relayLogStream copied a pod-log follow to the client with a plain
flusher.Flush per event. On a client that stays connected but stops
reading (its TCP receive window shut), net/http buffers the small
"data:" line and only touches the socket at Flush, which then blocks
forever inside the write. The select's <-ctx.Done() branch is never
reached, because r.Context() cancels on an actual disconnect, not on a
stall, so the relay goroutine and its upstream apiserver follow leak for
the life of the process.
Route every event's write+flush through http.ResponseController with a
per-write deadline (writeTimeout, 30s): a stalled flush now returns
os.ErrDeadlineExceeded, the error plain http.Flusher.Flush swallows, and
the relay abandons the stream so the deferred cancel + src.Close release
the follow. SetWriteDeadline and rc.Flush are best-effort: a writer
without deadline support (httptest recorder; some HTTP/2 origins) ignores
the deadline and behaves exactly as before, so the guard degrades
gracefully.
This closes the leak the per-principal stream cap only bounded the blast
radius of. Verified by a deterministic test with a deadline-aware
ResponseWriter whose flush blocks until the deadline; the test times out
(fails closed) if the guard is removed.
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