Do not abort the connection on authentication errors

[PapaNappa]

At line 218 of eventsource.js you check for error code ≥ 500 and retry the connection:

EventSource/eventsource.js

Line 218 in 1859fa4

if (xhr.status >= 500) {

Errors in the 400 range, on the other hand, will lead to an abort:

EventSource/eventsource.js

Lines 306 to 318 in 1859fa4

	if (status !== 0 && (status !== 200 || contentType !== "")) {
	var message = "";
	if (status !== 200) {
	message = "EventSource's response has a status " + status + " " + statusText.replace(/\s+/g, " ") + " that is not 200. Aborting the connection.";
	} else {
	message = "EventSource's response has a Content-Type specifying an unsupported type: " + contentType.replace(/\s+/g, " ") + ". Aborting the connection.";
	}
	setTimeout(function () {
	var ev = new Event("error", status, message);
	fire(that, that.onerror, ev);
	throw new Error(message);
	}, 0);
	isWrongStatusCodeOrContentType = true;

Retrying the connection on errors that are not internal server errors would favor our use case (where we update authentication headers when they become invalid).

I see two possible options: always retry on errors ≥ 400 (instead of 500), or add a return value to the onError callback and retry if the error handler allows this (this is probably over-engineering?).

[sguiheux]

It's normal to retry on error >= 500 because it's a server error, so we retry until it works
With error < 500, the problem come from the client, so you can retry any time it will not work (404 will be alway 404), so no retry on error < 500.

If your problem is about loosing lastEventID maybe we can add it on onErrorEvent and accept it on EventSource constructor or update function

[PapaNappa]

This sounds good to me!