source: main/trunk/greenstone2/perllib/cpan/Mojolicious/Guides/Cookbook.pod@ 32205

=encoding utf8

=head1 NAME

Mojolicious::Guides::Cookbook - Cooking with Mojolicious

=head1 OVERVIEW

This document contains many fun recipes for cooking with L<Mojolicious>.

=head1 CONCEPTS

Essentials every L<Mojolicious> developer should know.

=head2 Blocking and non-blocking operations

A I<blocking> operation is a subroutine that blocks the execution of the
calling subroutine until the subroutine is finished.

  sub foo {
    my $result = blocking_subroutine();
    ...
  }

A I<non-blocking> operation on the other hand lets the calling subroutine
continue execution even though the subroutine is not yet finished. Instead of
waiting, the calling subroutine passes along a callback to be executed once the
subroutine is finished, this is called continuation-passing style.

  sub foo {
    non_blocking_subroutine(sub {
      my $result = shift;
      ...
    });
    ...
  }

While L<Mojolicious> has been designed from the ground up for non-blocking I/O
and event loops, it is not possible to magically make Perl code non-blocking.
You have to use specialized non-blocking code available through modules like
L<Mojo::IOLoop> and L<Mojo::UserAgent>, or third-party event loops. You can wrap
your blocking code in L<subprocesses|Mojo::IOLoop/"subprocess"> though to
prevent it from interfering with your non-blocking code.

=head2 Event loops

An event loop is basically a loop that continually tests for external events
and executes the appropriate callbacks to handle them, it is often the main
loop in a program. Non-blocking tests for readability/writability of file
descriptors and timers are commonly used events for highly scalable network
servers, because they allow a single process to handle thousands of client
connections concurrently.

  while (1) {
    my @readable = test_fds_for_readability();
    handle_readable_fds(@readable);

    my @writable = test_fds_for_writability();
    handle_writable_fds(@writable);

    my @expired = test_timers();
    handle_timers(@expired);
  }

In L<Mojolicious> this event loop is L<Mojo::IOLoop>.

=head2 Reverse proxy

A reverse proxy architecture is a deployment technique used in many production
environments, where a I<reverse proxy> server is put in front of your
application to act as the endpoint accessible by external clients. It can
provide a lot of benefits, like terminating SSL connections from the outside,
limiting the number of concurrent open sockets towards the Mojolicious
application (or even using Unix sockets), balancing load across multiple
instances, or supporting several applications through the same IP/port.

                   ..........................................
                   :                                        :
   +--------+      :  +-----------+      +---------------+  :
   |        |-------->|           |      |               |  :
   | client |      :  |  reverse  |----->|  Mojolicious  |  :
   |        |<--------|   proxy   |      |  application  |  :
   +--------+      :  |           |<-----|               |  :
                   :  +-----------+      +---------------+  :
                   :                                        :
                   .. system boundary (e.g. same host) ......

This setup introduces some problems, though: the application will receive
requests from the reverse proxy instead of the original client; the
address/hostname where your application lives internally will be different from
the one visible from the outside; and if terminating SSL, the reverse proxy
exposes services via HTTPS while using HTTP towards the Mojolicious application.

As an example, compare a sample request from the client and what the Mojolicious
application receives:

   client                       reverse proxy                Mojolicious app
    __|__              _______________|______________             ____|____
   /     \            /                              \           /         \
   1.2.3.4 --HTTPS--> api.example.com      10.20.30.39 --HTTP--> 10.20.30.40

   GET /foo/1 HTTP/1.1                |    GET /foo/1 HTTP/1.1
   Host: api.example.com              |    Host: 10.20.30.40
   User-Agent: Firefox                |    User-Agent: ShinyProxy/1.2
   ...                                |    ...

However, now the client address is no longer available (which might be useful
for analytics, or Geo-IP) and URLs generated via
L<Mojolicious::Controller/"url_for"> will look like this:

   http://10.20.30.40/bar/2

instead of something meaningful for the client, like this:

   https://api.example.com/bar/2

To solve these problems, you can configure your reverse proxy to send the
missing data (see L</Nginx> and L</"Apache/mod_proxy">) and tell your
application about it by setting the environment variable C<MOJO_REVERSE_PROXY>.
For finer control, L</Rewriting> includes examples of how the changes could be
implemented manually.

=head1 DEPLOYMENT

Getting L<Mojolicious> and L<Mojolicious::Lite> applications running on
different platforms. Note that many real-time web features are based on the
L<Mojo::IOLoop> event loop, and therefore require one of the built-in web
servers to be able to use them to their full potential.

=head2 Built-in web server

L<Mojolicious> contains a very portable non-blocking I/O HTTP and WebSocket
server with L<Mojo::Server::Daemon>. It is usually used during development and
in the construction of more advanced web servers, but is solid and fast enough
for small to mid sized applications.

  $ ./script/my_app daemon
  Server available at http://127.0.0.1:3000

It is available to every application through the command
L<Mojolicious::Command::daemon>, which has many configuration options and is
known to work on every platform Perl works on with its single-process
architecture.

  $ ./script/my_app daemon -h
  ...List of available options...

Another huge advantage is that it supports TLS and WebSockets out of the box, a
development certificate for testing purposes is built right in, so it just
works, but you can specify all listen locations supported by
L<Mojo::Server::Daemon/"listen">.

  $ ./script/my_app daemon -l https://[::]:3000
  Server available at https://[::]:3000

To manage the web server with systemd, you can use a unit configuration file
like this.

  [Unit]
  Description=My Mojolicious application
  After=network.target

  [Service]
  Type=simple
  ExecStart=/home/sri/myapp/script/my_app daemon -m production -l http://*:8080

  [Install]
  WantedBy=multi-user.target

=head2 Pre-forking

On UNIX platforms you can also add pre-forking to the built-in web server and
switch to a multi-process architecture with L<Mojolicious::Command::prefork>, to
take advantage of multiple CPU cores and copy-on-write memory management.

  $ ./script/my_app prefork
  Server available at http://127.0.0.1:3000

Since all built-in web servers are based on the L<Mojo::IOLoop> event loop,
they scale best with non-blocking operations. But if your application for some
reason needs to perform many blocking operations, you can improve performance
by increasing the number of worker processes and decreasing the number of
concurrent connections each worker is allowed to handle (often as low as C<1>).

  $ ./script/my_app prefork -m production -w 10 -c 1
  Server available at http://127.0.0.1:3000

During startup your application is preloaded in the manager process, which does
not run an event loop, so you can use L<Mojo::IOLoop/"next_tick"> to run code
whenever a new worker process has been forked and its event loop gets started.

  use Mojolicious::Lite;

  Mojo::IOLoop->next_tick(sub {
    app->log->info("Worker $$ star...ALL GLORY TO THE HYPNOTOAD!");
  });

  get '/' => {text => 'Hello Wor...ALL GLORY TO THE HYPNOTOAD!'};

  app->start;

And to manage the pre-forking web server with systemd, you can use a unit
configuration file like this.

  [Unit]
  Description=My Mojolicious application
  After=network.target

  [Service]
  Type=simple
  ExecStart=/home/sri/myapp/script/my_app prefork -m production -l http://*:8080

  [Install]
  WantedBy=multi-user.target

=head2 Morbo

After reading the L<Mojolicious::Guides::Tutorial>, you should already be
familiar with L<Mojo::Server::Morbo>.

