lib/AnyEvent/Handle.pm

package AnyEvent::Handle;

no warnings;
use strict;

use AnyEvent ();
use AnyEvent::Util ();
use Scalar::Util ();
use Carp ();
use Fcntl ();
use Errno qw/EAGAIN EINTR/;

=head1 NAME

AnyEvent::Handle - non-blocking I/O on filehandles via AnyEvent

=cut

our $VERSION = '0.02';

=head1 SYNOPSIS

   use AnyEvent;
   use AnyEvent::Handle;

   my $cv = AnyEvent->condvar;

   my $ae_fh = AnyEvent::Handle->new (fh => \*STDIN);

   #TODO

   # or use the constructor to pass the callback:

   my $ae_fh2 =
      AnyEvent::Handle->new (
         fh => \*STDIN,
         on_eof => sub {
            $cv->broadcast;
         },
         #TODO
      );

   $cv->wait;

=head1 DESCRIPTION

This module is a helper module to make it easier to do event-based I/O on
filehandles (and sockets, see L<AnyEvent::Socket> for an easy way to make
non-blocking resolves and connects).

In the following, when the documentation refers to of "bytes" then this
means characters. As sysread and syswrite are used for all I/O, their
treatment of characters applies to this module as well.

All callbacks will be invoked with the handle object as their first
argument.

=head1 METHODS

=over 4

=item B<new (%args)>

The constructor supports these arguments (all as key => value pairs).

=over 4

=item fh => $filehandle [MANDATORY]

The filehandle this L<AnyEvent::Handle> object will operate on.

NOTE: The filehandle will be set to non-blocking (using
AnyEvent::Util::fh_nonblocking).

=item on_error => $cb->($self) [MANDATORY]

This is the fatal error callback, that is called when a fatal error ocurs,
such as not being able to resolve the hostname, failure to connect or a
read error.

The object will not be in a usable state when this callback has been
called.

On callback entrance, the value of C<$!> contains the opertaing system
error (or C<ENOSPC> or C<EPIPE>).

=item on_eof => $cb->($self) [MANDATORY]

Set the callback to be called on EOF.

=item on_read => $cb->($self)

This sets the default read callback, which is called when data arrives
and no read request is in the queue.  If the read callback is C<undef>
or has never been set, than AnyEvent::Handle will cease reading from the
filehandle.

To access (and remove data from) the read buffer, use the C<< ->rbuf >>
method or acces sthe C<$self->{rbuf}> member directly.

When an EOF condition is detected then AnyEvent::Handle will first try to
feed all the remaining data to the queued callbacks and C<on_read> before
calling the C<on_eof> callback. If no progress can be made, then a fatal
error will be raised (with C<$!> set to C<EPIPE>).

=item on_drain => $cb->()

This sets the callback that is called when the write buffer becomes empty
(or when the callback is set and the buffer is empty already).

To append to the write buffer, use the C<< ->push_write >> method.

=item rbuf_max => <bytes>

If defined, then a fatal error will be raised (with C<$!> set to C<ENOSPC>)
when the read buffer ever (strictly) exceeds this size. This is useful to
avoid denial-of-service attacks.

For example, a server accepting connections from untrusted sources should
be configured to accept only so-and-so much data that it cannot act on
(for example, when expecting a line, an attacker could send an unlimited
amount of data without a callback ever being called as long as the line
isn't finished).

=item read_size => <bytes>

The default read block size (the amount of bytes this module will try to read
on each [loop iteration). Default: C<4096>.

=item low_water_mark => <bytes>

Sets the amount of bytes (default: C<0>) that make up an "empty" write
buffer: If the write reaches this size or gets even samller it is
considered empty.

=back

=cut

sub new {
   my $class = shift;

   my $self = bless { @_ }, $class;

   $self->{fh} or Carp::croak "mandatory argument fh is missing";

   AnyEvent::Util::fh_nonblocking $self->{fh}, 1;

   $self->on_error ((delete $self->{on_error}) or Carp::croak "mandatory argument on_error is missing");
   $self->on_eof   ((delete $self->{on_eof}  ) or Carp::croak "mandatory argument on_eof is missing");

   $self->on_drain (delete $self->{on_drain}) if $self->{on_drain};
   $self->on_read  (delete $self->{on_read} ) if $self->{on_read};

   $self
}

sub _shutdown {
   my ($self) = @_;

   delete $self->{rw};
   delete $self->{ww};
   delete $self->{fh};
}

sub error {
   my ($self) = @_;

   {
      local $!;
      $self->_shutdown;
   }

   $self->{on_error}($self);
}

=item $fh = $handle->fh

This method returns the filehandle of the L<AnyEvent::Handle> object.

