update SQS receiveMessage to return no messages error when no message…

…s received from the quque

aws/sqs/sqs.go

@@ -27,6 +27,9 @@ type SQS struct {
 	client *sqs.Client
 }
 
+// specific error to return when no messages are received from the queue
+var ErrNoMessages = errors.New("no messages received from queue")
+
 // New returns an SQS struct which wraps an SQS client using the default AWS credentials chain.
 // This consults (in order) environment vars, config files, EC2 and ECS roles.
 // It is an error if the AWS_REGION environment variable is not set.
@@ -135,7 +138,8 @@ func (s *SQS) receiveMessage(ctx context.Context, input *sqs.ReceiveMessageInput
 		switch {
 		case r == nil || len(r.Messages) == 0:
 			// no message received
-			continue
+			return Raw{}, ErrNoMessages
+
 		case len(r.Messages) == 1:
 			raw := r.Messages[0]
 
@@ -333,3 +337,7 @@ func Cancelled(err error) bool {
 	}
 	return false
 }
+
+func IsNoMessagesError(err error) bool {
+	return errors.Is(err, ErrNoMessages)
+}