Building a simple HTTP server in Clojure: Part I — Setting up server

In my previous post I discussed about my experience with Clojure. This blog will focus on how to build a very basic HTTP server which will display local time whenever hit.

This should take utmost 5 min to bring the server up (if Clojure and Leiningen is already setup).

Basic Setup

I use leiningen to set-up and run Clojure project. Here is a detailed tutorial to setup Leiningen and start with development:

1. https://clojure.org/guides/getting_started
2. https://github.com/technomancy/leiningen

Once the setup is done, we can proceed further to start with Clojure HTTP Server.

Getting Started

We shall be creating a new project using lein:

lein new clojure-simple-http

The above command makes a new project clojure-simple-http with the following structure

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

Dependencies

We are using http-kit library, so we need to add this as a dependency in our project.clj. It will look something like this:

Also core.clj will contain main function, so we define the file where main will be present in project.clj too.

Creating Server

I have used the default code from http-kit-server to create bare minimum server. We make the changes in core.clj. This file shall also contain the main function to start the server.

We first need to require http-kit library

(:require [org.httpkit.server :refer [run-server]])

The final code will look like this:

The response of request is a map with status, headers and body.

Display Current Time (Local)
To display current time we shall use clj-time library of clojure.

Firstly we need to add it to the dependency in project.clj as [clj-time “0.14.0”] and import [clj-time.core :as t] in core.clj

Then to return the time, we use time-now function which returns time object. So we convert it to string using (str (t/time-now)) which returns time in correct format.

Final Run
Now goto the directory and do lein run . This will start the server on port 8080.

Tada! We made a very simple server in Clojure.

The complete code can be found on Github.

In my next blog I shall be focussing on how to add routing to the server using compojure and how to dockerize the app.

If you have any questions/suggestions, feel free to drop it in comments and if you found this article useful, clap below.