Bind a stream consumer again when the bus ends its loop, so a module is not left deaf when the controller deletes and makes again a consumer it cannot narrow (hq issue 725)

node-tools/internal/bus/bus.go

@@ -170,7 +170,7 @@ type Conn struct {
 	cred   Credential
 	mu     sync.Mutex
 	issued map[string]*Membership // module → membership; present with nil = followed, none issued
-	onNew  []func(Membership)
+	onNew  []*func(Membership)
 	subs   []*nats.Subscription
 	Logf   func(format string, args ...any)
 	// answering is every subject this runtime answers on, so a subscription the bus refused can be
@@ -368,7 +368,10 @@ func (c *Conn) Follow(module string) {
 		}
 		c.mu.Lock()
 		c.issued[module] = &m
-		handlers := append([]func(Membership){}, c.onNew...)
+		handlers := make([]func(Membership), 0, len(c.onNew))
+		for _, h := range c.onNew {
+			handlers = append(handlers, *h)
+		}
 		c.mu.Unlock()
 		c.Logf("[mesh-tools] %s on %s was issued a new membership; re-serving on it", module, c.node)
 		for _, h := range handlers {
@@ -410,10 +413,28 @@ func (c *Conn) Serving() []string {
 // OnMembership is called with every new membership any followed module is issued.
 func (c *Conn) OnMembership(h func(Membership)) {
 	c.mu.Lock()
-	c.onNew = append(c.onNew, h)
+	c.onNew = append(c.onNew, &h)
 	c.mu.Unlock()
 }
 
+// onMembership is OnMembership until the answered function is called, which drops the handler.
+func (c *Conn) onMembership(h func(Membership)) func() {
+	mine := &h
+	c.mu.Lock()
+	c.onNew = append(c.onNew, mine)
+	c.mu.Unlock()
+	return func() {
+		c.mu.Lock()
+		defer c.mu.Unlock()
+		for i, had := range c.onNew {
+			if had == mine {
+				c.onNew = append(c.onNew[:i:i], c.onNew[i+1:]...)
+				return
+			}
+		}
+	}
+}
+
 func (c *Conn) track(s *nats.Subscription) {
 	c.mu.Lock()
 	c.subs = append(c.subs, s)
@@ -958,7 +979,7 @@ func (c *Conn) ConsumeAs(module string, deliver func(Envelope) error) (func(), e
 	h := newHearing(c, js, module, deliver)
 	// Bound by name, never created and never matched against a subject: the consumer and its
 	// filters are the controller's (design 29 §3), exactly as the module's own runtime bound it.
-	events, doing, err := h.bind(EventsStream, durable)
+	events, doing, err := h.bind(EventsStream, durable, nil)
 	if err != nil {
 		return nil, fmt.Errorf("%s %s's consumer %s: %w", doing, module, durable, err)
 	}