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Upgrade to Rails 2.2.0 As a side benefit, fix an (non-user-visible) bug in display_s5(). Also fixed a bug where removing orphaned pages did not expire cached summary pages.
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<title>Action Controller basics</title>
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<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="#_what_does_a_controller_do">What does a controller do?</a>
</li>
<li>
<a href="#_methods_and_actions">Methods and actions</a>
</li>
<li>
<a href="#_parameters">Parameters</a>
<ul>
<li><a href="#_hash_and_array_parameters">Hash and array parameters</a></li>
<li><a href="#_routing_parameters">Routing parameters</a></li>
</ul>
</li>
<li>
<a href="#_session">Session</a>
<ul>
<li><a href="#_disabling_the_session">Disabling the session</a></li>
<li><a href="#_accessing_the_session">Accessing the session</a></li>
<li><a href="#_the_flash">The flash</a></li>
</ul>
</li>
<li>
<a href="#_cookies">Cookies</a>
</li>
<li>
<a href="#_filters">Filters</a>
<ul>
<li><a href="#_after_filters_and_around_filters">After filters and around filters</a></li>
<li><a href="#_other_ways_to_use_filters">Other ways to use filters</a></li>
</ul>
</li>
<li>
<a href="#_verification">Verification</a>
</li>
<li>
<a href="#_the_request_and_response_objects">The request and response objects</a>
<ul>
<li><a href="#_the_request">The request</a></li>
<li><a href="#_the_response">The response</a></li>
</ul>
</li>
<li>
<a href="#_http_basic_authentication">HTTP Basic Authentication</a>
</li>
<li>
<a href="#_streaming_and_file_downloads">Streaming and file downloads</a>
<ul>
<li><a href="#_sending_files">Sending files</a></li>
<li><a href="#_restful_downloads">RESTful downloads</a></li>
</ul>
</li>
<li>
<a href="#_parameter_filtering">Parameter filtering</a>
</li>
<li>
<a href="#_rescue">Rescue</a>
<ul>
<li><a href="#_the_default_500_and_404_templates">The default 500 and 404 templates</a></li>
<li><a href="#_tt_rescue_from_tt"><tt>rescue_from</tt></a></li>
</ul>
</li>
</ol>
</div>
<div id="content">
<h1>Action Controller basics</h1>
<div id="preamble">
<div class="sectionbody">
<div class="para"><p>In this guide you will learn how controllers work and how they fit into the request cycle in your application. You will learn how to make use of the many tools provided by Action Controller to work with the session, cookies and filters and how to use the built-in HTTP authentication and data streaming facilities. In the end, we will take a look at some tools that will be useful once your controllers are ready and working, like how to filter sensitive parameters from the log and how to rescue and deal with exceptions that may be raised during the request.</p></div>
</div>
</div>
<h2 id="_what_does_a_controller_do">1. What does a controller do?</h2>
<div class="sectionbody">
<div class="para"><p>Action Controller is the C in MVC. After routing has determined which controller to use for a request, your controller is responsible for making sense of the request and producing the appropriate output. Luckily, Action Controller does most of the groundwork for you and uses smart conventions to make this as straight-forward as possible.</p></div>
<div class="para"><p>For most conventional RESTful applications, the controller will receive the request (this is invisible to you as the developer), fetch or save data from a model and use a view to create HTML output. If your controller needs to do things a little differently, that's not a problem, this is just the most common way for a controller to work.</p></div>
<div class="para"><p>A controller can thus be thought of as a middle man between models and views. It makes the model data available to the view so it can display it to the user, and it saves or updates data from the user to the model.</p></div>
</div>
<h2 id="_methods_and_actions">2. Methods and actions</h2>
<div class="sectionbody">
<div class="para"><p>A controller is a Ruby class which inherits from ActionController::Base and has methods just like any other class. Usually these methods correspond to actions in MVC, but they can just as well be helpful methods which can be called by actions. When your application receives a request, the routing will determine which controller and action to run. Then an instance of that controller will be created and the method corresponding to the action (the method with the same name as the action) gets run.</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">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
<span style="font-style: italic"><span style="color: #9A1900"># Actions are public methods</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> new
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># These methods are responsible for producing output</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># Helper methods are private and can not be used as actions</span></span>
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> foo
<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="para"><p>Private methods in a controller are also used as filters, which will be covered later in this guide.</p></div>
<div class="para"><p>As an example, if the user goes to <tt>/clients/new</tt> in your application to add a new client, a ClientsController instance will be created and the <tt>new</tt> method will be run. Note that the empty method from the example above could work just fine because Rails will by default render the <tt>new.html.erb</tt> view unless the action says otherwise. The <tt>new</tt> method could make available to the view a <tt>@client</tt> instance variable by creating a new Client:</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> new
<span style="color: #009900">@client</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>new
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The Layouts &amp; rendering guide explains this in more detail.</p></div>
</div>
<h2 id="_parameters">3. Parameters</h2>
<div class="sectionbody">
<div class="para"><p>You will probably want to access data sent in by the user or other parameters in your controller actions. There are two kinds of parameters possible in a web application. The first are parameters that are sent as part of the URL, query string parameters. The query string is everything after "?" in the URL. The second type of parameter is usually referred to as POST data. This information usually comes from a HTML form which has been filled in by the user. It's called POST data because it can only be sent as part of an HTTP POST request. Rails does not make any distinction between query string parameters and POST parameters, and both are available in the <tt>params</tt> hash in your controller:</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">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
<span style="font-style: italic"><span style="color: #9A1900"># This action uses query string parameters because it gets run by a HTTP GET request,</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># but this does not make any difference to the way in which the parameters are accessed.</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># The URL for this action would look like this in order to list activated clients: /clients?status=activated</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> index
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> params<span style="color: #990000">[:</span>status<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"activated"</span>
<span style="color: #009900">@clients</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>activated
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
<span style="color: #009900">@clients</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>unativated
