symfony · javiereguiluz · Oct 30, 2018 · Sep 10, 2018 · Sep 10, 2018 · Sep 10, 2018
diff --git a/_images/components/weblink/homepage-requests.png b/_images/components/weblink/homepage-requests.png
diff --git a/_images/components/weblink/http2-server-push.png b/_images/components/weblink/http2-server-push.png
diff --git a/_images/components/weblink/response-headers.png b/_images/components/weblink/response-headers.png
diff --git a/_images/components/weblink/symfony4-http2.png b/_images/components/weblink/symfony4-http2.png
diff --git a/components/weblink.rst b/components/weblink.rst
@@ -0,0 +1,49 @@
+.. index::
+   single: WebLink
+   single: Components; WebLink
+
+The WebLink Component
+======================
+
+   The WebLink component provides tools to create `Web Links`_.
+   It allows to easily leverage `HTTP/2 Server Push`_ as well as `Resource Hints`_.
+
+.. versionadded:: 3.3
+    The WebLink component was introduced in Symfony 3.3.
+
+Installation
+------------
+
+.. code-block:: terminal
+
+    $ composer require symfony/weblink
+
+Alternatively, you can clone the `<https://github.com/symfony/weblink>`_ repository.
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+Basic usage::
+
+   use Fig\Link\GenericLinkProvider;
+   use Fig\Link\Link;
+   use Symfony\Component\WebLink\HttpHeaderSerializer;
+
+   $linkProvider = (new GenericLinkProvider())
+       ->withLink(new Link('preload', '/bootstrap.min.css'));
+
+   header('Link: '.(new HttpHeaderSerializer())->serialize($linkProvider->getLinks()));
+
+   echo 'Hello';
+
+
+.. seealso::
+
+    Read the :doc:`WebLink documentation </weblink>` to learn how
+    to use the features implemented by this component.
+
+.. _`Web Links`: https://tools.ietf.org/html/rfc5988
+.. _`HTTP/2 Server Push`: https://tools.ietf.org/html/rfc7540#section-8.2
+.. _`Resource Hints`: https://www.w3.org/TR/resource-hints/
diff --git a/index.rst b/index.rst
@@ -54,6 +54,7 @@ Topics
     testing
     translation
     validation
+    weblink
     workflow
 
 Best Practices

diff --git a/weblink.rst b/weblink.rst
@@ -0,0 +1,275 @@
+WebLink
+=======
+
+Symfony natively supports `Web Linking`_. It is especially useful to improve
+the performance of your application by leveraging the HTTP/2 protocol and
+preloading capabilities of modern web browsers.
+
+By implementing cutting edge web standards, namely `HTTP/2 Server Push`_ and
+W3C's `Resource Hints`_, the WebLink component
+brings great opportunities to boost webapp's performance.
+
+Thanks to WebLink, HTTP/2 (**h2**) servers are able to push resources to clients
+before they even know that they need them (think about CSS or JavaScript
+files, or relations of an API resource). WebLink also enables other very
+efficient optimisations that work with HTTP 1.x:
+
+-  telling the browser to fetch or to render another webpage in the
+   background ;
+-  initializing early DNS lookups, TCP handshakes or TLS negotiations
+
+To benefit from HTTP/2 Server Pushes, an HTTP/2 server and an HTTPS connection
+are required (even local ones).
+Both Apache, Nginx and Caddy support these protocols.
+Be sure they are properly configured before reading.
+
+Alternatively, you can use the `Docker installer and runtime for
+Symfony`_ provided by Kévin Dunglas (community supported).
+
+Unzip the downloaded archive, open a shell in the resulting directory and run
+the following command:
+
+.. code-block:: terminal
+
+   # Install Symfony and start the project
+   $ docker-compose up
+
+Open ``https://localhost``, if this nice page appears, you
+successfully created your first Symfony 4 project and are browsing it in
+HTTP/2!
+
+.. image:: /_images/components/weblink/symfony4-http2.png
+
+Let's create a very simple homepage using
+the Twig_ templating engine.
+
+The first step is to install the library itself:
+
+.. code-block:: terminal
+
+    composer req twig
+
+Symfony is smart enough to download Twig, to automatically register it,
+and to enable Symfony features requiring the library.
+It also generates a base HTML5 layout in the ``templates/`` directory.
