Documentation
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Overview ¶
Package fleet provides a generic, coalescing snapshot-broadcast hub for an agent's dashboard WebSocket endpoint.
A single broadcaster goroutine builds at most one snapshot per coalescing window (driven by Trigger() calls and/or an optional periodic tick) and fans it out to all subscribers. Each subscriber has a conflating 1-slot mailbox: when a consumer is slow, the broadcaster REPLACES the pending frame with the newer one rather than dropping the newer one or stalling. A snapshot is a full replacing state, so a consumer only ever needs the latest — never a backlog of stale snapshots. This matters because the agent broadcasts on job state-change only: if a fast backup's final "completed" frame were dropped (the old cap-4 drop-newest behaviour), the controller's fleet cache would stay stale for ~24h until the next job. The broadcaster NEVER unregisters a subscriber itself — cleanup happens exactly once, via the closure returned by Subscribe(), guarded against double-close. That guard is not defensive programming: a hand-rolled predecessor had two unregister paths plus an unconditional close, which double-closed the send channel and panicked the whole process ("close of closed channel") under bursty job churn.
Generic over the agent-specific snapshot payload T so each agent broadcasts its own shape while sharing the hub machinery.
Index ¶
Constants ¶
const DefaultLivenessTick = 30 * time.Second
DefaultLivenessTick is the standard periodic rebuild cadence agents pass to NewHub. With conflating delivery the event-driven Trigger() path already guarantees the latest snapshot is never dropped, so this tick is pure belt-and-suspenders (it only covers the rare connect/subscribe race) and is deliberately slow to stay cheap on low-power hosts (e.g. a Pi querying a large events.sqlite). Both agents build their hub with this constant so they cannot drift apart again.
Variables ¶
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Functions ¶
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Types ¶
type Hub ¶
type Hub[T any] struct { // contains filtered or unexported fields }
Hub fans coalesced snapshots out to all current subscribers.
func NewHub ¶
NewHub returns a hub that builds snapshots via build. If tick > 0 the hub also rebuilds on that interval (liveness); tick == 0 means trigger-only.
func (*Hub[T]) Run ¶
Run is the broadcaster loop. Cancel ctx to terminate. Build errors are skipped (the next trigger/tick retries) so a transient read failure never kills the loop.
func (*Hub[T]) SnapshotNow ¶
SnapshotNow builds one snapshot synchronously without broadcasting — used to greet a freshly-connected subscriber so it doesn't wait for the next tick.
Source Files