=cut

sub fh { $_[0]->{fh} }

=item $handle->on_error ($cb)

Replace the current C<on_error> callback (see the C<on_error> constructor argument).

=cut

sub on_error {
   $_[0]{on_error} = $_[1];
}

=item $handle->on_eof ($cb)

Replace the current C<on_eof> callback (see the C<on_eof> constructor argument).

=cut

sub on_eof {
   $_[0]{on_eof} = $_[1];
}

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

=back

=head2 WRITE QUEUE

AnyEvent::Handle manages two queues per handle, one for writing and one
for reading.

The write queue is very simple: you can add data to its end, and
AnyEvent::Handle will automatically try to get rid of it for you.

When data could be writtena nd the write buffer is shorter then the low
water mark, the C<on_drain> callback will be invoked.

=over 4

=item $handle->on_drain ($cb)

Sets the C<on_drain> callback or clears it (see the description of
C<on_drain> in the constructor).

=cut

sub on_drain {
   my ($self, $cb) = @_;

   $self->{on_drain} = $cb;

   $cb->($self)
      if $cb && $self->{low_water_mark} >= length $self->{wbuf};
}

=item $handle->push_write ($data)

Queues the given scalar to be written. You can push as much data as you
want (only limited by the available memory), as C<AnyEvent::Handle>
buffers it independently of the kernel.

=cut

sub push_write {
   my ($self, $data) = @_;

   $self->{wbuf} .= $data;

   unless ($self->{ww}) {
      Scalar::Util::weaken $self;
      my $cb = sub {
         my $len = syswrite $self->{fh}, $self->{wbuf};

         if ($len > 0) {
            substr $self->{wbuf}, 0, $len, "";


            $self->{on_drain}($self)
               if $self->{low_water_mark} >= length $self->{wbuf}
                  && $self->{on_drain};

            delete $self->{ww} unless length $self->{wbuf};
         } elsif ($! != EAGAIN && $! != EINTR) {
            $self->error;
         }
      };

      $self->{ww} = AnyEvent->io (fh => $self->{fh}, poll => "w", cb => $cb);

      $cb->($self);
   };
}

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

=back

=head2 READ QUEUE

AnyEvent::Handle manages two queues per handle, one for writing and one
for reading.

The read queue is more complex than the write queue. It can be used in two
ways, the "simple" way, using only C<on_read> and the "complex" way, using
a queue.

In the simple case, you just install an C<on_read> callback and whenever
new data arrives, it will be called. You can then remove some data (if
enough is there) from the read buffer (C<< $handle->rbuf >>) if you want
or not.

In the more complex case, you want to queue multiple callbacks. In this
case, AnyEvent::Handle will call the first queued callback each time new
data arrives and removes it when it has done its job (see C<push_read>,
below).

This way you can, for example, push three line-reads, followed by reading
a chunk of data, and AnyEvent::Handle will execute them in order.

Example 1: EPP protocol parser. EPP sends 4 byte length info, followed by
the specified number of bytes which give an XML datagram.

   # in the default state, expect some header bytes
   $handle->on_read (sub {
      # some data is here, now queue the length-header-read (4 octets)
      shift->unshift_read_chunk (4, sub {
         # header arrived, decode
         my $len = unpack "N", $_[1];

         # now read the payload
         shift->unshift_read_chunk ($len, sub {
            my $xml = $_[1];
            # handle xml
         });
      });
   });

Example 2: Implement a client for a protocol that replies either with
"OK" and another line or "ERROR" for one request, and 64 bytes for the
second request. Due tot he availability of a full queue, we can just
pipeline sending both requests and manipulate the queue as necessary in
the callbacks:

   # request one
   $handle->push_write ("request 1\015\012");

   # we expect "ERROR" or "OK" as response, so push a line read
   $handle->push_read_line (sub {
      # if we got an "OK", we have to _prepend_ another line,
      # so it will be read before the second request reads its 64 bytes
      # which are already in the queue when this callback is called
      # we don't do this in case we got an error
      if ($_[1] eq "OK") {
         $_[0]->unshift_read_line (sub {
            my $response = $_[1];
            ...
         });
      }
   });

