Add support for setting the idempotency key on a BusMessage (#208)

* Added x-idempotency-key header and the ability for client code to set it

#106

* Set the value of BusMessage.ID as the default value of BusMessage.IdempotencyKey

gbus/messages.go

@@ -3,6 +3,7 @@ package gbus
 import (
 	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/opentracing/opentracing-go/log"
 	"github.com/rs/xid"
@@ -12,6 +13,7 @@ import (
 //BusMessage the structure that gets sent to the underlying transport
 type BusMessage struct {
 	ID                string
+	IdempotencyKey    string
 	CorrelationID     string
 	SagaID            string
 	SagaCorrelationID string
@@ -26,6 +28,7 @@ func NewBusMessage(payload Message) *BusMessage {
 	bm := &BusMessage{
 		ID: xid.New().String(),
 	}
+	bm.SetIdempotencyKey(bm.ID)
 	bm.SetPayload(payload)
 	return bm
 }
@@ -57,6 +60,7 @@ func GetMessageName(delivery amqp.Delivery) string {
 //GetAMQPHeaders convert to AMQP headers Table everything but a payload
 func (bm *BusMessage) GetAMQPHeaders() (headers amqp.Table) {
 	headers = amqp.Table{}
+	headers["x-idempotency-key"] = bm.IdempotencyKey
 	headers["x-msg-saga-id"] = bm.SagaID
 	headers["x-msg-saga-correlation-id"] = bm.SagaCorrelationID
 	headers["x-grabbit-msg-rpc-id"] = bm.RPCID
@@ -68,6 +72,7 @@ func (bm *BusMessage) GetAMQPHeaders() (headers amqp.Table) {
 //SetFromAMQPHeaders convert from AMQP headers Table everything but a payload
 func (bm *BusMessage) SetFromAMQPHeaders(delivery amqp.Delivery) {
 	headers := delivery.Headers
+	bm.IdempotencyKey = castToString(headers["x-idempotency-key"])
 	bm.SagaID = castToString(headers["x-msg-saga-id"])
 	bm.SagaCorrelationID = castToString(headers["x-msg-saga-correlation-id"])
 	bm.RPCID = castToString(headers["x-grabbit-msg-rpc-id"])
@@ -81,6 +86,10 @@ func (bm *BusMessage) SetPayload(payload Message) {
 	bm.Payload = payload
 }
 
+func (bm *BusMessage) SetIdempotencyKey(idempotencyKey string) {
+	bm.IdempotencyKey = strings.TrimSpace(idempotencyKey)
+}
+
 //TargetSaga allows sending the message to a specific Saga instance
 func (bm *BusMessage) TargetSaga(sagaID string) {
 	bm.SagaCorrelationID = sagaID
@@ -91,6 +100,7 @@ func (bm *BusMessage) GetTraceLog() (fields []log.Field) {
 	return []log.Field{
 		log.String("message", bm.PayloadFQN),
 		log.String("ID", bm.ID),
+		log.String("IdempotencyKey", bm.IdempotencyKey),
 		log.String("SagaID", bm.SagaID),
 		log.String("CorrelationID", bm.CorrelationID),
 		log.String("SagaCorrelationID", bm.SagaCorrelationID),

tests/bus_test.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
+	"sync"
 	"testing"
 	"time"
 
@@ -760,6 +761,40 @@ func TestSanitizingSvcName(t *testing.T) {
 	fmt.Println("succeeded sanitizing service name")
 }
 
+func TestIdempotencyKeyHeaders(t *testing.T) {
+	var wg sync.WaitGroup
+	wg.Add(2)
+	keys := make([]string, 0)
+	handler := func(invocation gbus.Invocation, message *gbus.BusMessage) error {
+		keys = append(keys, message.IdempotencyKey)
+		wg.Done()
+		return nil
+	}
+
+	bus := createNamedBusForTest(testSvc1)
+
+	bus.HandleMessage(Command1{}, handler)
+	bus.Start()
+	defer bus.Shutdown()
+
+	cmd1 := gbus.NewBusMessage(Command1{})
+	cmd1.SetIdempotencyKey("some-unique-key")
+
+	cmd2 := gbus.NewBusMessage(Command1{})
+	cmd2.SetIdempotencyKey("some-unique-key")
+
+	//send two commands with the same IdempotencyKey to test that the same IdempotencyKey is propogated
+	bus.Send(context.Background(), testSvc1, cmd1)
+	bus.Send(context.Background(), testSvc1, cmd2)
+
+	wg.Wait()
+
+	if keys[0] != keys[1] && keys[0] != "" {
+		t.Errorf("expected same IdempotencyKey. actual key1:%s, key2%s", keys[0], keys[1])
+	}
+
+}
+
 func amqpDeliveryToPublishing(del *amqp.Delivery) (pub amqp.Publishing) {
 	pub.Headers = del.Headers
 	pub.ContentType = del.ContentType