+
+Now, download Bootstrap_, extract the archive and copy the file
+``dist/css/bootstrap.min.css`` in the ``public/`` directory of our
+project.
+
+Symfony comes with `an integration of the most popular CSS framework`_.
+
+.. note::
+
+    In a real project, you should use Yarn or NPM with
+    :doc:`Symfony Encore </frontend/encore/bootstrap>`
+    to install Bootstrap.
+
+Now, it's time to create the template of our homepage:
+
+.. code-block:: twig
+
+   {# templates/homepage.html.twig #}
+   <!DOCTYPE html>
+   <html>
+   <head>
+       <meta charset="UTF-8">
+       <title>Welcome!</title>
+       <link rel="stylesheet" href="/bootstrap.min.css">
+   </head>
+   <body>
+       <main role="main" class="container">
+           <h1>Hello World</h1>
+           <p class="lead">That's a lot of highly dynamic content, right?</p>
+       </main>
+   </body>
+   </html>
+
+And finally, register our new template as the homepage using the builtin
+:doc:`TemplateController </templating/render_without_controller>`:
+
+.. code-block:: yaml
+
+   # config/routes.yaml
+   index:
+       path: /
+       defaults:
+         _controller: 'Symfony\Bundle\FrameworkBundle\Controller\TemplateController::templateAction'
+         template: 'homepage.html.twig'
+
+Refresh your browser, this homepage should appear:
+
+.. image:: /_images/components/weblink/homepage-requests.png
+
+HTTP requests are issued by the browser, one for the homepage, and
+another one for Bootstrap. But we know from the very beginning that the
+browser **will** need Bootstrap. Instead of waiting that the browser
+downloads the homepage, parses the HTML (notice "Initiator: Parser" in
+Chrome DevTools), encounters the reference to ``bootstrap.min.css`` and
+finally sends a new HTTP request, we could take benefit of the HTTP/2
+Push feature to directly send both resources to the browser.
+
+Let's do it! Install the WebLink component:
+
+.. code-block:: terminal
+
+    composer req weblink
+
+As for Twig, Symfony will automatically download and register this component into our app.
+Now, update the template to use the ``preload`` Twig helper that
+leverages the WebLink component:
+
+.. code:: html+twig
+
+   {# ... #}
+       <link rel="stylesheet" href="{{ preload('/bootstrap.min.css') }}">
+   {# ... #}
+
+Reload the page:
+
+.. image:: /_images/components/weblink/http2-server-push.png
+
+As you can see (Initiator: Push), both
+responses have been sent directly by the server.
+``bootstrap.min.css`` has started to be received before the browser even requested it!
+
+.. note::
+
+    Google Chrome provides an interface to debug HTTP/2 connections.
+    Open ``chrome://net-internals/#http2`` to start the tool.
+
+How does it works?
+~~~~~~~~~~~~~~~~~~
+
+The WebLink component tracks ``Link`` HTTP headers to add to the response.
+When using the ``preload()`` helper, a ``Link`` header
+with a `preload`_
+``rel`` attribute is added to the response:
+
+.. image:: /_images/components/weblink/response-headers.png
+
+According to `the Preload specification`_,
+when an HTTP/2 server detects that the original (HTTP 1.x) response
+contains this HTTP header, it will automatically trigger a push for the
+related file in the same HTTP/2 connection.
+The Apache server provided in the Docker setup supports this feature.
+It's why Bootstrap is pushed
+to the client!
+
+Popular proxy services and CDN including
+`Cloudflare`_, `Fastly`_ and `Akamai`_ also leverage this feature.
+It means that you can push resources to
+clients and improve performance of your apps in production right now!
+All you need is Symfony 3.3+ and a compatible web server or CDN service.
+
+If you want to prevent the push but let the browser preload the resource by
+issuing an early separate HTTP request, use the ``nopush`` attribute:
+
+.. code-block:: html+twig
+
+   {# ... #}
+       <link rel="stylesheet" href="{{ preload('/bootstrap.min.css', {nopush: true}) }}">
+   {# ... #}
+
+Before using HTTP/2 Push, be sure to read `this great article`_ about
+known issues, cache implications and the state of the support in popular
+browsers.