   # request two
   $handle->push_write ("request 2\015\012");

   # simply read 64 bytes, always
   $handle->push_read_chunk (64, sub {
      my $response = $_[1];
      ...
   });

=over 4

sub _drain_rbuf {
   my ($self) = @_;

   return if exists $self->{in_drain};
   local $self->{in_drain} = 1;

   while (my $len = length $self->{rbuf}) {
      no strict 'refs';
      if (@{ $self->{queue} }) {
         if ($self->{queue}[0]($self)) {
            shift @{ $self->{queue} };
         } elsif ($self->{eof}) {
            # no progress can be made (not enough data and no data forthcoming)
            $! = &Errno::EPIPE; return $self->error;
         } else {
            return;
         }
      } elsif ($self->{on_read}) {
         $self->{on_read}($self);

         if (
            $self->{eof}                    # if no further data will arrive
            && $len == length $self->{rbuf} # and no data has been consumed
            && !@{ $self->{queue} }         # and the queue is still empty
            && $self->{on_read}             # and we still want to read data
         ) {
            # then no progress can be made
            $! = &Errno::EPIPE; return $self->error;
         }
      } else {
         # read side becomes idle
         delete $self->{rw};
         return;
      }
   }

   if ($self->{eof}) {
      $self->_shutdown;
      $self->{on_eof}($self);
   }
}

=item $handle->on_read ($cb)

This replaces the currently set C<on_read> callback, or clears it (when
the new callback is C<undef>). See the description of C<on_read> in the
constructor.

=cut

sub on_read {
   my ($self, $cb) = @_;

   $self->{on_read} = $cb;

   unless ($self->{rw} || $self->{eof}) {
      Scalar::Util::weaken $self;

      $self->{rw} = AnyEvent->io (fh => $self->{fh}, poll => "r", cb => sub {
         my $len = sysread $self->{fh}, $self->{rbuf}, $self->{read_size} || 8192, length $self->{rbuf};

         if ($len > 0) {
            if (exists $self->{rbuf_max}) {
               if ($self->{rbuf_max} < length $self->{rbuf}) {
                  $! = &Errno::ENOSPC; return $self->error;
               }
            }

         } elsif (defined $len) {
            $self->{eof} = 1;
            delete $self->{rw};

         } elsif ($! != EAGAIN && $! != EINTR) {
            return $self->error;
         }

         $self->_drain_rbuf;
      });
   }
}

=item $handle->rbuf

Returns the read buffer (as a modifiable lvalue).

You can access the read buffer directly as the C<< ->{rbuf} >> member, if
you want.

NOTE: The read buffer should only be used or modified if the C<on_read>,
C<push_read> or C<unshift_read> methods are used. The other read methods
automatically manage the read buffer.

=cut

sub rbuf : lvalue {
   $_[0]{rbuf}
}

=item $handle->push_read ($cb)

=item $handle->unshift_read ($cb)

Append the given callback to the end of the queue (C<push_read>) or
prepend it (C<unshift_read>).

The callback is called each time some additional read data arrives.

It must check wether enough data is in the read buffer already.

If not enough data is available, it must return the empty list or a false
value, in which case it will be called repeatedly until enough data is
available (or an error condition is detected).

If enough data was available, then the callback must remove all data it is
interested in (which can be none at all) and return a true value. After returning
true, it will be removed from the queue.

=cut

sub push_read {
   my ($self, $cb) = @_;

   push @{ $self->{queue} }, $cb;
   $self->_drain_rbuf;
}

sub unshift_read {
   my ($self, $cb) = @_;

   push @{ $self->{queue} }, $cb;
   $self->_drain_rbuf;
}

=item $handle->push_read_chunk ($len, $cb->($self, $data))

=item $handle->unshift_read_chunk ($len, $cb->($self, $data))

Append the given callback to the end of the queue (C<push_read_chunk>) or
prepend it (C<unshift_read_chunk>).

The callback will be called only once C<$len> bytes have been read, and
these C<$len> bytes will be passed to the callback.

=cut

sub _read_chunk($$) {
   my ($len, $cb) = @_;

   sub {
      $len <= length $_[0]{rbuf} or return;
      $cb->($_[0], substr $_[0]{rbuf}, 0, $len, "");
      1
   }
}

sub push_read_chunk {
   my ($self, $len, $cb) = @_;

   $self->push_read (_read_chunk $len, $cb);
}


sub unshift_read_chunk {
   my ($self, $len, $cb) = @_;

   $self->unshift_read (_read_chunk $len, $cb);
}

=item $handle->push_read_line ([$eol, ]$cb->($self, $line, $eol))

=item $handle->unshift_read_line ([$eol, ]$cb->($self, $line, $eol))

Append the given callback to the end of the queue (C<push_read_line>) or
prepend it (C<unshift_read_line>).

