oxbow

A Server Sent Events (SSE) client for Clojurescript based on js/fetch

This library uses js/fetch to expose the full functionality of HTTP and processes the SSE data for you.

It's ready for use as a standalone functional Clojurescript library and also has re-frame bindings for integration into a re-frame application.

Rationale

js/EventSource is generally moribund and does not support sending headers. Discussions generally reference js/fetch as a modern alternative but it does not natively process streams.

⚠️Chrome Devtools will not show events under the EventSource tab for requests made by js/fetch. See: Issue 1025893

Usage

Clojurescript

You can start a new connection using sse-client, which returns a map containing a no-arg abort function under the :abort key.

(require '[oxbow.core :as o])

(let [{:keys [abort]} (o/sse-client {:uri "/events"
                                     :on-event #(js/console.log "Got an event!" %)})]

  ;; events are passed to the callback
  ;; call abort to close the client

  (abort))

re-frame

The re-frame bindings behave the same way, with the addition of :id which gives you a handle to abort with.

(require '[oxbow.re-frame :as o])
(require '[re-frame.core :as rf])

(rf/reg-event-db
  ::on-event
  (fn [db [_ {:keys [data] :as event}]]
    (update db :events conj data)))


(rf/dispatch [::o/sse-client {:id ::my-events
                              :uri "/events"
                              :on-event [::on-event]}])

;; events are passed to the callback
;; call abort to close the client

(rf/dispatch [::o/abort ::my-events])

Options

{:fetch-options     {:headers {"Authorization" "xyz"}}        ;; options passed to js/fetch, see https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
 :on-open           #(js/console.log "Stream connected" %)    ;; invoked when the stream opens
 :on-close          #(js/console.log "Stream ended")          ;; invoked when the stream ends
 :on-event          #(js/console.log "Message received: " %)  ;; invoked for every event
 :on-error          #(js/console.warn "Error: " %)            ;; invoked on error
 :data-parser       identity                                  ;; parses the `data` value of the event
 :auto-reconnect?   true                                      ;; whether it should automatically reconnect upon disconnection
 :reconnect-timeout 2000                                      ;; ms to wait before attempting reconnect
 }

Development

cider-jack-in-cljs and open the test page http://localhost:9500/figwheel-extra-main/auto-testing

You will need to also run (oxbow.server-stub/start-server!) for the integration tests.

Build

License

Copyright © 2020 oliyh

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