<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-style: italic"><span style="color: #9A1900"># This action uses POST parameters. They are most likely coming from an HTML</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># form which the user has submitted. The URL for this RESTful request will</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># be "/clients", and the data will be sent as part of the request body.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
<span style="color: #009900">@client</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>new<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>client<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@client</span><span style="color: #990000">.</span>save
redirect_to <span style="color: #009900">@client</span>
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># This line overrides the default rendering behavior, which would have been</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># to render the "create" view.</span></span>
render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</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>
<h3 id="_hash_and_array_parameters">3.1. Hash and array parameters</h3>
<div class="para"><p>The params hash is not limited to one-dimensional keys and values. It can contain arrays and (nested) hashes. To send an array of values, append "[]" to the key name:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>GET /clients?ids[]=1&amp;ids[2]&amp;ids[]=3</tt></pre>
</div></div>
<div class="para"><p>The value of <tt>params[:ids]</tt> will now be <tt>["1", "2", "3"]</tt>. Note that parameter values are always strings; Rails makes no attempt to guess or cast the type.</p></div>
<div class="para"><p>To send a hash you include the key name inside the brackets:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>&lt;form action="/clients" method="post"&gt;
&lt;input type="text" name="client[name]" value="Acme" /&gt;
&lt;input type="text" name="client[phone]" value="12345" /&gt;
&lt;input type="text" name="client[address][postcode]" value="12345" /&gt;
&lt;input type="text" name="client[address][city]" value="Carrot City" /&gt;
&lt;/form&gt;</tt></pre>
</div></div>
<div class="para"><p>The value of <tt>params[:client]</tt> when this form is submitted will be <tt>{:name &#8658; "Acme", :phone &#8658; "12345", :address &#8658; {:postcode &#8658; "12345", :city &#8658; "Carrot City"}}</tt>. Note the nested hash in <tt>params[:client][:address]</tt>.</p></div>
<h3 id="_routing_parameters">3.2. Routing parameters</h3>
<div class="para"><p>The <tt>params</tt> hash will always contain the <tt>:controller</tt> and <tt>:action</tt> keys, but you should use the methods <tt>controller_name</tt> and <tt>action_name</tt> instead to access these values. Any other parameters defined by the routing, such as <tt>:id</tt> will also be available.</p></div>
</div>
<h2 id="_session">4. Session</h2>
<div class="sectionbody">
<div class="para"><p>Your application has a session for each user in which you can store small amounts of data that will be persisted between requests. The session is only available in the controller and can use one of a number of different storage mechanisms:</p></div>
<div class="ilist"><ul>
<li>
<p>
CookieStore - Stores everything on the client.
</p>
</li>
<li>
<p>
DRBStore - Stores the data on a DRb client.
</p>
</li>
<li>
<p>
MemCacheStore - Stores the data in MemCache.
</p>
</li>
<li>
<p>
ActiveRecordStore - Stores the data in a database using Active Record.
</p>
</li>
</ul></div>
<div class="para"><p>All session stores store the session id in a cookie - there is no other way of passing it to the server. Most stores also use this key to locate the session data on the server.</p></div>
<div class="para"><p>The default and recommended store, the Cookie Store, does not store session data on the server, but in the cookie itself. The data is cryptographically signed to make it tamper-proof, but it is not encrypted, so anyone with access to it can read its contents. It can only store about 4kB of data - much less than the others - but this is usually enough. Storing large amounts of data is discouraged no matter which session store your application uses. Expecially discouraged is storing complex objects (anything other than basic Ruby objects, the primary example being model instances) in the session, as the server might not be able to reassemble them between requests, which will result in an error. The Cookie Store has the added advantage that it does not require any setting up beforehand - Rails will generate a "secret key" which will be used to sign the cookie when you create the application.</p></div>
<div class="para"><p>If you need a different session storage mechanism, you can change it in the <tt>config/environment.rb</tt> file:</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"># Set to one of [:active_record_store, :drb_store, :mem_cache_store, :cookie_store]</span></span>
config<span style="color: #990000">.</span>action_controller<span style="color: #990000">.</span>session_store <span style="color: #990000">=</span> <span style="color: #990000">:</span>active_record_store
</tt></pre></div></div>
<h3 id="_disabling_the_session">4.1. Disabling the session</h3>
<div class="para"><p>Sometimes you don't need a session, and you can turn it off to avoid the unnecessary overhead. To do this, use the <a href="http://api.rubyonrails.org/classes/ActionController/SessionManagement/ClassMethods.html#M000649">session</a> class method in your controller:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
session <span style="color: #990000">:</span>off
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>You can also turn the session on or off for a single controller:</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"># The session is turned off by default in ApplicationController, but we</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># want to turn it on for log in/out.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
session <span style="color: #990000">:</span>on
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>Or even a single action:</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">class</span></span> ProductsController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
session <span style="color: #990000">:</span>on<span style="color: #990000">,</span> <span style="color: #990000">:</span>only <span style="color: #990000">=&gt;</span> <span style="color: #990000">[:</span>create<span style="color: #990000">,</span> <span style="color: #990000">:</span>update<span style="color: #990000">]</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<h3 id="_accessing_the_session">4.2. Accessing the session</h3>
<div class="para"><p>In your controller you can access the session through the <tt>session</tt> instance method.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">There are two <tt>session</tt> methods, the class and the instance method. The class method which is described above is used to turn the session on and off while the instance method described below is used to access session values. The class method is used outside of method definitions while the instance methods is used inside methods, in actions or filters.</td>
</tr></table>
</div>
<div class="para"><p>Session values are stored using key/value pairs like a hash:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
private
<span style="font-style: italic"><span style="color: #9A1900"># Finds the User with the ID stored in the session with the key :current_user_id</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># This is a common way to do user login in a Rails application; logging in sets the</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># session value and logging out removes it.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> current_user
<span style="color: #009900">@_current_user</span> <span style="color: #990000">||=</span> session<span style="color: #990000">[:</span>current_user_id<span style="color: #990000">]</span> <span style="color: #990000">&amp;&amp;</span> User<span style="color: #990000">.</span>find<span style="color: #990000">(</span>session<span style="color: #990000">[:</span>current_user_id<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>
