We are expecting the SseEventSource connection to fail when a response other than 200 is received.
In this case, it must be closed and must notify:
- error listeners since it is an unrecoverable error.
- completion listener since no further events will be received.

We are expecting the SseEventSource connection to fail when a 200 response with a Content-Type header unspecified
or other than text/event-stream is received.
In this case, it must be closed and must notify:
- error listeners since it is an unrecoverable error.
- completion listener since no further events will be received.

We are expecting the SseEventSource to close itself and not try to reconnect on a 204 response.
In this case, it must be closed and must notify:
- completion listener since no further events will be received.
Error listeners are not notified in this case since it is a normal behavior.

We are expecting the SseEventSource to reconnect when the connection is closed (gracefully or not).
In this case, no error listener will be notified since it is not an unrecoverable error since we are trying to reconnect.
Completion listener will not be notified neither since other events will be received.

Clients will reconnect if the connection is closed; a client can be told to stop reconnecting using the
HTTP 204 No Content response code.

HTTP 200 OK responses that have a Content-Type specifying an unsupported type, or that have no
Content-Type at all, must cause the user agent to fail the connection.

Any other HTTP response code not listed here, as well as the cancelation of the fetch algorithm by the
user agent (e.g. in response to window.stop() or the user canceling the network connection manually) must cause
the user agent to fail the connection.

 Once the user agent has failed the connection, it does not attempt to reconnect!