# POE::Filter::Map - phpMan

## 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.