Your own server

Injecting a :ring-handler into the Jetty server that Figwheel uses primarily for REPL communication is a convenient way to start building server side functionality. However it is easy to outgrow this built-in server. This guide will detail how to setup a separate HTTP server for your application and still benefit from working with Figwheel.

It normally doesn’t take long to outgrow using :ring-handler to embed server side functionality in Figwheel. If there is a server side component to your application, it is inevitable that you will need to setup a server to serve your app when you deploy it. So in many cases you can’t get by without it.

Requirements for working with Figwheel

Normally there is very little that needs to be done so that you can continue to develop using Figwheel while serving your application from a different server.

You will need to run Figwheel as well as your application server. It can be helpful to think of Figwheel as a separate tooling process that has its own Websocket server to handle REPL communication.

Figwheel’s tooling process is not required to be in a separate JVM process from your application server but it can be. Your application server can be written in Ruby, Node, Python, C#, Clojure, and Figwheel will still work.

There are only two things you need to ensure to make Figwheel work along side your own application server.

The separate server should:

  1. serve an HTML host page that loads your CLJS app correctly
  2. serve the compiled ClojureScript artifacts of your application

In most of the cases that is all that is needed to use your own server.

No need to proxy

Many folks worry about Cross Origin problems and believe that they need to proxy an endpoint on their app server to the Figwheel server. This is not needed at all. Figwheel has been setup to handle CORS problems.

How this works

The reason why Figwheel works as a Cross Origin Websocket is the same reason that services like Firebase and Pusher work as Cross Origin services.

In this case, Figwheel is responsible for compiling your ClojureScript into JavaScript artifacts that get loaded by the browser. When it compiles these artifacts it inserts a URL that points to the Figwheel server to establish a Websocket connection. So when your app server serves these compiled artifacts the Figwheel client will call home to the Figwheel server to establish a REPL connection. Since the Figwheel server allows CORS requests this works just fine.

Figwheel was designed to work this way to support the inevitable need to use your own server.

Connecting Remotely

When you are not developing locally and connecting to localhost you will need to set the :connect-url config option so that Figwheel knows which server host to connect back to.

This is something that is required whether you use your own server or not.

Example of using your own server

We will start from the base hello-world example app.

We will create a Ring server and launch it via a script. Create a file at scripts/server.clj with the following content:

(require '[ring.adapter.jetty :refer [run-jetty]])
(require '[ring.middleware.defaults :refer [wrap-defaults site-defaults]])
(require '[ring.util.response :refer [resource-response content-type]])

(defn handler [req]
   (when (= "/" (:uri req))
     (some-> (resource-response "index.html" {:root "public"})
             (content-type "text/html; charset=utf-8"))) 
   {:status 404
    :headers {"Content-Type" "text/html"}
    :body "Not found"}))

 (wrap-defaults handler site-defaults)
 {:port 4000
  :join? false})

The above Clojure file defines a Ring handler and runs the server when it is loaded.

If you haven’t defined an index.html file yet, create a file like the following at resources/public/index.html:

<!DOCTYPE html>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <div id="app"></div>
    <!-- include your ClojureScript at the bottom of body like this -->
    <script src="/cljs-out/dev-main.js" type="text/javascript"></script>

If you don’t already have a host page for your application and you are not sure how to create one, please see the documentation on this subject.

Of course we can generate and serve the above HTML directly from the server, but I’m choosing this to keep things simple and consistent with the other guides.

This is all you need to start your own server while you are running a Figwheel tooling process.

You can start the server along with your Figwheel build with the following command:

$ clojure -i scripts/server.clj -m figwheel.main -b dev -r

You can also add these CLI options to an alias in your deps.edn file to make things more concise on the command line.