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package POE::Filter::Block;
use strict;
use POE::Filter;
use vars qw($VERSION @ISA);
$VERSION = '1.293'; # NOTE - Should be #.### (three decimal places)
@ISA = qw(POE::Filter);
use Carp qw(croak);
sub FRAMING_BUFFER () { 0 }
sub BLOCK_SIZE () { 1 }
sub EXPECTED_SIZE () { 2 }
sub ENCODER () { 3 }
sub DECODER () { 4 }
#------------------------------------------------------------------------------
sub _default_decoder {
my $stuff = shift;
unless ($$stuff =~ s/^(\d+)\0//s) {
warn length($1), " strange bytes removed from stream"
if $$stuff =~ s/^(\D+)//s;
return;
}
return $1;
}
sub _default_encoder {
my $stuff = shift;
substr($$stuff, 0, 0) = length($$stuff) . "\0";
return;
}
sub new {
my $type = shift;
croak "$type must be given an even number of parameters" if @_ & 1;
my %params = @_;
my ($encoder, $decoder);
my $block_size = delete $params{BlockSize};
if (defined $block_size) {
croak "$type doesn't support zero or negative block sizes"
if $block_size < 1;
croak "Can't use both LengthCodec and BlockSize at the same time"
if exists $params{LengthCodec};
}
else {
my $codec = delete $params{LengthCodec};
if ($codec) {
croak "LengthCodec must be an array reference"
unless ref($codec) eq "ARRAY";
croak "LengthCodec must contain two items"
unless @$codec == 2;
($encoder, $decoder) = @$codec;
croak "LengthCodec encoder must be a code reference"
unless ref($encoder) eq "CODE";
croak "LengthCodec decoder must be a code reference"
unless ref($decoder) eq "CODE";
}
else {
$encoder = \&_default_encoder;
$decoder = \&_default_decoder;
}
}
my $self = bless [
'', # FRAMING_BUFFER
$block_size, # BLOCK_SIZE
undef, # EXPECTED_SIZE
$encoder, # ENCODER
$decoder, # DECODER
], $type;
$self;
}
#------------------------------------------------------------------------------
# get() is inherited from POE::Filter.
#------------------------------------------------------------------------------
# 2001-07-27 RCC: The get_one() variant of get() allows Wheel::Xyz to
# retrieve one filtered block at a time. This is necessary for filter
# changing and proper input flow control.
sub get_one_start {
my ($self, $stream) = @_;
$self->[FRAMING_BUFFER] .= join '', @$stream;
}
sub get_one {
my $self = shift;
# Need to check lengths in octets, not characters.
BEGIN { eval { require bytes } and bytes->import; }
# If a block size is specified, then pull off a block of that many
# bytes.
if (defined $self->[BLOCK_SIZE]) {
return [ ] unless length($self->[FRAMING_BUFFER]) >= $self->[BLOCK_SIZE];
my $block = substr($self->[FRAMING_BUFFER], 0, $self->[BLOCK_SIZE]);
substr($self->[FRAMING_BUFFER], 0, $self->[BLOCK_SIZE]) = '';
return [ $block ];
}
# Otherwise we're doing the variable-length block thing. Look for a
# length marker, and then pull off a chunk of that length. Repeat.
if (
defined($self->[EXPECTED_SIZE]) ||
defined(
$self->[EXPECTED_SIZE] = $self->[DECODER]->(\$self->[FRAMING_BUFFER])
)
) {
return [ ] if length($self->[FRAMING_BUFFER]) < $self->[EXPECTED_SIZE];
# Four-arg substr() would be better here, but it's not compatible
# with Perl as far back as we support.
my $block = substr($self->[FRAMING_BUFFER], 0, $self->[EXPECTED_SIZE]);
substr($self->[FRAMING_BUFFER], 0, $self->[EXPECTED_SIZE]) = '';
$self->[EXPECTED_SIZE] = undef;
return [ $block ];
}
return [ ];
}
#------------------------------------------------------------------------------
sub put {
my ($self, $blocks) = @_;
my @raw;
# Need to check lengths in octets, not characters.
BEGIN { eval { require bytes } and bytes->import; }
# If a block size is specified, then just assume the put is right.
# This will cause quiet framing errors on the receiving side. Then
# again, we'll have quiet errors if the block sizes on both ends
# differ. Ah, well!
if (defined $self->[BLOCK_SIZE]) {
@raw = join '', @$blocks;
}
# No specified block size. Do the variable-length block thing. This
# steals a lot of Artur's code from the Reference filter.
else {
@raw = @$blocks;
foreach (@raw) {
$self->[ENCODER]->(\$_);
}
}
\@raw;
}
#------------------------------------------------------------------------------
sub get_pending {
my $self = shift;
return undef unless length $self->[FRAMING_BUFFER];
[ $self->[FRAMING_BUFFER] ];
}
1;
__END__
=head1 NAME
POE::Filter::Block - translate data between streams and blocks
=head1 SYNOPSIS
#!perl
use warnings;
use strict;
use POE::Filter::Block;
my $filter = POE::Filter::Block->new( BlockSize => 8 );
# Prints three lines: abcdefgh, ijklmnop, qrstuvwx.
# Bytes "y" and "z" remain in the buffer and await completion of the
# next 8-byte block.
$filter->get_one_start([ "abcdefghijklmnopqrstuvwxyz" ]);
while (1) {
my $block = $filter->get_one();
last unless @$block;
print $block->[0], "\n";
}
# Print one line: yz123456
$filter->get_one_start([ "123456" ]);
while (1) {
my $block = $filter->get_one();
last unless @$block;
print $block->[0], "\n";
}
=head1 DESCRIPTION
POE::Filter::Block translates data between serial streams and blocks.
It can handle fixed-length and length-prepended blocks, and it may be
extended to handle other block types.
Fixed-length blocks are used when Block's constructor is called with a
BlockSize value. Otherwise the Block filter uses length-prepended
blocks.
Users who specify block sizes less than one deserve what they get.
In variable-length mode, a LengthCodec parameter may be specified.
The LengthCodec value should be a reference to a list of two
functions: the length encoder, and the length decoder:
LengthCodec => [ \&encoder, \&decoder ]
The encoder takes a reference to a buffer and prepends the buffer's
length to it. The default encoder prepends the ASCII representation
of the buffer's length and a chr(0) byte to separate the length from
the actual data:
sub _default_encoder {
my $stuff = shift;
substr($$stuff, 0, 0) = length($$stuff) . "\0";
return;
}
The corresponding decoder returns the block length after removing it
and the separator from the buffer. It returns nothing if no length
can be determined.
sub _default_decoder {
my $stuff = shift;
unless ($$stuff =~ s/^(\d+)\0//s) {
warn length($1), " strange bytes removed from stream"
if $$stuff =~ s/^(\D+)//s;
return;
}
return $1;
}
This filter holds onto incomplete blocks until they are completed.
=head1 PUBLIC FILTER METHODS
POE::Filter::Block has no additional public methods.
=head1 SEE ALSO
Please see L<POE::Filter> for documentation regarding the base
interface.
The SEE ALSO section in L<POE> contains a table of contents covering
the entire POE distribution.
=head1 BUGS
The put() method doesn't verify block sizes.
=head1 AUTHORS & COPYRIGHTS
The Block filter was contributed by Dieter Pearcey, with changes by
Rocco Caputo.
Please see L<POE> for more information about authors and contributors.
=cut
# rocco // vim: ts=2 sw=2 expandtab
# TODO - Edit.
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