  Mojo::Server::Morbo
  +- Mojo::Server::Daemon

It is basically a restarter that forks a new L<Mojo::Server::Daemon> web server
whenever a file in your project changes, and should therefore only be used
during development. To start applications with it you can use the L<morbo>
script.

  $ morbo ./script/my_app
  Server available at http://127.0.0.1:3000

=head2 Hypnotoad

For bigger applications L<Mojolicious> contains the UNIX optimized pre-forking
web server L<Hypnotoad|Mojo::Server::Hypnotoad>, which can take advantage of
multiple CPU cores and copy-on-write memory management to scale up to thousands
of concurrent client connections.

  Mojo::Server::Hypnotoad
  |- Mojo::Server::Daemon [1]
  |- Mojo::Server::Daemon [2]
  |- Mojo::Server::Daemon [3]
  +- Mojo::Server::Daemon [4]

It is based on the L<Mojo::Server::Prefork> web server, which adds pre-forking
to L<Mojo::Server::Daemon>, but optimized specifically for production
environments out of the box. To start applications with it you can use the
L<hypnotoad> script, which listens on port C<8080>, automatically daemonizes
the server process and defaults to C<production> mode for L<Mojolicious> and
L<Mojolicious::Lite> applications.

  $ hypnotoad ./script/my_app

Many configuration settings can be tweaked right from within your application
with L<Mojolicious/"config">, for a full list see
L<Mojo::Server::Hypnotoad/"SETTINGS">.

  use Mojolicious::Lite;

  app->config(hypnotoad => {listen => ['http://*:80']});

  get '/' => {text => 'Hello Wor...ALL GLORY TO THE HYPNOTOAD!'};

  app->start;

Or just add a C<hypnotoad> section to your L<Mojolicious::Plugin::Config> or
L<Mojolicious::Plugin::JSONConfig> configuration file.

  # myapp.conf
  {
    hypnotoad => {
      listen  => ['https://*:443?cert=/etc/server.crt&key=/etc/server.key'],
      workers => 10
    }
  };

But one of its biggest advantages is the support for effortless zero downtime
software upgrades (hot deployment). That means you can upgrade L<Mojolicious>,
Perl or even system libraries at runtime without ever stopping the server or
losing a single incoming connection, just by running the command above again.

  $ hypnotoad ./script/my_app
  Starting hot deployment for Hypnotoad server 31841.

You might also want to enable proxy support if you're using
L<Hypnotoad|Mojo::Server::Hypnotoad> behind a reverse proxy. This allows
L<Mojolicious> to automatically pick up the C<X-Forwarded-For> and
C<X-Forwarded-Proto> headers.

  # myapp.conf
  {hypnotoad => {proxy => 1}};

To manage L<Hypnotoad|Mojo::Server::Hypnotoad> with systemd, you can use a unit
configuration file like this.

  [Unit]
  Description=My Mojolicious application
  After=network.target

  [Service]
  Type=forking
  PIDFile=/home/sri/myapp/script/hypnotoad.pid
  ExecStart=/path/to/hypnotoad /home/sri/myapp/script/my_app
  ExecReload=/path/to/hypnotoad /home/sri/myapp/script/my_app
  KillMode=process

  [Install]
  WantedBy=multi-user.target

=head2 Zero downtime software upgrades

L<Hypnotoad|Mojo::Server::Hypnotoad> makes zero downtime software upgrades (hot
deployment) very simple, as you can see above, but on modern operating systems
that support the C<SO_REUSEPORT> socket option, there is also another method
available that works with all built-in web servers.

  $ ./script/my_app prefork -P /tmp/first.pid -l http://*:8080?reuse=1
  Server available at http://127.0.0.1:8080

All you have to do, is to start a second web server listening to the same port,
and stop the first web server gracefully afterwards.

  $ ./script/my_app prefork -P /tmp/second.pid -l http://*:8080?reuse=1
  Server available at http://127.0.0.1:8080
  $ kill -s TERM `cat /tmp/first.pid`

Just remember that both web servers need to be started with the C<reuse>
parameter.

=head2 Nginx

One of the most popular setups these days is
L<Hypnotoad|Mojo::Server::Hypnotoad> behind an L<Nginx|http://nginx.org> reverse
proxy, which even supports WebSockets in newer versions.

  upstream myapp {
    server 127.0.0.1:8080;
  }
  server {
    listen 80;
    server_name localhost;
    location / {
      proxy_pass http://myapp;
      proxy_http_version 1.1;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection "upgrade";
      proxy_set_header Host $host;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header X-Forwarded-Proto $scheme;
    }
  }

=head2 Apache/mod_proxy

Another good reverse proxy is L<Apache|http://httpd.apache.org> with
C<mod_proxy>, the configuration looks quite similar to the Nginx one above. And
if you need WebSocket support, newer versions come with C<mod_proxy_wstunnel>.

  <VirtualHost *:80>
    ServerName localhost
    <Proxy *>
      Require all granted
    </Proxy>
    ProxyRequests Off
    ProxyPreserveHost On
    ProxyPass /echo ws://localhost:8080/echo
    ProxyPass / http://localhost:8080/ keepalive=On
    ProxyPassReverse / http://localhost:8080/
    RequestHeader set X-Forwarded-Proto "http"
  </VirtualHost>

=head2 Apache/CGI

C<CGI> is supported out of the box and your L<Mojolicious> application will
automatically detect that it is executed as a C<CGI> script. Its use in
production environments is discouraged though, because as a result of how
C<CGI> works, it is very slow and many web servers are making it exceptionally
hard to configure properly. Additionally, many real-time web features, such as
WebSockets, are not available.

  ScriptAlias / /home/sri/my_app/script/my_app/

=head2 PSGI/Plack

L<PSGI> is an interface between Perl web frameworks and web servers, and
L<Plack> is a Perl module and toolkit that contains L<PSGI> middleware, helpers
and adapters to web servers. L<PSGI> and L<Plack> are inspired by Python's WSGI
and Ruby's Rack. L<Mojolicious> applications are ridiculously simple to deploy
with L<Plack>, but be aware that many real-time web features, such as
WebSockets, are not available.

  $ plackup ./script/my_app

L<Plack> provides many server and protocol adapters for you to choose from,
such as C<FCGI>, C<uWSGI> and C<mod_perl>.

  $ plackup ./script/my_app -s FCGI -l /tmp/myapp.sock

The C<MOJO_REVERSE_PROXY> environment variable can be used to enable proxy
support, this allows L<Mojolicious> to automatically pick up the
C<X-Forwarded-For> and C<X-Forwarded-Proto> headers.

  $ MOJO_REVERSE_PROXY=1 plackup ./script/my_app

If an older server adapter is unable to correctly detect the application home
directory, you can simply use the C<MOJO_HOME> environment variable.

  $ MOJO_HOME=/home/sri/my_app plackup ./script/my_app

There is no need for a C<.psgi> file, just point the server adapter at your
application script, it will automatically act like one if it detects the
presence of a C<PLACK_ENV> environment variable.

=head2 Plack middleware

Wrapper scripts like C<myapp.fcgi> are a great way to separate deployment and
application logic.