The callback will be called only once a full line (including the end of
line marker, C<$eol>) has been read. This line (excluding the end of line
marker) will be passed to the callback as second argument (C<$line>), and
the end of line marker as the third argument (C<$eol>).

The end of line marker, C<$eol>, can be either a string, in which case it
will be interpreted as a fixed record end marker, or it can be a regex
object (e.g. created by C<qr>), in which case it is interpreted as a
regular expression.

The end of line marker argument C<$eol> is optional, if it is missing (NOT
undef), then C<qr|\015?\012|> is used (which is good for most internet
protocols).

Partial lines at the end of the stream will never be returned, as they are
not marked by the end of line marker.

=cut

sub _read_line($$) {
   my $cb = pop;
   my $eol = @_ ? shift : qr|(\015?\012)|;
   my $pos;

   $eol = qr|(\Q$eol\E)| unless ref $eol;
   $eol = qr|^(.*?)($eol)|;

   sub {
      $_[0]{rbuf} =~ s/$eol// or return;

      $cb->($1, $2);
      1
   }
}

sub push_read_line {
   my $self = shift;

   $self->push_read (&_read_line);
}

sub unshift_read_line {
   my $self = shift;

   $self->unshift_read (&_read_line);
}

=back

=head1 AUTHOR

Robin Redeker C<< <elmex at ta-sa.org> >>, Marc Lehmann <schmorp@schmorp.de>.

