Is an EventSource (SSE) supposed to try to reconnect indefinitely?

Question

I\'m working on a project utilizing Server-Sent-Events and have just run into something interesting: connection loss is handled differently between Chrome and Firefox.

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Answer 1

As someone already mentioned different browsers do different things depending on the return code. What I do instead is just close the connection regardless then check server health to make sure its up again. I think its silly trying to re-open a stream if we don't actually know if the server/proxy is back yet.

Tested in FF and Chrome:

let sseClient

function sseInit() {
  console.log('SSE init')
  sseClient = new EventSource('/server/events')
  sseClient.onopen = function () { console.log('SSE open ') }
  sseClient.onmessage = onMessageHandler
  sseClient.onerror = function(event) {
    if (event.target.readyState === EventSource.CLOSED) {
      console.log('SSE closed ' + '(' + event.target.readyState + ')')
    } else if (event.target.readyState === EventSource.CONNECTING) {
      console.log('SSE reconnecting ' + '(' + event.target.readyState + ')')
      sseClient.close()
    }
  }
}

sseInit()

setInterval(function() {
  let sseOK
  if (sseClient === null) {
    sseOK = false
  } else {
    sseOK = (sseClient.readyState === EventSource.OPEN)
  }
  if (!sseOK) {
    // only try reconnect if server health is OK
    axios.get('/server/health')
      .then(r => {
        sseInit()
        store.commit('setServerOK_true')
      })
      .catch(e => {
        store.commit('setServerOK_false')
        sseClient = null
      })
  }
}, 5000)

Note, I am using Vue with ECMAScript and tracking state in a store so some things might not make immediate sense.