The timeout arm of the connection actor's select: HEARTBEAT_INTERVAL (1s)
paces outbound Frame::Heartbeat (first at spawn, so the peer's window
starts fed) and LIVENESS_TIMEOUT (4s = 4 intervals) declares the peer dead
when no inbound frame arrives inside it — any frame resets the window, so
heartbeats keep an idle connection alive and real traffic (c8+) counts for
free. Fire => close + exit; the manager's monitor reaps the table entry as
on every other exit path. Fixed timeout per RFC v2 §5 (control connection,
heartbeats can't queue behind bulk). Intervals are the one-viable-answer
call flagged for veto at diff review.
The pump was made non-blocking to keep the deadlines honest: a plain recv()
blocks into the socket while the buffer holds a partial frame, parking the
actor past its timers. Two additive FramedConn methods (read_once,
next_buffered): exactly one socket read per level-triggered readable wake
(cannot block, cannot strand — leftovers re-signal), then drain every
complete buffered frame. Liveness resets only on complete frames.
No-fd transports (loopback) still get the command-only loop: no readiness
means no timers, same caveat as recv_deadline.
tests/cluster_conn_liveness.rs 3/0, stable over 5 runs (raw far end over
localhost TCP: heartbeats appear unprompted; mute peer still up at half
the window, gone after it; heartbeat-only peer survives 1.5x the window,
then reaped once silenced). Cluster suites regression-clean; clippy --lib
green both configs; fmt clean.
