| Current File : //usr/local/share/man/man3/POE::Filter::Block.3pm |
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.\" ========================================================================
.\"
.IX Title "POE::Filter::Block 3"
.TH POE::Filter::Block 3 "2022-03-23" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
POE::Filter::Block \- translate data between streams and blocks
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #!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], "\en";
\& }
\&
\& # Print one line: yz123456
\&
\& $filter\->get_one_start([ "123456" ]);
\& while (1) {
\& my $block = $filter\->get_one();
\& last unless @$block;
\& print $block\->[0], "\en";
\& }
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
Fixed-length blocks are used when Block's constructor is called with a
BlockSize value. Otherwise the Block filter uses length-prepended
blocks.
.PP
Users who specify block sizes less than one deserve what they get.
.PP
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:
.PP
.Vb 1
\& LengthCodec => [ \e&encoder, \e&decoder ]
.Ve
.PP
The encoder takes a reference to a buffer and prepends the buffer's
length to it. The default encoder prepends the \s-1ASCII\s0 representation
of the buffer's length and a \fBchr\fR\|(0) byte to separate the length from
the actual data:
.PP
.Vb 5
\& sub _default_encoder {
\& my $stuff = shift;
\& substr($$stuff, 0, 0) = length($$stuff) . "\e0";
\& return;
\& }
.Ve
.PP
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.
.PP
.Vb 9
\& sub _default_decoder {
\& my $stuff = shift;
\& unless ($$stuff =~ s/^(\ed+)\e0//s) {
\& warn length($1), " strange bytes removed from stream"
\& if $$stuff =~ s/^(\eD+)//s;
\& return;
\& }
\& return $1;
\& }
.Ve
.PP
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 \s-1MB\s0 (512*1024*1024 octets). You
may change this size limit with the \f(CW\*(C`MaxBuffer\*(C'\fR parameter.
.PP
.Vb 1
\& MaxBuffer => 1099511627776 # One terabyte!
.Ve
.PP
The size of each individual block is also limited. By default, each block
may be no more then 64 \s-1MB.\s0 You may change this size limit with the
\&\f(CW\*(C`MaxLength\*(C'\fR parameter.
.PP
.Vb 1
\& MaxLength => 10 # small blocks
.Ve
.PP
Remember that MaxBuffer needs to be larger then MaxLength. What's more, it
needs to have room for the length prefix.
.PP
If either the \f(CW\*(C`MaxLength\*(C'\fR or \f(CW\*(C`MaxBuffer\*(C'\fR constraint is exceeded,
\&\f(CW\*(C`POE::Filter::Bock\*(C'\fR will throw an exception.
.SH "PUBLIC FILTER METHODS"
.IX Header "PUBLIC FILTER METHODS"
POE::Filter::Block has no additional public methods.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Please see POE::Filter for documentation regarding the base
interface.
.PP
The \s-1SEE ALSO\s0 section in \s-1POE\s0 contains a table of contents covering
the entire \s-1POE\s0 distribution.
.SH "BUGS"
.IX Header "BUGS"
The \fBput()\fR method doesn't verify block sizes.
.SH "AUTHORS & COPYRIGHTS"
.IX Header "AUTHORS & COPYRIGHTS"
The Block filter was contributed by Dieter Pearcey, with changes by
Rocco Caputo.
.PP
Please see \s-1POE\s0 for more information about authors and contributors.