factor dispatcher out into Web::Dispatch

[catagits/Web-Simple.git] / lib / Web / Simple.pm

package Web::Simple;

use strict;
use warnings FATAL => 'all';
use 5.008;

our $VERSION = '0.004';

sub setup_all_strictures {
  strict->import;
  warnings->import(FATAL => 'all');
}

sub setup_dispatch_strictures {
  setup_all_strictures();
  warnings->unimport('syntax');
  warnings->import(FATAL => qw(
    ambiguous bareword digit parenthesis precedence printf
    prototype qw reserved semicolon
  ));
}

sub import {
  setup_dispatch_strictures();
  my ($class, $app_package) = @_;
  $class->_export_into($app_package||caller);
}

sub _export_into {
  my ($class, $app_package) = @_;
  {
    no strict 'refs';
    *{"${app_package}::dispatch"} = sub (&) {
      $app_package->_setup_dispatcher($_[0]);
    };
    *{"${app_package}::response_filter"} = sub (&) {
      $app_package->_construct_response_filter($_[0]);
    };
    *{"${app_package}::redispatch_to"} = sub {
      $app_package->_construct_redispatch($_[0]);
    };
    *{"${app_package}::default_config"} = sub {
      $app_package->_setup_default_config(@_);
    };
    *{"${app_package}::PSGI_ENV"} = sub () { -1 };
    *{"${app_package}::self"} = \${"${app_package}::self"};
    require Web::Simple::Application;
    unshift(@{"${app_package}::ISA"}, 'Web::Simple::Application');
  }
  (my $name = $app_package) =~ s/::/\//g;
  $INC{"${name}.pm"} = 'Set by "use Web::Simple;" invocation';
}

=head1 NAME

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

=head1 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
L<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.

=head1 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. To get help with Web::Simple,
please connect to the irc.perl.org IRC network and join #web-simple.

=head1 WHY?

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

=head1 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 (...) { ... }, ... };

  response_filter { ... };

  redispatch_to '/somewhere';

  subdispatch sub (...) { ... }

and creates a $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).

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.

=head1 DISPATCH STRATEGY

=head2 Examples

 dispatch {
   # 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];
      subdispatch sub {
         [
            # 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];
              ...
            },
         ];
      }
   },
 }

=head2 Description of the dispatcher object

Web::Simple::Dispatcher objects have three components:

=over 4

=item * match - an optional test if this dispatcher matches the request

=item * call - a routine to call if this dispatcher matches (or has no match)

=item * next - the next dispatcher to call

=back

When a dispatcher is invoked, it checks its match routine against the
request environment. The match routine may provide alterations to the
request as a result of matching, and/or arguments for the call routine.

If no match routine has been provided then Web::Simple treats this as
a success, and supplies the request environment to the call routine as
an argument.

Given a successful match, the call routine is now invoked in list context
with any arguments given to the original dispatch, plus any arguments
provided by the match result.

If this routine returns (), Web::Simple treats this identically to a failure
to match.

If this routine returns a Web::Simple::Dispatcher, the environment changes
are merged into the environment and the new dispatcher's next pointer is
set to our next pointer.

If this routine returns anything else, that is treated as the end of dispatch
and the value is returned.

On a failed match, Web::Simple invokes the next dispatcher with the same
arguments and request environment passed to the current one. On a successful
match that returned a new dispatcher, Web::Simple invokes the new dispatcher
with the same arguments but the modified request environment.

=head2 How Web::Simple builds dispatcher objects for you

In the case of the Web::Simple L</dispatch> export the match is constructed
from the subroutine prototype - i.e.

  sub (<match specification>) {
    <call code>
  }

and the 'next' pointer is populated with the next element of the array,
expect for the last element, which is given a next that will throw a 500
error if none of your dispatchers match. If you want to provide something
else as a default, a routine with no match specification always matches, so -

  sub () {
    [ 404, [ 'Content-type', 'text/plain' ], [ 'Error: Not Found' ] ]
  }

will produce a 404 result instead of a 500 by default. You can also override
the L<Web::Simple::Application/_build_final_dispatcher> method in your app.

Note that the code in the subroutine is executed as a -method- on your
application object, so if your match specification provides arguments you
should unpack them like so:

  sub (<match specification>) {
    my ($self, @args) = @_;
    ...
  }

=head2 Web::Simple match specifications

=head3 Method matches

  sub (GET) {

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

=head3 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, much like
.html strips the extension. 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'

=head3 Extension matches

  sub (.html) {

will match and strip .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 stripped extension as a match
argument.

=head3 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.

So, 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 L<DBIx::Class::ResultSet> object.

Note that if a parameter is specified as single and multiple values are found,
the last one will be used.

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.

=head3 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 + .html) | (POST + .html)) {

and

  sub (GET + .html | POST + .html) {

are not - the latter is equivalent to

  sub (GET + (.html|POST) + .html) {

which will never match.

=head3 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/*) {

=head3 Accessing the PSGI env hash

To gain the benefit of using some middleware, specifically
Plack::Middleware::Session access to the ENV hash is needed. This is provided
in arguments to the dispatched handler. You can access this hash with the
exported +PSGI_ENV constant.

    sub (GET + /foo + ?some_param=) {
        my($self, $some_param, $env) = @_[0, 1, +PSGI_ENV];

=head1 EXPORTED SUBROUTINES

=head2 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 - calling it a second time will
cause an exception to be thrown.

=head2 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_dispatcher with
the return value of the block passed to it, which then creates your Web::Simple
application's dispatcher from these subs. The prototype of each subroutine
is expected to be a Web::Simple dispatch specification (see
L</DISPATCH SPECIFICATIONS> below for more details), and the body of the
subroutine is the code to execute if the specification matches.

Each dispatcher is given the dispatcher constructed from the next subroutine
returned as its next dispatcher, except for the final subroutine, which
is given the return value of NameOfApplication->_build_final_dispatcher
as its next dispatcher (by default this returns a 500 error response).

See L</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_dispatcher creates a

  sub _dispatcher {
    return <root dispatcher object here>;
  }

method in your class so as with default_config, calling dispatch a second time
will result in an exception.

=head2 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 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.

=head2 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 redipstch to
'/other/url', the dispatch behaviour will be exactly as if the same POST
request had been made to '/other/url' instead.

=head2 subdispatch

  subdispatch sub (/user/*/) {
    my $u = $self->user($_[1]);
    [
      sub (GET) { $u },
      sub (DELETE) { $u->delete },
    ]
  }

The subdispatch subroutine is designed for use in dispatcher construction.

It creates a dispatcher which, if it matches, treats its return value not
as a final value but an arrayref of dispatch specifications such as could
be passed to the dispatch subroutine itself. These are turned into a dispatcher
which is then invoked. Any changes the match makes to the request are in
scope for this inner dispatcher only - so if the initial match is a
destructive one like .html the full path will be restored if the
subdispatch fails.

=head1 CHANGES BETWEEN RELEASES

=head2 Changes since Antiquated Perl

=over 4

=item * filter_response renamed to response_filter

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

=item * dispatch [] changed to dispatch {}

Simply changing

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

to

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

should work fine.

=back

=head1 COMMUNITY AND SUPPORT

=head2 IRC channel

irc.perl.org #web-simple

=head2 No mailing list yet

Because mst's non-work email is a bombsite so he'd never read it anyway.

=head2 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

=head1 AUTHOR

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

=head1 CONTRIBUTORS

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

=head1 COPYRIGHT

Copyright (c) 2009 the Web::Simple L</AUTHOR> and L</CONTRIBUTORS>
as listed above.

=head1 LICENSE

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

=cut

1;