Cogs and Levers A blog full of technical stuff

Simple web server with Clojure

15 Nov 2016

In today’s post, we’re going to use the Clojure HTTP server abstraction called ring to stand a web server up, and attach some some routes. This allows us to expose our Clojure functions over the web in a relatively simple fashion.

Getting started

This blog post is mainly centered around the getting started guide from the ring documentation pages, found here.

We’re going to get started by creating a project using lein.

lein new jetty-test

After this process finishes, you’ll end up with a directory called jetty-test that has a project structure something like this:

.
├── CHANGELOG.md
├── doc
│   └── intro.md
├── LICENSE
├── project.clj
├── README.md
├── resources
├── src
│   └── jetty_test
│       └── core.clj
└── test
    └── jetty_test
        └── core_test.clj

Dependencies

Now we need to make our newly created project depend on ring. We need to add references to ring-core and ring-jetty-adapter in the project.clj file. So it should read something like this:

(defproject jetty-test "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.8.0"]
           [ring/ring-core "1.5.0"]
           [ring/ring-jetty-adapter "1.5.0"]])

We can now install these dependencies into the project.

lein deps

Server code

We can start writing our route code now that the server will respond to. We’ll define a function that simply returns the current date and time:

(defn now [] (java.util.Date.))

We’ll also create a route that will use this function, and send back the text each time the route is requested:

(defn current-time [request]
  {:status 200
   :headers {"Content-Type" "text/plain"}
   :body (str (now))})

That’s it for the server code. We still need to fire up Jetty and attach the handler to it. We need to import ring.adapter.jetty as it contains run-jetty for us:

(use 'ring.adapter.jetty)

(run-jetty current-time {:port 3000})

Running

We run our project using lein:

lein run

Our output now looks something like this:

. . .
. . .
. . .

Retrieving clj-time/clj-time/0.11.0/clj-time-0.11.0.jar from clojars
Retrieving ring/ring-core/1.5.0/ring-core-1.5.0.jar from clojars
Retrieving ring/ring-servlet/1.5.0/ring-servlet-1.5.0.jar from clojars
Retrieving clojure-complete/clojure-complete/0.2.4/clojure-complete-0.2.4.jar from clojars
2016-11-15 22:34:11.551:INFO::main: Logging initialized @877ms
2016-11-15 22:34:11.620:INFO:oejs.Server:main: jetty-9.2.10.v20150310
2016-11-15 22:34:11.646:INFO:oejs.ServerConnector:main: Started ServerConnector@795f253{HTTP/1.1}{0.0.0.0:3000}
2016-11-15 22:34:11.647:INFO:oejs.Server:main: Started @973ms

. . . suggesting that our server is ready to take requests. We can use curl to test it out for us:

$ curl -v http://localhost:3000/

*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 3000 (#0)
> GET / HTTP/1.1
> Host: localhost:3000
> User-Agent: curl/7.47.0
> Accept: */*
> 
< HTTP/1.1 200 OK
< Date: Tue, 15 Nov 2016 22:36:34 GMT
< Content-Type: text/plain; charset=ISO-8859-1
< Content-Length: 28
< Server: Jetty(9.2.10.v20150310)
< 
* Connection #0 to host localhost left intact
Tue Nov 15 22:36:34 UTC 2016

That’s it. Pretty simple.

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