=cut

1; # End of AnyEvent::Handle
Revision:	1.9
Committed:	Fri May 2 16:07:46 2008 UTC (16 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.8:	+93 -2 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	elmex	1.1	package AnyEvent::Handle;
2
3	elmex	1.6	no warnings;
4	elmex	1.1	use strict;
5
6	root	1.8	use AnyEvent ();
7			use AnyEvent::Util ();
8			use Scalar::Util ();
9			use Carp ();
10			use Fcntl ();
11	elmex	1.1	use Errno qw/EAGAIN EINTR/;
12
13			=head1 NAME
14
15			AnyEvent::Handle - non-blocking I/O on filehandles via AnyEvent
16
17			=cut
18
19	root	1.8	our $VERSION = '0.02';
20	elmex	1.1
21			=head1 SYNOPSIS
22
23			use AnyEvent;
24			use AnyEvent::Handle;
25
26			my $cv = AnyEvent->condvar;
27
28			my $ae_fh = AnyEvent::Handle->new (fh => \*STDIN);
29
30	root	1.8	#TODO
31	elmex	1.1
32	elmex	1.2	# or use the constructor to pass the callback:
33
34			my $ae_fh2 =
35			AnyEvent::Handle->new (
36			fh => \*STDIN,
37			on_eof => sub {
38			$cv->broadcast;
39			},
40	root	1.8	#TODO
41	elmex	1.2	);
42
43	elmex	1.1	$cv->wait;
44
45			=head1 DESCRIPTION
46
47	root	1.8	This module is a helper module to make it easier to do event-based I/O on
48			filehandles (and sockets, see L<AnyEvent::Socket> for an easy way to make
49			non-blocking resolves and connects).
50
51			In the following, when the documentation refers to of "bytes" then this
52			means characters. As sysread and syswrite are used for all I/O, their
53			treatment of characters applies to this module as well.
54	elmex	1.1
55	root	1.8	All callbacks will be invoked with the handle object as their first
56			argument.
57	elmex	1.1
58			=head1 METHODS
59
60			=over 4
61
62			=item B<new (%args)>
63
64	root	1.8	The constructor supports these arguments (all as key => value pairs).
65	elmex	1.1
66			=over 4
67
68	root	1.8	=item fh => $filehandle [MANDATORY]
69	elmex	1.1
70			The filehandle this L<AnyEvent::Handle> object will operate on.
71
72	root	1.8	NOTE: The filehandle will be set to non-blocking (using
73			AnyEvent::Util::fh_nonblocking).
74
75			=item on_error => $cb->($self) [MANDATORY]
76
77			This is the fatal error callback, that is called when a fatal error ocurs,
78			such as not being able to resolve the hostname, failure to connect or a
79			read error.
80
81			The object will not be in a usable state when this callback has been
82			called.
83
84			On callback entrance, the value of C<$!> contains the opertaing system
85			error (or C<ENOSPC> or C<EPIPE>).
86
87			=item on_eof => $cb->($self) [MANDATORY]
88
89			Set the callback to be called on EOF.
90
91			=item on_read => $cb->($self)
92
93			This sets the default read callback, which is called when data arrives
94			and no read request is in the queue. If the read callback is C<undef>
95			or has never been set, than AnyEvent::Handle will cease reading from the
96			filehandle.
97
98			To access (and remove data from) the read buffer, use the C<< ->rbuf >>
99			method or acces sthe C<$self->{rbuf}> member directly.
100
101			When an EOF condition is detected then AnyEvent::Handle will first try to
102			feed all the remaining data to the queued callbacks and C<on_read> before
103			calling the C<on_eof> callback. If no progress can be made, then a fatal
104			error will be raised (with C<$!> set to C<EPIPE>).
105	elmex	1.1
106	root	1.8	=item on_drain => $cb->()
107	elmex	1.1
108	root	1.8	This sets the callback that is called when the write buffer becomes empty
109			(or when the callback is set and the buffer is empty already).
110	elmex	1.1
111	root	1.8	To append to the write buffer, use the C<< ->push_write >> method.
112	elmex	1.2
113	root	1.8	=item rbuf_max => <bytes>
114	elmex	1.2
115	root	1.8	If defined, then a fatal error will be raised (with C<$!> set to C<ENOSPC>)
116			when the read buffer ever (strictly) exceeds this size. This is useful to
117			avoid denial-of-service attacks.
118	elmex	1.2
119	root	1.8	For example, a server accepting connections from untrusted sources should
120			be configured to accept only so-and-so much data that it cannot act on
121			(for example, when expecting a line, an attacker could send an unlimited
122			amount of data without a callback ever being called as long as the line
123			isn't finished).
124	elmex	1.2
125	root	1.8	=item read_size => <bytes>
126	elmex	1.2
127	root	1.8	The default read block size (the amount of bytes this module will try to read
128			on each [loop iteration). Default: C<4096>.
129
130			=item low_water_mark => <bytes>
131
132			Sets the amount of bytes (default: C<0>) that make up an "empty" write
