=encoding utf8

=head1 NAME

Mojolicious::Guides::Cookbook - Cookbook

=head1 OVERVIEW

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

=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/myapp daemon
  Server available at http://127.0.0.1:3000.

It has many configuration options and is known to work on every platform Perl
works on.

  $ ./script/myapp 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/myapp daemon -l https://*:3000
  Server available at https://127.0.0.1:3000.

On UNIX platforms you can also add preforking with L<Mojo::Server::Prefork>.

  $ ./script/myapp 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.

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

Your application is preloaded in the manager process during startup, to run
code whenever a new worker process has been forked you can use L<Mojo::IOLoop>
timers.

  use Mojolicious::Lite;

  Mojo::IOLoop->timer(0 => sub {
    app->log->info("Worker $$ star...ALL GLORY TO THE HYPNOTOAD!");
  });

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

  app->start;

=head2 Morbo

After reading the L<Mojolicious::Lite> 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.

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

=head2 Hypnotoad

For bigger applications L<Mojolicious> contains the UNIX optimized preforking
web server L<Mojo::Server::Hypnotoad> that will allow you to take advantage of
multiple CPU cores and copy-on-write.

  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 preforking
to L<Mojo::Server::Daemon>, but optimized specifically for production
environments out of the box.

  $ hypnotoad script/myapp
  Server available at http://127.0.0.1:8080.

You can tweak many configuration settings right from within your application
with L<Mojo/"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/myapp
  Starting hot deployment for Hypnotoad server 31841.

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

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

=head2 Zero downtime software upgrades

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/myapp 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 start a second web server listening to the same port and
stop the first web server gracefully afterwards.

  $ ./script/myapp 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 Hypnotoad behind an Nginx 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-HTTPS 0;
    }
  }

=head2 Apache/mod_proxy

Another good reverse proxy is Apache with C<mod_proxy>, the configuration
looks quite similar to the Nginx one above.

  <VirtualHost *:80>
    ServerName localhost
    <Proxy *>
      Order deny,allow
      Allow from all
    </Proxy>
    ProxyRequests Off
    ProxyPreserveHost On
    ProxyPass / http://localhost:8080/ keepalive=On
    ProxyPassReverse / http://localhost:8080/
    RequestHeader set X-Forwarded-HTTPS "0"
  </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.

  ScriptAlias / /home/sri/myapp/script/myapp/

=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>.

  $ plackup ./script/myapp
  HTTP::Server::PSGI: Accepting connections at http://0:5000/

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/myapp -s FCGI -l /tmp/myapp.sock

If an older server adapter is not be able to correctly detect the application
home directory, you can simply use the MOJO_HOME environment variable.

  $ MOJO_HOME=/home/sri/myapp plackup ./script/myapp
  HTTP::Server::PSGI: Accepting connections at http://0:5000/

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 'myapp.pl';
  };

But you could even use middleware right in your application.

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

  get '/welcome' => sub {
    my $self = shift;
    $self->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-*> headers. In such cases
you can use the hook L<Mojolicious/"before_dispatch"> to rewrite incoming
requests.

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

  # 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'});

=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 clients.

=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 $self = shift;
    $self->ua->get('api.metacpan.org/v0/module/_search?q=mojolicious' => sub {
      my ($ua, $tx) = @_;
      $self->render('metacpan', hits => $tx->res->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>

Multiple events such as parallel requests can be easily synchronized with
L<Mojo::IOLoop/"delay">.

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

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

    # Prepare response in two steps
    Mojo::IOLoop->delay(

      # Parallel requests
      sub {
        my $delay = shift;
        my $url   = Mojo::URL->new('api.metacpan.org/v0/module/_search');
        $url->query({sort => 'date:desc'});
        $self->ua->get($url->clone->query({q => 'mojo'})  => $delay->begin);
        $self->ua->get($url->clone->query({q => 'mango'}) => $delay->begin);
      },

      # Delayed rendering
      sub {
        my ($delay, $mojo, $mango) = @_;
        $self->render(json => {
          mojo  => $mojo->res->json('/hits/hits/0/_source/release'),
          mango => $mango->res->json('/hits/hits/0/_source/release')
        });
      }
    );
  };

  app->start;

=head2 Timers

Another primary feature of the L<Mojo::IOLoop> event loop are timers, which
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 in parallel.

