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rails_on_rack.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Rails on Rack</title>
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<body>
<div id="header" >
<div id="logo">
<a href="index.html" title="Ruby on Rails"><img src="images/rails_logo_remix.gif" alt="Rails" height="140" width="110" /></a>
</div>
<h1 id="site_title"><span>Ruby on Rails</span></h1>
<h2 id="site_title_tagline">Sustainable productivity for web-application development</h2>
<ul id="navMain">
<li class="first-child"><a href="http://www.rubyonrails.org/" title="Ruby on Rails" class="ruby_on_rails">Ruby on Rails</a></li>
<li><a class="manuals" href="index.html" title="Manuals Index">Guides Index</a></li>
</ul>
</div>
<div id="container">
<div id="sidebar">
<h2>Chapters</h2>
<ol>
<li>
<a href="#_introduction_to_rack">Introduction to Rack</a>
</li>
<li>
<a href="#_rails_on_rack">Rails on Rack</a>
<ul>
<li><a href="#_actioncontroller_dispatcher_new">ActionController::Dispatcher.new</a></li>
<li><a href="#_script_server">script/server</a></li>
<li><a href="#_rackup">rackup</a></li>
</ul>
</li>
<li>
<a href="#_action_controller_middleware_stack">Action Controller Middleware Stack</a>
<ul>
<li><a href="#_adding_middlewares">Adding Middlewares</a></li>
<li><a href="#_internal_middleware_stack">Internal Middleware Stack</a></li>
<li><a href="#_customizing_internal_middleware_stack">Customizing Internal Middleware Stack</a></li>
<li><a href="#_inspecting_middleware_stack">Inspecting Middleware Stack</a></li>
</ul>
</li>
<li>
<a href="#_rails_metal_applications">Rails Metal Applications</a>
<ul>
<li><a href="#_generating_a_metal_application">Generating a Metal Application</a></li>
<li><a href="#_execution_order">Execution Order</a></li>
</ul>
</li>
<li>
<a href="#_middlewares_and_rails">Middlewares and Rails</a>
</li>
<li>
<a href="#_changelog">Changelog</a>
</li>
</ol>
</div>
<div id="content">
<h1>Rails on Rack</h1>
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>This guide covers Rails integration with Rack and interfacing with other Rack components. By referring to this guide, you will be able to:</p></div>
<div class="ulist"><ul>
<li>
<p>
Create Rails Metal applications
</p>
</li>
<li>
<p>
Use Rack Middlewares in your Rails applications
</p>
</li>
<li>
<p>
Understand Action Pack’s internal Middleware stack
</p>
</li>
<li>
<p>
Define custom internal Middleware stack
</p>
</li>
<li>
<p>
Understand the best practices for developing a middleware aimed at Rails applications
</p>
</li>
</ul></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">This guide assumes a working knowledge of Rack protocol and Rack concepts such as middlewares, url maps and Rack::Builder.</td>
</tr></table>
</div>
</div>
</div>
<h2 id="_introduction_to_rack">1. Introduction to Rack</h2>
<div class="sectionbody">
<div class="sidebarblock">
<div class="sidebar-content">
<div class="paragraph"><p>Rack provides a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.</p></div>
<div class="ulist"><ul>
<li>
<p>
<a href="http://rack.rubyforge.org/doc">Rack API Documentation</a>
</p>
</li>
</ul></div>
</div></div>
<div class="paragraph"><p>Explaining Rack is not really in the scope of this guide. In case you are not familiar with Rack’s basics, you should check out the following links:</p></div>
<div class="ulist"><ul>
<li>
<p>
<a href="http://rack.github.com">Official Rack Website</a>
</p>
</li>
<li>
<p>
<a href="http://chneukirchen.org/blog/archive/2007/02/introducing-rack.html">Introducing Rack</a>
</p>
</li>
<li>
<p>
<a href="http://m.onkey.org/2008/11/17/ruby-on-rack-1">Ruby on Rack #1 - Hello Rack!</a>
</p>
</li>
<li>
<p>
<a href="http://m.onkey.org/2008/11/18/ruby-on-rack-2-rack-builder">Ruby on Rack #2 - The Builder</a>
</p>
</li>
</ul></div>
</div>
<h2 id="_rails_on_rack">2. Rails on Rack</h2>
<div class="sectionbody">
<h3 id="_actioncontroller_dispatcher_new">2.1. ActionController::Dispatcher.new</h3>
<div class="paragraph"><p><tt>ActionController::Dispatcher.new</tt> is the primary Rack application object of a Rails application. It responds to <tt>call</tt> method with a single <tt>env</tt> argument and returns a Rack response. Any Rack compliant web server should be using <tt>ActionController::Dispatcher.new</tt> object to serve a Rails application.</p></div>
<h3 id="_script_server">2.2. script/server</h3>
<div class="paragraph"><p><tt>script/server</tt> does the basic job of creating a <tt>Rack::Builder</tt> object and starting the webserver. This is Rails equivalent of Rack’s <tt>rackup</tt> script.</p></div>
