Haslett

A lightweight WebSocket library for ClojureScript that uses core.async.

Installation

Add the following dependency to your project.clj file:

[haslett "0.1.7"]

Usage

Haslett provides a simple and idiomatic interface to using WebSockets:

(ns example.core
  (:require-macros [cljs.core.async.macros :refer [go]])
  (:require [cljs.core.async :as a :refer [<! >!]]
            [haslett.client :as ws]
            [haslett.format :as fmt]))

(go (let [stream (<! (ws/connect "ws://echo.websocket.org"))]
      (>! (:sink stream) "Hello World")
      (js/console.log (<! (:source stream)))
      (ws/close stream)))

The connect function returns a promise channel that produces a map with four keys: :socket, :close-status, :source and :sink.

• :socket contains the JavaScript WebSocket object, in case you need to access it directly.

• :close-status contains a promise channel that a status map is delivered to when the socket is closed. The status map will provide a :code and :reason keys that will explain why the socket was closed.

• :source is a core.async channel to read from.

• :sink is a core.async channel to write to.

By default, Haslett sends raw strings, but we can change that by supplying a formatter. Haslett includes formatters for JSON, edn and Transit:

(go (let [stream (<! (ws/connect "ws://echo.websocket.org" {:format fmt/transit}))]
      (>! (:sink stream) {:foo [1 2 3]})
      (js/console.log (pr-str (<! (:source stream))))
      (ws/close stream)))

You can customize the behaviour further by supplying your own channels for the source and sink. This allows you to tune the channel buffer, and add tranducers:

(ws/connect "ws://echo.websocket.org"
            {:source (a/chan 10)
             :sink   (a/chan 10)})

When the WebSocket is closed, the :sink and :source channels are also closed. In addition, a final status map will be delivered to a promise channel held in the :close-status key on the stream.

License

Copyright © 2022 James Reeves

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.