</tt></pre></div></div>
<div class="para"><p>To store something in the session, just assign it to the key like a hash:</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">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># "Create" a login, aka "log the user in"</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> user <span style="color: #990000">=</span> User<span style="color: #990000">.</span>authenticate<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>username<span style="color: #990000">,</span> params<span style="color: #990000">[:</span>password<span style="color: #990000">])</span>
<span style="font-style: italic"><span style="color: #9A1900"># Save the user ID in the session so it can be used in subsequent requests</span></span>
session<span style="color: #990000">[:</span>current_user_id<span style="color: #990000">]</span> <span style="color: #990000">=</span> user<span style="color: #990000">.</span>id
redirect_to root_url
<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="para"><p>To remove something from the session, assign that key to be <tt>nil</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-weight: bold"><span style="color: #0000FF">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># "Delete" a login, aka "log the user out"</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> destroy
<span style="font-style: italic"><span style="color: #9A1900"># Remove the user id from the session</span></span>
session<span style="color: #990000">[:</span>current_user_id<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #0000FF">nil</span></span>
redirect_to root_url
<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="para"><p>To reset the entire session, use <a href="http://api.rubyonrails.org/classes/ActionController/Base.html#M000855">reset_session</a>.</p></div>
<h3 id="_the_flash">4.3. The flash</h3>
<div class="para"><p>The flash is a special part of the session which is cleared with each request. This means that values stored there will only be available in the next request, which is useful for storing error messages etc. It is accessed in much the same way as the session, like a hash. Let's use the act of logging out as an example. The controller can set a message which will be displayed to the user on the next request:</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">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> destroy
session<span style="color: #990000">[:</span>current_user_id<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #0000FF">nil</span></span>
flash<span style="color: #990000">[:</span>notice<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"You have successfully logged out"</span>
redirect_to root_url
<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="para"><p>The <tt>destroy</tt> action redirects to the application's <tt>root_url</tt>, where the message will be displayed. Note that it's entirely up to the next action to decide what, if anything, it will do with what the previous action put in the flash. It's conventional to a display eventual errors or notices from the flash in the application's layout:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>&lt;html&gt;
&lt;!-- &lt;head/&gt; --&gt;
&lt;body&gt;
&lt;% if flash[:notice] -%&gt;
&lt;p class="notice"&gt;&lt;%= flash[:notice] %&gt;&lt;/p&gt;
&lt;% end -%&gt;
&lt;% if flash[:error] -%&gt;
&lt;p class="error"&gt;&lt;%= flash[:error] %&gt;&lt;/p&gt;
&lt;% end -%&gt;
&lt;!-- more content --&gt;
&lt;/body&gt;
&lt;/html&gt;</tt></pre>
</div></div>
<div class="para"><p>This way, if an action sets an error or a notice message, the layout will display it automatically.</p></div>
<div class="para"><p>If you want a flash value to be carried over to another request, use the <tt>keep</tt> method:</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">class</span></span> MainController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># Let's say this action corresponds to root_url, but you want all requests here to be redirected to</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># UsersController#index. If an action sets the flash and redirects here, the values would normally be</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># lost when another redirect happens, but you can use keep to make it persist for another request.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> index
flash<span style="color: #990000">.</span>keep <span style="font-style: italic"><span style="color: #9A1900"># Will persist all flash values. You can also use a key to keep only that value: flash.keep(:notice)</span></span>
redirect_to users_url
<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>
<h4 id="_flash_now">4.3.1. flash.now</h4>
<div class="para"><p>By default, adding values to the flash will make them available to the next request, but sometimes you may want to access those values in the same request. For example, if the <tt>create</tt> action fails to save a resource and you render the <tt>new</tt> template directly, that's not going to result in a new request, but you may still want to display a message using the flash. To do this, you can use <tt>flash.now</tt> in the same way you use the normal <tt>flash</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-weight: bold"><span style="color: #0000FF">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
<span style="color: #009900">@client</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>new<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>client<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@client</span><span style="color: #990000">.</span>save
<span style="font-style: italic"><span style="color: #9A1900"># ...</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
flash<span style="color: #990000">.</span>now<span style="color: #990000">[:</span>error<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"Could not save client"</span>
render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</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>
<h2 id="_cookies">5. Cookies</h2>
<div class="sectionbody">
<div class="para"><p>Your application can store small amounts of data on the client - called cookies - that will be persisted across requests and even sessions. Rails provides easy access to cookies via the <tt>cookies</tt> method, which - much like the <tt>session</tt> - works like a hash:</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">class</span></span> CommentsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> new
<span style="font-style: italic"><span style="color: #9A1900">#Auto-fill the commenter's name if it has been stored in a cookie</span></span>
<span style="color: #009900">@comment</span> <span style="color: #990000">=</span> Comment<span style="color: #990000">.</span>new<span style="color: #990000">(:</span>name <span style="color: #990000">=&gt;</span> cookies<span style="color: #990000">[:</span>commenter_name<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">def</span></span> create
<span style="color: #009900">@comment</span> <span style="color: #990000">=</span> Comment<span style="color: #990000">.</span>new<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>comment<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@comment</span><span style="color: #990000">.</span>save
flash<span style="color: #990000">[:</span>notice<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"Thanks for your comment!"</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> params<span style="color: #990000">[:</span>remember_name<span style="color: #990000">]</span>
<span style="font-style: italic"><span style="color: #9A1900"># Remember the commenter's name</span></span>
cookies<span style="color: #990000">[:</span>commenter_name<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #009900">@comment</span><span style="color: #990000">.</span>name
