dnsx/transport: avoid stopping dnscrypt transport

DNSCrypt transport lifecycle is handled by DcMulti and so stopping
transports against any existing id being replaced is likely to step on the
newly added transport and not the previous replaced one.

Author: ignoramous

intra/dnsx/transport.go

@@ -349,7 +349,20 @@ func (r *resolver) Add(dt x.DNSTransport) (ok bool) {
 
 	caching := false
 	switch t.Type() {
-	case DNS53, DNSCrypt, DOH, DOT, ODOH:
+	case DNSCrypt:
+		// DNSCrypt transports must not be explicitly stopped here
+		// as the stop/start for it is handled DcMulti
+		r.Lock()
+		r.transports[tid] = t
+		if ct := NewCachingTransport(r.ctx, t, ttl10m); ct != nil {
+			ctid := idstr(ct)
+			r.transports[ctid] = ct
+			caching = true
+		}
+		r.Unlock()
+		core.Go("r.onAdd", func() { r.listener.OnDNSAdded(tid) })
+		ok = true
+	case DNS53, DOH, DOT, ODOH:
 		r.Lock()
 		// stop existing transport if different
 		if oldt := r.transports[tid]; !core.PtrEq(t, oldt) {
@@ -375,14 +388,13 @@ func (r *resolver) Add(dt x.DNSTransport) (ok bool) {
 		}
 
 		core.Go("r.onAdd", func() { r.listener.OnDNSAdded(tid) })
-		log.I("dns: add transport %s@%s; caching? %t",
-			t.ID(), t.GetAddr(), caching)
-
-		return true
+		ok = true
 	default:
 		log.E("dns: unknown transport(%s) type: %s", t.ID(), t.Type())
 	}
-	return false
+	log.I("dns: add transport %s@%s; caching? %t",
+		t.ID(), t.GetAddr(), caching)
+	return ok
 }
 
 func (r *resolver) GetMult(id string) (x.DNSTransportMult, error) {