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2.2 - November 2008</option> </optgroup> </select> </li> </ul> </nav> </div> </header> <hr class="hide" /> <main id="main"> <article> <header id="feature"> <div class="wrapper"> <h1>Using Rails for API-only Applications</h1>In this guide you will learn: <ul> <li>What Rails provides for API-only applications</li> <li>How to configure Rails to start without any browser features</li> <li>How to decide which middleware you will want to include</li> <li>How to decide which modules to use in your controller</li> </ul> <nav id="column-side" aria-label="Chapter" class="guide-index" data-turbo="false"> <a id="chapter-nav-skip-link" href="#article-body" class="skip-link"> Skip to article body </a> <h2 class="chapter"> <picture aria-hidden="true">  <source srcset="images/icon_book-close-bookmark-1-wht.svg" media="(prefers-color-scheme: dark)" /> <img src="images/icon_book-close-bookmark-1.svg" alt="Chapter Icon" /> </picture> Chapters </h2> <ol class="chapters"> <li><a href="#what-is-an-api-application-questionmark">What is an API Application?</a></li> <li><a href="#why-use-rails-for-json-apis-questionmark">Why Use Rails for JSON APIs?</a></li> <li><a href="#the-basic-configuration">The Basic Configuration</a> <ul> <li><a href="#creating-a-new-application">Creating a New Application</a></li> <li><a href="#generating-a-new-resource">Generating a New Resource</a></li> <li><a href="#changing-an-existing-application">Changing an Existing Application</a></li> </ul></li> <li><a href="#choosing-middleware">Choosing Middleware</a> <ul> <li><a href="#using-rack-cache">Using Rack::Cache</a></li> <li><a href="#using-rack-sendfile">Using Rack::Sendfile</a></li> <li><a href="#using-actiondispatch-request">Using ActionDispatch::Request</a></li> <li><a href="#using-session-middlewares">Using Session Middlewares</a></li> <li><a href="#other-middleware">Other Middleware</a></li> <li><a href="#removing-middleware">Removing Middleware</a></li> </ul></li> <li><a href="#choosing-controller-modules">Choosing Controller Modules</a> <ul> <li><a href="#adding-other-modules">Adding Other Modules</a></li> </ul></li> </ol> </nav> </div> </header> <div class="wrapper"> <div id="column-main"> <section id="article-body"> <h2 id="what-is-an-api-application-questionmark"><a class="anchorlink" href="#what-is-an-api-application-questionmark" data-turbo="false">1 What is an API Application?</a></h2>Traditionally, when people said that they used Rails as an "API", they meant providing a programmatically accessible API alongside their web application. For example, GitHub provides <a href="https://developer.github.com">an API</a> that you can use from your own custom clients.With the advent of client-side frameworks, more developers are using Rails to build a back-end that is shared between their web application and other native applications.For example, X uses its <a href="https://developer.x.com/">public API</a> in its web application, which is built as a static site that consumes JSON resources.Instead of using Rails to generate HTML that communicates with the server through forms and links, many developers are treating their web application as just an API client delivered as HTML with JavaScript that consumes a JSON API.This guide covers building a Rails application that serves JSON resources to an API client, including client-side frameworks.<h2 id="why-use-rails-for-json-apis-questionmark"><a class="anchorlink" href="#why-use-rails-for-json-apis-questionmark" data-turbo="false">2 Why Use Rails for JSON APIs?</a></h2>The first question a lot of people have when thinking about building a JSON API using Rails is: "isn't using Rails to spit out some JSON overkill? Shouldn't I just use something like Sinatra?".For very simple APIs, this may be true. However, even in very HTML-heavy applications, most of an application's logic lives outside of the view layer.The reason most people use Rails is that it provides a set of defaults that allows developers to get up and running quickly, without having to make a lot of trivial decisions.Let's take a look at some of the things that Rails provides out of the box that are still applicable to API applications.Handled at the middleware layer: <ul> <li>Reloading: Rails applications support transparent reloading. This works even if your application gets big and restarting the server for every request becomes non-viable.</li> <li>Development Mode: Rails applications come with smart defaults for development, making development pleasant without compromising production-time performance.</li> <li>Test Mode: Ditto development mode.