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># Don't remember, and delete the name if it has been remembered before</span></span>
cookies<span style="color: #990000">.</span>delete<span style="color: #990000">(:</span>commenter_name<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
redirect_to <span style="color: #009900">@comment</span><span style="color: #990000">.</span>article
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</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="para"><p>Note that while for session values, you set the key to <tt>nil</tt>, to delete a cookie value, you use <tt>cookies.delete(:key)</tt>.</p></div>
</div>
<h2 id="_filters">6. Filters</h2>
<div class="sectionbody">
<div class="para"><p>Filters are methods that are run before, after or "around" a controller action. For example, one filter might check to see if the logged in user has the right credentials to access that particular controller or action. Filters are inherited, so if you set a filter on ApplicationController, it will be run on every controller in your application. A common, simple filter is one which requires that a user is logged in for an action to be run. Let's define the filter method first:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> require_login
<span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> logged_in?
flash<span style="color: #990000">[:</span>error<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"You must be logged in to access this section"</span>
redirect_to new_login_url <span style="font-style: italic"><span style="color: #9A1900"># Prevents the current action from running</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>
<span style="font-style: italic"><span style="color: #9A1900"># The logged_in? method simply returns true if the user is logged in and</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># false otherwise. It does this by "booleanizing" the current_user method</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># we created previously using a double ! operator. Note that this is not</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># common in Ruby and is discouraged unless you really mean to convert something</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># into true or false.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> logged_in?
<span style="color: #990000">!!</span>current_user
<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="para"><p>The method simply stores an error message in the flash and redirects to the login form if the user is not logged in. If a before filter (a filter which is run before the action) renders or redirects, the action will not run. If there are additional filters scheduled to run after the rendering/redirecting filter, they are also cancelled. To use this filter in a controller, use the <a href="http://api.rubyonrails.org/classes/ActionController/Filters/ClassMethods.html#M000704">before_filter</a> method:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
before_filter <span style="color: #990000">:</span>require_login
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>In this example, the filter is added to ApplicationController and thus all controllers in the application. This will make everything in the application require the user to be logged in in order to use it. For obvious reasons (the user wouldn't be able to log in in the first place!), not all controllers or actions should require this, so to prevent this filter from running you can use <a href="http://api.rubyonrails.org/classes/ActionController/Filters/ClassMethods.html#M000711">skip_before_filter</a> :</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">class</span></span> LoginsController <span style="color: #990000">&lt;</span> Application
skip_before_filter <span style="color: #990000">:</span>require_login<span style="color: #990000">,</span> <span style="color: #990000">:</span>only <span style="color: #990000">=&gt;</span> <span style="color: #990000">[:</span>new<span style="color: #990000">,</span> <span style="color: #990000">:</span>create<span style="color: #990000">]</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>Now, the LoginsController's "new" and "create" actions will work as before without requiring the user to be logged in. The <tt>:only</tt> option is used to only skip this filter for these actions, and there is also an <tt>:except</tt> option which works the other way. These options can be used when adding filters too, so you can add a filter which only runs for selected actions in the first place.</p></div>
<h3 id="_after_filters_and_around_filters">6.1. After filters and around filters</h3>
<div class="para"><p>In addition to the before filters, you can run filters after an action has run or both before and after. The after filter is similar to the before filter, but because the action has already been run it has access to the response data that's about to be sent to the client. Obviously, after filters can not stop the action from running. Around filters are responsible for running the action, but they can choose not to, which is the around filter's way of stopping it.</p></div>
<div class="para"><p>TODO: Find a real example for an around filter</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"># Example taken from the Rails API filter documentation:</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># http://api.rubyonrails.org/classes/ActionController/Filters/ClassMethods.html</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> Application
around_filter <span style="color: #990000">:</span>catch_exceptions
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> catch_exceptions
<span style="font-weight: bold"><span style="color: #0000FF">yield</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">rescue</span></span> <span style="color: #990000">=&gt;</span> exception
logger<span style="color: #990000">.</span>debug <span style="color: #FF0000">"Caught exception! #{exception}"</span>
<span style="font-weight: bold"><span style="color: #0000FF">raise</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>
<h3 id="_other_ways_to_use_filters">6.2. Other ways to use filters</h3>
<div class="para"><p>While the most common way to use filters is by creating private methods and using *_filter to add them, there are two other ways to do the same thing.</p></div>
<div class="para"><p>The first is to use a block directly with the *_filter methods. The block receives the controller as an argument, and the <tt>require_login</tt> filter from above could be rewritte to use a block:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
before_filter <span style="color: #FF0000">{</span> <span style="color: #990000">|</span>controller<span style="color: #990000">|</span> redirect_to new_login_url <span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> controller<span style="color: #990000">.</span>send<span style="color: #990000">(:</span>logged_in?<span style="color: #990000">)</span> <span style="color: #FF0000">}</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>Note that the filter in this case uses <tt>send</tt> because the <tt>logged_in?</tt> method is private and the filter is not run in the scope of the controller. This is not the recommended way to implement this particular filter, but in more simple cases it might be useful.</p></div>
<div class="para"><p>The second way is to use a class (actually, any object that responds to the right methods will do) to handle the filtering. This is useful in cases that are more complex than can not be implemented in a readable and reusable way using the two other methods. As an example, we will rewrite the login filter again to use a class:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
before_filter LoginFilter
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">class</span></span> LoginFilter
<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>filter<span style="color: #990000">(</span>controller<span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> logged_in?
