basic http requests and server handlers in clojure

I’ve been playing around a tiny bit with clojure, and wanted to document the process of doing something pretty basic: make a project that can request my website over HTTPs.

The first step is pretty easy:

brew install leiningen
lein new random-experimentation
cd random-experimentation

and add [clj-http "3.4.1"] to project.clj.

The HTTPS part is a bit trickier. The JDK doesn’t include the Letsencrypt certificates. But I found a simple script install-letsencrypt-in-jdk.sh that can set it up.

wget https://gist.githubusercontent.com/Firefishy/109b0f1a90156f6c933a50fe40aa777e/raw/15926be913682876ae68bb4f71e489bc53feaae3/install-letsencrypt-in-jdk.sh
sudo install-letsencrypt-in-jdk.sh $(...)

With that in place, it’s possible to start a lein repl and make a request:

$ lein repl
user=> (require '[clj-http.client :as client])
user=> (client/get "https://traviscj.com/_status.json")
{:request-time 877, :repeatable? false, :protocol-version {:name "HTTP", :major 1, :minor 1}, :streaming? true, :chunked? false, :reason-phrase "OK", :headers {"Server" "nginx/1.10.0 (Ubuntu)", "Date" "Thu, 02 Feb 2017 03:55:23 GMT", "Content-Type" "application/json", "Content-Length" "27", "Last-Modified" "Mon, 01 Aug 2016 02:31:03 GMT", "Connection" "close", "ETag" "\"579eb467-1b\"", "Strict-Transport-Security" "max-age=15768000", "Accept-Ranges" "bytes"}, :orig-content-encoding nil, :status 200, :length 27, :body "{\n  \"site\":\"traviscj.com\"\n}", :trace-redirects ["https://traviscj.com/_status.json"]}
user=> (def status (client/get "https://traviscj.com/_status.json"))
#'user/status
user=> (:body status)
"{\n  \"site\":\"traviscj.com\"\n}"

With a bit more repl-experimentation and judicious reloading, we can make a small script that applies a similar GET to a list of sites:

(ns random-experimentation.core
  (:require [clj-http.client :as client]))

(def sites [
            "traviscj.com"
            "pauljoos.com"
            "jdbeals.com"
            "thingsworthkeeping.com"
            "bovineherdhealth.com"
            ])

(defn get-status [site]
  (defn get-status-url [site]
    (str "https://" site "/_status.json"))
  (defn get-status-json [site]
    (client/get (get-status-url site) {:as :json}))
  [site (:status (get-status-json site))])

;; lein run -m random-experimentation.core
(defn -main []
  (println (map get-status sites))
  )

and use that within a new:

(use 'random-experimentation.core)

or existing:

(use 'random-experimentation.core :reload)

repl session.

I also tried out spinning up an HTTP server and responding to a request. This is also pretty easy; one must :require an additional module

    [ring.adapter.jetty :as j]

and define a handler:

(defn handler [request]
  (println request)
  {:status 200
   :headers {"Content-Type" "text/html"}
   :body (str "Hello World blah!" (:uri request))})

and j/run-jetty wtih that handler (and a particular port, of course):

(defn -main []
  (j/run-jetty handler {:port 3001}))

Pretty slick!