<div class="paragraph"><p>Here’s how <tt>script/server</tt> creates an instance of <tt>Rack::Builder</tt></p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>app <span style="color: #990000">=</span> Rack<span style="color: #990000">::</span>Builder<span style="color: #990000">.</span>new <span style="color: #FF0000">{</span>
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>LogTailer <span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> options<span style="color: #990000">[:</span>detach<span style="color: #990000">]</span>
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>Static
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>Debugger <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> options<span style="color: #990000">[:</span>debugger<span style="color: #990000">]</span>
run ActionController<span style="color: #990000">::</span>Dispatcher<span style="color: #990000">.</span>new
<span style="color: #FF0000">}</span><span style="color: #990000">.</span>to_app</tt></pre></div></div>
<div class="paragraph"><p>Middlewares used in the code above are most useful in development envrionment. The following table explains their usage:</p></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="50%" />
<col width="50%" />
<thead valign="top">
<tr>
<th align="left">Middleware </th>
<th align="left">Purpose</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left"><p class="table">Rails::Rack::LogTailer</p></td>
<td align="left"><p class="table">Appends log file output to console</p></td>
</tr>
<tr>
<td align="left"><p class="table">Rails::Rack::Static</p></td>
<td align="left"><p class="table">Serves static files inside <tt>RAILS_ROOT/public</tt> directory</p></td>
</tr>
<tr>
<td align="left"><p class="table">Rails::Rack::Debugger</p></td>
<td align="left"><p class="table">Starts Debugger</p></td>
</tr>
</tbody>
</table>
</div>
<h3 id="_rackup">2.3. rackup</h3>
<div class="paragraph"><p>To use <tt>rackup</tt> instead of Rails' <tt>script/server</tt>, you can put the following inside <tt>config.ru</tt> of your Rails application’s root directory:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900"># RAILS_ROOT/config.ru</span></span>
<span style="font-weight: bold"><span style="color: #000080">require</span></span> <span style="color: #FF0000">"config/environment"</span>
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>LogTailer
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>Static
run ActionController<span style="color: #990000">::</span>Dispatcher<span style="color: #990000">.</span>new</tt></pre></div></div>
<div class="paragraph"><p>And start the server:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #990000">[</span>lifo@null application<span style="color: #990000">]</span>$ rackup</tt></pre></div></div>
<div class="paragraph"><p>To find out more about different <tt>rackup</tt> options:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="color: #990000">[</span>lifo@null application<span style="color: #990000">]</span>$ rackup --help</tt></pre></div></div>
</div>
<h2 id="_action_controller_middleware_stack">3. Action Controller Middleware Stack</h2>
<div class="sectionbody">
<div class="paragraph"><p>Many of Action Controller’s internal components are implemented as Rack middlewares. <tt>ActionController::Dispatcher</tt> uses <tt>ActionController::MiddlewareStack</tt> to combine various internal and external middlewares to form a complete Rails Rack application.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">
<div class="title">What is ActionController::MiddlewareStack ?</div><tt>ActionController::MiddlewareStack</tt> is Rails equivalent of <tt>Rack::Builder</tt>, but built for better flexibility and more features to meet Rails' requirements.</td>
</tr></table>
</div>
<h3 id="_adding_middlewares">3.1. Adding Middlewares</h3>
<div class="paragraph"><p>Rails provides a very simple configuration interface for adding generic Rack middlewares to a Rails applications.</p></div>
<div class="paragraph"><p>Here’s how you can add middlewares via <tt>environment.rb</tt></p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900"># environment.rb</span></span>
config<span style="color: #990000">.</span>middleware<span style="color: #990000">.</span>use Rack<span style="color: #990000">::</span>BounceFavicon</tt></pre></div></div>
