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POE::Filter::Line(3pm) User Contributed Perl Documentation POE::Filter::Line(3pm)
NAME
POE::Filter::Line - serialize and parse terminated records (lines)
SYNOPSIS
#!perl
use POE qw(Wheel::FollowTail Filter::Line);
POE::Session->create(
inline_states => {
_start => sub {
$_[HEAP]{tailor} = POE::Wheel::FollowTail->new(
Filename => "/var/log/system.log",
InputEvent => "got_log_line",
Filter => POE::Filter::Line->new(),
);
},
got_log_line => sub {
print "Log: $_[ARG0]\n";
}
}
);
POE::Kernel->run();
exit;
DESCRIPTION
POE::Filter::Line parses stream data into terminated records. The default parser
interprets newlines as the record terminator, and the default serializer appends network
newlines (CR/LF, or "\x0D\x0A") to outbound records.
Record terminators are removed from the data POE::Filter::Line returns.
POE::Filter::Line supports a number of other ways to parse lines. Constructor parameters
may specify literal newlines, regular expressions, or that the filter should detect
newlines on its own.
PUBLIC FILTER METHODS
POE::Filter::Line's new() method has some interesting parameters.
new
new() accepts a list of named parameters.
In all cases, the data interpreted as the record terminator is stripped from the data
POE::Filter::Line returns.
"InputLiteral" may be used to parse records that are terminated by some literal string.
For example, POE::Filter::Line may be used to parse and emit C-style lines, which are
terminated with an ASCII NUL:
my $c_line_filter = POE::Filter::Line->new(
InputLiteral => chr(0),
OutputLiteral => chr(0),
);
"OutputLiteral" allows a filter to put() records with a different record terminator than
it parses. This can be useful in applications that must translate record terminators.
"Literal" is a shorthand for the common case where the input and output literals are
identical. The previous example may be written as:
my $c_line_filter = POE::Filter::Line->new(
Literal => chr(0),
);
An application can also allow POE::Filter::Line to figure out which newline to use. This
is done by specifying "InputLiteral" to be undef:
my $whichever_line_filter = POE::Filter::Line->new(
InputLiteral => undef,
OutputLiteral => "\n",
);
"InputRegexp" may be used in place of "InputLiteral" to recognize line terminators based
on a regular expression. In this example, input is terminated by two or more consecutive
newlines. On output, the paragraph separator is "---" on a line by itself.
my $paragraph_filter = POE::Filter::Line->new(
InputRegexp => "([\x0D\x0A]{2,})",
OutputLiteral => "\n---\n",
);
"MaxBuffer" sets the maximum amount of data that the filter will hold onto while trying to
find a line ending. Defaults to 512 MB.
"MaxLength" sets the maximum length of a line. Defaults to 64 MB.
If either the "MaxLength" or "MaxBuffer" constraint is exceeded, "POE::Filter::Line" will
throw an exception.
PUBLIC FILTER METHODS
POE::Filter::Line has no additional public methods.
SUBCLASSING
POE::Filter::Line exports the FIRST_UNUSED constant. This points to the first unused
element in the $self array reference. Subclasses should store their own data beginning
here, and they should export their own FIRST_UNUSED constants to help future subclassers.
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 default input newline parser is a regexp that has an unfortunate race condition.
First the regular expression:
/(\x0D\x0A?|\x0A\x0D?)/
While it quickly recognizes most forms of newline, it can sometimes detect an extra blank
line. This happens when a two-byte newline character is broken between two reads.
Consider this situation:
some stream dataCR
LFother stream data
The regular expression will see the first CR without its corresponding LF. The filter
will properly return "some stream data" as a line. When the next packet arrives, the
leading "LF" will be treated as the terminator for a 0-byte line. The filter will
faithfully return this empty line.
It is advised to specify literal newlines or use the autodetect feature in applications
where blank lines are significant.
AUTHORS & COPYRIGHTS
Please see POE for more information about authors and contributors.
perl v5.30.0 2020-02-07 POE::Filter::Line(3pm)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2025-11-07 20:17 @216.73.216.119 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)