Fix METADAPT-A not receiving more than one message

metadapta.go

@@ -102,7 +102,7 @@ func (this *a) receive() {
 	defer func() {
 		this.underlying.Close()
 		this.transLock.Lock()
-		defer this.transLock.Lock()
+		defer this.transLock.Unlock()
 		for _, trans := range this.transMap {
 			trans.Close()
 		}
@@ -124,22 +124,30 @@ func (this *a) receive() {
 }
 
 func (this *a) receiveMultiplex(transID int64, method uint16, payload []byte) error {
-	if transID == 0 || this.party == partyFromTransID(transID) {
-		return ErrMessageMalformed
-	}
-	
-	this.transLock.Lock()
-	defer this.transLock.Unlock()
+	if transID == 0 { return ErrMessageMalformed }
 
-	trans, ok := this.transMap[transID]
-	if !ok {
-		trans = &transA {
-			parent:   this,
-			id:       transID,
-			incoming: usync.NewGate[incomingMessage](),
+	trans, err := func() (*transA, error) {
+		this.transLock.Lock()
+		defer this.transLock.Unlock()
+
+		trans, ok := this.transMap[transID]
+		if !ok {
+			// it is forbidden for the other party to initiate a transaction
+			// with an ID from this party
+			if this.party == partyFromTransID(transID) {
+				return nil, ErrMessageMalformed
+			}
+			trans = &transA {
+				parent:   this,
+				id:       transID,
+				incoming: usync.NewGate[incomingMessage](),
+			}
+			this.transMap[transID] = trans
+			this.transChan <- trans
 		}
-		this.transChan <- trans
-	}
+		return trans, nil
+	}()
+	if err != nil { return err }
 
 	trans.incoming.Send(incomingMessage {
 		method:  method,