POE::Filter::LiUserpContributed Perl DocumenPOE::Filter::Line(3p)


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:







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POE::Filter::LiUserpContributed Perl DocumenPOE::Filter::Line(3p)


         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",
         );

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:

         /(\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:





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POE::Filter::LiUserpContributed Perl DocumenPOE::Filter::Line(3p)


         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.











































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