Clojure WebSocket Client

Gniazdo is a WebSocket client for Clojure. It wraps the Jetty's implementation of the protocol.

aleph has support for websockets on both server and client. It can take some time to get used to the asynchronous style and aleph's core abstractions, but it's a very good tool once you get the hang of it.

For those joining us in 2015: being new to this, I just spent a while trying out all the different options available, and it was pretty difficult to find a library that provides an easy way to set up a simple Clojure WebSocket client. (To be fair, it seems like it's not very common for a WebSocket client to be running in a non-browser/JavaScript context, which is why there seems to be so much emphasis on ClojureScript WebSocket clients.)

Although it is not well-documented, http.async.client ended up being the path of least resistance for me. I was able to successfully read streaming data from a WebSocket server and print it to the console by doing this:

(ns example.core
  (:require [http.async.client :as async]))

(def url "ws://localhost:1337")

(defn on-open [ws]
  (println "Connected to WebSocket."))

(defn on-close [ws code reason]
  (println "Connection to WebSocket closed.\n"
           (format "(Code %s, reason: %s)" code reason)))

(defn on-error [ws e]
  (println "ERROR:" e))

(defn handle-message [ws msg]
  (prn "got message:" msg))

(defn -main []
  (println "Connecting...")
  (-> (async/create-client)
      (async/websocket url
                       :open  on-open
                       :close on-close
                       :error on-error
                       :text  handle-message
                       :byte  handle-message))
  ;; Avoid exiting until the process is interrupted.
  (while true))

The infinite loop at the end is just to keep the process from ending. Until I press Ctrl-C, messages received from the socket are printed to STDOUT.

http-kit's client does not support WebSocket yet(I can't think of a good API for it). Aleph is a good option for this kind of use case. Another option is http.async.client, I've used it in http-kit's server's websocket unit test: here