  #!/usr/bin/env plackup -s FCGI
  use Plack::Builder;

  builder {
    enable 'Deflater';
    require './script/my_app';
  };

L<Mojo::Server::PSGI> can be used directly to load and customize applications
in the wrapper script.

  #!/usr/bin/env plackup -s FCGI
  use Mojo::Server::PSGI;
  use Plack::Builder;

  builder {
    enable 'Deflater';
    my $server = Mojo::Server::PSGI->new;
    $server->load_app('./script/my_app');
    $server->app->config(foo => 'bar');
    $server->to_psgi_app;
  };

But you could even use middleware right in your application.

  use Mojolicious::Lite;
  use Plack::Builder;

  get '/welcome' => sub {
    my $c = shift;
    $c->render(text => 'Hello Mojo!');
  };

  builder {
    enable 'Deflater';
    app->start;
  };

=head2 Rewriting

Sometimes you might have to deploy your application in a blackbox environment
where you can't just change the server configuration or behind a reverse proxy
that passes along additional information with C<X-Forwarded-*> headers. In such
cases you can use the hook L<Mojolicious/"before_dispatch"> to rewrite incoming
requests.

  # Change scheme if "X-Forwarded-HTTPS" header is set
  $app->hook(before_dispatch => sub {
    my $c = shift;
    $c->req->url->base->scheme('https')
      if $c->req->headers->header('X-Forwarded-HTTPS');
  });

Since reverse proxies generally don't pass along information about path
prefixes your application might be deployed under, rewriting the base path of
incoming requests is also quite common. This allows
L<Mojolicious::Controller/"url_for"> for example, to generate portable URLs
based on the current environment.

  # Move first part and slash from path to base path in production mode
  $app->hook(before_dispatch => sub {
    my $c = shift;
    push @{$c->req->url->base->path->trailing_slash(1)},
      shift @{$c->req->url->path->leading_slash(0)};
  }) if $app->mode eq 'production';

L<Mojo::URL> objects are very easy to manipulate, just make sure that the URL
(C<foo/bar?baz=yada>), which represents the routing destination, is always
relative to the base URL (C<http://example.com/myapp/>), which represents the
deployment location of your application.

=head2 Application embedding

From time to time you might want to reuse parts of L<Mojolicious> applications
like configuration files, database connection or helpers for other scripts,
with this little L<Mojo::Server> based mock server you can just embed them.

  use Mojo::Server;

  # Load application with mock server
  my $server = Mojo::Server->new;
  my $app = $server->load_app('./myapp.pl');

  # Access fully initialized application
  say for @{$app->static->paths};
  say $app->config->{secret_identity};
  say $app->dumper({just => 'a helper test'});
  say $app->build_controller->render_to_string(template => 'foo');

The plugin L<Mojolicious::Plugin::Mount> uses this functionality to allow you
to combine multiple applications into one and deploy them together.

  use Mojolicious::Lite;

  app->config(hypnotoad => {listen => ['http://*:80']});

  plugin Mount => {'test1.example.com' => '/home/sri/myapp1.pl'};
  plugin Mount => {'test2.example.com' => '/home/sri/myapp2.pl'};

  app->start;

=head2 Web server embedding

You can also use L<Mojo::IOLoop/"one_tick"> to embed the built-in web server
L<Mojo::Server::Daemon> into alien environments like foreign event loops that
for some reason can't just be integrated with a new reactor backend.

  use Mojolicious::Lite;
  use Mojo::IOLoop;
  use Mojo::Server::Daemon;

  # Normal action
  get '/' => {text => 'Hello World!'};

  # Connect application with web server and start accepting connections
  my $daemon
    = Mojo::Server::Daemon->new(app => app, listen => ['http://*:8080']);
  $daemon->start;

  # Call "one_tick" repeatedly from the alien environment
  Mojo::IOLoop->one_tick while 1;

=head1 REAL-TIME WEB

The real-time web is a collection of technologies that include Comet (long
polling), EventSource and WebSockets, which allow content to be pushed to
consumers with long-lived connections as soon as it is generated, instead of
relying on the more traditional pull model. All built-in web servers use
non-blocking I/O and are based on the L<Mojo::IOLoop> event loop, which
provides many very powerful features that allow real-time web applications to
scale up to thousands of concurrent client connections.

=head2 Backend web services

Since L<Mojo::UserAgent> is also based on the L<Mojo::IOLoop> event loop, it
won't block the built-in web servers when used non-blocking, even for high
latency backend web services.

  use Mojolicious::Lite;

  # Search MetaCPAN for "mojolicious"
  get '/' => sub {
    my $c = shift;
    $c->ua->get('fastapi.metacpan.org/v1/module/_search?q=mojolicious' => sub {
      my ($ua, $tx) = @_;
      $c->render('metacpan', hits => $tx->result->json->{hits}{hits});
    });
  };

  app->start;
  __DATA__

  @@ metacpan.html.ep
  <!DOCTYPE html>
  <html>
    <head><title>MetaCPAN results for "mojolicious"</title></head>
    <body>
      % for my $hit (@$hits) {
        <p><%= $hit->{_source}{release} %></p>
      % }
    </body>
  </html>

The callback passed to L<Mojo::UserAgent/"get"> will be executed once the
request to the backend web service has been finished, this is called
continuation-passing style.

=head2 Synchronizing non-blocking operations

Multiple non-blocking operations, such as concurrent requests, can be easily
synchronized with promises and L<Mojo::Promise/"all">. You create
L<Mojo::Promise> objects manually or use methods like L<Mojo::UserAgent/"get_p">
that create them for you.

  use Mojolicious::Lite;
  use Mojo::Promise;
  use Mojo::URL;

  # Search MetaCPAN for "mojo" and "minion"
  get '/' => sub {
    my $c = shift;

    # Create two promises
    my $url   = Mojo::URL->new('fastapi.metacpan.org/v1/module/_search');
    my $mojo   = $c->ua->get_p($url->clone->query({q => 'mojo'}));
    my $minion = $c->ua->get_p($url->clone->query({q => 'minion'}));

    # Render a response once both promises have been resolved
    Mojo::Promise->all($mojo, $minion)->then(sub {
      my ($mojo, $minion) = @_;
      $c->render(json => {
        mojo   => $mojo->[0]->result->json('/hits/hits/0/_source/release'),
        minion => $minion->[0]->result->json('/hits/hits/0/_source/release')
      });
    })->catch(sub {
      my $err = shift;
      $c->reply->exception($err);
    })->wait;
  };

  app->start;

To create promises manually you just wrap your continuation-passing style APIs
in functions that return promises. Here's an example for how
L<Mojo::UserAgent/"get_p"> works internally.

  use Mojo::UserAgent;
  use Mojo::Promise;

  # Wrap a user agent method with a promise
  my $ua = Mojo::UserAgent->new;
  sub get_p {
    my $promise = Mojo::Promise->new;
    $ua->get(@_ => sub {
      my ($ua, $tx) = @_;
      my $err = $tx->error;
      $promise->resolve($tx) if !$err || $err->{code};
      $promise->reject($err->{message});
    });
    return $promise;
  }

  # Use our new promise generating function
  get_p('https://mojolicious.org')->then(sub {
    my $tx = shift;
    say $tx->result->dom->at('title')->text;
  })->wait;

Promises have three states, they start out as C<pending> and you call
L<Mojo::Promise/"resolve"> to transition them to C<fulfilled>, or
L<Mojo::Promise/"reject"> to transition them to C<rejected>.

