Ensure that Underlay never return nil on MultiChannel. Fixes #228

Author: plorenz

multi.go

@@ -70,11 +70,10 @@ type multiChannelImpl struct {
 	// https://github.com/golang/go/issues/36606
 	lastRead int64
 
-	ownerId     string
-	channelId   string
-	logicalName string
-	certs       concurrenz.AtomicValue[[]*x509.Certificate]
-	headers     concurrenz.AtomicValue[map[int32][]byte]
+	ownerId          string
+	channelId        string
+	logicalName      string
+	fallbackUnderlay concurrenz.AtomicValue[Underlay]
 
 	options           *Options
 	waiters           waiterMap
@@ -115,8 +114,7 @@ func NewMultiChannel(config *MultiChannelConfig) (MultiChannel, error) {
 	impl.flags.Set(flagInjectUnderlayType, config.InjectUnderlayTypeIntoMessages)
 
 	impl.ownerId = config.Underlay.Id()
-	impl.certs.Store(config.Underlay.Certificates())
-	impl.headers.Store(config.Underlay.Headers())
+	impl.fallbackUnderlay.Store(config.Underlay)
 	impl.underlays.Append(config.Underlay)
 
 	groupSecret := config.Underlay.Headers()[GroupSecretHeader]
@@ -164,8 +162,7 @@ func (self *multiChannelImpl) AcceptUnderlay(underlay Underlay) error {
 		return fmt.Errorf("new underlay for '%s' not accepted: multi-channel is closed", self.ConnectionId())
 	}
 
-	self.certs.Store(underlay.Certificates())
-	self.headers.Store(underlay.Headers())
+	self.fallbackUnderlay.Store(underlay)
 	self.underlays.Append(underlay)
 
 	self.startMultiplex(underlay)
@@ -223,19 +220,15 @@ func (self *multiChannelImpl) ConnectionId() string {
 }
 
 func (self *multiChannelImpl) Certificates() []*x509.Certificate {
-	return self.certs.Load()
+	return self.fallbackUnderlay.Load().Certificates()
 }
 
 func (self *multiChannelImpl) Headers() map[int32][]byte {
-	return self.headers.Load()
+	return self.fallbackUnderlay.Load().Headers()
 }
 
 func (self *multiChannelImpl) Label() string {
-	if u := self.Underlay(); u != nil {
-		return fmt.Sprintf("ch{%s}->%s", self.LogicalName(), u.Label())
-	} else {
-		return fmt.Sprintf("ch{%s}->{}", self.LogicalName())
-	}
+	return fmt.Sprintf("ch{%s}->%s", self.LogicalName(), self.fallbackUnderlay.Load().Label())
 }
 
 func (self *multiChannelImpl) GetOptions() *Options {
@@ -329,10 +322,7 @@ func (self *multiChannelImpl) IsClosed() bool {
 }
 
 func (self *multiChannelImpl) Underlay() Underlay {
-	if underlays := self.underlays.Value(); len(underlays) > 0 {
-		return underlays[0]
-	}
-	return nil
+	return self.fallbackUnderlay.Load()
 }
 
 func (self *multiChannelImpl) Rx(m *Message) {
@@ -453,6 +443,13 @@ func (self *multiChannelImpl) closeUnderlay(underlay Underlay, notifier *CloseNo
 		}
 		return false
 	})
+	if self.fallbackUnderlay.Load() == underlay {
+		underlays := self.underlays.Value()
+		if len(underlays) > 0 {
+			lastUnderlay := underlays[len(underlays)-1]
+			self.fallbackUnderlay.Store(lastUnderlay)
+		}
+	}
 	self.lock.Unlock()
 
 	if underlayRemoved {
@@ -617,7 +614,7 @@ func (self *UnderlayConstraints) countsShowValidState(ch MultiChannel, counts ma
 				WithField("underlays", counts).
 				Info("not enough total open underlays, closing multi-underlay channel")
 			if err := ch.Close(); err != nil {
-				pfxlog.Logger().WithError(err).Error("error closing underlay")
+				pfxlog.Logger().WithError(err).Error("error closing channel")
 			}
 		}
 		return false