util/eventbus: track additional event context in subscribe queue

Updates #15160

Signed-off-by: David Anderson <dave@tailscale.com>

util/eventbus/bus.go

@@ -8,6 +8,7 @@ import (
 	"reflect"
 	"slices"
 	"sync"
+	"time"
 
 	"tailscale.com/util/set"
 )
@@ -93,11 +94,18 @@ func (b *Bus) pump(ctx context.Context) {
 		for !vals.Empty() {
 			val := vals.Peek()
 			dests := b.dest(reflect.ValueOf(val.Event).Type())
+			routed := time.Now()
 			for _, d := range dests {
+				evt := queuedEvent{
+					Event:     val.Event,
+					From:      val.From,
+					Published: val.Published,
+					Routed:    routed,
+				}
 			deliverOne:
 				for {
 					select {
-					case d.write <- val.Event:
+					case d.write <- evt:
 						break deliverOne
 					case <-d.closed():
 						// Queue closed, don't block but continue

util/eventbus/subscribe.go

@@ -8,8 +8,16 @@ import (
 	"fmt"
 	"reflect"
 	"sync"
+	"time"
 )
 
+type queuedEvent struct {
+	Event     any
+	From      *Client
+	Published time.Time
+	Routed    time.Time
+}
+
 // subscriber is a uniformly typed wrapper around Subscriber[T], so
 // that debugging facilities can look at active subscribers.
 type subscriber interface {
@@ -27,7 +35,7 @@ type subscriber interface {
 	// processing other potential sources of wakeups, which is how we end
 	// up at this awkward type signature and sharing of internal state
 	// through dispatch.
-	dispatch(ctx context.Context, vals *queue[any], acceptCh func() chan any) bool
+	dispatch(ctx context.Context, vals *queue[queuedEvent], acceptCh func() chan queuedEvent) bool
 	Close()
 }
 
@@ -36,8 +44,8 @@ type subscribeState struct {
 	client *Client
 
 	dispatcher *worker
-	write      chan any
-	snapshot   chan chan []any
+	write      chan queuedEvent
+	snapshot   chan chan []queuedEvent
 
 	outputsMu sync.Mutex
 	outputs   map[reflect.Type]subscriber
@@ -46,8 +54,8 @@ type subscribeState struct {
 func newSubscribeState(c *Client) *subscribeState {
 	ret := &subscribeState{
 		client:   c,
-		write:    make(chan any),
-		snapshot: make(chan chan []any),
+		write:    make(chan queuedEvent),
+		snapshot: make(chan chan []queuedEvent),
 		outputs:  map[reflect.Type]subscriber{},
 	}
 	ret.dispatcher = runWorker(ret.pump)
@@ -55,8 +63,8 @@ func newSubscribeState(c *Client) *subscribeState {
 }
 
 func (q *subscribeState) pump(ctx context.Context) {
-	var vals queue[any]
-	acceptCh := func() chan any {
+	var vals queue[queuedEvent]
+	acceptCh := func() chan queuedEvent {
 		if vals.Full() {
 			return nil
 		}
@@ -65,7 +73,7 @@ func (q *subscribeState) pump(ctx context.Context) {
 	for {
 		if !vals.Empty() {
 			val := vals.Peek()
-			sub := q.subscriberFor(val)
+			sub := q.subscriberFor(val.Event)
 			if sub == nil {
 				// Raced with unsubscribe.
 				vals.Drop()
@@ -155,8 +163,8 @@ func (s *Subscriber[T]) subscribeType() reflect.Type {
 	return reflect.TypeFor[T]()
 }
 
-func (s *Subscriber[T]) dispatch(ctx context.Context, vals *queue[any], acceptCh func() chan any) bool {
-	t := vals.Peek().(T)
+func (s *Subscriber[T]) dispatch(ctx context.Context, vals *queue[queuedEvent], acceptCh func() chan queuedEvent) bool {
+	t := vals.Peek().Event.(T)
 	for {
 		// Keep the cases in this select in sync with subscribeState.pump
 		// above. The only different should be that this select