NAME¶
POE::Filter::Block - translate data between streams and blocks
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";
}
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 in a framing
buffer. To control memory usage, a maximum framing buffer size is imposed.
This maximum size defaults to 512 MB (512*1024*1024 octets). You may change
this size limit with the "MaxBuffer" parameter.
MaxBuffer => 1099511627776 # One terabyte!
The size of each individual block is also limited. By default, each block may be
no more then 64 MB. You may change this size limit with the
"MaxLength" parameter.
MaxLength => 10 # small blocks
Remember that MaxBuffer needs to be larger then MaxLength. What's more, it needs
to have room for the length prefix.
If either the "MaxLength" or "MaxBuffer" constraint is
exceeded, "POE::Filter::Bock" will throw an exception.
PUBLIC FILTER METHODS¶
POE::Filter::Block has no additional public methods.
SEE ALSO¶
Please see POE::Filter for documentation regarding the base interface.
The SEE ALSO section in POE contains a table of contents covering the entire POE
distribution.
BUGS¶
The
put() method doesn't verify block sizes.
AUTHORS & COPYRIGHTS¶
The Block filter was contributed by Dieter Pearcey, with changes by Rocco
Caputo.
Please see POE for more information about authors and contributors.