<h3 id="_internal_middleware_stack">3.2. Internal Middleware Stack</h3>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>use <span style="color: #FF0000">"ActionController::Lock"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span><span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #990000">=></span> lambda <span style="color: #FF0000">{</span>
<span style="color: #990000">!</span>ActionController<span style="color: #990000">::</span>Base<span style="color: #990000">.</span>allow_concurrency
<span style="color: #FF0000">}</span>
use <span style="color: #FF0000">"ActionController::Failsafe"</span>
use <span style="color: #FF0000">"ActiveRecord::QueryCache"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span><span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #990000">=></span> lambda <span style="color: #FF0000">{</span> <span style="font-weight: bold"><span style="color: #0000FF">defined</span></span><span style="color: #990000">?(</span>ActiveRecord<span style="color: #990000">)</span> <span style="color: #FF0000">}</span>
<span style="color: #990000">[</span><span style="color: #FF0000">"ActionController::Session::CookieStore"</span><span style="color: #990000">,</span>
<span style="color: #FF0000">"ActionController::Session::MemCacheStore"</span><span style="color: #990000">,</span>
<span style="color: #FF0000">"ActiveRecord::SessionStore"</span><span style="color: #990000">].</span>each <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>store<span style="color: #990000">|</span>
use<span style="color: #990000">(</span>store<span style="color: #990000">,</span> ActionController<span style="color: #990000">::</span>Base<span style="color: #990000">.</span>session_options<span style="color: #990000">,</span>
<span style="color: #990000">:</span><span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #990000">=></span> lambda <span style="color: #FF0000">{</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> session_store <span style="color: #990000">=</span> ActionController<span style="color: #990000">::</span>Base<span style="color: #990000">.</span>session_store
session_store<span style="color: #990000">.</span>name <span style="color: #990000">==</span> store
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="color: #FF0000">}</span>
<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
use ActionController<span style="color: #990000">::</span>VerbPiggybacking</tt></pre></div></div>
<div class="tableblock">
<table rules="all"
width="100%"
frame="border"
cellspacing="0" cellpadding="4">
<col width="50%" />
<col width="50%" />
<thead valign="top">
<tr>
<th align="left">Middleware </th>
<th align="left">Purpose</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left"><p class="table">ActionController::Lock</p></td>
<td align="left"><p class="table">Sets <tt>env["rack.multithread"]</tt> flag to <tt>true</tt> and wraps the application within a Mutex.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActionController::Failsafe</p></td>
<td align="left"><p class="table">Returns HTTP Status <tt>500</tt> to the client if an exception gets raised while dispatching.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActiveRecord::QueryCache</p></td>
<td align="left"><p class="table">Enable the Active Record query cache.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActionController::Session::CookieStore</p></td>
<td align="left"><p class="table">Uses the cookie based session store.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActionController::Session::MemCacheStore</p></td>
<td align="left"><p class="table">Uses the memcached based session store.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActiveRecord::SessionStore</p></td>
<td align="left"><p class="table">Uses the database based session store.</p></td>
</tr>
<tr>
<td align="left"><p class="table">ActionController::VerbPiggybacking</p></td>
<td align="left"><p class="table">Sets HTTP method based on <tt>_method</tt> parameter or <tt>env["HTTP_X_HTTP_METHOD_OVERRIDE"]</tt>.</p></td>
</tr>
</tbody>
</table>
</div>
<h3 id="_customizing_internal_middleware_stack">3.3. Customizing Internal Middleware Stack</h3>
<div class="paragraph"><p>VERIFY THIS WORKS. Just a code dump at the moment.</p></div>
<div class="paragraph"><p>Put the following in an initializer.</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>ActionController<span style="color: #990000">::</span>Dispatcher<span style="color: #990000">.</span>middleware <span style="color: #990000">=</span> ActionController<span style="color: #990000">::</span>MiddlewareStack<span style="color: #990000">.</span>new <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>m<span style="color: #990000">|</span>