</li> <li>Logging: Rails applications log every request, with a level of verbosity appropriate for the current mode. Rails logs in development include information about the request environment, database queries, and basic performance information.</li> <li>Security: Rails detects and thwarts <a href="https://en.wikipedia.org/wiki/IP_address_spoofing">IP spoofing attacks</a> and handles cryptographic signatures in a <a href="https://en.wikipedia.org/wiki/Timing_attack">timing attack</a> aware way. Don't know what an IP spoofing attack or a timing attack is? Exactly.</li> <li>Parameter Parsing: Want to specify your parameters as JSON instead of as a URL-encoded String? No problem. Rails will decode the JSON for you and make it available in <code>params</code>. Want to use nested URL-encoded parameters? That works too.</li> <li>Conditional GETs: Rails handles conditional <code>GET</code> (<code>ETag</code> and <code>Last-Modified</code>) processing request headers and returning the correct response headers and status code. All you need to do is use the <a href="https://api.rubyonrails.org/v8.0.1/classes/ActionController/ConditionalGet.html#method-i-stale-3F"><code>stale?</code></a> check in your controller, and Rails will handle all of the HTTP details for you.</li> <li>HEAD requests: Rails will transparently convert <code>HEAD</code> requests into <code>GET</code> ones, and return just the headers on the way out. This makes <code>HEAD</code> work reliably in all Rails APIs.</li> </ul> While you could obviously build these up in terms of existing Rack middleware, this list demonstrates that the default Rails middleware stack provides a lot of value, even if you're "just generating JSON".Handled at the Action Pack layer: <ul> <li>Resourceful Routing: If you're building a RESTful JSON API, you want to be using the Rails router. Clean and conventional mapping from HTTP to controllers means not having to spend time thinking about how to model your API in terms of HTTP.</li> <li>URL Generation: The flip side of routing is URL generation. A good API based on HTTP includes URLs (see <a href="https://docs.github.com/en/rest/reference/gists">the GitHub Gist API</a> for an example).</li> <li>Header and Redirection Responses: <code>head :no_content</code> and <code>redirect_to user_url(current_user)</code> come in handy. Sure, you could manually add the response headers, but why?</li> <li>Caching: Rails provides page, action, and fragment caching. Fragment caching is especially helpful when building up a nested JSON object.</li> <li>Basic, Digest, and Token Authentication: Rails comes with out-of-the-box support for three kinds of HTTP authentication.</li> <li>Instrumentation: Rails has an instrumentation API that triggers registered handlers for a variety of events, such as action processing, sending a file or data, redirection, and database queries. The payload of each event comes with relevant information (for the action processing event, the payload includes the controller, action, parameters, request format, request method, and the request's full path).</li> <li>Generators: It is often handy to generate a resource and get your model, controller, test stubs, and routes created for you in a single command for further tweaking. Same for migrations and others.</li> <li>Plugins: Many third-party libraries come with support for Rails that reduce or eliminate the cost of setting up and gluing together the library and the web framework. This includes things like overriding default generators, adding Rake tasks, and honoring Rails choices (like the logger and cache back-end).</li> </ul> Of course, the Rails boot process also glues together all registered components. For example, the Rails boot process is what uses your <code>config/database.yml</code> file when configuring Active Record.The short version is: you may not have thought about which parts of Rails are still applicable even if you remove the view layer, but the answer turns out to be most of it.<h2 id="the-basic-configuration"><a class="anchorlink" href="#the-basic-configuration" data-turbo="false">3 The Basic Configuration</a></h2>If you're building a Rails application that will be an API server first and foremost, you can start with a more limited subset of Rails and add in features as needed.<h3 id="creating-a-new-application"><a class="anchorlink" href="#creating-a-new-application" data-turbo="false">3.1 Creating a New Application</a></h3>You can generate a new api Rails app:<div class="interstitial code"> <pre><code class="highlight console">$ rails new my_api --api </code></pre> <button class="clipboard-button" data-clipboard-text="rails new my_api --api ">Copy</button> </div> This will do three main things for you: <ul> <li>Configure your application to start with a more limited set of middleware than normal. Specifically, it will not include any middleware primarily useful for browser applications (like cookies support) by default.