=head2 Timers

Timers, another primary feature of the event loop, are created with
L<Mojo::IOLoop/"timer"> and can, for example, be used to delay rendering of a
response, and unlike C<sleep>, won't block any other requests that might be
processed concurrently.

  use Mojolicious::Lite;
  use Mojo::IOLoop;

  # Wait 3 seconds before rendering a response
  get '/' => sub {
    my $c = shift;
    Mojo::IOLoop->timer(3 => sub {
      $c->render(text => 'Delayed by 3 seconds!');
    });
  };

  app->start;

Recurring timers created with L<Mojo::IOLoop/"recurring"> are slightly more
powerful, but need to be stopped manually, or they would just keep getting
emitted.

  use Mojolicious::Lite;
  use Mojo::IOLoop;

  # Count to 5 in 1 second steps
  get '/' => sub {
    my $c = shift;

    # Start recurring timer
    my $i = 1;
    my $id = Mojo::IOLoop->recurring(1 => sub {
      $c->write_chunk($i);
      $c->finish if $i++ == 5;
    });

    # Stop recurring timer
    $c->on(finish => sub { Mojo::IOLoop->remove($id) });
  };

  app->start;

Timers are not tied to a specific request or connection, and can even be
created at startup time.

  use Mojolicious::Lite;
  use Mojo::IOLoop;

  # Check title in the background every 10 seconds
  my $title = 'Got no title yet.';
  Mojo::IOLoop->recurring(10 => sub {
    app->ua->get('https://mojolicious.org' => sub {
      my ($ua, $tx) = @_;
      $title = $tx->result->dom->at('title')->text;
    });
  });

  # Show current title
  get '/' => sub {
    my $c = shift;
    $c->render(json => {title => $title});
  };

  app->start;

Just remember that all these non-blocking operations are processed
cooperatively, so your callbacks shouldn't block for too long.

=head2 Subprocesses

You can also use subprocesses, created with L<Mojo::IOLoop/"subprocess">, to
perform computationally expensive operations without blocking the event loop.

  use Mojolicious::Lite;
  use Mojo::IOLoop;

  # Operation that would block the event loop for 5 seconds
  get '/' => sub {
    my $c = shift;
    Mojo::IOLoop->subprocess(
      sub {
        my $subprocess = shift;
        sleep 5;
        return '♥', 'Mojolicious';
      },
      sub {
        my ($subprocess, $err, @results) = @_;
        $c->reply->exception($err) and return if $err;
        $c->render(text => "I $results[0] $results[1]!");
      }
    );
  };

  app->start;

The first callback will be executed in a child process, without blocking the
event loop of the parent process. The results of the first callback will then be
shared between both processes, and the second callback executed in the parent
process.

=head2 Exceptions in non-blocking operations

Since timers and other non-blocking operations are running solely in the event
loop, outside of the application, exceptions that get thrown in callbacks can't
get caught and handled automatically. But you can handle them manually by
subscribing to the event L<Mojo::Reactor/"error"> or catching them inside the
callback.

  use Mojolicious::Lite;
  use Mojo::IOLoop;

  # Forward error messages to the application log
  Mojo::IOLoop->singleton->reactor->on(error => sub {
    my ($reactor, $err) = @_;
    app->log->error($err);
  });

  # Exception only gets logged (and connection times out)
  get '/connection_times_out' => sub {
    my $c = shift;
    Mojo::IOLoop->timer(2 => sub {
      die 'This request will not be getting a response';
    });
  };

  # Exception gets caught and handled
  get '/catch_exception' => sub {
    my $c = shift;
    Mojo::IOLoop->timer(2 => sub {
      eval { die 'This request will be getting a response' };
      $c->reply->exception($@) if $@;
    });
  };

  app->start;

A default subscriber that turns all errors into warnings will usually be added
by L<Mojo::IOLoop> as a fallback.

  Mojo::IOLoop->singleton->reactor->unsubscribe('error');

During development or for applications where crashing is simply preferable, you
can also make every exception that gets thrown in a callback fatal by removing
all of its subscribers.

=head2 WebSocket web service

The WebSocket protocol offers full bi-directional low-latency communication
channels between clients and servers. Receive messages just by subscribing to
events such as L<Mojo::Transaction::WebSocket/"message"> with
L<Mojolicious::Controller/"on"> and return them with
L<Mojolicious::Controller/"send">.

  use Mojolicious::Lite;

  # Template with browser-side code
  get '/' => 'index';

  # WebSocket echo service
  websocket '/echo' => sub {
    my $c = shift;

    # Opened
    $c->app->log->debug('WebSocket opened');

    # Increase inactivity timeout for connection a bit
    $c->inactivity_timeout(300);

    # Incoming message
    $c->on(message => sub {
      my ($c, $msg) = @_;
      $c->send("echo: $msg");
    });

    # Closed
    $c->on(finish => sub {
      my ($c, $code, $reason) = @_;
      $c->app->log->debug("WebSocket closed with status $code");
    });
  };

  app->start;
  __DATA__

  @@ index.html.ep
  <!DOCTYPE html>
  <html>
    <head><title>Echo</title></head>
    <body>
      <script>
        var ws = new WebSocket('<%= url_for('echo')->to_abs %>');

        // Incoming messages
        ws.onmessage = function (event) {
          document.body.innerHTML += event.data + '<br/>';
        };

        // Outgoing messages
        ws.onopen = function (event) {
          window.setInterval(function () { ws.send('Hello Mojo!') }, 1000);
        };
      </script>
    </body>
  </html>

The event L<Mojo::Transaction::WebSocket/"finish"> will be emitted right after
the WebSocket connection has been closed.

  $c->tx->with_compression;

You can activate C<permessage-deflate> compression with
L<Mojo::Transaction::WebSocket/"with_compression">, this can result in much
better performance, but also increases memory usage by up to 300KiB per
connection.

  my $proto = $c->tx->with_protocols('v2.proto', 'v1.proto');

You can also use L<Mojo::Transaction::WebSocket/"with_protocols"> to negotiate a
subprotocol.

=head2 EventSource web service

EventSource is a special form of long polling where you can use
L<Mojolicious::Controller/"write"> to directly send DOM events from servers to
clients. It is uni-directional, that means you will have to use Ajax requests
for sending data from clients to servers, the advantage however is low
infrastructure requirements, since it reuses the HTTP protocol for transport.

  use Mojolicious::Lite;

  # Template with browser-side code
  get '/' => 'index';

  # EventSource for log messages
  get '/events' => sub {
    my $c = shift;

    # Increase inactivity timeout for connection a bit
    $c->inactivity_timeout(300);

    # Change content type and finalize response headers
    $c->res->headers->content_type('text/event-stream');
    $c->write;

    # Subscribe to "message" event and forward "log" events to browser
    my $cb = $c->app->log->on(message => sub {
      my ($log, $level, @lines) = @_;
      $c->write("event:log\ndata: [$level] @lines\n\n");
    });

    # Unsubscribe from "message" event again once we are done
    $c->on(finish => sub {
      my $c = shift;
      $c->app->log->unsubscribe(message => $cb);
    });
  };

  app->start;
  __DATA__

  @@ index.html.ep
  <!DOCTYPE html>
  <html>
    <head><title>LiveLog</title></head>
    <body>
      <script>
        var events = new EventSource('<%= url_for 'events' %>');

        // Subscribe to "log" event
        events.addEventListener('log', function (event) {
          document.body.innerHTML += event.data + '<br/>';
        }, false);
      </script>
    </body>
  </html>

The event L<Mojo::Log/"message"> will be emitted for every new log message and
the event L<Mojo::Transaction/"finish"> right after the transaction has been
finished.