133			buffer: If the write reaches this size or gets even samller it is
134			considered empty.
135	elmex	1.2
136	elmex	1.1	=back
137
138			=cut
139
140			sub new {
141	root	1.8	my $class = shift;
142
143			my $self = bless { @_ }, $class;
144
145			$self->{fh} or Carp::croak "mandatory argument fh is missing";
146
147			AnyEvent::Util::fh_nonblocking $self->{fh}, 1;
148	elmex	1.1
149	root	1.8	$self->on_error ((delete $self->{on_error}) or Carp::croak "mandatory argument on_error is missing");
150			$self->on_eof ((delete $self->{on_eof} ) or Carp::croak "mandatory argument on_eof is missing");
151	elmex	1.1
152	root	1.8	$self->on_drain (delete $self->{on_drain}) if $self->{on_drain};
153			$self->on_read (delete $self->{on_read} ) if $self->{on_read};
154	elmex	1.1
155	root	1.8	$self
156			}
157	elmex	1.2
158	root	1.8	sub _shutdown {
159			my ($self) = @_;
160	elmex	1.2
161	root	1.8	delete $self->{rw};
162			delete $self->{ww};
163			delete $self->{fh};
164			}
165
166			sub error {
167			my ($self) = @_;
168
169			{
170			local $!;
171			$self->_shutdown;
172	elmex	1.1	}
173
174	root	1.8	$self->{on_error}($self);
175	elmex	1.1	}
176
177	root	1.8	=item $fh = $handle->fh
178	elmex	1.1
179			This method returns the filehandle of the L<AnyEvent::Handle> object.
180
181			=cut
182
183			sub fh { $_[0]->{fh} }
184
185	root	1.8	=item $handle->on_error ($cb)
186	elmex	1.1
187	root	1.8	Replace the current C<on_error> callback (see the C<on_error> constructor argument).
188	elmex	1.1
189	root	1.8	=cut
190
191			sub on_error {
192			$_[0]{on_error} = $_[1];
193			}
194
195			=item $handle->on_eof ($cb)
196
197			Replace the current C<on_eof> callback (see the C<on_eof> constructor argument).
198	elmex	1.1
199			=cut
200
201	root	1.8	sub on_eof {
202			$_[0]{on_eof} = $_[1];
203			}
204
205	root	1.9	#############################################################################
206
207			=back
208
209			=head2 WRITE QUEUE
210
211			AnyEvent::Handle manages two queues per handle, one for writing and one
212			for reading.
213
214			The write queue is very simple: you can add data to its end, and
215			AnyEvent::Handle will automatically try to get rid of it for you.
216
217			When data could be writtena nd the write buffer is shorter then the low
218			water mark, the C<on_drain> callback will be invoked.
219
220			=over 4
221
222	root	1.8	=item $handle->on_drain ($cb)
223
224			Sets the C<on_drain> callback or clears it (see the description of
225			C<on_drain> in the constructor).
226
227			=cut
228
229			sub on_drain {
230	elmex	1.1	my ($self, $cb) = @_;
231
232	root	1.8	$self->{on_drain} = $cb;
233
234			$cb->($self)
235			if $cb && $self->{low_water_mark} >= length $self->{wbuf};
236			}
237
238			=item $handle->push_write ($data)
239
240			Queues the given scalar to be written. You can push as much data as you
241			want (only limited by the available memory), as C<AnyEvent::Handle>
242			buffers it independently of the kernel.
243
244			=cut
245
246			sub push_write {
247			my ($self, $data) = @_;
248
249			$self->{wbuf} .= $data;
250
251			unless ($self->{ww}) {
252			Scalar::Util::weaken $self;
253			my $cb = sub {
254			my $len = syswrite $self->{fh}, $self->{wbuf};
255
256			if ($len > 0) {
257			substr $self->{wbuf}, 0, $len, "";
258
259
260			$self->{on_drain}($self)
261			if $self->{low_water_mark} >= length $self->{wbuf}
262			&& $self->{on_drain};
263
264			delete $self->{ww} unless length $self->{wbuf};
265			} elsif ($! != EAGAIN && $! != EINTR) {
266			$self->error;
267	elmex	1.1	}
268	root	1.8	};
269
270			$self->{ww} = AnyEvent->io (fh => $self->{fh}, poll => "w", cb => $cb);
271
272			$cb->($self);
273			};
274			}
275
276			#############################################################################
277
278	root	1.9	=back
279
280			=head2 READ QUEUE
281
282			AnyEvent::Handle manages two queues per handle, one for writing and one
283			for reading.
284
285			The read queue is more complex than the write queue. It can be used in two
286			ways, the "simple" way, using only C<on_read> and the "complex" way, using
287			a queue.
288
289			In the simple case, you just install an C<on_read> callback and whenever
290			new data arrives, it will be called. You can then remove some data (if
291			enough is there) from the read buffer (C<< $handle->rbuf >>) if you want
292			or not.
293
294			In the more complex case, you want to queue multiple callbacks. In this
295			case, AnyEvent::Handle will call the first queued callback each time new
296			data arrives and removes it when it has done its job (see C<push_read>,
