    my $pn = getpeername($self->{sock});
    return _undef("peer_ip_string undef: getpeername") unless $pn;

    my ($port, $iaddr) = eval {
        if (length($pn) >= 28) {
            return Socket6::unpack_sockaddr_in6($pn);
        } else {
            return Socket::sockaddr_in($pn);
        }
    };

    if ($@) {
        $self->{peer_port} = "[Unknown peerport '$@']";
        return "[Unknown peername '$@']";
    }

    $self->{peer_port} = $port;

    if (length($iaddr) == 4) {
        return $self->{peer_ip} = Socket::inet_ntoa($iaddr);
    } else {
        $self->{peer_v6} = 1;
        return $self->{peer_ip} = Socket6::inet_ntop(Socket6::AF_INET6(),
                                                     $iaddr);
    }
}

=head2 C<< $obj->peer_addr_string() >>

Returns the string describing the peer for the socket which underlies this
object in form "ip:port"

=cut
sub peer_addr_string {
    my Danga::Socket $self = shift;
    my $ip = $self->peer_ip_string
        or return undef;
    return $self->{peer_v6} ?
        "[$ip]:$self->{peer_port}" :
        "$ip:$self->{peer_port}";
}

=head2 C<< $obj->local_ip_string() >>

Returns the string describing the local IP

=cut
sub local_ip_string {
    my Danga::Socket $self = shift;
    return _undef("local_ip_string undef: no sock") unless $self->{sock};
    return $self->{local_ip} if defined $self->{local_ip};

    my $pn = getsockname($self->{sock});
    return _undef("local_ip_string undef: getsockname") unless $pn;

    my ($port, $iaddr) = Socket::sockaddr_in($pn);
    $self->{local_port} = $port;

    return $self->{local_ip} = Socket::inet_ntoa($iaddr);
}

=head2 C<< $obj->local_addr_string() >>

Returns the string describing the local end of the socket which underlies this
object in form "ip:port"

=cut
sub local_addr_string {
    my Danga::Socket $self = shift;
    my $ip = $self->local_ip_string;
    return $ip ? "$ip:$self->{local_port}" : undef;
}


=head2 C<< $obj->as_string() >>

Returns a string describing this socket.

=cut
sub as_string {
    my Danga::Socket $self = shift;
    my $rw = "(" . ($self->{event_watch} & POLLIN ? 'R' : '') .
                   ($self->{event_watch} & POLLOUT ? 'W' : '') . ")";
    my $ret = ref($self) . "$rw: " . ($self->{closed} ? "closed" : "open");
    my $peer = $self->peer_addr_string;
    if ($peer) {
        $ret .= " to " . $self->peer_addr_string;
    }
    return $ret;
}

sub _undef {
    return undef unless $ENV{DS_DEBUG};
    my $msg = shift || "";
    warn "Danga::Socket: $msg\n";
    return undef;
}

package # Hide from PAUSE
    Danga::Socket::Timer;
# [$cancel_coderef];
sub cancel {
    $_[0][0]->();
}

=head1 AUTHORS

Martin Atkins

Based on L by Brad Fitzpatrick  and others.

=head1 LICENSE

License is granted to use and distribute this module under the same
terms as Perl itself.

=cut

# Pretend that we loaded Danga::Socket so that
# later "use Danga::Socket" calls don't conflict.
$INC{"Danga/Socket.pm"} = __FILE__;

1;