=head2 Streaming multipart uploads

L<Mojolicious> contains a very sophisticated event system based on
L<Mojo::EventEmitter>, with ready-to-use events on almost all layers, and which
can be combined to solve some of the hardest problems in web development.

  use Mojolicious::Lite;
  use Scalar::Util 'weaken';

  # Intercept multipart uploads and log each chunk received
  hook after_build_tx => sub {
    my $tx = shift;

    # Subscribe to "upgrade" event to identify multipart uploads
    weaken $tx;
    $tx->req->content->on(upgrade => sub {
      my ($single, $multi) = @_;
      return unless $tx->req->url->path->contains('/upload');

      # Subscribe to "part" event to find the right one
      $multi->on(part => sub {
        my ($multi, $single) = @_;

        # Subscribe to "body" event of part to make sure we have all headers
        $single->on(body => sub {
          my $single = shift;

          # Make sure we have the right part and replace "read" event
          return unless $single->headers->content_disposition =~ /example/;
          $single->unsubscribe('read')->on(read => sub {
            my ($single, $bytes) = @_;

            # Log size of every chunk we receive
            app->log->debug(length($bytes) . ' bytes uploaded');
          });
        });
      });
    });
  };

  # Upload form in DATA section
  get '/' => 'index';

  # Streaming multipart upload
  post '/upload' => {text => 'Upload was successful.'};

  app->start;
  __DATA__

  @@ index.html.ep
  <!DOCTYPE html>
  <html>
    <head><title>Streaming multipart upload</title></head>
    <body>
      %= form_for upload => (enctype => 'multipart/form-data') => begin
        %= file_field 'example'
        %= submit_button 'Upload'
      % end
    </body>
  </html>

=head2 More event loops

Internally, the L<Mojo::IOLoop> event loop can use multiple reactor backends,
L<EV> for example, will be automatically used if possible. Which in turn allows
other event loops like L<AnyEvent> to just work.

  use Mojolicious::Lite;
  use EV;
  use AnyEvent;

  # Wait 3 seconds before rendering a response
  get '/' => sub {
    my $c = shift;
    my $w;
    $w = AE::timer 3, 0, sub {
      $c->render(text => 'Delayed by 3 seconds!');
      undef $w;
    };
  };

  app->start;

Who actually controls the event loop backend is not important.

  use Mojo::UserAgent;
  use EV;
  use AnyEvent;

  # Search MetaCPAN for "mojolicious"
  my $cv = AE::cv;
  my $ua = Mojo::UserAgent->new;
  $ua->get('fastapi.metacpan.org/v1/module/_search?q=mojolicious' => sub {
    my ($ua, $tx) = @_;
    $cv->send($tx->result->json('/hits/hits/0/_source/release'));
  });
  say $cv->recv;

You could, for example, just embed the built-in web server into an L<AnyEvent>
application.

  use Mojolicious::Lite;
  use Mojo::Server::Daemon;
  use EV;
  use AnyEvent;

  # Normal action
  get '/' => {text => 'Hello World!'};

  # Connect application with web server and start accepting connections
  my $daemon
    = Mojo::Server::Daemon->new(app => app, listen => ['http://*:8080']);
  $daemon->start;

  # Let AnyEvent take control
  AE::cv->recv;

=head1 USER AGENT

When we say L<Mojolicious> is a web framework we actually mean it, with
L<Mojo::UserAgent> there's a full featured HTTP and WebSocket user agent built
right in.

=head2 REST web services

Requests can be performed very comfortably with methods like
L<Mojo::UserAgent/"get">, and always result in a L<Mojo::Transaction::HTTP>
object, which has many useful attributes and methods. You can check for
connection errors with L<Mojo::Transaction/"result">, or access HTTP request and
response information directly through L<Mojo::Transaction/"req"> and
L<Mojo::Transaction/"res">.

  use Mojo::UserAgent;

  # Request a resource and make sure there were no connection errors
  my $ua = Mojo::UserAgent->new;
  my $tx = $ua->get('mojolicious.org/perldoc/Mojo' => {Accept => 'text/plain'});
  my $res = $tx->result;

  # Decide what to do with its representation
  if    ($res->is_success)  { say $res->body }
  elsif ($res->is_error)    { say $res->message }
  elsif ($res->code == 301) { say $res->headers->location }
  else                      { say 'Whatever...' }

While methods like L<Mojo::Message::Response/"is_success"> and
L<Mojo::Message::Response/"is_error"> serve as building blocks for more
sophisticated REST clients.

=head2 Web scraping

Scraping information from websites has never been this much fun before. The
built-in HTML/XML parser L<Mojo::DOM> is accessible through
L<Mojo::Message/"dom"> and supports all CSS selectors that make sense for a
standalone parser, it can be a very powerful tool especially for testing web
application.

  use Mojo::UserAgent;

  # Fetch website
  my $ua = Mojo::UserAgent->new;
  my $res = $ua->get('mojolicious.org/perldoc')->result;

  # Extract title
  say 'Title: ', $res->dom->at('head > title')->text;

  # Extract headings
  $res->dom('h1, h2, h3')->each(sub { say 'Heading: ', shift->all_text });

  # Visit all nodes recursively to extract more than just text
  for my $n ($res->dom->descendant_nodes->each) {

    # Text or CDATA node
    print $n->content if $n->type eq 'text' || $n->type eq 'cdata';

    # Also include alternate text for images
    print $n->{alt} if $n->type eq 'tag' && $n->tag eq 'img';
  }

For a full list of available CSS selectors see L<Mojo::DOM::CSS/"SELECTORS">.

=head2 JSON web services

Most web services these days are based on the JSON data-interchange format.
That's why L<Mojolicious> comes with the possibly fastest pure-Perl
implementation L<Mojo::JSON> built right in, which is accessible through
L<Mojo::Message/"json">.

  use Mojo::UserAgent;
  use Mojo::URL;

  # Fresh user agent
  my $ua = Mojo::UserAgent->new;

  # Search MetaCPAN for "mojolicious" and list latest releases
  my $url = Mojo::URL->new('http://fastapi.metacpan.org/v1/release/_search');
  $url->query({q => 'mojolicious', sort => 'date:desc'});
  for my $hit (@{$ua->get($url)->result->json->{hits}{hits}}) {
    say "$hit->{_source}{name} ($hit->{_source}{author})";
  }

=head2 Basic authentication

You can just add username and password to the URL, an C<Authorization> header
will be automatically generated.

  use Mojo::UserAgent;

  my $ua = Mojo::UserAgent->new;
  say $ua->get('https://sri:[email protected]/hideout')->result->body;

=head2 Decorating follow-up requests

L<Mojo::UserAgent> can automatically follow redirects, the event
L<Mojo::UserAgent/"start"> allows you direct access to each transaction right
after they have been initialized and before a connection gets associated with
them.

  use Mojo::UserAgent;

  # User agent following up to 10 redirects
  my $ua = Mojo::UserAgent->new(max_redirects => 10);

  # Add a witty header to every request
  $ua->on(start => sub {
    my ($ua, $tx) = @_;
    $tx->req->headers->header('X-Bender' => 'Bite my shiny metal ass!');
    say 'Request: ', $tx->req->url->clone->to_abs;
  });

  # Request that will most likely get redirected
  say 'Title: ', $ua->get('google.com')->result->dom->at('head > title')->text;

This even works for proxy C<CONNECT> requests.

