Crystal engine for Turbolinks integration.
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README.md

Turbolinks

Build Status License GitHub release

Crystal engine for Turbolinks integration. Extends HTTP::Handler, so you can use it as middleware in any web application. Don't forget to grab the frontend code for Turbolinks.

Installation

Add this to your application's shard.yml:

dependencies:
  turbolinks:
    github: bentranter/turbolinks

Usage

Turbolinks extends HTTP::Handler, so it can be used as HTTP middleware. You can use it with the standard library like so:

require "http/server"
require "turbolinks"

HTTP::Server.new("127.0.0.1", 3000, [
  Turbolinks::Handler.new,
]).listen

or with a framework that supports standard HTTP middleware. For example, you can use Turbolinks with Kemal like so:

require "kemal"
require "turbolinks"

# Calling `add_handler` is Kemal's way of registering HTTP middleware.
add_handler Turbolinks::Handler.new

get "/"
  "Served by Turbolinks!"
end

Kemal.run

A Note About Security

A common pattern if you're coming from the Rails world (and using something like rails-ujs) a common approach is to handle a POST request, and then redirect to another route. Turbolinks handles this case by intercepting the redirection after the POST request executes, and then responding with a JavaScript snippet to execute Turbolinks.visit("#{location}") for the location to redirect to.

While this is typically safe, if your handler allows the user to input this location, you open yourself up to JavaScript injection. Lets look at two examples where a user is leaving a comment, submitted through a form post request.

require "kemal"
require "turbolinks"

add_handler Turbolinks::Handler.new

# Unsafe approach!
post "/unsafe-comment" do |env|
  title = env.params.body["title"]
  comment = env.params.body["comment"]

  # Imagine `new_comment` does something to handle a new commment, for
  # example's sake.
  new_comment(title, comment)

  # This is dangerous because the value of `title` here could be anything --
  # including malicious JavaScript. Since the frontend will excute JavaScript
  # containing the value of this redirect here, any malicious JavaScript will
  # execute.
  env.redirect "/comments/#{title}"
end

# Safe approach.
post "/safe-comment" do |env|
  title = env.params.body["title"]
  comment = env.params.body["comment"]

  # Imagine `new_comment` does something to handle a new commment, for
  # example's sake.
  comment_id = new_comment(title, comment)

  # This is safe because there's no way for the user submitted `title` or
  # `comment` to be available in the returned JavaScript -- you generate an
  # ID, and redirect to that route.
  env.redirect "/comments/#{comment_id}"
end

Kemal.run

If you must do something like the unsafe approach, you'll need to sanitize the input yourself.

A Note For Non rails-ujs Users

In order for form submissions not to trigger a full page reload, you'll need to ensure that those submissions are submitted as AJAX requests. While a library like Rails-UJS or JQuery-UJS would handle this for you, it's straightforward to implement this yourself. The following JavaScript snippet adds bare-minimum support for AJAX form submissions that work with Turbolinks, but I encourage to look at what rails-ujs does as well.

(function() {
  "use strict";
  /*
   * For Google Analytics, you need this:
   * <body>
   * <script>_gaq.push(['_trackPageview']);</script>
   *  ...the rest of the body here...
   * </body>
   * See https://coderwall.com/p/ypzfdw/faster-page-loads-with-turbolinks for
   * more info.
   */

   /*
    * By default, Turbolinks submits forms normally. While this may feel
    * frustrating as a consumer of the library, it makes sense:
    *   - No specialized logic on the backend
    *   - Cache is purged since the page refreshed.
    * However, that's not always what you want. By using the functionality
    * below, forms are submitted via AJAX, as recommended in the Turbolinks
    * documentation.
    */
    document.addEventListener("DOMContentLoaded", function() {
      /**
       * submit sends an HTTP request via XHR.
       * @param {*Object} formEl - the form element to submit via XHR.
       */
      function submit(formEl) {
        var xhr = new XMLHttpRequest();
        xhr.open(formEl.method, formEl.action, true);

        /* See
         * https://github.com/rails/rails/blob/master/actionview/app/assets/javascripts/rails-ujs/utils/ajax.coffee
         * for a more in-depth usage.
         */
        xhr.onreadystatechange = function() {
          if (xhr.readyState === 4 && xhr.status === 200) {
            var script = document.createElement("script");
            script.innerText = xhr.responseText;
            document.head.appendChild(script).parentNode.removeChild(script);
          }
        }
        /* Set relevant headers that some backends check for */
        xhr.setRequestHeader("Turbolinks-Referrer", window.location.href);
        xhr.setRequestHeader("X-Requested-With", "xhr");
        xhr.send(new FormData(formEl));
        return false;
      }

      /* Intercept **any** submit event to submit via XHR instead. */
      document.addEventListener("submit", function(e) {
        e.preventDefault();
        if (e.srcElement) {
          submit(e.srcElement);
        }
      });
    });
})();

Development

Turbolinks follows the typical Crystal project structure, so cloning the repo and making changes is all you need to do. However, you're encouraged to run this backend alongside the Turbolinks frontend to make sure it works as expected, especially when compared to the Rails backend. The Turbolinks frontend is available at github.com/turbolinks/turbolinks, and the Rails gem is available at github.com/turbolinks/turbolinks-rails.

Contributing

  1. Fork it ( https://github.com/[your-github-name]/turbolinks/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Make sure the tests pass, adding any necessary new tests
  4. Format your code with crystal tool format
  5. Commit your changes (git commit -am 'Add some feature')
  6. Push to the branch (git push origin my-new-feature)
  7. Create a new Pull Request

Contributors

License

The MIT License (MIT). Copyright (c) 2017-2018 Ben Tranter. See the LICENSE for more info.