HTTP

Aleph follows the Ring spec fully, and can be a drop-in replacement for any existing Ring-compliant server. However, it also allows for the handler function to return a Manifold deferred to represent an eventual response. This feature may not play nicely with Ring middleware which modifies the response, but this can be easily fixed by reimplementing the middleware using Manifold's let-flow operator.

(require '[aleph.http :as http])

(defn handler [req]
  {:status 200
   :headers {"content-type" "text/plain"}
   :body "hello!"})

(http/start-server handler {:port 8080})

The body of the response may also be a Manifold stream, where each message from the stream is sent as a chunk, allowing for precise control over streamed responses for server-sent events and other purposes.

For HTTP client requests, Aleph models itself after clj-http, except that every request immediately returns a Manifold deferred representing the response.

(require
  '[manifold.deferred :as d]
  '[byte-streams :as bs])

(-> @(http/get "https://google.com/")
  :body
  bs/to-string
  prn)

(d/chain (http/get "https://google.com")
  :body
  bs/to-string
  prn)

To learn more, read the example code.

WebSockets

On any HTTP request which has the proper Upgrade headers, you may call (aleph.http/websocket-connection req), which returns a deferred which yields a duplex stream, which uses a single stream to represent bidirectional communication. Messages from the client can be received via take!, and sent to the client via put!. An echo WebSocket handler, then, would just consist of:

(require '[manifold.stream :as s])

(defn echo-handler [req]
  (let [s @(http/websocket-connection req)]
    (s/connect s s))))

This takes all messages from the client, and feeds them back into the duplex socket, returning them to the client. WebSocket text messages will be emitted as strings, and binary messages as byte arrays.

WebSocket clients can be created via (aleph.http/websocket-client url), which returns a deferred which yields a duplex stream that can send and receive messages from the server.

To learn more, read the example code.