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A first taste of Web::Simple

Wed Nov 4 01:15:00 2009

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NAME

Web::Simple - A quick and easy way to build simple web applications

SYNOPSIS

  #!/usr/bin/perl
  use Web::Simple 'HelloWorld';
  {
    package HelloWorld;
    dispatch [
      sub (GET) {
        [ 200, [ 'Content-type', 'text/plain' ], [ 'Hello world!' ] ]
      },
      sub () {
        [ 405, [ 'Content-type', 'text/plain' ], [ 'Method not allowed' ] ]
      }
    ];
  }
  HelloWorld->run_if_script;

If you save this file into your cgi-bin as hello-world.cgi and then visit

  http://my.server.name/cgi-bin/hello-world.cgi/

you'll get the ``Hello world!'' string output to your browser. For more complex examples and non-CGI deployment, see below.

WHY?

The philosophy of Web::Simple is to keep to an absolute bare minimum, for everything. It is not designed to be used for large scale applications; the Catalyst web framework already works very nicely for that and is a far more mature, well supported piece of software.

However, if you have an application that only does a couple of things, and want to not have to think about complexities of deployment, then Web::Simple might be just the thing for you.

While I originally wrote Web::Simple as part of my Antiquated Perl talk for Italian Perl Workshop 2009, I've found that having a bare minimum system for writing web applications that doesn't drive me insane is rather nice.

The Antiquated Perl talk can be found at http://www.shadowcat.co.uk/archive/conference-video/.

DESCRIPTION

The only public interface the Web::Simple module itself provides is an import based one -

  use Web::Simple 'NameOfApplication';

This imports 'strict' and 'warnings FATAL => ``all''' into your code as well, so you can skip the usual

  use strict;
  use warnings;

provided you 'use Web::Simple' at the top of the file. Note that we turn on *fatal* warnings so if you have any warnings at any point from the file that you did 'use Web::Simple' in, then your application will die. This is, so far, considered a feature.

Calling the import also makes NameOfApplication isa Web::Simple::Application - i.e. does the equivalent of

  {
    package NameOfApplication;
    use base qw(Web::Simple::Application);
  }

It also exports the following subroutines:

  default_config(
    key => 'value',
    ...
  );
  dispatch [ sub (...) { ... }, ... ];
  filter_response { ... };
  redispatch_to '/somewhere';

and creates the $self global variable in your application package, so you can use $self in dispatch subs without violating strict (Web::Simple::Application arranges for dispatch subroutines to have the correct $self in scope when this happens).

EXPORTED SUBROUTINES

default_config

  default_config(
    one_key => 'foo',
    another_key => 'bar',
  );
  ...
  $self->config->{one_key} # 'foo'

This creates the default configuration for the application, by creating a

  sub _default_config {
     return (one_key => 'foo', another_key => 'bar');
  }

in the application namespace when executed. Note that this means that you should only run default_config once - a second run will cause a warning that you are override the _default_config method in your application, which under Web::Simple will of course be fatal.

dispatch

  dispatch [
    sub (GET) {
      [ 200, [ 'Content-type', 'text/plain' ], [ 'Hello world!' ] ]
    },
    sub () {
      [ 405, [ 'Content-type', 'text/plain' ], [ 'Method not allowed' ] ]
    }
  ];

The dispatch subroutine calls NameOfApplication->_setup_dispatchables with the subroutines passed to it, which then create's your Web::Simple application's dispatcher from these subs. The prototype of the subroutine is expected to be a Web::Simple dispatch specification (see DISPATCH SPECIFICATIONS below for more details), and the body of the subroutine is the code to execute if the specification matches. See DISPATCH STRATEGY below for details on how the Web::Simple dispatch system uses the return values of these subroutines to determine how to continue, alter or abort dispatch.

Note that _setup_dispatchables creates a

  sub _dispatchables {
    return (<dispatchable objects here>);
  }

method in your class so as with default_config, calling dispatch a second time will result in a fatal warning from your application.

response_filter

  response_filter {
    # Hide errors from the user because we hates them, preciousss
    if (ref($_[1]) eq 'ARRAY' && $_[1]->[0] == 500) {
      $_[1] = [ 200, @{$_[1]}[1..$#{$_[1]}] ];
    }
    return $_[1];
  };

The response_filter subroutine is designed for use inside dispatch subroutines.

It creates and returns a response filter object to the dispatcher, encapsulating the block passed to it as the filter routine to call. See DISPATCH STRATEGY below for how a response filter affects dispatch.

redispatch_to

  redispatch_to '/some/path'

The redispatch_to subroutine is designed for use inside dispatch subroutines.

redispatch_to accepts a single string containing a new path for the request.

Web::Simple will then redispatch the request internally to that path and return the response given for the new path. For more details, see the DISPATCH STRATEGY section.