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1 PAUSE user

Peter Makholm


Plack::Middleware::EasyHooks - Writing PSGI Middleware using simple hooks


  package Plack::Middleware::MyAccessLog;

  use parent qw(Plack::Middleware::EasyHooks);
  sub before {
      my ($self, $env) = @_;

      $env->{MyAccessLog} = {
          start_time    => time(),
          response_size => 0,

  sub filter {
      my ($self, $env, $chunk) = @_;

      $env->{MyAccessLog]->{response_size} += length $chunk;

      return $chunk;

  sub finalize {
      my ($self, $env) = shift;

      my $time = time() - $env->{MyAccessLog}->{start_time};
      my $size = $env->{MyAccessLog}->{response_size};

      warn "Request took $time seconds and sent $size bytes";


Or as an inline middleware

  use Plack::Builder;

  my $app = ...; 

  builder {
      enable 'Plack::Middleware::EasyHooks', 
          before    => sub { $_[0]->{start_time} = time(); },
          finalize  => sub {
              my $time = time() - $_[0]->{start};
              warn "Request took $time seconds";



Plack::Middleware::EasyHooks takes care of the complexities handling streaming in PSGI middleware. Just provide hooks to be called before, during and after the wrapped PSGI application.

The hooks are called in the following order (much simplified):

    filter($_) for @body;


The following methods are available for hooking into the request handling

before( $env )

This method is called before processing the wrapped PSGI application. It receives the PSGI $env hash ref as argument.

The return value is ignored.

after( $env, $res )

This method is called when the app starts to respond. It receives the PSGI $env and a array ref containing the status code and headers as arguments.

The middleware can override the status code and headers either by updating the elements of this array ref or by returning a array ref with the new status code and headers.

filter ( $env, $chunk )

This method allows you to filter the content of the response. It is called on each chunk of the response.

The return value is passed to the next level. If the return value is undef proccessing of the request is stopped.

tail( $env );

This methods allows you to add some additional content at the end of the body.

finalize( $env )

This method is called after the request has been processed.


Unless your PSGI server supports cleanup handles, the finalize() method might be calles before the final chunk is successfully sent to the client.


Peter Makholm <peter@makholm.net>


Copyright (C) 2012 by Peter Makholm.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.