Provided by: libpoe-perl_1.3670-2_all bug


       POE::Filter::Line - serialize and parse terminated records (lines)



         use POE qw(Wheel::FollowTail Filter::Line);

           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::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.


       POE::Filter::Line's new() method has some interesting parameters.

       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.


       POE::Filter::Line has no additional public methods.


       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.


       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


       The default input newline parser is a regexp that has an unfortunate race condition.
       First the regular expression:


       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.


       Please see POE for more information about authors and contributors.