phpman > perldoc > 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.