controller<span style="color: #990000">.</span>flash<span style="color: #990000">[:</span>error<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"You must be logged in to access this section"</span>
controller<span style="color: #990000">.</span>redirect_to controller<span style="color: #990000">.</span>new_login_url
<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="para"><p>Again, this is not an ideal example for this filter, because it's not run in the scope of the controller but gets it passed as an argument. The filter class has a class method <tt>filter</tt> which gets run before or after the action, depending on if it's a before or after filter. Classes used as around filters can also use the same <tt>filter</tt> method, which will get run in the same way. The method must <tt>yield</tt> to execute the action. Alternatively, it can have both a <tt>before</tt> and an <tt>after</tt> method that are run before and after the action.</p></div>
<div class="para"><p>The Rails API documentation has <a href="http://api.rubyonrails.org/classes/ActionController/Filters/ClassMethods.html">more information on using filters</a>.</p></div>
</div>
<h2 id="_verification">7. Verification</h2>
<div class="sectionbody">
<div class="para"><p>Verifications make sure certain criterias are met in order for a controller or action to run. They can specify that a certain key (or several keys in the form of an array) is present in the <tt>params</tt>, <tt>session</tt> or <tt>flash</tt> hashes or that a certain HTTP method was used or that the request was made using XMLHTTPRequest (Ajax). The default action taken when these criterias are not met is to render a 400 Bad Request response, but you can customize this by specifying a redirect URL or rendering something else and you can also add flash messages and HTTP headers to the response. It is described in the <a href="http://api.rubyonrails.org/classes/ActionController/Verification/ClassMethods.html">API codumentation</a> as "essentially a special kind of before_filter".</p></div>
<div class="para"><p>Let's see how we can use verification to make sure the user supplies a username and a password in order to log in:</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">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ApplicationController
verify <span style="color: #990000">:</span>params <span style="color: #990000">=&gt;</span> <span style="color: #990000">[:</span>username<span style="color: #990000">,</span> <span style="color: #990000">:</span>password<span style="color: #990000">],</span>
<span style="color: #990000">:</span>render <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">{</span><span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</span><span style="color: #FF0000">}</span><span style="color: #990000">,</span>
<span style="color: #990000">:</span>add_flash <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">{</span><span style="color: #990000">:</span>error <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"Username and password required to log in"</span><span style="color: #FF0000">}</span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> create
<span style="color: #009900">@user</span> <span style="color: #990000">=</span> User<span style="color: #990000">.</span>authenticate<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>username<span style="color: #990000">],</span> params<span style="color: #990000">[:</span>password<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #009900">@user</span>
flash<span style="color: #990000">[:</span>notice<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"You're logged in"</span>
redirect_to root_url
<span style="font-weight: bold"><span style="color: #0000FF">else</span></span>
render <span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</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="para"><p>Now the <tt>create</tt> action won't run unless the "username" and "password" parameters are present, and if they're not, an error message will be added to the flash and the "new" action will be rendered. But there's something rather important missing from the verification above: It will be used for <strong>every</strong> action in LoginsController, which is not what we want. You can limit which actions it will be used for with the <tt>:only</tt> and <tt>:except</tt> options just like a filter:</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">class</span></span> LoginsController <span style="color: #990000">&lt;</span> ApplicationController
verify <span style="color: #990000">:</span>params <span style="color: #990000">=&gt;</span> <span style="color: #990000">[:</span>username<span style="color: #990000">,</span> <span style="color: #990000">:</span>password<span style="color: #990000">],</span>
<span style="color: #990000">:</span>render <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">{</span><span style="color: #990000">:</span>action <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"new"</span><span style="color: #FF0000">}</span><span style="color: #990000">,</span>
<span style="color: #990000">:</span>add_flash <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">{</span><span style="color: #990000">:</span>error <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"Username and password required to log in"</span><span style="color: #FF0000">}</span><span style="color: #990000">,</span>
<span style="color: #990000">:</span>only <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>create <span style="font-style: italic"><span style="color: #9A1900">#Only run this verification for the "create" action</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
</div>
<h2 id="_the_request_and_response_objects">8. The request and response objects</h2>
<div class="sectionbody">
<div class="para"><p>In every controller there are two accessor methods pointing to the request and the response objects associated with the request cycle that is currently in execution. The <tt>request</tt> method contains an instance of <a href="http://api.rubyonrails.org/classes/ActionController/AbstractRequest.html">AbstractRequest</a> and the <tt>response</tt> method contains the <a href="http://github.com/rails/rails/tree/master/actionpack/lib/action_controller/response.rb">response object</a> representing what is going to be sent back to the client.</p></div>
<h3 id="_the_request">8.1. The request</h3>
<div class="para"><p>The request object contains a lot of useful information about the request coming in from the client. To get a full list of the available methods, refer to the <a href="http://api.rubyonrails.org/classes/ActionController/AbstractRequest.html">API documentation</a>.</p></div>
<div class="ilist"><ul>
<li>
<p>
host - The hostname used for this request.
