Aleph is a Clojure framework for asynchronous communication, built on top of Netty and Lamina.

What is Aleph good for?

Aleph allows the creation of both clients and servers that can communicate using an array of protocols (HTTP, WebSockets, TCP, UDP, and others), and represents that communication via a single abstraction, channels. Thanks to the underlying libraries and the event-driven approach to communication, these clients and servers can be highly scalable.

Using Aleph in your project

In the project.clj file at the top level of your project, add Aleph as a dependency:

(defproject my-project "1.0.0"
  :dependencies [[org.clojure/clojure "1.2.1"]
				 [aleph "0.2.0-rc1"]])

Code examples

HTTP Server

Aleph conforms to the interface described by Ring, with one small difference: the request and response are decoupled.

(use 'lamina.core 'aleph.http)
        
(defn hello-world [channel request]
  (enqueue channel
    {:status 200
     :headers {"content-type" "text/html"}
     :body "Hello World!"}))

(start-http-server hello-world {:port 8080})

For more on HTTP functionality, read the wiki.

HTTP Client

This snippet prints out a never-ending sequence of tweets:

(use 'lamina.core 'aleph.http 'aleph.formats)
        
(let [ch (:body
           (sync-http-request
             {:method :get
              :basic-auth ["aleph_example" "_password"]
              :url "http://stream.twitter.com/1/statuses/sample.json"
              :delimiters ["\r"]}))]
  (doseq [tweet (map decode-json (lazy-channel-seq ch))]
    (prn tweet)))

A more in-depth exploration of this example can be found here.

WebSockets

Making a simple chat client is trivial. In this, we assume that the first message sent by the client is the user's name:

(use 'lamina.core 'aleph.http)

(def broadcast-channel (channel))

(defn chat-handler [ch handshake]
  (receive ch
    (fn [name]
      (siphon (map* #(str name ": " %) ch) broadcast-channel)
      (siphon broadcast-channel ch))))

(start-http-server chat-handler {:port 8080 :websocket true})

TCP Client/Server

Here is a basic echo server:

(use 'lamina.core 'aleph.tcp)
        
(defn echo-handler [channel client-info]
  (siphon channel channel))

(start-tcp-server echo-handler {:port 1234})

For more on TCP functionality, visit the wiki.

--

Other protocols are supported, and still more are forthcoming.

Aleph is meant to be a sandbox for exploring how Clojure can be used effectively in this context. Contributions and ideas are welcome.

For more information, visit the wiki or the API documentation. If you have questions, please visit the mailing list.