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

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

  app->start;

Recurring timers 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 $self = shift;

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

    # Stop recurring timer
    $self->on(finish => sub { Mojo::IOLoop->remove($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;

  # Count seconds since startup
  my $i = 0;
  Mojo::IOLoop->recurring(1 => sub { $i++ });

  # Show counter
  get '/' => sub {
    my $self = shift;
    $self->render(text => "About $i seconds running!");
  };

  app->start;

Since timers and other low level event watchers are also independent from
applications, errors can't get logged automatically, you can change that by
subscribing to the event L<Mojo::Reactor/"error">.

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

Just remember that all events are processed cooperatively, so your callbacks
shouldn't block for too long.

=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 the method
L<Mojolicious::Controller/"on"> and return them with
L<Mojolicious::Controller/"send">.

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

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

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

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

    # Increase inactivity timeout for connection a bit
    Mojo::IOLoop->stream($self->tx->connection)->timeout(300);

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

    # Closed
    $self->on(finish => sub {
      my ($self, $code, $reason) = @_;
      $self->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
        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.

=head2 Testing WebSocket web services

While the message flow on WebSocket connections can be rather dynamic, it
more often than not is quite predictable, which allows this rather pleasant
L<Test::Mojo> API to be used.

  use Test::More;
  use Test::Mojo;

  # Include application
  use FindBin;
  require "$FindBin::Bin/../echo.pl";

  # Test echo web service
  my $t = Test::Mojo->new;
  $t->websocket_ok('/echo')
    ->send_ok('Hello Mojo!')
    ->message_ok
    ->message_is('echo: Hello Mojo!')
    ->finish_ok;

  # Test JSON web service
  $t->websocket_ok('/echo.json')
    ->send_ok({json => {test => [1, 2, 3]}})
    ->message_ok
    ->json_message_is('/test', [1, 2, 3])
    ->finish_ok;

  done_testing();

=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;
  use Mojo::IOLoop;

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

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

    # Increase inactivity timeout for connection a bit
    Mojo::IOLoop->stream($self->tx->connection)->timeout(300);

    # Change content type
    $self->res->headers->content_type('text/event-stream');

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

    # Unsubscribe from "message" event again once we are done
    $self->on(finish => sub {
      my $self = shift;
      $self->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 hardest problems in web development.

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

  # Emit "request" event early for requests that get upgraded to multipart
  hook after_build_tx => sub {
    my $tx = shift;
    weaken $tx;
    $tx->req->content->on(upgrade => sub { $tx->emit('request') });
  };

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

  # Streaming multipart upload (invoked twice, due to early "request" event)
  post '/upload' => sub {
    my $self = shift;

    # First invocation, subscribe to "part" event to find the right one
    return $self->req->content->on(part => sub {
      my ($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
          $self->app->log->debug(length($bytes) . ' bytes uploaded.');
        });
      });
    }) unless $self->req->is_finished;

    # Second invocation, render response
    $self->render(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 Event loops

Internally the L<Mojo::IOLoop> event loop can use multiple reactor backends,
L<EV> for example will be automatically used if installed. 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 $self = shift;
    my $w;
    $w = AE::timer 3, 0, sub {
      $self->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;
  $ua->get('api.metacpan.org/v0/module/_search?q=mojolicious' => sub {
    my ($ua, $tx) = @_;
    $cv->send($tx->res->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.

=head2 Web scraping

Scraping information from web sites 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 unit testing
web application.

  use Mojo::UserAgent;

  # Fetch web site
  my $ua = Mojo::UserAgent->new;
  my $tx = $ua->get('mojolicio.us/perldoc');

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

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

  # Visit all elements recursively to extract more than just text
  for my $e ($tx->res->dom('*')->each) {

    # Text before this element
    print $e->text_before(0);

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

    # Text for elements without children
    print $e->text(0) unless $e->children->size;

    # Text after last element
    print $e->text_after(0) unless $e->next;
  }

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, it 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://api.metacpan.org/v0/release/_search');
  $url->query({q => 'mojolicious', sort => 'date:desc'});
  for my $hit (@{$ua->get($url)->res->json->{hits}{hits}}) {
    say "$hit->{_source}{name} ($hit->{_source}{author})";
  }

=head2 Basic authentication

You can just add username and password to the URL.

  use Mojo::UserAgent;

  my $ua = Mojo::UserAgent->new;
  say $ua->get('https://sri:secret@example.com/hideout')->res->body;

=head2 Decorating followup 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')->res->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/mango.png');

The C<json> and C<form> 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('http://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('http://upload.example.com' =>
    form => {test => {content => '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 C<250KB> into a temporary file, which can then be moved into a permanent
file with L<Mojo::Asset::File/"move_to">.

  use Mojo::UserAgent;

  # Lets fetch the latest Mojolicious tarball
  my $ua = Mojo::UserAgent->new(max_redirects => 5);
  my $tx = $ua->get('latest.mojolicio.us');
  $tx->res->content->asset->move_to('mojo.tar.gz');

To protect you from excessively large files there is also a limit of C<10MB>
by default, which you can tweak with the MOJO_MAX_MESSAGE_SIZE environment
variable.