m<span style="color: #990000">.</span>use ActionController<span style="color: #990000">::</span>Lock
m<span style="color: #990000">.</span>use ActionController<span style="color: #990000">::</span>Failsafe
m<span style="color: #990000">.</span>use ActiveRecord<span style="color: #990000">::</span>QueryCache
m<span style="color: #990000">.</span>use ActionController<span style="color: #990000">::</span>Session<span style="color: #990000">::</span>CookieStore
m<span style="color: #990000">.</span>use ActionController<span style="color: #990000">::</span>VerbPiggybacking
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span></tt></pre></div></div>
<div class="paragraph"><p>Josh says :</p></div>
<div class="sidebarblock">
<div class="sidebar-content">
<div class="paragraph"><p>3.3: I wouldn’t recommend this: custom internal stack
i’d recommend using config.middleware.use api
we still need a better api for swapping out existing middleware, etc
config.middleware.swap AC::Sessions, My::Sessoins
or something like that</p></div>
</div></div>
<h3 id="_inspecting_middleware_stack">3.4. Inspecting Middleware Stack</h3>
<div class="paragraph"><p>Rails has a handy rake task for inspecting the middleware stack in use:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>$ rake middleware</tt></pre></div></div>
<div class="paragraph"><p>For a freshly generated Rails application, this will produce:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>use ActionController<span style="color: #990000">::</span>Lock
use ActionController<span style="color: #990000">::</span>Failsafe
use ActiveRecord<span style="color: #990000">::</span>QueryCache
use ActionController<span style="color: #990000">::</span>Session<span style="color: #990000">::</span>CookieStore<span style="color: #990000">,</span> <span style="color: #FF0000">{</span><span style="color: #990000">:</span>secret<span style="color: #990000">=></span><span style="color: #FF0000">"aa5150a22c1a5f24112260c33ae2131a88d7539117bfdcd5696fb2be385b60c6da9f7d4ed0a67e3b8cc85cc4e653ba0111dd1f3f8999520f049e2262068c16a6"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>session_key<span style="color: #990000">=></span><span style="color: #FF0000">"_edge_session"</span><span style="color: #FF0000">}</span>
use Rails<span style="color: #990000">::</span>Rack<span style="color: #990000">::</span>Metal
use ActionController<span style="color: #990000">::</span>VerbPiggybacking
run ActionController<span style="color: #990000">::</span>Dispatcher<span style="color: #990000">.</span>new</tt></pre></div></div>
<div class="paragraph"><p>This rake task is very useful if the application requires highly customized Rack middleware setup.</p></div>
</div>
<h2 id="_rails_metal_applications">4. Rails Metal Applications</h2>
<div class="sectionbody">
<div class="paragraph"><p>Rails Metal applications are minimal Rack applications specially designed for integrating with a typical Rails application. As Rails Metal Applications skip all of the Action Controller stack, serving a request has no overhead from the Rails framework itself. This is especially useful for infrequent cases where the performance of the full stack Rails framework is an issue.</p></div>
<h3 id="_generating_a_metal_application">4.1. Generating a Metal Application</h3>
<div class="paragraph"><p>Rails provides a generator called <tt>performance_test</tt> for creating new performance tests:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt>script/generate metal poller</tt></pre></div></div>
<div class="paragraph"><p>This generates <tt>poller.rb</tt> in the <tt>app/metal</tt> directory:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-style: italic"><span style="color: #9A1900"># Allow the metal piece to run in isolation</span></span>
<span style="font-weight: bold"><span style="color: #000080">require</span></span><span style="color: #990000">(</span>File<span style="color: #990000">.</span>dirname<span style="color: #990000">(</span><span style="font-weight: bold"><span style="color: #0000FF">__FILE__</span></span><span style="color: #990000">)</span> <span style="color: #990000">+</span> <span style="color: #FF0000">"/../../config/environment"</span><span style="color: #990000">)</span> <span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> <span style="font-weight: bold"><span style="color: #0000FF">defined</span></span><span style="color: #990000">?(</span>Rails<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">class</span></span> Poller