</p>
</li>
<li>
<p>
domain - The hostname without the first part (usually "www").
</p>
</li>
<li>
<p>
format - The content type requested by the client.
</p>
</li>
<li>
<p>
method - The HTTP method used for the request.
</p>
</li>
<li>
<p>
get?, post?, put?, delete?, head? - Returns true if the HTTP method is get/post/put/delete/head.
</p>
</li>
<li>
<p>
headers - Returns a hash containing the headers associated with the request.
</p>
</li>
<li>
<p>
port - The port number (integer) used for the request.
</p>
</li>
<li>
<p>
protocol - The protocol used for the request.
</p>
</li>
<li>
<p>
query_string - The query string part of the URL - everything after "?".
</p>
</li>
<li>
<p>
remote_ip - The IP address of the client.
</p>
</li>
<li>
<p>
url - The entire URL used for the request.
</p>
</li>
</ul></div>
<h4 id="_path_parameters_query_parameters_and_request_parameters">8.1.1. path_parameters, query_parameters and request_parameters</h4>
<div class="para"><p>TODO: Does this belong here?</p></div>
<div class="para"><p>Rails collects all of the parameters sent along with the request in the <tt>params</tt> hash, whether they are sent as part of the query string or the post body. The request object has three accessors that give you access to these parameters depending on where they came from. The <tt>query_parameters</tt> hash contains parameters that were sent as part of the query string while the <tt>request_parameters</tt> hash contains parameters sent as part of the post body. The <tt>path_parameters</tt> hash contains parameters that were recognised by the routing as being part of the path leading to this particular controller and action.</p></div>
<h3 id="_the_response">8.2. The response</h3>
<div class="para"><p>The response objects is not usually used directly, but is built up during the execution of the action and rendering of the data that is being sent back to the user, but sometimes - like in an after filter - it can be useful to access the response directly. Some of these accessor methods also have setters, allowing you to change their values.</p></div>
<div class="ilist"><ul>
<li>
<p>
body - This is the string of data being sent back to the client. This is most often HTML.
</p>
</li>
<li>
<p>
status - The HTTP status code for the response, like 200 for a successful request or 404 for file not found.
</p>
</li>
<li>
<p>
location - The URL the client is being redirected to, if any.
</p>
</li>
<li>
<p>
content_type - The content type of the response.
</p>
</li>
<li>
<p>
charset - The character set being used for the response. Default is "utf8".
</p>
</li>
</ul></div>
</div>
<h2 id="_http_basic_authentication">9. HTTP Basic Authentication</h2>
<div class="sectionbody">
<div class="para"><p>Rails comes with built-in HTTP Basic authentication. This is an authentication scheme that is supported by the majority of browsers and other HTTP clients. As an example, we will create an administration section which will only be available by entering a username and a password into the browser's HTTP Basic dialog window. Using the built-in authentication is quite easy and only requires you to use one method, <a href="http://api.rubyonrails.org/classes/ActionController/HttpAuthentication/Basic/ControllerMethods.html#M000610">authenticate_or_request_with_http_basic</a>.</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">class</span></span> AdminController <span style="color: #990000">&lt;</span> ApplicationController
USERNAME<span style="color: #990000">,</span> PASSWORD <span style="color: #990000">=</span> <span style="color: #FF0000">"humbaba"</span><span style="color: #990000">,</span> <span style="color: #FF0000">"f59a4805511bf4bb61978445a5380c6c"</span>
before_filter <span style="color: #990000">:</span>authenticate
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> authenticate
authenticate_or_request_with_http_basic <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>username<span style="color: #990000">,</span> password<span style="color: #990000">|</span>
username <span style="color: #990000">==</span> USERNAME <span style="color: #990000">&amp;&amp;</span> Digest<span style="color: #990000">::</span>MD5<span style="color: #990000">.</span>hexdigest<span style="color: #990000">(</span>password<span style="color: #990000">)</span> <span style="color: #990000">==</span> PASSWORD
<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="para"><p>With this in place, you can create namespaced controllers that inherit from AdminController. The before filter will thus be run for all actions in those controllers, protecting them with HTTP Basic authentication.</p></div>
</div>
<h2 id="_streaming_and_file_downloads">10. Streaming and file downloads</h2>
<div class="sectionbody">
<div class="para"><p>Sometimes you may want to send a file to the user instead of rendering an HTML page. All controllers in Rails have the <a href="http://api.rubyonrails.org/classes/ActionController/Streaming.html#M000624">send_data</a> and the <a href="http://api.rubyonrails.org/classes/ActionController/Streaming.html#M000623">send_file</a> methods, that will both stream data to the client. <tt>send_file</tt> is a convenience method which lets you provide the name of a file on the disk and it will stream the contents of that file for you.</p></div>
<div class="para"><p>To stream data to the client, use <tt>send_data</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-weight: bold"><span style="color: #000080">require</span></span> <span style="color: #FF0000">"prawn"</span>
<span style="font-weight: bold"><span style="color: #0000FF">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># Generate a PDF document with information on the client and return it.</span></span>
<span style="font-style: italic"><span style="color: #9A1900"># The user will get the PDF as a file download.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> download_pdf
client <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
send_data<span style="color: #990000">(</span>generate_pdf<span style="color: #990000">,</span> <span style="color: #990000">:</span>filename <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"#{client.name}.pdf"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>type <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"application/pdf"</span><span style="color: #990000">)</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> generate_pdf<span style="color: #990000">(</span>client<span style="color: #990000">)</span>
