dnsx/alg: invalidate caches when transport stopped

Author: ignoramous

intra/dnsx/alg.go

@@ -82,6 +82,8 @@ type Gateway interface {
 	translate(yes bool)
 	// Query using t1 as primary transport and t2 as secondary and preset as pre-determined ip answers
 	q(t1, t2 Transport, preset []netip.Addr, network string, q *dns.Msg, s *x.DNSSummary) (*dns.Msg, error)
+	// onStopped is called when a transport tid is stopped. Gateway invalidates its local caches, if any.
+	onStopped(tid string)
 	// clear obj state
 	stop()
 }
@@ -116,6 +118,7 @@ func (a expaddr) alive() []netip.Addr {
 	return a.get(true /*live*/)
 }
 
+// fresh returns false if a has expired or if a is zero-value.
 func (a expaddr) fresh() bool {
 	return !a.ttl.IsZero() && time.Now().Before(a.ttl)
 }
@@ -250,6 +253,20 @@ func (p *xips) sec() []netip.Addr {
 	return p.aux
 }
 
+func (p *xips) rmv(tid string) (done bool) {
+	if p == nil {
+		return
+	}
+	p.pmu.Lock()
+	defer p.pmu.Unlock()
+	if xaddr := p.pri[tid]; xaddr.fresh() {
+		done = true
+		xaddr.ttl = time.Now() // mark as expired
+		p.pri[tid] = xaddr
+	}
+	return
+}
+
 // block returns true if any secondary ip is unspecified
 func anyUnspecified(ips []netip.Addr) bool {
 	// unspecified ips expected to be in aux
@@ -399,6 +416,33 @@ func (t *dnsgateway) translate(yes bool) {
 	log.I("alg: translate? prev(%t) > now(%t)", prev, yes)
 }
 
+func (t *dnsgateway) onStopped(tid string) {
+	if len(tid) <= 0 {
+		return
+	}
+
+	ach := make(chan *xips, len(t.alg))
+	defer close(ach)
+
+	go func() {
+		n := 0
+		for x := range ach {
+			if x.rmv(tid) {
+				n++
+			}
+		}
+		log.I("alg: onStopped(%s): removed %d alg<>realip translations", tid, n)
+	}()
+
+	t.RLock()
+	defer t.RUnlock()
+	for _, algans := range t.alg {
+		if algans != nil {
+			ach <- algans.ips
+		}
+	}
+}
+
 // Implements Gateway
 func (t *dnsgateway) stop() {
 	t.Lock()

intra/dnsx/transport.go

@@ -249,6 +249,9 @@ func (r *resolver) Translate(b bool) {
 func (r *resolver) stopIfExistsLocked(id string) {
 	if t, ok := r.transports[id]; ok && t != nil {
 		err := t.Stop() // todo: async?
+		core.Go("r.gateway.stopTid", func() {
+			r.gateway.onStopped(id)
+		})
 		log.VV("dns: stop: %s; err? %v", id, err)
 		delete(r.transports, id)
 	}