297			below).
298
299			This way you can, for example, push three line-reads, followed by reading
300			a chunk of data, and AnyEvent::Handle will execute them in order.
301
302			Example 1: EPP protocol parser. EPP sends 4 byte length info, followed by
303			the specified number of bytes which give an XML datagram.
304
305			# in the default state, expect some header bytes
306			$handle->on_read (sub {
307			# some data is here, now queue the length-header-read (4 octets)
308			shift->unshift_read_chunk (4, sub {
309			# header arrived, decode
310			my $len = unpack "N", $_[1];
311
312			# now read the payload
313			shift->unshift_read_chunk ($len, sub {
314			my $xml = $_[1];
315			# handle xml
316			});
317			});
318			});
319
320			Example 2: Implement a client for a protocol that replies either with
321			"OK" and another line or "ERROR" for one request, and 64 bytes for the
322			second request. Due tot he availability of a full queue, we can just
323			pipeline sending both requests and manipulate the queue as necessary in
324			the callbacks:
325
326			# request one
327			$handle->push_write ("request 1\015\012");
328
329			# we expect "ERROR" or "OK" as response, so push a line read
330			$handle->push_read_line (sub {
331			# if we got an "OK", we have to _prepend_ another line,
332			# so it will be read before the second request reads its 64 bytes
333			# which are already in the queue when this callback is called
334			# we don't do this in case we got an error
335			if ($_[1] eq "OK") {
336			$_[0]->unshift_read_line (sub {
337			my $response = $_[1];
338			...
339			});
340			}
341			});
342
343			# request two
344			$handle->push_write ("request 2\015\012");
345
346			# simply read 64 bytes, always
347			$handle->push_read_chunk (64, sub {
348			my $response = $_[1];
349			...
350			});
351
352			=over 4
353
354	root	1.8	sub _drain_rbuf {
355			my ($self) = @_;
356	elmex	1.1
357	root	1.8	return if exists $self->{in_drain};
358			local $self->{in_drain} = 1;
359	elmex	1.1
360	root	1.8	while (my $len = length $self->{rbuf}) {
361			no strict 'refs';
362			if (@{ $self->{queue} }) {
363			if ($self->{queue}[0]($self)) {
364			shift @{ $self->{queue} };
365			} elsif ($self->{eof}) {
366			# no progress can be made (not enough data and no data forthcoming)
367			$! = &Errno::EPIPE; return $self->error;
368	elmex	1.1	} else {
369	root	1.8	return;
370			}
371			} elsif ($self->{on_read}) {
372			$self->{on_read}($self);
373
374			if (
375			$self->{eof} # if no further data will arrive
376			&& $len == length $self->{rbuf} # and no data has been consumed
377			&& !@{ $self->{queue} } # and the queue is still empty
378			&& $self->{on_read} # and we still want to read data
379			) {
380			# then no progress can be made
381			$! = &Errno::EPIPE; return $self->error;
382	elmex	1.1	}
383	root	1.8	} else {
384			# read side becomes idle
385			delete $self->{rw};
386			return;
387			}
388			}
389
390			if ($self->{eof}) {
391			$self->_shutdown;
392			$self->{on_eof}($self);
393			}
394	elmex	1.1	}
395
396	root	1.8	=item $handle->on_read ($cb)
397	elmex	1.1
398	root	1.8	This replaces the currently set C<on_read> callback, or clears it (when
399			the new callback is C<undef>). See the description of C<on_read> in the
400			constructor.
401	elmex	1.1
402	root	1.8	=cut
403
404			sub on_read {
405			my ($self, $cb) = @_;
406	elmex	1.1
407	root	1.8	$self->{on_read} = $cb;
408
409			unless ($self->{rw} \|\| $self->{eof}) {
410			Scalar::Util::weaken $self;
411	elmex	1.1
412	root	1.8	$self->{rw} = AnyEvent->io (fh => $self->{fh}, poll => "r", cb => sub {
413			my $len = sysread $self->{fh}, $self->{rbuf}, $self->{read_size} \|\| 8192, length $self->{rbuf};
414	elmex	1.1
415	root	1.8	if ($len > 0) {
416			if (exists $self->{rbuf_max}) {
417			if ($self->{rbuf_max} < length $self->{rbuf}) {
418			$! = &Errno::ENOSPC; return $self->error;
419			}
420			}
421	elmex	1.1
422	root	1.8	} elsif (defined $len) {
423			$self->{eof} = 1;
424			delete $self->{rw};
425	elmex	1.1
426	root	1.8	} elsif ($! != EAGAIN && $! != EINTR) {
427			return $self->error;
428			}
429	elmex	1.1
430	root	1.8	$self->_drain_rbuf;
431			});
432			}
433	elmex	1.1	}
434
435	root	1.8	=item $handle->rbuf
436
437			Returns the read buffer (as a modifiable lvalue).
438	elmex	1.1
439	root	1.8	You can access the read buffer directly as the C<< ->{rbuf} >> member, if
440			you want.
441	elmex	1.1
442	root	1.8	NOTE: The read buffer should only be used or modified if the C<on_read>,