+
+In addition to HTTP/2 Push and preloading, the WebLink component also
+provides some helpers to send `Resource
+Hints <https://www.w3.org/TR/resource-hints/#resource-hints>`__ to
+clients, the following helpers are available:
+
+-  ``dns_prefetch``: "indicate an origin that will be used to fetch
+   required resources, and that the user agent should resolve as early
+   as possible"
+-  ``preconnect``: "indicate an origin that will be used to fetch
+   required resources. Initiating an early connection, which includes
+   the DNS lookup, TCP handshake, and optional TLS negotiation, allows
+   the user agent to mask the high latency costs of establishing a
+   connection"
+-  ``prefetch``: "identify a resource that might be required by the next
+   navigation, and that the user agent *should* fetch, such that the
+   user agent can deliver a faster response once the resource is
+   requested in the future"
+-  ``prerender``: "identify a resource that might be required by the
+   next navigation, and that the user agent *should* fetch and
+   execute, such that the user agent can deliver a faster response once
+   the resource is requested in the future"
+
+The component can also be used to send HTTP link not related to
+performance. For instance, any `link defined in the HTML specification`_:
+
+.. code:: html+twig
+
+   {# ... #}
+       <link rel="alternate" href="{{ link('/index.jsonld', 'alternate') }}">
+       <link rel="stylesheet" href="{{ preload('/bootstrap.min.css', {nopush: true}) }}">
+   {# ... #}
+
+The previous snippet will result in this HTTP header being sent to the
+client:
+``Link: </index.jsonld>; rel="alternate",</bootstrap.min.css>; rel="preload"; nopush``
+
+You can also add links to the HTTP response directly from a controller
+or any service:
+
+.. code:: php
+
+   // src/Controller/BlogPostAction.php
+   namespace App\Controller;
+
+   use Fig\Link\GenericLinkProvider;
+   use Fig\Link\Link;
+   use Symfony\Component\HttpFoundation\Request;
+   use Symfony\Component\HttpFoundation\Response;
+
+   final class BlogPostAction
+   {
+       public function __invoke(Request $request): Response
+       {
+           $linkProvider = $request->attributes->get('_links', new GenericLinkProvider());
+           $request->attributes->set('_links', $linkProvider->withLink(new Link('preload', '/bootstrap.min.css')));
+
+           return new Response('Hello');
+       }
+   }
+
+.. code-block:: yaml
+
+   # app/config/routes.yaml
+   blog_post:
+       path: /post
+       defaults:
+         _controller: 'App\Controller\BlogPostAction'
+
+.. seealso::
+
+    As all Symfony components, WebLink can be used :doc:`as a
+    standalone PHP library </components/weblink>`.
+
+To see how WebLink is used in the wild, take a look to the `Bolt`_
+and `Sulu`_ CMS, they both use WebLink to trigger HTTP/2 pushes.
+
+While we're speaking about interoperability, WebLink can deal with any link implementing
+`PSR-13`_.
+
+Thanks to Symfony WebLink, there is no excuses to not to switch to HTTP/2!
+
+.. _`Web Linking`: https://tools.ietf.org/html/rfc5988
+.. _`HTTP/2 Server Push`: https://tools.ietf.org/html/rfc7540#section-8.2
+.. _`Resource Hints`: https://www.w3.org/TR/resource-hints/
+.. _`Twig`: https://twig.symfony.com/
+.. _`Docker installer and runtime for Symfony`: https://github.com/dunglas/symfony-docker
+.. _`Bootstrap`: https://getbootstrap.com/
+.. _`an integration of the most popular CSS framework`: https://symfony.com/blog/new-in-symfony-3-4-bootstrap-4-form-theme
+.. _`preload`: https://developer.mozilla.org/en-US/docs/Web/HTML/Preloading_content
+.. _`the Preload specification`: https://www.w3.org/TR/preload/#server-push-(http/2)
+.. _`Cloudflare`: https://blog.cloudflare.com/announcing-support-for-http-2-server-push-2/
+.. _`Fastly`: https://docs.fastly.com/guides/performance-tuning/http2-server-push
+.. _`Akamai`: https://blogs.akamai.com/2017/03/http2-server-push-the-what-how-and-why.html
+.. _`this great article`: https://www.shimmercat.com/en/blog/articles/whats-push/
+.. _`link defined in the HTML specification`: https://html.spec.whatwg.org/dev/links.html#linkTypes
+.. _`Bolt`: https://bolt.cm/
+.. _`Sulu`: https://sulu.io/
+.. _`PSR-13`: http://www.php-fig.org/psr/psr-13/