</li> <li>Make <code>ApplicationController</code> inherit from <code>ActionController::API</code> instead of <code>ActionController::Base</code>. As with middleware, this will leave out any Action Controller modules that provide functionalities primarily used by browser applications.</li> <li>Configure the generators to skip generating views, helpers, and assets when you generate a new resource.</li> </ul> <h3 id="generating-a-new-resource"><a class="anchorlink" href="#generating-a-new-resource" data-turbo="false">3.2 Generating a New Resource</a></h3>To see how our newly created API handles generating a new resource, let's create a new Group resource. Each group will have a name.<div class="interstitial code"> <pre><code class="highlight console">$ bin/rails g scaffold Group name:string </code></pre> <button class="clipboard-button" data-clipboard-text="bin/rails g scaffold Group name:string ">Copy</button> </div> Before we can use our scaffolded code, we need to update our database scheme.<div class="interstitial code"> <pre><code class="highlight console">$ bin/rails db:migrate </code></pre> <button class="clipboard-button" data-clipboard-text="bin/rails db:migrate ">Copy</button> </div> Now if we open our <code>GroupsController</code>, we should notice that with an API Rails app we are rendering JSON data only. On the index action we query for <code>Group.all</code> and assign it to an instance variable called <code>@groups</code>. Passing it to <code>render</code> with the <code>:json</code> option will automatically render the groups as JSON.<div class="interstitial code"> <pre><code class="highlight ruby"># app/controllers/groups_controller.rb class GroupsController < ApplicationController before_action :set_group, only: %i[ show update destroy ] # GET /groups def index @groups = Group.all render json: @groups end # GET /groups/1 def show render json: @group end # POST /groups def create @group = Group.new(group_params) if @group.save render json: @group, status: :created, location: @group else render json: @group.errors, status: :unprocessable_entity end end # PATCH/PUT /groups/1 def update if @group.update(group_params) render json: @group else render json: @group.errors, status: :unprocessable_entity end end # DELETE /groups/1 def destroy @group.destroy end private # Use callbacks to share common setup or constraints between actions. def set_group @group = Group.find(params[:id]) end # Only allow a list of trusted parameters through. def group_params params.expect(group: [:name]) end end </code></pre> <button class="clipboard-button" data-clipboard-text="class GroupsController < ApplicationController before_action :set_group, only: %i[ show update destroy ] # GET /groups def index @groups = Group.all render json: @groups end # GET /groups/1 def show render json: @group end # POST /groups def create @group = Group.new(group_params) if @group.save render json: @group, status: :created, location: @group else render json: @group.errors, status: :unprocessable_entity end end # PATCH/PUT /groups/1 def update if @group.update(group_params) render json: @group else render json: @group.errors, status: :unprocessable_entity end end # DELETE /groups/1 def destroy @group.destroy end private # Use callbacks to share common setup or constraints between actions. def set_group @group = Group.find(params[:id]) end # Only allow a list of trusted parameters through. def group_params params.expect(group: [:name]) end end ">Copy</button> </div> Finally we can add some groups to our database from the Rails console:<div class="interstitial code"> <pre><code class="highlight irb">irb> Group.create(name: "Rails Founders") irb> Group.create(name: "Rails Contributors") </code></pre> <button class="clipboard-button" data-clipboard-text="Group.create(name: "Rails Founders") Group.create(name: "Rails Contributors") ">Copy</button> </div> With some data in the app, we can boot up the server and visit <a href="http://localhost:3000/groups.json">http://localhost:3000/groups.json</a> to see our JSON data.<div class="interstitial code"> <pre><code class="highlight json">[ {"id":1, "name":"Rails Founders", "created_at": ...}, {"id":2, "name":"Rails Contributors", "created_at": ...} ] </code></pre> <button class="clipboard-button" data-clipboard-text="[ {"id":1, "name":"Rails Founders", "created_at": ...}, {"id":2, "name":"Rails Contributors", "created_at": ...