Web::Simple(3)

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

WARNING
This is really quite new. If you're reading this on CPAN, it means the stuff that's here we're probably happy with. But only probably. So we may have to change stuff. And if you're reading this from git, come check with irc.perl.org #web-simple that we're actually sure we're going to keep anything that's different from the CPAN version.

If we do find we have to change stuff we'll add to the "CHANGES BETWEEN RELEASES" section explaining how to switch your code across to the new version, and we'll do our best to make it as painless as possible because we've got Web::Simple applications too. But we can't promise not to change things at all. Not yet. Sorry.

SYNOPSIS
  #!/usr/bin/env perl

  use Web::Simple 'HelloWorld';

  {
    package HelloWorld;

    sub dispatch_request {
      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. To get help with Web::Simple, please connect to the irc.perl.org IRC network and join #web-simple.

DESCRIPTION
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.

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

  use Web::Simple 'NameOfApplication';

This sets up your package (in this case "NameOfApplication" is your package) so that it inherits from Web::Simple::Application and imports strictures, as well as installs a "PSGI_ENV" constant for convenience, as well as some other subroutines.

Importing strictures will automatically make your code use the "strict" and "warnings" pragma, so you can skip the usual:

  use strict;
  use warnings FATAL => 'aa';

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.

When we inherit from Web::Simple::Application we also use <Moo>, which is the the equivalent of:

  {
    package NameOfApplication;
    use Moo;
    extends 'Web::Simple::Application';
  }

So you can use Moo features in your application, such as creating attributes using the "has" subroutine, etc. Please see the documentation for Moo for more information.

It also exports the following subroutines for use in dispatchers:

  response_filter { ... };

  redispatch_to '/somewhere';

Finally, import sets

  $INC{"NameOfApplication.pm"} = 'Set by "use Web::Simple;" invocation';

so that perl will not attempt to load the application again even if

  require NameOfApplication;

is encountered in other code.

DISPATCH STRATEGY
Web::Simple despite being straightforward to use, has a powerful system for matching all sorts of incoming URLs to one or more subroutines. These subroutines can be simple actions to take for a given URL, or something more complicated, including entire Plack applications, Plack::Middleware and nested subdispatchers.

  Examples
 sub dispatch_request {
   # matches: GET /user/1.htm?show_details=1
   #          GET /user/1.htm
   sub (GET + /user/* + ?show_details~ + .htm|.html|.xhtml) {
     my ($self, $user_id, $show_details) = @_;
     ...
   },
   # matches: POST /user?username=frew
   #          POST /user?username=mst&first_name=matt&last_name=trout
   sub (POST + /user + ?username=&*) {
      my ($self, $username, $misc_params) = @_;
     ...
   },
   # matches: DELETE /user/1/friend/2
   sub (DELETE + /user/*/friend/*) {
     my ($self, $user_id, $friend_id) = @_;
     ...
   },
   # matches: PUT /user/1?first_name=Matt&last_name=Trout
   sub (PUT + /user/* + ?first_name~&last_name~) {
     my ($self, $user_id, $first_name, $last_name) = @_;
     ...
   },
   sub (/user/*/...) {
     my $user_id = $_[1];
     # matches: PUT /user/1/role/1
     sub (PUT + /role/*) {
       my $role_id = $_[1];
       ...
     },
     # matches: DELETE /user/1/role/1
     sub (DELETE + /role/*) {
       my $role_id = $_[1];
       ...
     },
   },
 }

  The dispatch cycle
At the beginning of a request, your app's dispatch_request method is called with the PSGI $env as an argument. You can handle the request entirely in here and return a PSGI response arrayref if you want:

  sub dispatch_request {
    my ($self, $env) = @_;
    [ 404, [ 'Content-type' => 'text/plain' ], [ 'Amnesia == fail' ] ]
  }

However, generally, instead of that, you return a set of dispatch subs:

  sub dispatch_request {
    my $self = shift;
    sub (/) { redispatch_to '/index.html' },
    sub (/user/*) { $self->show_user($_[1]) },
    ...
  }

If you return a subroutine with a prototype, the prototype is treated as a match specification - and if the test is passed, the body of the sub is called as a method any matched arguments (see below for more details).

You can also return a plain subroutine which will be called with just $env - remember that in this case if you need $self you -must- close over it.

If you return a normal object, Web::Simple will simply return it upwards on the assumption that a response_filter (or some arbitrary Plack::Middleware) somewhere will convert it to something useful. This allows:

  sub dispatch_request {
    my $self = shift;
    sub (.html) { response_filter { $self->render_zoom($_[0]) } },
    sub (/user/*) { $self->users->get($_[1]) },
  }

to render a user object to HTML, if there is an incoming URL such as:

  http://myweb.org/user/111.html

This works because as we descend down the dispachers, we first match "sub (.html)", which adds a "response_filter" (basically a specialized routine that follows the Plack::Middleware specification), and then later we also match "sub (/user/*)" which gets a user and returns that as the response. This user object 'bubbles up' through all the wrapping middleware until it hits the "response_filter" we defined, after which the return is converted to a true html response.

