Module sse

Expand description

Server-sent events: Event encodes one event of the text/event-stream format, and Sse streams events as a response.

Data may hold any text: each line becomes its own data: line (\n, \r\n and \r all end a line), so a client receives the text back with \n line ends.
Event names and ids are single lines: a CR or LF in them (or a NUL in an id, which clients ignore) is rejected with SseError instead of splitting the event.
Responses carry Content-Type: text/event-stream and Cache-Control: no-store, so no cache stores or replays a stream.
An Err from the event stream ends the response body abruptly; the error itself is never sent (clients see the connection end and may reconnect). Send an event first if the client should know why.
Events are pulled only as fast as the connection takes them, so a slow reader never makes the stream buffer events (feed it from a bounded channel, never an unbounded one). A client that disconnects drops the stream, and with it the work behind it.
Sse::keep_alive sends a comment after an idle interval, so proxies and clients do not close a quiet connection; Sse::until ends the stream when a future resolves, such as Readiness::stopping(), so graceful shutdown need not time out.

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