} ] ">Copy</button> </div> <h3 id="changing-an-existing-application"><a class="anchorlink" href="#changing-an-existing-application" data-turbo="false">3.3 Changing an Existing Application</a></h3>If you want to take an existing application and make it an API one, read the following steps.In <code>config/application.rb</code>, add the following line at the top of the <code>Application</code> class definition:<div class="interstitial code"> <pre><code class="highlight ruby">config.api_only = true </code></pre> <button class="clipboard-button" data-clipboard-text="config.api_only = true ">Copy</button> </div> In <code>config/environments/development.rb</code>, set <a href="configuring.html#config-debug-exception-response-format"><code>config.debug_exception_response_format</code></a> to configure the format used in responses when errors occur in development mode.To render an HTML page with debugging information, use the value <code>:default</code>.<div class="interstitial code"> <pre><code class="highlight ruby">config.debug_exception_response_format = :default </code></pre> <button class="clipboard-button" data-clipboard-text="config.debug_exception_response_format = :default ">Copy</button> </div> To render debugging information preserving the response format, use the value <code>:api</code>.<div class="interstitial code"> <pre><code class="highlight ruby">config.debug_exception_response_format = :api </code></pre> <button class="clipboard-button" data-clipboard-text="config.debug_exception_response_format = :api ">Copy</button> </div> By default, <code>config.debug_exception_response_format</code> is set to <code>:api</code>, when <code>config.api_only</code> is set to true.Finally, inside <code>app/controllers/application_controller.rb</code>, instead of:<div class="interstitial code"> <pre><code class="highlight ruby">class ApplicationController < ActionController::Base end </code></pre> <button class="clipboard-button" data-clipboard-text="class ApplicationController < ActionController::Base end ">Copy</button> </div> do:<div class="interstitial code"> <pre><code class="highlight ruby">class ApplicationController < ActionController::API end </code></pre> <button class="clipboard-button" data-clipboard-text="class ApplicationController < ActionController::API end ">Copy</button> </div> <h2 id="choosing-middleware"><a class="anchorlink" href="#choosing-middleware" data-turbo="false">4 Choosing Middleware</a></h2>An API application comes with the following middleware by default: <ul> <li><code>ActionDispatch::HostAuthorization</code></li> <li><code>Rack::Sendfile</code></li> <li><code>ActionDispatch::Static</code></li> <li><code>ActionDispatch::Executor</code></li> <li><code>ActionDispatch::ServerTiming</code></li> <li><code>ActiveSupport::Cache::Strategy::LocalCache::Middleware</code></li> <li><code>Rack::Runtime</code></li> <li><code>ActionDispatch::RequestId</code></li> <li><code>ActionDispatch::RemoteIp</code></li> <li><code>Rails::Rack::Logger</code></li> <li><code>ActionDispatch::ShowExceptions</code></li> <li><code>ActionDispatch::DebugExceptions</code></li> <li><code>ActionDispatch::ActionableExceptions</code></li> <li><code>ActionDispatch::Reloader</code></li> <li><code>ActionDispatch::Callbacks</code></li> <li><code>ActiveRecord::Migration::CheckPending</code></li> <li><code>Rack::Head</code></li> <li><code>Rack::ConditionalGet</code></li> <li><code>Rack::ETag</code></li> </ul> See the <a href="rails_on_rack.html#internal-middleware-stack">internal middleware</a> section of the Rack guide for further information on them.Other plugins, including Active Record, may add additional middleware. In general, these middleware are agnostic to the type of application you are building, and make sense in an API-only Rails application.You can get a list of all middleware in your application via:<div class="interstitial code"> <pre><code class="highlight console">$ bin/rails middleware </code></pre> <button class="clipboard-button" data-clipboard-text="bin/rails middleware ">Copy</button> </div> <h3 id="using-rack-cache"><a class="anchorlink" href="#using-rack-cache" data-turbo="false">4.1 Using Rack::Cache</a></h3>When used with Rails, <code>Rack::Cache</code> uses the Rails cache store for its entity and meta stores. This means that if you use memcache, for your Rails app, for instance, the built-in HTTP cache will use memcache.To make use of <code>Rack::Cache</code>, you first need to add the <code>rack-cache</code> gem to <code>Gemfile</code>, and set <code>config.action_dispatch.rack_cache</code> to <code>true</code>. To enable its functionality, you will want to use <code>stale?</code> in your controller. Here’s an example of <code>stale?</code> in use.<div class="interstitial code"> <pre><code class="highlight ruby">def show @post = Post.find(params[:id]) if stale?(last_modified: @post.updated_at) render json: @post end end </code></pre> <button class="clipboard-button" data-clipboard-text="def show @post = Post.find(params[:id]) if stale?