Prawn<span style="color: #990000">::</span>Document<span style="color: #990000">.</span>new <span style="font-weight: bold"><span style="color: #0000FF">do</span></span>
text client<span style="color: #990000">.</span>name<span style="color: #990000">,</span> <span style="color: #990000">:</span>align <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>center
text <span style="color: #FF0000">"Address: #{client.address}"</span>
text <span style="color: #FF0000">"Email: #{client.email}"</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span>render
<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="para"><p>The <tt>download_pdf</tt> action in the example above will call a private method which actually generates the file (a PDF document) and returns it as a string. This string will then be streamed to the client as a file download and a filename will be suggested to the user. Sometimes when streaming files to the user, you may not want them to download the file. Take images, for example, which can be embedded into HTML pages. To tell the browser a file is not meant to be downloaded, you can set the <tt>:disposition</tt> option to "inline". The opposite and default value for this option is "attachment".</p></div>
<h3 id="_sending_files">10.1. Sending files</h3>
<div class="para"><p>If you want to send a file that already exists on disk, use the <tt>send_file</tt> method. This is usually not recommended, but can be useful if you want to perform some authentication before letting the user download the file.</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">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># Stream a file that has already been generated and stored on disk</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> download_pdf
client <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
send_data<span style="color: #990000">(</span><span style="color: #FF0000">"#{RAILS_ROOT}/files/clients/#{client.id}.pdf"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>filename <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"#{client.name}.pdf"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>type <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"application/pdf"</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>
</tt></pre></div></div>
<div class="para"><p>This will read and stream the file 4Kb at the time, avoiding loading the entire file into memory at once. You can turn off streaming with the <tt>stream</tt> option or adjust the block size with the <tt>buffer_size</tt> option.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/warning.png" alt="Warning" />
</td>
<td class="content">Be careful when using (or just don't use) "outside" data (params, cookies, etc) to locate the file on disk, as this is a security risk as someone could gain access to files they are not meant to have access to.</td>
</tr></table>
</div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/tip.png" alt="Tip" />
</td>
<td class="content">It is not recommended that you stream static files through Rails if you can instead keep them in a public folder on your web server. It is much more efficient to let the user download the file directly using Apache or another web server, keeping the request from unnecessarily going through the whole Rails stack.</td>
</tr></table>
</div>
<h3 id="_restful_downloads">10.2. RESTful downloads</h3>
<div class="para"><p>While <tt>send_data</tt> works just fine, if you are creating a RESTful application having separate actions for file downloads is usually not necessary. In REST terminology, the PDF file from the example above can be considered just another representation of the client resource. Rails provides an easy and quite sleek way of doing "RESTful downloads". Let's try to rewrite the example so that the PDF download is a part of the <tt>show</tt> action:</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">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># The user can request to receive this resource as HTML or PDF.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> show
<span style="color: #009900">@client</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
respond_to <span style="font-weight: bold"><span style="color: #0000FF">do</span></span> <span style="color: #990000">|</span>format<span style="color: #990000">|</span>
format<span style="color: #990000">.</span>html
format<span style="color: #990000">.</span>pdf<span style="color: #FF0000">{</span> render <span style="color: #990000">:</span>pdf <span style="color: #990000">=&gt;</span> generate_pdf<span style="color: #990000">(</span><span style="color: #009900">@client</span><span style="color: #990000">)</span> <span style="color: #FF0000">}</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="para"><p>In order for this example to work, we have to add the PDF MIME type to Rails. This can be done by adding the following line to the file <tt>config/initializers/mime_types.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>Mime<span style="color: #990000">::</span>Type<span style="color: #990000">.</span>register <span style="color: #FF0000">"application/pdf"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>pdf
</tt></pre></div></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<img src="./images/icons/note.png" alt="Note" />
</td>
<td class="content">Configuration files are not reloaded on each request, so you have to restart the server in order for their changes to take effect.</td>
</tr></table>
</div>
<div class="para"><p>Now the user can request to get a PDF version of a client just by adding ".pdf" to the URL:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>GET /clients/1.pdf</tt></pre>
</div></div>
</div>
<h2 id="_parameter_filtering">11. Parameter filtering</h2>
<div class="sectionbody">
<div class="para"><p>Rails keeps a log file for each environment (development, test and production) in the "log" folder. These are extremely useful when debugging what's actually going on in your application, but in a live application you may not want every bit of information to be stored in the log file. The <a href="http://api.rubyonrails.org/classes/ActionController/Base.html#M000837">filter_parameter_logging</a> method can be used to filter out sensitive information from the log. It works by replacing certain keys in the <tt>params</tt> hash with "[FILTERED]" as they are written to the log. As an example, let's see how to filter all parameters with keys that include "password":</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
