fixup! TalkMaster: Switch master if dialed M is secondary

- validate received NotPrimaryMaster
- use Address.String() instead of printf with format that works only for ipv6
- add some logging, comments and TODO

go/neo/mastered.go

@@ -122,19 +122,29 @@ func (node *_MasteredNode) TalkMaster(ctx context.Context, f func(context.Contex
 		node.updateOperational(func() {
 			node.mlink = nil
 		})
+		// TODO log "trying maddr as PM"
 		err := node.talkMaster1(ctx, ctx0, maddr, f)
 		log.Warning(ctx, err)	// XXX Warning -> Error?
 		if errors.Is(err, cmdShutdown) {
 			return err // M commands to shutdown
 		}
 
+		// NotPrimaryMaster -> jump to trying what it says is primary
 		var notPrimaryMaster *proto.NotPrimaryMaster
 		if errors.As(err, &notPrimaryMaster) {
-			primary := notPrimaryMaster.KnownMasterList[notPrimaryMaster.Primary]
-			maddr = fmt.Sprintf("[%s]:%v", primary.Host, primary.Port)
+			p := int(notPrimaryMaster.Primary)
+			if !(0 <= p && p < len(notPrimaryMaster.KnownMasterList)) {
+				log.Warning(ctx, "malformed NotPrimaryMaster reply - ignoring")
+			} else {
+				// TODO update masterRegistry from received KnownMasterList
+				primary := notPrimaryMaster.KnownMasterList[p]
+				maddr = primary.Address.String()
+				log.Info(ctx, "switching to try %s as primary master", maddr)
+			}
 		}
 
 		// TODO if err == "reject identification / protocol error" -> shutdown client?
+		// TODO if err == "cannot connect" -> start trying other master nodes from MasterAddrSlice
 
 		// exit on cancel / throttle reconnecting
 		select {