Do not ack to AckNxt

This causes nil messages mid content stream and is confusing,
the test for this is amended to test the content received for
validity - where previously the test assumed any content is
good content but in fact it only received half the content.

Removing this behaviour until we can design this properly

Signed-off-by: R.I.Pienaar <rip@devco.net>

server/consumer.go

@@ -698,12 +698,15 @@ func (o *Consumer) sendAckReply(subj string) {
 func (o *Consumer) processAck(_ *subscription, _ *client, subject, reply string, msg []byte) {
 	sseq, dseq, dcount, _ := o.ReplyInfo(subject)
 
+	var skipAckReply bool
+
 	switch {
 	case len(msg) == 0, bytes.Equal(msg, AckAck), bytes.Equal(msg, AckOK):
 		o.ackMsg(sseq, dseq, dcount)
 	case bytes.Equal(msg, AckNext):
 		o.ackMsg(sseq, dseq, dcount)
 		o.processNextMsgReq(nil, nil, subject, reply, nil)
+		skipAckReply = true
 	case bytes.Equal(msg, AckNak):
 		o.processNak(sseq, dseq)
 	case bytes.Equal(msg, AckProgress):
@@ -713,7 +716,7 @@ func (o *Consumer) processAck(_ *subscription, _ *client, subject, reply string,
 	}
 
 	// Ack the ack if requested.
-	if len(reply) > 0 {
+	if len(reply) > 0 && !skipAckReply {
 		o.sendAckReply(reply)
 	}
 }
@@ -956,6 +959,7 @@ func (o *Consumer) ackMsg(sseq, dseq, dcount uint64) {
 
 func (o *Consumer) processAckMsg(sseq, dseq, dcount uint64, doSample bool) {
 	var sagap uint64
+
 	o.mu.Lock()
 	switch o.config.AckPolicy {
 	case AckExplicit:

test/jetstream_test.go

@@ -1665,6 +1665,11 @@ func TestJetStreamWorkQueueAckAndNext(t *testing.T) {
 				if err != nil {
 					t.Fatalf("Unexpected error waiting for messages: %v", err)
 				}
+
+				if !bytes.Equal(m.Data, []byte("Hello World!")) {
+					t.Fatalf("Got an invalid message from the stream: %q", m.Data)
+				}
+
 				nc.PublishRequest(m.Reply, sub.Subject, server.AckNext)
 			}
 		})