However, two types of object are treated specially - a Plack::App object will have its "-"to_app> method called and be used as a dispatcher:

  sub dispatch_request {
    my $self = shift;
    sub (/static/...) { Plack::App::File->new(...) },
    ...
  }

A Plack::Middleware object will be used as a filter for the rest of the dispatch being returned into:

  ## responds to /admin/track_usage AND /admin/delete_accounts

  sub dispatch_request {
    my $self = shift;
    sub (/admin/**) {
      Plack::Middleware::Session->new(%opts);
    },
    sub (/admin/track_usage) {
      ## something that needs a session
    },
    sub (/admin/delete_accounts) {
      ## something else that needs a session
    },
  }

Note that this is for the dispatch being -returned- to, so if you want to provide it inline you need to do:

  ## ALSO responds to /admin/track_usage AND /admin/delete_accounts

  sub dispatch_request {
    my $self = shift;
    sub (/admin/...) {
      sub {
        Plack::Middleware::Session->new(%opts);
      },
      sub (/track_usage) {
        ## something that needs a session
      },
      sub (/delete_accounts) {
        ## something else that needs a session
      },
    }
  }

And that's it - but remember that all this happens recursively - it's dispatchers all the way down. A URL incoming pattern will run all matching dispatchers and then hit all added filters or Plack::Middleware.

  Web::Simple match specifications
Method matches

  sub (GET) {

A match specification beginning with a capital letter matches HTTP requests with that request method.

Path matches

  sub (/login) {

A match specification beginning with a / is a path match. In the simplest case it matches a specific path. To match a path with a wildcard part, you can do:

  sub (/user/*) {
    $self->handle_user($_[1])

This will match /user/<anything> where <anything> does not include a literal / character. The matched part becomes part of the match arguments. You can also match more than one part:

  sub (/user/*/*) {
    my ($self, $user_1, $user_2) = @_;

  sub (/domain/*/user/*) {
    my ($self, $domain, $user) = @_;

and so on. To match an arbitrary number of parts, use -

  sub (/page/**) {

This will result in an element per /-separated part so matched. Note that you can do

  sub (/page/**/edit) {

to match an arbitrary number of parts up to but not including some final part.

Finally,

  sub (/foo/...) {

Will match /foo/ on the beginning of the path -and- strip it. This is designed to be used to construct nested dispatch structures, but can also prove useful for having e.g. an optional language specification at the start of a path.

Note that the '...' is a "maybe something here, maybe not" so the above specification will match like this:

  /foo         # no match
  /foo/        # match and strip path to '/'
  /foo/bar/baz # match and strip path to '/bar/baz'

Extension matches

  sub (.html) {

will match .html from the path (assuming the subroutine itself returns something, of course). This is normally used for rendering - e.g.

  sub (.html) {
    response_filter { $self->render_html($_[1]) }
  }

Additionally,

  sub (.*) {

will match any extension and supplies the extension as a match argument.

Query and body parameter matches

Query and body parameters can be match via

  sub (?<param spec>) { # match URI query
  sub (%<param spec>) { # match body params

The body is only matched if the content type is application/x-www-form-urlencoded (note this means that Web::Simple does not yet handle uploads; this will be addressed in a later release).

The param spec is elements of one of the following forms -

  param~        # optional parameter
  param=        # required parameter
  @param~       # optional multiple parameter
  @param=       # required multiple parameter
  :param~       # optional parameter in hashref
  :param=       # required parameter in hashref
  :@param~      # optional multiple in hashref
  :@param=      # required multiple in hashref
  *             # include all other parameters in hashref
  @*            # include all other parameters as multiple in hashref

separated by the & character. The arguments added to the request are one per non-:/* parameter (scalar for normal, arrayref for multiple), plus if any :/* specs exist a hashref containing those values.

Please note that if you specify a multiple type parameter match, you are ensured of getting an arrayref for the value, EVEN if the current incoming request has only one value. However if a parameter is specified as single and multiple values are found, the last one will be used.

For example to match a page parameter with an optional order_by parameter one would write:

  sub (?page=&order_by~) {
    my ($self, $page, $order_by) = @_;
    return unless $page =~ /^\d+$/;
    $page ||= 'id';
    response_filter {
      $_[1]->search_rs({}, $p);
    }
  }

to implement paging and ordering against a DBIx::Class::ResultSet object.

Another Example: To get all parameters as a hashref of arrayrefs, write:

  sub(?@*) {
    my ($self, $params) = @_;
    ...

To get two parameters as a hashref, write:

  sub(?:user~&:domain~) {
    my ($self, $params) = @_; # params contains only 'user' and 'domain' keys

You can also mix these, so:

  sub (?foo=&@bar~&:coffee=&@*) {
     my ($self, $foo, $bar, $params);

where $bar is an arrayref (possibly an empty one), and $params contains arrayref values for all parameters -not- mentioned and a scalar value for the 'coffee' parameter.

Note, in the case where you combine arrayref, single parameter and named hashref style, the arrayref and single parameters will appear in @_ in the order you defined them in the protoype, but all hashrefs will merge into a single $params, as in the example above.

