NAME

       POE::Filter::Map - transform input and/or output within a filter stack

SYNOPSIS

         #!perl

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

         POE::Session->create(
           inline_states => {
             _start => sub {
               my $parse_input_as_lines = POE::Filter::Line->new();

               my $redact_some_lines = POE::Filter::Map->new(
                 Code => sub {
                   my $input = shift;
                   $input = "[REDACTED]" unless $input =~ /sudo\[\d+\]/i;
                   return $input;
                 },
               );

               my $filter_stack = POE::Filter::Stackable->new(
                 Filters => [
                   $parse_input_as_lines, # first on get, last on put
                   $redact_some_lines, # first on put, last on get
                 ]
               );

               $_[HEAP]{tailor} = POE::Wheel::FollowTail->new(
                 Filename => "/var/log/system.log",
                 InputEvent => "got_log_line",
                 Filter => $filter_stack,
               );
             },
             got_log_line => sub {
               print "Log: $_[ARG0]\n";
             }
           }
         );

         POE::Kernel->run();
         exit;

DESCRIPTION

       POE::Filter::Map transforms data inside the filter stack.  It may be used to transform
       input, output, or both depending on how it is constructed.  This filter is named and
       modeled after Perl's built-in map() function.

       POE::Filter::Map is designed to be combined with other filters through
       POE::Filter::Stackable.  In the "SYNOPSIS" example, a filter stack is created to parse
       logs as lines and redact all entries that don't pertain to a sudo process.

PUBLIC FILTER METHODS

       In addition to the usual POE::Filter methods, POE::Filter::Map also supports the
       following.

   new
       new() constructs a new POE::Filter::Map object.  It must either be called with a single
       Code parameter, or both a Put and a Get parameter.  The values for Code, Put and Get are
       code references that, when invoked, return transformed versions of their sole parameters.
       A Code function will be used for both input and output, while Get and Put functions allow
       input and output to be filtered in different ways.

         # Decrypt rot13.
         sub decrypt_rot13 {
           my $encrypted = shift;
           $encrypted =~ tr[a-zA-Z][n-za-mN-ZA-M];
           return $encrypted;
         }

         # Encrypt rot13.
         sub encrypt_rot13 {
           my $plaintext = shift;
           $plaintext =~ tr[a-zA-Z][n-za-mN-ZA-M];
           return $plaintext;
         }

         # Decrypt rot13 on input, and encrypt it on output.
         my $rot13_transcrypter = POE::Filter::Map->new(
           Get => \&decrypt_rot13,
           Put => \&encrypt_rot13,
         );

       Rot13 is symmetric, so the above example can be simplified to use a single Code function.

         my $rot13_transcrypter = POE::Filter::Map->new(
           Code => sub {
             local $_ = shift;
             tr[a-zA-Z][n-za-mN-ZA-M];
             return $_;
           }
         );

   modify
       modify() changes a POE::Filter::Map object's behavior at run-time.  It accepts the same
       parameters as new(), and it replaces the existing transforms with new ones.

         # Switch to "reverse" encryption for testing.
         $rot13_transcrypter->modify(
           Code => sub { return scalar reverse shift }
         );

SEE ALSO

       POE::Filter for more information about filters in general.

       POE::Filter::Stackable for more details on stacking filters.

BUGS

       None known.

AUTHORS & COPYRIGHTS

       The Map filter was contributed by Dieter Pearcey.  Documentation is provided by Rocco
       Caputo.

       Please see the POE manpage for more information about authors and contributors.