=head2 Content generators

Content generators can be registered with
L<Mojo::UserAgent::Transactor/"add_generator"> to generate the same type of
content repeatedly for multiple requests.

  use Mojo::UserAgent;
  use Mojo::Asset::File;

  # Add "stream" generator
  my $ua = Mojo::UserAgent->new;
  $ua->transactor->add_generator(stream => sub {
    my ($transactor, $tx, $path) = @_;
    $tx->req->content->asset(Mojo::Asset::File->new(path => $path));
  });

  # Send multiple files streaming via PUT and POST
  $ua->put('http://example.com/upload'  => stream => '/home/sri/mojo.png');
  $ua->post('http://example.com/upload' => stream => '/home/sri/minion.png');

The C<json>, C<form> and C<multipart> content generators are always available.

  use Mojo::UserAgent;

  # Send "application/json" content via PATCH
  my $ua = Mojo::UserAgent->new;
  my $tx = $ua->patch('http://api.example.com' => json => {foo => 'bar'});

  # Send query parameters via GET
  my $tx2 = $ua->get('search.example.com' => form => {q => 'test'});

  # Send "application/x-www-form-urlencoded" content via POST
  my $tx3 = $ua->post('http://search.example.com' => form => {q => 'test'});

  # Send "multipart/form-data" content via PUT
  my $tx4 = $ua->put(
    'upload.example.com' => form => {test => {content => 'Hello World!'}});

  # Send custom multipart content via PUT
  my $tx5 = $ua->put('api.example.com' => multipart => ['Hello', 'World!']);

For more information about available content generators see also
L<Mojo::UserAgent::Transactor/"tx">.

=head2 Large file downloads

When downloading large files with L<Mojo::UserAgent> you don't have to worry
about memory usage at all, because it will automatically stream everything
above 250KiB into a temporary file, which can then be moved into a permanent
file with L<Mojo::Asset::File/"move_to">.

  use Mojo::UserAgent;

  # Fetch the latest Mojolicious tarball
  my $ua = Mojo::UserAgent->new(max_redirects => 5);
  my $tx = $ua->get('https://www.github.com/kraih/mojo/tarball/master');
  $tx->result->content->asset->move_to('mojo.tar.gz');

To protect you from excessively large files there is also a limit of 2GiB by
default, which you can tweak with the attribute
L<Mojo::UserAgent/"max_response_size">.

  # Increase limit to 10GiB
  $ua->max_response_size(10737418240);

=head2 Large file upload

Uploading a large file is even easier.

  use Mojo::UserAgent;

  # Upload file via POST and "multipart/form-data"
  my $ua = Mojo::UserAgent->new;
  $ua->post('example.com/upload' =>
    form => {image => {file => '/home/sri/hello.png'}});

And once again you don't have to worry about memory usage, all data will be
streamed directly from the file.

=head2 Streaming response

Receiving a streaming response can be really tricky in most HTTP clients, but
L<Mojo::UserAgent> makes it actually easy.

  use Mojo::UserAgent;

  # Accept responses of indefinite size
  my $ua = Mojo::UserAgent->new(max_response_size => 0);

  # Build a normal transaction
  my $tx = $ua->build_tx(GET => 'http://example.com');

  # Replace "read" events to disable default content parser
  $tx->res->content->unsubscribe('read')->on(read => sub {
    my ($content, $bytes) = @_;
    say "Streaming: $bytes";
  });

  # Process transaction
  $tx = $ua->start($tx);

The event L<Mojo::Content/"read"> will be emitted for every chunk of data that
is received, even chunked transfer encoding and gzip content encoding will be
handled transparently if necessary.

=head2 Streaming request

Sending a streaming request is almost just as easy.

  use Mojo::UserAgent;

  # Build a normal transaction
  my $ua = Mojo::UserAgent->new;
  my $tx = $ua->build_tx(GET => 'http://example.com');

  # Prepare body
  my $body = 'Hello World!';
  $tx->req->headers->content_length(length $body);

  # Start writing directly with a drain callback
  my $drain;
  $drain = sub {
    my $content = shift;
    my $chunk = substr $body, 0, 1, '';
    $drain = undef unless length $body;
    $content->write($chunk, $drain);
  };
  $tx->req->content->$drain;

  # Process transaction
  $tx = $ua->start($tx);

The drain callback passed to L<Mojo::Content/"write"> will be executed whenever
the entire previous chunk of data has actually been written.

=head2 Non-blocking

L<Mojo::UserAgent> has been designed from the ground up to be non-blocking, the
whole blocking API is just a simple convenience wrapper. Especially for high
latency tasks like web crawling this can be extremely useful, because you can
keep many concurrent connections active at the same time.

  use Mojo::UserAgent;
  use Mojo::IOLoop;

  # Concurrent non-blocking requests
  my $ua = Mojo::UserAgent->new;
  $ua->get('https://metacpan.org/search?q=mojo' => sub {
    my ($ua, $mojo) = @_;
    say $mojo->result->dom->at('title')->text;
  });
  $ua->get('https://metacpan.org/search?q=minion' => sub {
    my ($ua, $minion) = @_;
    say $minion->result->dom->at('title')->text;
  });

  # Start event loop if necessary
  Mojo::IOLoop->start unless Mojo::IOLoop->is_running;

But don't try to open too many connections to one server at the same time, it
might get overwhelmed. Better use a queue to process requests in smaller
batches.

  use Mojo::UserAgent;
  use Mojo::IOLoop;

  my @urls = (
    'mojolicious.org/perldoc/Mojo/DOM',  'mojolicious.org/perldoc/Mojo',
    'mojolicious.org/perldoc/Mojo/File', 'mojolicious.org/perldoc/Mojo/URL'
  );

  # User agent with a custom name, following up to 5 redirects
  my $ua = Mojo::UserAgent->new(max_redirects => 5);
  $ua->transactor->name('MyParallelCrawler 1.0');

  # Use a delay to keep the event loop running until we are done
  my $delay = Mojo::IOLoop->delay;
  my $fetch;
  $fetch = sub {

    # Stop if there are no more URLs
    return unless my $url = shift @urls;

    # Fetch the next title
    my $end = $delay->begin;
    $ua->get($url => sub {
      my ($ua, $tx) = @_;
      say "$url: ", $tx->result->dom->at('title')->text;

      # Next request
      $fetch->();
      $end->();
    });
  };

  # Process two requests at a time
  $fetch->() for 1 .. 2;
  $delay->wait;

It is also strongly recommended to respect every sites C<robots.txt> file as
well as terms of service, and to wait a little before reopening connections to
the same host, or the operators might be forced to block your access.