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> <span style="font-weight: bold"><span style="color: #0000FF">self</span></span><span style="color: #990000">.</span>call<span style="color: #990000">(</span>env<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> env<span style="color: #990000">[</span><span style="color: #FF0000">"PATH_INFO"</span><span style="color: #990000">]</span> <span style="color: #990000">=~</span> <span style="color: #FF6600">/^\/poller/</span>
<span style="color: #990000">[</span><span style="color: #993399">200</span><span style="color: #990000">,</span> <span style="color: #FF0000">{</span><span style="color: #FF0000">"Content-Type"</span> <span style="color: #990000">=></span> <span style="color: #FF0000">"text/html"</span><span style="color: #FF0000">}</span><span style="color: #990000">,</span> <span style="color: #990000">[</span><span style="color: #FF0000">"Hello, World!"</span><span style="color: #990000">]]</span>
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
<span style="color: #990000">[</span><span style="color: #993399">404</span><span style="color: #990000">,</span> <span style="color: #FF0000">{</span><span style="color: #FF0000">"Content-Type"</span> <span style="color: #990000">=></span> <span style="color: #FF0000">"text/html"</span><span style="color: #FF0000">}</span><span style="color: #990000">,</span> <span style="color: #990000">[</span><span style="color: #FF0000">"Not Found"</span><span style="color: #990000">]]</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span></tt></pre></div></div>
<div class="paragraph"><p>Metal applications are an optimization. You should make sure to <a href="http://weblog.rubyonrails.org/2008/12/20/performance-of-rails-metal">understand the related performance implications</a> before using it.</p></div>
<h3 id="_execution_order">4.2. Execution Order</h3>
<div class="paragraph"><p>All Metal Applications are executed by <tt>Rails::Rack::Metal</tt> middleware, which is a part of the <tt>ActionController::MiddlewareStack</tt> chain.</p></div>
<div class="paragraph"><p>Here’s the primary method responsible for running the Metal applications:</p></div>
<div class="listingblock">
<div class="content"><!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">def</span></span> call<span style="color: #990000">(</span>env<span style="color: #990000">)</span>
<span style="color: #009900">@metals</span><span style="color: #990000">.</span>keys<span style="color: #990000">.</span>each <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>app<span style="color: #990000">|</span>
result <span style="color: #990000">=</span> app<span style="color: #990000">.</span>call<span style="color: #990000">(</span>env<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">return</span></span> result <span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> result<span style="color: #990000">[</span><span style="color: #993399">0</span><span style="color: #990000">].</span>to_i <span style="color: #990000">==</span> <span style="color: #993399">404</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="color: #009900">@app</span><span style="color: #990000">.</span>call<span style="color: #990000">(</span>env<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span></tt></pre></div></div>
<div class="paragraph"><p>In the code above, <tt>@metals</tt> is an ordered ( alphabetical ) hash of metal applications. Due to the alphabetical ordering, <tt>aaa.rb</tt> will come before <tt>bbb.rb</tt> in the metal chain.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/important.png" alt="Important" />
</td>
<td class="content">Metal applications cannot return the HTTP Status <tt>404</tt> to a client, as it is used for continuing the Metal chain execution. Please use normal Rails controllers or a custom middleware if returning <tt>404</tt> is a requirement.</td>
</tr></table>
</div>
</div>
<h2 id="_middlewares_and_rails">5. Middlewares and Rails</h2>
<div class="sectionbody">
</div>
<h2 id="_changelog">6. Changelog</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/4">Lighthouse ticket</a></p></div>
<div class="ulist"><ul>
<li>
<p>
January 11, 2009: First version by <a href="../authors.html#lifo">Pratik</a>
</p>
</li>
</ul></div>
</div>
</div>
</div>
</body>
</html>