Comment by mikojan

> The SSE spec has an event id and the spec states sending last event id on reconnection.

Last event ID is not mandatory. You may omit event IDs and not deal with last event ID headers at all.

More importantly, the client is sending the last event ID header. Not the server. The only state in the server is a list of events somewhere which you would have to have anyway if you want clients to receive events that occurred when they were not connected or if you allowed clients to fetch a subset of them like with long-polling.

So there is really no difference at all here with regards to long-polling