(last_modified: @post.updated_at) render json: @post end end ">Copy</button> </div> The call to <code>stale?</code> will compare the <code>If-Modified-Since</code> header in the request with <code>@post.updated_at</code>. If the header is newer than the last modified, this action will return a "304 Not Modified" response. Otherwise, it will render the response and include a <code>Last-Modified</code> header in it.Normally, this mechanism is used on a per-client basis. <code>Rack::Cache</code> allows us to share this caching mechanism across clients. We can enable cross-client caching in the call to <code>stale?</code>:<div class="interstitial code"> <pre><code class="highlight ruby">def show @post = Post.find(params[:id]) if stale?(last_modified: @post.updated_at, public: true) render json: @post end end </code></pre> <button class="clipboard-button" data-clipboard-text="def show @post = Post.find(params[:id]) if stale?(last_modified: @post.updated_at, public: true) render json: @post end end ">Copy</button> </div> This means that <code>Rack::Cache</code> will store off the <code>Last-Modified</code> value for a URL in the Rails cache, and add an <code>If-Modified-Since</code> header to any subsequent inbound requests for the same URL.Think of it as page caching using HTTP semantics.<h3 id="using-rack-sendfile"><a class="anchorlink" href="#using-rack-sendfile" data-turbo="false">4.2 Using Rack::Sendfile</a></h3>When you use the <code>send_file</code> method inside a Rails controller, it sets the <code>X-Sendfile</code> header. <code>Rack::Sendfile</code> is responsible for actually sending the file.If your front-end server supports accelerated file sending, <code>Rack::Sendfile</code> will offload the actual file sending work to the front-end server. This enables Rails to finish request handling and free resources earlier.You can configure the name of the header that your front-end server uses for this purpose using <a href="configuring.html#config-action-dispatch-x-sendfile-header"><code>config.action_dispatch.x_sendfile_header</code></a> in the appropriate environment's configuration file.You can learn more about how to use <code>Rack::Sendfile</code> with popular front-ends in <a href="https://www.rubydoc.info/gems/rack/Rack/Sendfile">the Rack::Sendfile documentation</a>.Here are some values for this header for some popular servers, once these servers are configured to support accelerated file sending:<div class="interstitial code"> <pre><code class="highlight ruby"># Apache and lighttpd config.action_dispatch.x_sendfile_header = "X-Sendfile" # Nginx config.action_dispatch.x_sendfile_header = "X-Accel-Redirect" </code></pre> <button class="clipboard-button" data-clipboard-text="# Apache and lighttpd config.action_dispatch.x_sendfile_header = "X-Sendfile" # Nginx config.action_dispatch.x_sendfile_header = "X-Accel-Redirect" ">Copy</button> </div> Make sure to configure your server to support these options following the instructions in the <code>Rack::Sendfile</code> documentation.<h3 id="using-actiondispatch-request"><a class="anchorlink" href="#using-actiondispatch-request" data-turbo="false">4.3 Using ActionDispatch::Request</a></h3><code>ActionDispatch::Request#params</code> will take parameters from the client in the JSON format and make them available in your controller inside <code>params</code>.To use this, your client will need to make a request with JSON-encoded parameters and specify the <code>Content-Type</code> as <code>application/json</code>.Here's an example:<div class="interstitial code"> <pre><code class="highlight js">fetch('/people', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ person: { firstName: 'Yehuda', lastName: 'Katz' } }) }).then(response => response.json()) </code></pre> <button class="clipboard-button" data-clipboard-text="fetch('/people', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ person: { firstName: 'Yehuda', lastName: 'Katz' } }) }).then(response => response.json()) ">Copy</button> </div> <code>ActionDispatch::Request</code> will see the <code>Content-Type</code> and your parameters will be:<div class="interstitial code"> <pre><code class="highlight ruby">{ person: { firstName: "Yehuda", lastName: "Katz" } } </code></pre> <button class="clipboard-button" data-clipboard-text="{ person: { firstName: "Yehuda", lastName: "Katz" } } ">Copy</button> </div> <h3 id="using-session-middlewares"><a class="anchorlink" href="#using-session-middlewares" data-turbo="false">4.4 Using Session Middlewares</a></h3>The following middlewares, used for session management, are excluded from API apps since they normally don't need sessions. If one of your API clients is a browser, you