=head2 Concurrent blocking requests

You might have seen L<Mojo::Promise/"wait"> already in some examples
above. It is used to make non-blocking operations portable, allowing them to
work inside an already running event loop or start one on demand.

  use Mojo::UserAgent;
  use Mojo::Promise;

  # Synchronize non-blocking requests with promises
  my $ua = Mojo::UserAgent->new;
  my $mojo   = $ua->get_p('https://metacpan.org/search?q=mojo');
  my $minion = $ua->get_p('https://metacpan.org/search?q=minion');
  Mojo::Promise->all($mojo, $minion)->then(sub {
    my ($mojo, $minion) = @_;
    say $mojo->[0]->result->dom->at('title')->text;
    say $minion->[0]->result->dom->at('title')->text;
  })->wait;

=head2 WebSockets

WebSockets are not just for the server-side, you can use
L<Mojo::UserAgent/"websocket_p"> to open new connections, which are always
non-blocking. The WebSocket handshake uses HTTP, and is a normal C<GET> request
with a few additional headers. It can even contain cookies, and is followed by
a C<101> response from the server, notifying our user agent that the connection
has been established and it can start using the bi-directional WebSocket
protocol.

  use Mojo::UserAgent;
  use Mojo::Promise;

  # Open WebSocket to echo service
  my $ua = Mojo::UserAgent->new;
  $ua->websocket_p('ws://echo.websocket.org')->then(sub {
    my $tx = shift;

    # Prepare a followup promise so we can wait for messages
    my $promise = Mojo::Promise->new;

    # Wait for WebSocket to be closed
    $tx->on(finish => sub {
      my ($tx, $code, $reason) = @_;
      say "WebSocket closed with status $code.";
      $promise->resolve;
    });

    # Close WebSocket after receiving one message
    $tx->on(message => sub {
      my ($tx, $msg) = @_;
      say "WebSocket message: $msg";
      $tx->finish;
    });

    # Send a message to the server
    $tx->send('Hi!');

    # Insert a new promise into the promise chain
    return $promise;
  })->catch(sub {
    my $err = shift;

    # Handle failed WebSocket handshakes and other exceptions
    warn "WebSocket error: $err";
  })->wait;

=head2 UNIX domain sockets

Not just TCP/IP sockets are supported, but also UNIX domain sockets, which can
have significant security and performance benefits when used for inter-process
communication. Instead of C<http://> and C<ws://> you can use the
C<http+unix://> and C<ws+unix://> schemes, and pass along a percent encoded path
(C</> becomes C<%2F>) instead of a hostname.

  use Mojo::UserAgent;
  use Mojo::Promise;

  # GET request via UNIX domain socket "/tmp/foo.sock"
  my $ua = Mojo::UserAgent->new;
  say $ua->get('http+unix://%2Ftmp%2Ffoo.sock/index.html')->result->body;

  # GET request with HOST header via UNIX domain socket "/tmp/bar.sock"
  my $tx = $ua->get('http+unix://%2Ftmp%2Fbar.sock' => {Host => 'example.com'});
  say $tx->result->body;

  # WebSocket connection via UNIX domain socket "/tmp/baz.sock"
  $ua->websocket_p('ws+unix://%2Ftmp%2Fbaz.sock/echo')->then(sub {
    my $tx = shift;

    my $promise = Mojo::Promise->new;
    $tx->on(finish => sub { $promise->resolve });

    $tx->on(message => sub {
      my ($tx, $msg) = @_;
      say "WebSocket message: $msg";
      $tx->finish;
    });
    $tx->send('Hi!');

    return $promise;
  })->catch(sub {
    my $err = shift;
    warn "WebSocket error: $err";
  })->wait;

You can set the C<Host> header manually to pass along a hostname.

=head2 Command line

Don't you hate checking huge HTML files from the command line? Thanks to the
command L<Mojolicious::Command::get> that is about to change. You can just pick
the parts that actually matter with the CSS selectors from L<Mojo::DOM> and
JSON Pointers from L<Mojo::JSON::Pointer>.

  $ mojo get https://mojolicious.org 'head > title'

How about a list of all id attributes?

  $ mojo get https://mojolicious.org '*' attr id

Or the text content of all heading tags?

  $ mojo get https://mojolicious.org 'h1, h2, h3' text

Maybe just the text of the third heading?

  $ mojo get https://mojolicious.org 'h1, h2, h3' 3 text

You can also extract all text from nested child elements.

  $ mojo get https://mojolicious.org '#mojobar' all

The request can be customized as well.

  $ mojo get -M POST -H 'X-Bender: Bite my shiny metal ass!' http://google.com

Store response data by redirecting C<STDOUT>.

  $ mojo get mojolicious.org > example.html

Pass request data by redirecting C<STDIN>.

  $ mojo get -M PUT mojolicious.org < example.html

Or use the output of another program.

  $ echo 'Hello World' | mojo get -M PUT https://mojolicious.org

Submit forms as C<application/x-www-form-urlencoded> content.

  $ mojo get -M POST -f 'q=Mojo' -f 'size=5' https://metacpan.org/search

And upload files as C<multipart/form-data> content.

  $ mojo get -M POST -f '[email protected]' mojolicious.org

You can follow redirects and view the headers for all messages.

  $ mojo get -r -v http://google.com 'head > title'

Extract just the information you really need from JSON data structures.

  $ mojo get https://fastapi.metacpan.org/v1/author/SRI /name

This can be an invaluable tool for testing your applications.

  $ ./myapp.pl get /welcome 'head > title'

=head2 One-liners

For quick hacks and especially testing, L<ojo> one-liners are also a great
choice.

  $ perl -Mojo -E 'say g("mojolicious.org")->dom->at("title")->text'

=head1 APPLICATIONS

Fun L<Mojolicious> application hacks for all occasions.

=head2 Basic authentication

Basic authentication data will be automatically extracted from the
C<Authorization> header.

  use Mojolicious::Lite;
  use Mojo::Util 'secure_compare';

  get '/' => sub {
    my $c = shift;

    # Check for username "Bender" and password "rocks"
    return $c->render(text => 'Hello Bender!')
      if secure_compare $c->req->url->to_abs->userinfo, 'Bender:rocks';

    # Require authentication
    $c->res->headers->www_authenticate('Basic');
    $c->render(text => 'Authentication required!', status => 401);
  };

  app->start;

This can be combined with TLS for a secure authentication mechanism.

  $ ./myapp.pl daemon -l 'https://*:3000?cert=./server.crt&key=./server.key'

=head2 Adding a configuration file

Adding a configuration file to your application is as easy as adding a file to
its home directory and loading the plugin L<Mojolicious::Plugin::Config>. The
default name is based on the value of L<Mojolicious/"moniker"> (C<myapp>),
appended with a C<.conf> extension (C<myapp.conf>).

