Server-Sent Events stream one way
Server-Sent Events carry server-to-client updates in a streaming HTTP response. They do not turn HTTP into a bidirectional socket, and automatic reconnection does not make delivery durable. Treat event framing, connection lifetime, retained history, and application acknowledgment as separate contracts. A response contains framed text events An SSE response uses text/event-stream and UTF-8. Fields are line-based, and a blank line ends a block. Multiple data lines within one event are joined with newline characters. A colon-prefixed comment is ignored as event data, so it can carry a heartbeat without triggering an application message. ...