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]
";
}
}
);
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 "x0Dx0A") 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 => "
",
);
"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 => "([x0Dx0A]{2,})",
OutputLiteral => "
---
",
);
PUBLIC FILTER METHODS
POE::Filter::Line 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 default input newline parser is a regexp that has an unfortunate race condition. First the regular expression:
/(x0Dx0A?|x0Ax0D?)/
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 v5.14.2 2012-05-15 POE::Filter::Line(3pm)