A lightweight Clojure/ClojureScript library designed to bridge the gap between the triad of CLJ/CLJS, web-sockets and core.async.
Include the following in your project.clj:
Chord now supports EDN, JSON, Transit and Fressian out of the box - please remove dependencies to ‘chord-fressian’ and ‘chord-transit’ if you have them. Thanks to Luke Snape, Jeff Rose and Thomas Getgood for their help supporting these formats!
There is a simple example server/client project under the example-project directory. The client sends websocket messages to the server, that get echoed back to the client and written on the page.
You can run it with lein dev - an alias that starts up an http-kit server using Frodo and automatically re-compiles the CLJS.
Once it is running - navigate to http://localhost:3000/ and you should see Send a message to the server:
Chord only has one function, chord.client/ws-ch, which takes a web-socket URL and returns a map, containing either :ws-channel or :error. When the connection opens successfully, this channel then returns a two-way channel that you can use to communicate with the web-socket server:
(:require [chord.client :refer [ws-ch]]
[cljs.core.async :refer [<! >! put! close!]])
(:require-macros [cljs.core.async.macros :refer [go]])
(go
(let [{:keys [ws-channel error]} (<! (ws-ch "ws://localhost:3000/ws"))]
(if-not error
(>! ws-channel "Hello server from client!")
(js/console.log "Error:" (pr-str error)))))
Messages that come from the server are received as a map with a :message key:
(go
(let [{:keys [ws-channel]} (<! (ws-ch "ws://localhost:3000/ws"))
{:keys [message]} (<! ws-channel)]
(js/console.log "Got message from server:" (pr-str message))))
Errors in the web-socket channel (i.e. if the server goes away) are returned as a map with an :error key:
(go
(let [{:keys [ws-channel]} (<! (ws-ch "ws://localhost:3000/ws"))
{:keys [message error]} (<! ws-channel)]
(if error
(js/console.log "Uh oh:" error)
(js/console.log "Hooray! Message:" (pr-str message)))))
As of 0.3.0, you can pass a :format option, to pass messages over the channel as EDN (default), as raw strings, or JSON (0.3.1). Valid formats are #{:edn :json :json-kw :str :fressian :transit-json}, defaulting to :edn.
(If you do use fressian, you’ll need to require chord.format.fressian, in addition to the usual Chord namespaces)
(:require [cljs.core.async :as a])
(ws-ch "ws://localhost:3000/ws"
{:format :json-kw})
As of 0.2.1, you can configure the buffering of the channel by (optionally) passing custom read/write channels, as follows:
(:require [cljs.core.async :as a])
(ws-ch "ws://localhost:3000/ws"
{:read-ch (a/chan (a/sliding-buffer 10))
:write-ch (a/chan 5)})
By default, Chord uses unbuffered channels, like core.async itself.
Chord wraps the websocket support provided by http-kit, a fast Clojure web server compatible with Ring.
N.B. Currently, Ring’s standard Jetty adapter ~does not~ support Websockets. http-kit is a Ring-compatible alternative.
Again, there’s only one entry point to remember here: a wrapper around http-kit’s with-channel macro. The only difference is that, rather than using http-kit’s functions to interface with the channel, you can use core.async’s primitives.
Chord’s with-channel is used as follows:
(:require [chord.http-kit :refer [with-channel]]
[org.httpkit.server :refer [run-server]]
[clojure.core.async :refer [<! >! put! close! go]])
(defn your-handler [req]
(with-channel req ws-ch
(go
(let [{:keys [message]} (<! ws-ch)]
(prn "Message received:" message)
(>! ws-ch "Hello client from server!")
(close! ws-ch)))))
This can take a :format option, and custom buffered read/write channels as well:
(require '[clojure.core.async :as a])
(defn your-handler [req]
(with-channel req ws-ch
{:read-ch (a/chan (a/dropping-buffer 10))
:format :str} ; again, :edn is default
(go
(let [{:keys [message]} (<! ws-ch)]
(prn "Message received:" message)
(>! ws-ch "Hello client from server!")
(close! ws-ch)))))
You can also use the wrap-websocket-handler middleware, which will put a :ws-channel key in the request map:
(require '[chord.http-kit :refer [wrap-websocket-handler]]
'[org.httpkit.server :refer [run-server]]
'[clojure.core.async :as a])
(defn your-handler [{:keys [ws-channel] :as req}]
(go
(let [{:keys [message]} (<! ws-channel)]
(println "Message received:" message)
(>! ws-channel "Hello client from server!")
(close! ws-channel))))
(run-server (-> #'your-handler wrap-websocket-handler) {:port 3000})
You can pass custom channels to wrap-websocket-handler as a second (optional) parameter:
(run-server (-> #'your-handler
(wrap-websocket-handler {:read-ch ...}))
{:port 3000}) Bug reports/pull requests/comments/suggestions etc?
Yes please! Please submit these in the traditional GitHub manner.
Chord’s contributors are listed in the ChangeLog - thank you all for your help!
Copyright © 2013-2015 James Henderson
Distributed under the Eclipse Public License, the same as Clojure.
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