Combining matches

Matches may be combined with the + character - e.g.

  sub (GET + /user/*) {

to create an AND match. They may also be combined withe the | character - e.g.

  sub (GET|POST) {

to create an OR match. Matches can be nested with () - e.g.

  sub ((GET|POST) + /user/*) {

and negated with ! - e.g.

  sub (!/user/foo + /user/*) {

! binds to the immediate rightmost match specification, so if you want to negate a combination you will need to use

  sub ( !(POST|PUT|DELETE) ) {

and | binds tighter than +, so

  sub ((GET|POST) + /user/*) {

and

  sub (GET|POST + /user/*) {

are equivalent, but

  sub ((GET + /admin/...) | (POST + /admin/...)) {

and

  sub (GET + /admin/... | POST + /admin/...) {

are not - the latter is equivalent to

  sub (GET + (/admin/...|POST) + /admin/...) {

which will never match!

Whitespace

Note that for legibility you are permitted to use whitespace -

  sub (GET + /user/*) {

but it will be ignored. This is because the perl parser strips whitespace from subroutine prototypes, so this is equivalent to

  sub (GET+/user/*) {

Accessing the PSGI env hash

In some cases you may wish to get the raw PSGI env hash - to do this, you can either use a plain sub -

  sub {
    my ($env) = @_;
    ...
  }

or use the PSGI_ENV constant exported to retrieve it:

  sub (GET + /foo + ?some_param=) {
    my $param = $_[1];
    my $env = $_[PSGI_ENV];
  }

but note that if you're trying to add a middleware, you should simply use Web::Simple's direct support for doing so.

EXPORTED SUBROUTINES

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

The response_filter subroutine is designed for use inside dispatch subroutines.

It creates and returns a special dispatcher that always matches, and calls the block passed to it as a filter on the result of running the rest of the current dispatch chain.

Thus the filter above runs further dispatch as normal, but if the result of dispatch is a 500 (Internal Server Error) response, changes this to a 200 (OK) response without altering the headers or body.

  redispatch_to
  redispatch_to '/other/url';

The redispatch_to subroutine is designed for use inside dispatch subroutines.

It creates and returns a special dispatcher that always matches, and instead of continuing dispatch re-delegates it to the start of the dispatch process, but with the path of the request altered to the supplied URL.

Thus if you receive a POST to '/some/url' and return a redispatch to '/other/url', the dispatch behaviour will be exactly as if the same POST request had been made to '/other/url' instead.

Note, this is not the same as returning an HTTP 3xx redirect as a response; rather it is a much more efficient internal process.

CHANGES BETWEEN RELEASES

  Changes between 0.004 and 0.005

•   dispatch {} replaced by declaring a dispatch_request method

    dispatch {} has gone away - instead, you write:

      sub dispatch_request {
        my $self = shift;
        sub (GET /foo/) { ... },
        ...
      }

    Note that this method is still -returning- the dispatch code - just like dispatch did.

    Also note that you need the 'my $self = shift' since the magic $self variable went away.

•   the magic $self variable went away.

    Just add 'my $self = shift;' while writing your 'sub dispatch_request {' like a normal perl method.

•   subdispatch deleted - all dispatchers can now subdispatch

    In earlier releases you needed to write:

      subdispatch sub (/foo/...) {
        ...
        [
          sub (GET /bar/) { ... },
          ...
        ]
      }

    As of 0.005, you can instead write simply:

      sub (/foo/...) {
        ...
        (
          sub (GET /bar/) { ... },
          ...
        )
      }

  Changes since Antiquated Perl

•   filter_response renamed to response_filter

    This is a pure rename; a global search and replace should fix it.

•   dispatch [] changed to dispatch {}

    Simply changing

      dispatch [ sub(...) { ... }, ... ];

    to

      dispatch { sub(...) { ... }, ... };

    should work fine.

DEVELOPMENT HISTORY
Web::Simple was originally written to form part of my Antiquated Perl talk for Italian Perl Workshop 2009, but in writing the bloggery example I realised that having a bare minimum system for writing web applications that doesn't drive me insane was rather nice and decided to spend my attempt at nanowrimo for 2009 improving and documenting it to the point where others could use it.

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

COMMUNITY AND SUPPORT

  IRC channel
irc.perl.org #web-simple

  No mailing list yet
Because mst's non-work email is a bombsite so he'd never read it anyway.

  Git repository
Gitweb is on http://git.shadowcat.co.uk/ and the clone URL is:

  git clone git://git.shadowcat.co.uk/catagits/Web-Simple.git

AUTHOR
Matt S. Trout <mst@shadowcat.co.uk>

CONTRIBUTORS
None required yet. Maybe this module is perfect (hahahahaha ...).

COPYRIGHT
Copyright (c) 2010 the Web::Simple "AUTHOR" and "CONTRIBUTORS" as listed above.

LICENSE
This library is free software and may be distributed under the same terms as perl itself.

POD ERRORS
Hey! The above document had some coding errors, which are explained below:

Around line 599:
    You forgot a '=back' before '=head2'