might want to add one of these back in: <ul> <li><code>ActionDispatch::Session::CacheStore</code></li> <li><code>ActionDispatch::Session::CookieStore</code></li> <li><code>ActionDispatch::Session::MemCacheStore</code></li> </ul> The trick to adding these back in is that, by default, they are passed <code>session_options</code> when added (including the session key), so you can't just add a <code>session_store.rb</code> initializer, add <code>use ActionDispatch::Session::CookieStore</code> and have sessions functioning as usual. (To be clear: sessions may work, but your session options will be ignored - i.e. the session key will default to <code>_session_id</code>)Instead of the initializer, you'll have to set the relevant options somewhere before your middleware is built (like <code>config/application.rb</code>) and pass them to your preferred middleware, like this:<div class="interstitial code"> <pre><code class="highlight ruby"># This also configures session_options for use below config.session_store :cookie_store, key: "_your_app_session" # Required for all session management (regardless of session_store) config.middleware.use ActionDispatch::Cookies config.middleware.use config.session_store, config.session_options </code></pre> <button class="clipboard-button" data-clipboard-text="# This also configures session_options for use below config.session_store :cookie_store, key: "_your_app_session" # Required for all session management (regardless of session_store) config.middleware.use ActionDispatch::Cookies config.middleware.use config.session_store, config.session_options ">Copy</button> </div> <h3 id="other-middleware"><a class="anchorlink" href="#other-middleware" data-turbo="false">4.5 Other Middleware</a></h3>Rails ships with a number of other middleware that you might want to use in an API application, especially if one of your API clients is the browser: <ul> <li><code>Rack::MethodOverride</code></li> <li><code>ActionDispatch::Cookies</code></li> <li><code>ActionDispatch::Flash</code></li> </ul> Any of these middleware can be added via:<div class="interstitial code"> <pre><code class="highlight ruby">config.middleware.use Rack::MethodOverride </code></pre> <button class="clipboard-button" data-clipboard-text="config.middleware.use Rack::MethodOverride ">Copy</button> </div> <h3 id="removing-middleware"><a class="anchorlink" href="#removing-middleware" data-turbo="false">4.6 Removing Middleware</a></h3>If you don't want to use a middleware that is included by default in the API-only middleware set, you can remove it with:<div class="interstitial code"> <pre><code class="highlight ruby">config.middleware.delete ::Rack::Sendfile </code></pre> <button class="clipboard-button" data-clipboard-text="config.middleware.delete ::Rack::Sendfile ">Copy</button> </div> Keep in mind that removing these middlewares will remove support for certain features in Action Controller.<h2 id="choosing-controller-modules"><a class="anchorlink" href="#choosing-controller-modules" data-turbo="false">5 Choosing Controller Modules</a></h2>An API application (using <code>ActionController::API</code>) comes with the following controller modules by default: <div class="table-wrapper"><table><thead> <tr> <th></th> <th></th> </tr> </thead><tbody> <tr> <td><code>ActionController::UrlFor</code></td> <td>Makes <code>url_for</code> and similar helpers available.</td> </tr> <tr> <td><code>ActionController::Redirecting</code></td> <td>Support for <code>redirect_to</code>.</td> </tr> <tr> <td><code>AbstractController::Rendering</code> and <code>ActionController::ApiRendering</code></td> <td>Basic support for rendering.</td> </tr> <tr> <td><code>ActionController::Renderers::All</code></td> <td>Support for <code>render :json</code> and friends.</td> </tr> <tr> <td><code>ActionController::ConditionalGet</code></td> <td>Support for <code>stale?</code>.</td> </tr> <tr> <td><code>ActionController::BasicImplicitRender</code></td> <td>Makes sure to return an empty response, if there isn't an explicit one.</td> </tr> <tr> <td><code>ActionController::StrongParameters</code></td> <td>Support for parameters filtering in combination with Active Model mass assignment.</td> </tr> <tr> <td><code>ActionController::DataStreaming</code></td> <td>Support for <code>send_file</code> and <code>send_data</code>.</td> </tr> <tr> <td><code>AbstractController::Callbacks</code></td> <td>Support for <code>before_action</code> and similar helpers.</td> </tr> <tr> <td><code>ActionController::Rescue</code></td> <td>Support for <code>rescue_from</code>.</td> </tr> <tr> <td><code>ActionController::Instrumentation</code></td> <td>Support for the instrumentation hooks defined by Action Controller (see <a href="active_support_instrumentation.html#action-controller">the instrumentation guide</a> for more information regarding this).