443			C<push_read> or C<unshift_read> methods are used. The other read methods
444			automatically manage the read buffer.
445	elmex	1.1
446			=cut
447
448	elmex	1.2	sub rbuf : lvalue {
449	root	1.8	$_[0]{rbuf}
450	elmex	1.2	}
451	elmex	1.1
452	root	1.8	=item $handle->push_read ($cb)
453
454			=item $handle->unshift_read ($cb)
455
456			Append the given callback to the end of the queue (C<push_read>) or
457			prepend it (C<unshift_read>).
458
459			The callback is called each time some additional read data arrives.
460	elmex	1.1
461	root	1.8	It must check wether enough data is in the read buffer already.
462	elmex	1.1
463	root	1.8	If not enough data is available, it must return the empty list or a false
464			value, in which case it will be called repeatedly until enough data is
465			available (or an error condition is detected).
466
467			If enough data was available, then the callback must remove all data it is
468			interested in (which can be none at all) and return a true value. After returning
469			true, it will be removed from the queue.
470	elmex	1.1
471			=cut
472
473	root	1.8	sub push_read {
474			my ($self, $cb) = @_;
475	elmex	1.1
476	root	1.8	push @{ $self->{queue} }, $cb;
477			$self->_drain_rbuf;
478	elmex	1.1	}
479
480	root	1.8	sub unshift_read {
481			my ($self, $cb) = @_;
482
483			push @{ $self->{queue} }, $cb;
484			$self->_drain_rbuf;
485			}
486	elmex	1.1
487	root	1.8	=item $handle->push_read_chunk ($len, $cb->($self, $data))
488	elmex	1.1
489	root	1.8	=item $handle->unshift_read_chunk ($len, $cb->($self, $data))
490	elmex	1.1
491	root	1.8	Append the given callback to the end of the queue (C<push_read_chunk>) or
492			prepend it (C<unshift_read_chunk>).
493	elmex	1.1
494	root	1.8	The callback will be called only once C<$len> bytes have been read, and
495			these C<$len> bytes will be passed to the callback.
496	elmex	1.1
497			=cut
498
499	root	1.8	sub _read_chunk($$) {
500			my ($len, $cb) = @_;
501	elmex	1.1
502	root	1.8	sub {
503			$len <= length $_[0]{rbuf} or return;
504			$cb->($_[0], substr $_[0]{rbuf}, 0, $len, "");
505			1
506			}
507			}
508
509			sub push_read_chunk {
510			my ($self, $len, $cb) = @_;
511	elmex	1.5
512	root	1.8	$self->push_read (_read_chunk $len, $cb);
513			}
514	elmex	1.1
515	elmex	1.5
516	root	1.8	sub unshift_read_chunk {
517			my ($self, $len, $cb) = @_;
518	elmex	1.1
519	root	1.8	$self->unshift_read (_read_chunk $len, $cb);
520	elmex	1.1	}
521
522	root	1.8	=item $handle->push_read_line ([$eol, ]$cb->($self, $line, $eol))
523	elmex	1.1
524	root	1.8	=item $handle->unshift_read_line ([$eol, ]$cb->($self, $line, $eol))
525	elmex	1.1
526	root	1.8	Append the given callback to the end of the queue (C<push_read_line>) or
527			prepend it (C<unshift_read_line>).
528	elmex	1.1
529	root	1.8	The callback will be called only once a full line (including the end of
530			line marker, C<$eol>) has been read. This line (excluding the end of line
531			marker) will be passed to the callback as second argument (C<$line>), and
532			the end of line marker as the third argument (C<$eol>).
533	elmex	1.1
534	root	1.8	The end of line marker, C<$eol>, can be either a string, in which case it
535			will be interpreted as a fixed record end marker, or it can be a regex
536			object (e.g. created by C<qr>), in which case it is interpreted as a
537			regular expression.
538	elmex	1.1
539	root	1.8	The end of line marker argument C<$eol> is optional, if it is missing (NOT
540			undef), then C<qr\|\015?\012\|> is used (which is good for most internet
541			protocols).
542	elmex	1.1
543	root	1.8	Partial lines at the end of the stream will never be returned, as they are
544			not marked by the end of line marker.
545	elmex	1.1
546	root	1.8	=cut
547	elmex	1.1
548	root	1.8	sub _read_line($$) {
549			my $cb = pop;
550			my $eol = @_ ? shift : qr\|(\015?\012)\|;
551			my $pos;
552	elmex	1.1
553	root	1.8	$eol = qr\|(\Q$eol\E)\| unless ref $eol;
554			$eol = qr\|^(.*?)($eol)\|;
555	elmex	1.1
556	root	1.8	sub {
557			$_[0]{rbuf} =~ s/$eol// or return;
558	elmex	1.1
559	root	1.8	$cb->($1, $2);
560			1
561			}
562			}
563	elmex	1.1
564	root	1.8	sub push_read_line {
565			my $self = shift;
566	elmex	1.1
567	root	1.8	$self->push_read (&_read_line);
568			}
569	elmex	1.1
570	root	1.8	sub unshift_read_line {
571			my $self = shift;
572	elmex	1.1
573	root	1.8	$self->unshift_read (&_read_line);
574	elmex	1.1	}
575
576			=back
577
578			=head1 AUTHOR
579
580	root	1.8	Robin Redeker C<< <elmex at ta-sa.org> >>, Marc Lehmann <schmorp@schmorp.de>.
581	elmex	1.1
582			=cut
583
584			1; # End of AnyEvent::Handle