From 23de885fdb1158858adbbb7ba7ee5a330f915f10 Mon Sep 17 00:00:00 2001
From: Neil Twigg <neil@nats.io>
Date: Thu, 17 Oct 2024 16:51:25 +0100
Subject: [PATCH] Revert "Fix consumer start sequence when sequence not yet in
 stream"

This reverts commit ec54164df357fb842ae2b636c56ad99f059bf418.
See discussion nats-io/nats-server#6005.
---
 server/consumer.go       | 16 +++++-------
 server/jetstream_test.go | 56 ----------------------------------------
 2 files changed, 6 insertions(+), 66 deletions(-)

diff --git a/server/consumer.go b/server/consumer.go
index 9ef8fa1b7ab..849fb1c5362 100644
--- a/server/consumer.go
+++ b/server/consumer.go
@@ -4907,16 +4907,12 @@ func (o *consumer) selectStartingSeqNo() {
 			o.sseq = o.cfg.OptStartSeq
 		}
 
-		// Only clip the sseq if the OptStartSeq is not provided, otherwise
-		// it's possible that the stream just doesn't contain OptStartSeq yet.
-		if o.cfg.OptStartSeq == 0 {
-			if state.FirstSeq == 0 {
-				o.sseq = 1
-			} else if o.sseq < state.FirstSeq {
-				o.sseq = state.FirstSeq
-			} else if o.sseq > state.LastSeq {
-				o.sseq = state.LastSeq + 1
-			}
+		if state.FirstSeq == 0 {
+			o.sseq = 1
+		} else if o.sseq < state.FirstSeq {
+			o.sseq = state.FirstSeq
+		} else if o.sseq > state.LastSeq {
+			o.sseq = state.LastSeq + 1
 		}
 	}
 
diff --git a/server/jetstream_test.go b/server/jetstream_test.go
index fe95d5009ce..d69ddd29a4d 100644
--- a/server/jetstream_test.go
+++ b/server/jetstream_test.go
@@ -22836,62 +22836,6 @@ func TestJetStreamConsumerInfoNumPending(t *testing.T) {
 	require_Equal(t, ci.NumPending, 100)
 }
 
-func TestJetStreamConsumerStartSequenceNotInStream(t *testing.T) {
-	// This test is checking that we still correctly set the start
-	// sequence of a consumer if that start sequence doesn't appear
-	// in the stream yet. Previously this would have been clipped
-	// back to between the first and last seq from the stream state.
-
-	s := RunBasicJetStreamServer(t)
-	defer s.Shutdown()
-
-	nc, js := jsClientConnect(t, s)
-	defer nc.Close()
-
-	_, err := js.AddStream(&nats.StreamConfig{
-		Name:     "TEST",
-		Subjects: []string{"test"},
-	})
-	require_NoError(t, err)
-
-	sub, err := js.PullSubscribe("test", "test_consumer", nats.StartSequence(10))
-	require_NoError(t, err)
-
-	stream, err := s.gacc.lookupStream("TEST")
-	require_NoError(t, err)
-	consumer := stream.lookupConsumer("test_consumer")
-
-	func() {
-		consumer.mu.RLock()
-		defer consumer.mu.RUnlock()
-
-		require_Equal(t, consumer.dseq, 1)
-		require_Equal(t, consumer.sseq, 10)
-	}()
-
-	for i := 1; i <= 10; i++ {
-		_, err = js.Publish("test", []byte{byte(i)})
-		require_NoError(t, err)
-	}
-
-	msgs, err := sub.Fetch(1)
-	require_NoError(t, err)
-	require_Len(t, len(msgs), 1)
-	require_Equal(t, msgs[0].Data[0], 10)
-
-	require_NoError(t, msgs[0].AckSync())
-
-	func() {
-		consumer.mu.RLock()
-		defer consumer.mu.RUnlock()
-
-		require_Equal(t, consumer.dseq, 2)
-		require_Equal(t, consumer.adflr, 1)
-		require_Equal(t, consumer.sseq, 11)
-		require_Equal(t, consumer.asflr, 10)
-	}()
-}
-
 func TestJetStreamInterestStreamWithDuplicateMessages(t *testing.T) {
 	s := RunBasicJetStreamServer(t)
 	defer s.Shutdown()