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.