bastion 0.55.3

client-go/beatnow.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"context"
+	"sync"
+	"time"
+)
+
+// A beat out of turn, for every pairing on this box.
+//
+// Each running pairing beats its own Host on a 60-second ticker, and every
+// beat carries the box's pairings as `peers` with the state of each (peers.go).
+// That is how every Host on the machine learns that a pairing went active or was
+// revoked. A pairing_grant_sync or pairing_grant_drop changes that state on disk
+// at once, but nothing beat: every Host kept the old state for up to a minute.
+// So a pairing approved a second after a beat still read as pending for the
+// next minute, and a Host asking to connect to it in that time was refused. The
+// anchor Host can read its own confirmed grant, but no other Host on the
+// machine has one, and a revoke reached the other Hosts no sooner.
+//
+// So a change to a pairing's state asks every running pairing's beat loop to beat
+// now. The signal carries nothing: the beat reads the pairings from disk as it
+// always does, so it reports the state the change wrote. One pending signal per
+// loop is kept and the rest are dropped, so a burst of changes is one extra beat
+// per Host, never one per change.
+
+var beatNow = struct {
+	sync.Mutex
+	subs map[chan struct{}]struct{}
+}{subs: map[chan struct{}]struct{}{}}
+
+// subscribeBeatNow registers one beat loop. The channel holds at most one
+// pending signal; stop unregisters it.
+func subscribeBeatNow() (<-chan struct{}, func()) {
+	ch := make(chan struct{}, 1)
+	beatNow.Lock()
+	beatNow.subs[ch] = struct{}{}
+	beatNow.Unlock()
+	return ch, func() {
+		beatNow.Lock()
+		delete(beatNow.subs, ch)
+		beatNow.Unlock()
+	}
+}
+
+// kickBeats asks every registered beat loop to beat now. It never blocks: a
+// loop that already has a signal pending, or is mid-beat, beats once more.
+func kickBeats() {
+	beatNow.Lock()
+	defer beatNow.Unlock()
+	for ch := range beatNow.subs {
+		select {
+		case ch <- struct{}{}:
+		default:
+		}
+	}
+}
+
+// runBeatLoop beats every `every`, and also whenever kickBeats asks. beforeTick
+// runs before a ticked beat only (the tunnel's path failover, which belongs to
+// the clock, not to a pairing change); it may be nil. It returns when ctx ends.
+func runBeatLoop(ctx context.Context, every time.Duration, beforeTick, beat func()) {
+	kick, stop := subscribeBeatNow()
+	defer stop()
+	t := time.NewTicker(every)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+			if beforeTick != nil {
+				beforeTick()
+			}
+			beat()
+		case <-kick:
+			beat()
+		}
+	}
+}