</td> </tr> <tr> <td><code>ActionController::ParamsWrapper</code></td> <td>Wraps the parameters hash into a nested hash, so that you don't have to specify root elements sending POST requests for instance.</td> </tr> <tr> <td><code>ActionController::Head</code></td> <td>Support for returning a response with no content, only headers.</td> </tr> </tbody></table></div> Other plugins may add additional modules. You can get a list of all modules included into <code>ActionController::API</code> in the rails console:<div class="interstitial code"> <pre><code class="highlight irb">irb> ActionController::API.ancestors - ActionController::Metal.ancestors => [ActionController::API, ActiveRecord::Railties::ControllerRuntime, ActionDispatch::Routing::RouteSet::MountedHelpers, ActionController::ParamsWrapper, ... , AbstractController::Rendering, ActionView::ViewPaths] </code></pre> <button class="clipboard-button" data-clipboard-text="ActionController::API.ancestors - ActionController::Metal.ancestors ">Copy</button> </div> <h3 id="adding-other-modules"><a class="anchorlink" href="#adding-other-modules" data-turbo="false">5.1 Adding Other Modules</a></h3>All Action Controller modules know about their dependent modules, so you can feel free to include any modules into your controllers, and all dependencies will be included and set up as well.Some common modules you might want to add: <ul> <li><code>AbstractController::Translation</code>: Support for the <code>l</code> and <code>t</code> localization and translation methods.</li> <li>Support for basic, digest, or token HTTP authentication: <ul> <li><code>ActionController::HttpAuthentication::Basic::ControllerMethods</code></li> <li><code>ActionController::HttpAuthentication::Digest::ControllerMethods</code></li> <li><code>ActionController::HttpAuthentication::Token::ControllerMethods</code></li> </ul></li> <li><code>ActionView::Layouts</code>: Support for layouts when rendering.</li> <li><code>ActionController::MimeResponds</code>: Support for <code>respond_to</code>.</li> <li><code>ActionController::Cookies</code>: Support for <code>cookies</code>, which includes support for signed and encrypted cookies. This requires the cookies middleware.</li> <li><code>ActionController::Caching</code>: Support view caching for the API controller. Please note that you will need to manually specify the cache store inside the controller like this:<div class="interstitial code"> <pre><code class="highlight ruby">class ApplicationController < ActionController::API include ::ActionController::Caching self.cache_store = :mem_cache_store end </code></pre> <button class="clipboard-button" data-clipboard-text="class ApplicationController < ActionController::API include ::ActionController::Caching self.cache_store = :mem_cache_store end ">Copy</button> </div> Rails does not pass this configuration automatically.</li> </ul> The best place to add a module is in your <code>ApplicationController</code>, but you can also add modules to individual controllers. </section> <hr> <footer aria-labelledby="heading-feedback" role="region"> <h2 id="heading-feedback">Feedback</h2> You're encouraged to help improve the quality of this guide. Please contribute if you see any typos or factual errors. To get started, you can read our <a href="https://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#contributing-to-the-rails-documentation">documentation contributions</a> section. You may also find incomplete content or stuff that is not up to date. Please do add any missing documentation for main. Make sure to check <a href="https://edgeguides.rubyonrails.org">Edge Guides</a> first to verify if the issues are already fixed or not on the main branch. Check the <a href="ruby_on_rails_guides_guidelines.html">Ruby on Rails Guides Guidelines</a> for style and conventions. If for whatever reason you spot something to fix but cannot patch it yourself, please <a href="https://github.com/rails/rails/issues">open an issue</a>. And last but not least, any kind of discussion regarding Ruby on Rails documentation is very welcome on the <a href="https://discuss.rubyonrails.org/c/rubyonrails-docs">official Ruby on Rails Forum</a>. </footer> </div> </article> </main> <hr class="hide" /> <footer id="complementary"> <div class="wrapper"> This work is licensed under a <a href="https://creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike 4.0 International</a> License "Rails", "Ruby on Rails", and the Rails logo are trademarks of David Heinemeier Hansson. All rights reserved. </div> </footer> <a href="#main-skip-link" class="back-to-top" data-turbo="false">Back to top</a> </body> </html>