A brief demo of real-time plotting with Plotly, Go, and server-sent events

  • By Damon P. Cortesi
  • Last update: Nov 28, 2022
  • Comments: 1

Golang SSE Demo

A brief demo of real-time plotting with Plotly, Go, and server-side events.

Overview

I first learned about Server-Sent Events from @mroth's How I Built Emojitracker and have been intrigued ever since.

However, it wasn't until I came across @benbjohnson's litestream-read-replica-demo that I realized just how easy they were to use. I thought there was all sorts of complexity, but no!

It's really simple...all you need to do is create a new EventSource in your JavaScript and feed it updates!

var sse = new EventSource("/api/stream");
sse.addEventListener("update", function (e) {
  // Do something!
});

Demo

This repo shows how to use Go to send events to the browser and, of course, draw a real-time chart with Plotly. :)

git clone https://github.com/dacort/golang-sse-demo.git
cd golang-sse-demo
go run *.go

Then browse to http://localhost:3000

💥

Screenshot

Download

golang-sse-demo.zip

Comments(1)

  • 1

    Setting channel is racy

    			notify.mu.Lock()
			notify.value = rand.Intn(100)
			notify.mu.Unlock()

			// notify.ch <- struct{}{}
			close(notify.ch)
			notify.ch = make(chan struct{})

    notify.ch = make(chan struct{}) is not in a lock, so it could race that someone reads it in the middle of a write.

    I think it would be simpler if you had something like:

    type broadcaster struct{ 
  value int
  notifier chan struct{} 
}

// in main 
for {
  lock.Lock()
  notify = broadcaster { notifier: make(chan struct{}) }  
  lock.Unlock()
  time.Sleep()
  notify.value = math.Rand()
  close(notify.notifier)
}

// in the handler
lock.RLock()
localnotify := notify
lock.RUnlock()
<- localnotify.notifier
send(localnotify.value)

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