Create a server

To create a web (http) server using a common library, e.g. Jetty or Http-kit

1. Require a library that provides the web server
2. Create a function to start a server, taking a port number as an option

Require Web Server Library

jettyhttpkit

Add the web server library to the namespace using a :reqiure directive.

(ns practicalli.web-server
  (:gen-class)
  (:require [ring.adapter.jetty :as http-server]))

Add the web server library to the namespace using a :reqiure directive.

(ns practicalli.web-server
  (:gen-class)
  (:require [org.httpkit.server :as http-server]))

Code a basic web server

jettyhttpkit

Define a function called server-start that takes a value for the port number which the server will listen too.

Call the run-jetty function from ring.adapter.jetty to start the Jetty Server. run-jetty takes several arguments

• the main request handler, initially just a function (usually a router function to handle many different types of requests)
• a hash-map of options, e.g. {:port 8080 :join? false}. Options are listed in the run-jetty function definition.

The :port key is associated with an integer value that represents the port number.

The :join key is associated with a boolean value, true if the the REPL process should attached to the Jetty thread (blocking input until server stops), false to continue in a separate thread.

  (defn server-start
    [port]
    (http-server/run-jetty #'app {:port port :join? false}))

Define a function called server-start that takes a value for the port number which the server will listen too.

Call the run-server function from org.httpkit.server to start the Http-kit server. run-jetty takes several arguments

• the main request handler, initially just a function (usually a router function to handle many different types of requests)
• a hash-map of options, e.g. {:port 8080 :join? false}. Options are listed in the run-server function definition.

The :port key is associated with an integer value that represents the port number.

(defn server-start
  "Start the application server and run the application"
  [port]
  (app-server/run-server #'app {:port port}))

Http-kit server documentation contains details of asynchronous websockets and HTTP streaming configurations.

Request handler function

The server passes all HTTP requests, converted to a request hash-map by ring, to the app function. The app function returns a ring response hash-map which is sent back to the client (browser) as an Http response.

Define a function that takes a request hash-map as an argument and returns a basic response hash-map.

(defn app [request]
  {:status  200
   :headers {:content-type "text/html"}
   :body    "<h1>Clojure Web Server Alive</h1>"})

:status http status code as an integer - 200 means okay

:header response headers such as content type, a hash-map with optional values (the value can be an empty hash-map {})

:body a string containing the body of the response, such as text, HTML or JSON.