fix wrongly set correlation ids when sending a command (#220)

* adding the SagaCorrelationID header only for replies

Fixing a bug where grabbit would set the message.CorrelationID and the message.SagaCorrelationID header even
if the message was a command and not a reply.

* fixing minor documentation issue

gbus/abstractions.go

@@ -18,6 +18,8 @@ const (
 	CMD Semantics = "cmd"
 	//EVT represenst a messge with event semantics in grabbit
 	EVT Semantics = "evt"
+	//REPLY represenst a messge with reply semantics in grabbit
+	REPLY Semantics = "reply"
 )
 
 //Bus interface provides the majority of functionality to Send, Reply and Publish messages to the Bus

gbus/saga/invocation.go

@@ -34,25 +34,21 @@ type sagaInvocation struct {
 	startedByRPCID string
 }
 
-func (si *sagaInvocation) setCorrelationIDs(message *gbus.BusMessage, isEvent bool, targetService string) {
+func (si *sagaInvocation) setCorrelationIDs(message *gbus.BusMessage, targetService string, semantics gbus.Semantics) {
 
-	message.CorrelationID = si.inboundMsg.ID
 	message.SagaID = si.sagaID
 
-	if !isEvent {
-		//support saga-to-saga communication
-		if si.inboundMsg.SagaID != "" {
-			message.SagaCorrelationID = si.inboundMsg.SagaID
-		}
+	if semantics == gbus.REPLY {
+		message.CorrelationID = si.inboundMsg.ID
+		message.SagaCorrelationID = si.inboundMsg.SagaID
+
+	} else if semantics == gbus.CMD {
 		//if the saga is potentially invoking itself then set the SagaCorrelationID to reflect that
 		//https://github.com/wework/grabbit/issues/64
-
 		if targetService == si.hostingSvc {
 			message.SagaCorrelationID = message.SagaID
 		}
-
 	}
-
 }
 func (si *sagaInvocation) HostingSvc() string {
 	return si.hostingSvc
@@ -64,13 +60,13 @@ func (si *sagaInvocation) InvokingSvc() string {
 
 func (si *sagaInvocation) Reply(ctx context.Context, message *gbus.BusMessage) error {
 	_, targetService := si.decoratedInvocation.Routing()
-	si.setCorrelationIDs(message, false, targetService)
+	si.setCorrelationIDs(message, targetService, gbus.REPLY)
 	return si.decoratedInvocation.Reply(ctx, message)
 }
 
 func (si *sagaInvocation) ReplyToInitiator(ctx context.Context, message *gbus.BusMessage) error {
 
-	si.setCorrelationIDs(message, false, si.startedBy)
+	si.setCorrelationIDs(message, si.startedBy, gbus.REPLY)
 
 	//override the correlation ids to those of the message creating the saga
 	message.SagaCorrelationID = si.startedBySaga
@@ -93,13 +89,13 @@ func (si *sagaInvocation) Ctx() context.Context {
 
 func (si *sagaInvocation) Send(ctx context.Context, toService string,
 	command *gbus.BusMessage, policies ...gbus.MessagePolicy) error {
-	si.setCorrelationIDs(command, false, toService)
+	si.setCorrelationIDs(command, toService, gbus.CMD)
 	return si.decoratedBus.Send(ctx, toService, command, policies...)
 }
 
 func (si *sagaInvocation) Publish(ctx context.Context, exchange, topic string,
 	event *gbus.BusMessage, policies ...gbus.MessagePolicy) error {
-	si.setCorrelationIDs(event, true, "")
+	si.setCorrelationIDs(event, "", gbus.EVT)
 	return si.decoratedBus.Publish(ctx, exchange, topic, event, policies...)
 }