Send SSE data only when it received POST method about go-sse

[alexandrevicenzi]

SSE opens a long term connection, that's how the protocol works, you may want to learn more about it here.

You send data to the client when you have new data, so you should call SendMessage only when you have new data. This is validation on your side, not the library.

By protocol standard, once a client connects it's ready to receive data, there's no need to receive some POST from clients to start receiving data, and also, the protocol and the library supports replay of old messages in case of disconnection (using the Last Event ID).