  $ mkdir myapp
  $ cd myapp
  $ touch myapp.pl
  $ chmod 744 myapp.pl
  $ echo '{name => "my Mojolicious application"};' > myapp.conf

Configuration files themselves are just Perl scripts that return a hash
reference with configuration settings of your choice. All those settings are
then available through the method L<Mojolicious/"config"> and the helper
L<Mojolicious::Plugin::DefaultHelpers/"config">.

  use Mojolicious::Lite;

  plugin 'Config';

  my $name = app->config('name');
  app->log->debug("Welcome to $name");

  get '/' => 'with_config';

  app->start;
  __DATA__
  @@ with_config.html.ep
  <!DOCTYPE html>
  <html>
    <head><title><%= config 'name' %></title></head>
    <body>Welcome to <%= config 'name' %></body>
  </html>

Alternatively you can also use configuration files in the JSON format with
L<Mojolicious::Plugin::JSONConfig>.

=head2 Adding a plugin to your application

To organize your code better and to prevent helpers from cluttering your
application, you can use application specific plugins.

  $ mkdir -p lib/MyApp/Plugin
  $ touch lib/MyApp/Plugin/MyHelpers.pm

They work just like normal plugins and are also subclasses of
L<Mojolicious::Plugin>. Nested helpers with a prefix based on the plugin name
are an easy way to avoid conflicts.

  package MyApp::Plugin::MyHelpers;
  use Mojo::Base 'Mojolicious::Plugin';

  sub register {
    my ($self, $app) = @_;
    $app->helper('my_helpers.render_with_header' => sub {
      my ($c, @args) = @_;
      $c->res->headers->header('X-Mojo' => 'I <3 Mojolicious!');
      $c->render(@args);
    });
  }

  1;

You can have as many application specific plugins as you like, the only
difference to normal plugins is that you load them using their full class name.

  use Mojolicious::Lite;

  use lib 'lib';

  plugin 'MyApp::Plugin::MyHelpers';

  get '/' => sub {
    my $c = shift;
    $c->my_helpers->render_with_header(text => 'I ♥ Mojolicious!');
  };

  app->start;

Of course these plugins can contain more than just helpers, take a look at
L<Mojolicious::Plugins/"PLUGINS"> for a few ideas.

=head2 Adding commands to Mojolicious

By now you've probably used many of the built-in commands described in
L<Mojolicious::Commands>, but did you know that you can just add new ones and
that they will be picked up automatically by the command line interface if they
are placed in a directory from C<@INC>?

  package Mojolicious::Command::spy;
  use Mojo::Base 'Mojolicious::Command';

  has description => 'Spy on application';
  has usage       => "Usage: APPLICATION spy [TARGET]\n";

  sub run {
    my ($self, @args) = @_;

    # Leak secret passphrases
    if ($args[0] eq 'secrets') { say for @{$self->app->secrets} }

    # Leak mode
    elsif ($args[0] eq 'mode') { say $self->app->mode }
  }

  1;

Command line arguments are passed right through and there are many useful
attributes and methods in L<Mojolicious::Command> that you can use or overload.

  $ mojo spy secrets
  HelloWorld

  $ ./script/myapp spy secrets
  secr3t

And to make your commands application specific, just add a custom namespace to
L<Mojolicious::Commands/"namespaces"> and use a class name like
C<MyApp::Command::spy> instead of C<Mojolicious::Command::spy>.

  # Application
  package MyApp;
  use Mojo::Base 'Mojolicious';

  sub startup {
    my $self = shift;

    # Add another namespace to load commands from
    push @{$self->commands->namespaces}, 'MyApp::Command';
  }

  1;

The options C<-h>/C<--help>, C<--home> and C<-m>/C<--mode> are handled
automatically by L<Mojolicious::Commands> and are shared by all commands.

  $ ./script/myapp spy -m production mode
  production

For a full list of shared options see L<Mojolicious::Commands/"SYNOPSIS">.

=head2 Running code against your application

Ever thought about running a quick one-liner against your L<Mojolicious>
application to test something? Thanks to the command
L<Mojolicious::Command::eval> you can do just that, the application object
itself can be accessed via C<app>.

  $ mojo generate lite_app myapp.pl
  $ ./myapp.pl eval 'say for @{app->static->paths}'
  $ ./myapp.pl eval 'say for sort keys %{app->renderer->helpers}'

The C<verbose> options will automatically print the return value or returned
data structure to C<STDOUT>.

  $ ./myapp.pl eval -v 'app->static->paths->[0]'
  $ ./myapp.pl eval -V 'app->static->paths'

=head2 Making your application installable

Ever thought about releasing your L<Mojolicious> application to CPAN? It's
actually much easier than you might think.

  $ mojo generate app MyApp
  $ cd my_app
  $ mv public lib/MyApp/
  $ mv templates lib/MyApp/

The trick is to move the C<public> and C<templates> directories so they can get
automatically installed with the modules.

  # Application
  package MyApp;
  use Mojo::Base 'Mojolicious';

  use Mojo::File 'path';
  use Mojo::Home;

  # Every CPAN module needs a version
  our $VERSION = '1.0';

  sub startup {
    my $self = shift;

    # Switch to installable home directory
    $self->home(Mojo::Home->new(path(__FILE__)->sibling('MyApp')));

    # Switch to installable "public" directory
    $self->static->paths->[0] = $self->home->child('public');

    # Switch to installable "templates" directory
    $self->renderer->paths->[0] = $self->home->child('templates');

    $self->plugin('PODRenderer');

    my $r = $self->routes;
    $r->get('/welcome')->to('example#welcome');
  }

  1;

Finally there is just one small change to be made to the application script. The
shebang line becomes the recommended C<#!perl>, which the toolchain can rewrite
to the proper shebang during installation.

  #!perl

  use strict;
  use warnings;

  use FindBin;
  BEGIN { unshift @INC, "$FindBin::Bin/../lib" }
  use Mojolicious::Commands;

  # Start command line interface for application
  Mojolicious::Commands->start_app('MyApp');

That's really everything, now you can package your application like any other
CPAN module.

  $ ./script/my_app generate makefile
  $ perl Makefile.PL
  $ make test
  $ make manifest
  $ make dist

And if you have a PAUSE account (which can be requested at
L<http://pause.perl.org>) even upload it.

  $ mojo cpanify -u USER -p PASS MyApp-0.01.tar.gz

=head2 Hello World

If every byte matters this is the smallest C<Hello World> application you can
write with L<Mojolicious::Lite>.

  use Mojolicious::Lite;
  any {text => 'Hello World!'};
  app->start;

It works because all routes without a pattern default to C</> and automatic
rendering kicks in even if no actual code gets executed by the router. The
renderer just picks up the C<text> value from the stash and generates a
response.

=head2 Hello World one-liners

The C<Hello World> example above can get even a little bit shorter in an L<ojo>
one-liner.

  $ perl -Mojo -E 'a({text => "Hello World!"})->start' daemon

And you can use all the commands from L<Mojolicious::Commands>.

  $ perl -Mojo -E 'a({text => "Hello World!"})->start' get -v /

=head1 MORE

You can continue with L<Mojolicious::Guides> now or take a look at the
L<Mojolicious wiki|http://github.com/kraih/mojo/wiki>, which contains a lot more
documentation and examples by many different authors.

=head1 SUPPORT

If you have any questions the documentation might not yet answer, don't
hesitate to ask on the
L<mailing list|http://groups.google.com/group/mojolicious> or the official IRC
channel C<#mojo> on C<irc.perl.org>
(L<chat now!|https://chat.mibbit.com/?channel=%23mojo&server=irc.perl.org>).

=cut