  # Increase limit to 1GB
  $ENV{MOJO_MAX_MESSAGE_SIZE} = 1073741824;

=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;

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

  # Accept response of indefinite size
  $tx->res->max_message_size(0);

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

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

The event L<Mojo::Content/"read"> will be emitted for every chunk of data that
is received, even C<chunked> 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
  $ua->start($tx);

The drain callback passed to L<Mojo::Content/"write"> will be invoked whenever
the entire previous chunk 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 parallel connections active at the same time.

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

  # Parallel non-blocking requests
  my $ua = Mojo::UserAgent->new;
  $ua->get('http://metacpan.org/search?q=mojo' => sub {
    my ($ua, $mojo) = @_;
    ...
  });
  $ua->get('http://metacpan.org/search?q=mango' => sub {
    my ($ua, $mango) = @_;
    ...
  });

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

You can take full control of the L<Mojo::IOLoop> event loop.

=head2 Parallel blocking requests

You can emulate blocking behavior by using L<Mojo::IOLoop/"delay"> to
synchronize multiple non-blocking requests.

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

  # Synchronize non-blocking requests and capture results
  my $ua    = Mojo::UserAgent->new;
  my $delay = Mojo::IOLoop->delay;
  $ua->get('http://metacpan.org/search?q=mojo'  => $delay->begin);
  $ua->get('http://metacpan.org/search?q=mango' => $delay->begin);
  my ($mojo, $mango) = $delay->wait;

The event L<Mojo::IOLoop::Delay/"finish"> can be used for code that needs to
be able to work standalone as well as inside an already running event loop.

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

  # Synchronize non-blocking requests portably
  my $ua    = Mojo::UserAgent->new;
  my $delay = Mojo::IOLoop->delay;
  $delay->on(finish => sub {
    my ($delay, $mojo, $mango) = @_;
    ...
  });
  $ua->get('http://metacpan.org/search?q=mojo'  => $delay->begin);
  $ua->get('http://metacpan.org/search?q=mango' => $delay->begin);
  $delay->wait unless Mojo::IOLoop->is_running;

=head2 Command line

Don't you hate checking huge HTML files from the command line? Thanks to the
C<mojo get> command 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 http://mojolicio.us 'head > title'

How about a list of all id attributes?

  $ mojo get http://mojolicio.us '*' attr id

Or the text content of all heading tags?

  $ mojo get http://mojolicio.us 'h1, h2, h3' text

Maybe just the text of the third heading?

  $ mojo get http://mojolicio.us 'h1, h2, h3' 3 text

You can also extract all text from nested child elements.

  $ mojo get http://mojolicio.us '#mojobar' all

The request can be customized as well.

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

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://api.metacpan.org/v0/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("mojolicio.us")->dom->html->head->title->text'

=head1 HACKS

Fun hacks you might not use very often but that might come in handy some day.

=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?

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

  has description => "Spy on application.\n";
  has usage       => "usage: $0 spy [TARGET]\n";

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

    # Leak secret passphrase
    if ($target eq 'secret') {
      my $secret = $self->app->secret;
      say qq{The secret of this application is "$secret".};
    }
  }

  1;

There are many more useful attributes and methods in L<Mojolicious::Command>
that you can use or overload.

  $ mojo spy secret
  The secret of this application is "HelloWorld".

  $ ./myapp.pl spy secret
  The secret of this application is "secr3t".

And to make your commands application specific, just put them in a different
namespace.

  # 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;

=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 C<eval> command 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}'

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 File::Basename 'dirname';
  use File::Spec::Functions 'catdir';

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

  sub startup {
    my $self = shift;

    # Switch to installable home directory
    $self->home->parse(catdir(dirname(__FILE__), 'MyApp'));

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

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

    $self->plugin('PODRenderer');

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

  1;

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 C<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>.

=cut