From 8fce45dfa7182924d8d60fffd9a51b245ada3546 Mon Sep 17 00:00:00 2001
From: Derek Collison <derek@nats.io>
Date: Tue, 1 Feb 2022 12:17:08 -0800
Subject: [PATCH] Under certain scenarios the pending for a consumer could
 appear to get stuck.

Under the covers we were calculating pending per msg block incorrectly when a single message existed beyond the requested sequence.

Signed-off-by: Derek Collison <derek@nats.io>
---
 server/filestore.go      |  2 +-
 server/filestore_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/server/filestore.go b/server/filestore.go
index 0aad6e2189d..d4b299e55fb 100644
--- a/server/filestore.go
+++ b/server/filestore.go
@@ -1115,7 +1115,7 @@ func (mb *msgBlock) filteredPendingLocked(subj string, wc bool, seq uint64) (tot
 	for i, subj := range subs {
 		// If the starting seq is less then or equal that means we want all and we do not need to load any messages.
 		ss := mb.fss[subj]
-		if ss == nil {
+		if ss == nil || seq > ss.Last {
 			continue
 		}
 
diff --git a/server/filestore_test.go b/server/filestore_test.go
index e9f4a5e1318..a6316024305 100644
--- a/server/filestore_test.go
+++ b/server/filestore_test.go
@@ -3480,6 +3480,33 @@ func TestFileStoreRemoveLastWriteIndex(t *testing.T) {
 	}
 }
 
+func TestFileStoreFilteredPendingBug(t *testing.T) {
+	storeDir := createDir(t, JetStreamStoreDir)
+	defer removeDir(t, storeDir)
+
+	fs, err := newFileStore(FileStoreConfig{StoreDir: storeDir}, StreamConfig{Name: "TEST", Storage: FileStorage})
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer fs.Stop()
+
+	fs.StoreMsg("foo", nil, []byte("msg"))
+	fs.StoreMsg("bar", nil, []byte("msg"))
+	fs.StoreMsg("baz", nil, []byte("msg"))
+
+	fs.mu.Lock()
+	mb := fs.lmb
+	fs.mu.Unlock()
+
+	total, f, l := mb.filteredPending("foo", false, 3)
+	if total != 0 {
+		t.Fatalf("Expected total of 0 but got %d", total)
+	}
+	if f != 0 || l != 0 {
+		t.Fatalf("Expected first and last to be 0 as well, but got %d %d", f, l)
+	}
+}
+
 // Test to optimize the selectMsgBlock with lots of blocks.
 func TestFileStoreFetchPerf(t *testing.T) {
 	// Comment out to run.