filter_parameter_logging <span style="color: #990000">:</span>password
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
</tt></pre></div></div>
<div class="para"><p>The method works recursively through all levels of the params hash and takes an optional second parameter which is used as the replacement string if present. It can also take a block which receives each key in return and replaces those for which the block returns true.</p></div>
</div>
<h2 id="_rescue">12. Rescue</h2>
<div class="sectionbody">
<div class="para"><p>Most likely your application is going to contain bugs or otherwise throw an exception that needs to be handled. For example, if the user follows a link to a resource that no longer exists in the database, Active Record will throw the ActiveRecord::RecordNotFound exception. Rails' default exception handling displays a 500 Server Error message for all exceptions. If the request was made locally, a nice traceback and some added information gets displayed so you can figure out what went wrong and deal with it. If the request was remote Rails will just display a simple "500 Server Error" message to the user, or a "404 Not Found" if there was a routing error or a record could not be found. Sometimes you might want to customize how these errors are caught and how they're displayed to the user. There are several levels of exception handling available in a Rails application:</p></div>
<h3 id="_the_default_500_and_404_templates">12.1. The default 500 and 404 templates</h3>
<div class="para"><p>By default a production application will render either a 404 or a 500 error message. These messages are contained in static HTML files in the <tt>public</tt> folder, in <tt>404.html</tt> and <tt>500.html</tt> respectively. You can customize these files to add some extra information and layout, but remember that they are static; i.e. you can't use RHTML or layouts in them, just plain HTML.</p></div>
<h3 id="_tt_rescue_from_tt">12.2. <tt>rescue_from</tt></h3>
<div class="para"><p>If you want to do something a bit more elaborate when catching errors, you can use <a href=":http://api.rubyonrails.org/classes/ActionController/Rescue/ClassMethods.html#M000620">rescue_from</a>, which handles exceptions of a certain type (or multiple types) in an entire controller and its subclasses. When an exception occurs which is caught by a rescue_from directive, the exception object is passed to the handler. The handler can be a method or a Proc object passed to the <tt>:with</tt> option. You can also use a block directly instead of an explicit Proc object.</p></div>
<div class="para"><p>Let's see how we can use rescue_from to intercept all ActiveRecord::RecordNotFound errors and do something with them.</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
rescue_from ActiveRecord<span style="color: #990000">::</span>RecordNotFound<span style="color: #990000">,</span> <span style="color: #990000">:</span>with <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>record_not_found
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> record_not_found
render <span style="color: #990000">:</span>text <span style="color: #990000">=&gt;</span> <span style="color: #FF0000">"404 Not Found"</span><span style="color: #990000">,</span> <span style="color: #990000">:</span>status <span style="color: #990000">=&gt;</span> <span style="color: #993399">404</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="para"><p>Of course, this example is anything but elaborate and doesn't improve the default exception handling at all, but once you can catch all those exceptions you're free to do whatever you want with them. For example, you could create custom exception classes that will be thrown when a user doesn't have access to a certain section of your application:</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">class</span></span> ApplicationController <span style="color: #990000">&lt;</span> ActionController<span style="color: #990000">::</span>Base
rescue_from User<span style="color: #990000">::</span>NotAuthorized<span style="color: #990000">,</span> <span style="color: #990000">:</span>with <span style="color: #990000">=&gt;</span> <span style="color: #990000">:</span>user_not_authorized
private
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> user_not_authorized
flash<span style="color: #990000">[:</span>error<span style="color: #990000">]</span> <span style="color: #990000">=</span> <span style="color: #FF0000">"You don't have access to this section."</span>
redirect_to <span style="color: #990000">:</span>back
<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">class</span></span> ClientsController <span style="color: #990000">&lt;</span> ApplicationController
<span style="font-style: italic"><span style="color: #9A1900"># Check that the user has the right authorization to access clients.</span></span>
before_filter <span style="color: #990000">:</span>check_authorization
<span style="font-style: italic"><span style="color: #9A1900"># Note how the actions don't have to worry about all the auth stuff.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> edit
<span style="color: #009900">@client</span> <span style="color: #990000">=</span> Client<span style="color: #990000">.</span>find<span style="color: #990000">(</span>params<span style="color: #990000">[:</span>id<span style="color: #990000">])</span>
<span style="font-weight: bold"><span style="color: #0000FF">end</span></span>
private
<span style="font-style: italic"><span style="color: #9A1900"># If the user is not authorized, just throw the exception.</span></span>
<span style="font-weight: bold"><span style="color: #0000FF">def</span></span> check_authorization
<span style="font-weight: bold"><span style="color: #0000FF">raise</span></span> User<span style="color: #990000">::</span>NotAuthorized <span style="font-weight: bold"><span style="color: #0000FF">unless</span></span> current_user<span style="color: #990000">.</span>admin?
<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>
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<img src="./images/icons/note.png" alt="Note" />
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<td class="content">Certain exceptions are only rescuable from the ApplicationController class, as they are raised before the controller gets initialized and the action gets executed. See Pratik Naik's <a href="http://m.onkey.org/2008/7/20/rescue-from-dispatching">article</a> on the subject for more information.</td>
</tr></table>
</div>
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