From 2e145196b89eecce02c4e8396e451f37e50bb0d1 Mon Sep 17 00:00:00 2001
From: Derek Collison <derek@nats.io>
Date: Tue, 22 Jun 2021 07:38:30 -0700
Subject: [PATCH] Fix for extended purge by sequence.

Signed-off-by: Derek Collison <derek@nats.io>
---
 server/filestore.go              |  2 +-
 server/jetstream_cluster_test.go | 68 +++++++++++++++++++++++++++++++-
 server/memstore.go               |  2 +-
 3 files changed, 69 insertions(+), 3 deletions(-)

diff --git a/server/filestore.go b/server/filestore.go
index cc9ca1c3..a458858d 100644
--- a/server/filestore.go
+++ b/server/filestore.go
@@ -3152,7 +3152,7 @@ func (fs *fileStore) PurgeEx(subject string, sequence, keep uint64) (purged uint
 		}
 		last := ss.Last
 		if sequence > 0 {
-			last = sequence + 1
+			last = sequence - 1
 		}
 		for seq := ss.First; seq <= last; seq++ {
 			if sm, _ := fs.msgForSeq(seq); sm != nil && eq(sm.subj, subject) {
diff --git a/server/jetstream_cluster_test.go b/server/jetstream_cluster_test.go
index e930992f..6497fa69 100644
--- a/server/jetstream_cluster_test.go
+++ b/server/jetstream_cluster_test.go
@@ -7454,7 +7454,7 @@ func TestJetStreamClusterExtendedStreamPurge(t *testing.T) {
 			purge(&JSApiStreamPurgeRequest{Subject: "kv.bar", Keep: 1}, 801)
 			expectLeft("kv.bar", 1)
 
-			purge(&JSApiStreamPurgeRequest{Subject: "kv.baz", Sequence: 2850}, 751)
+			purge(&JSApiStreamPurgeRequest{Subject: "kv.baz", Sequence: 2851}, 751)
 			expectLeft("kv.baz", 50)
 
 			purge(&JSApiStreamPurgeRequest{Subject: "kv.*"}, 0)
@@ -7503,7 +7503,73 @@ func TestJetStreamClusterExtendedStreamPurge(t *testing.T) {
 			expectLeft(">", 11)
 		})
 	}
+}
 
+func TestPurgeBySequence(t *testing.T) {
+	for _, st := range []StorageType{FileStorage, MemoryStorage} {
+		t.Run(st.String(), func(t *testing.T) {
+
+			c := createJetStreamClusterExplicit(t, "JSC", 3)
+			defer c.shutdown()
+
+			nc, js := jsClientConnect(t, c.randomServer())
+			defer nc.Close()
+
+			cfg := StreamConfig{
+				Name:       "KV",
+				Subjects:   []string{"kv.*.*"},
+				Storage:    st,
+				Replicas:   2,
+				MaxMsgsPer: 5,
+			}
+			req, err := json.Marshal(cfg)
+			if err != nil {
+				t.Fatalf("Unexpected error: %v", err)
+			}
+			nc.Request(fmt.Sprintf(JSApiStreamCreateT, cfg.Name), req, time.Second)
+			for i := 0; i < 20; i++ {
+				if _, err = js.Publish("kv.myapp.username", []byte(fmt.Sprintf("value %d", i))); err != nil {
+					t.Fatalf("request failed: %s", err)
+				}
+			}
+			for i := 0; i < 20; i++ {
+				if _, err = js.Publish("kv.myapp.password", []byte(fmt.Sprintf("value %d", i))); err != nil {
+					t.Fatalf("request failed: %s", err)
+				}
+			}
+			expectSequences := func(t *testing.T, subject string, seq ...int) {
+				sub, err := js.SubscribeSync(subject)
+				if err != nil {
+					t.Fatalf("sub failed: %s", err)
+				}
+				defer sub.Unsubscribe()
+				for _, i := range seq {
+					msg, err := sub.NextMsg(time.Second)
+					if err != nil {
+						t.Fatalf("didn't get message: %s", err)
+					}
+					meta, err := msg.Metadata()
+					if err != nil {
+						t.Fatalf("didn't get metadata: %s", err)
+					}
+					if meta.Sequence.Stream != uint64(i) {
+						t.Fatalf("expected sequence %d got %d", i, meta.Sequence.Stream)
+					}
+				}
+			}
+			expectSequences(t, "kv.myapp.username", 16, 17, 18, 19, 20)
+			expectSequences(t, "kv.myapp.password", 36, 37, 38, 39, 40)
+
+			// delete up to but not including 18 of username...
+			jr, _ := json.Marshal(&JSApiStreamPurgeRequest{Subject: "kv.myapp.username", Sequence: 18})
+			_, err = nc.Request(fmt.Sprintf(JSApiStreamPurgeT, "KV"), jr, time.Second)
+			if err != nil {
+				t.Fatalf("request failed: %s", err)
+			}
+			// 18 should still be there
+			expectSequences(t, "kv.myapp.username", 18, 19, 20)
+		})
+	}
 }
 
 // Support functions
diff --git a/server/memstore.go b/server/memstore.go
index de0cd20c..632960b4 100644
--- a/server/memstore.go
+++ b/server/memstore.go
@@ -417,7 +417,7 @@ func (ms *memStore) PurgeEx(subject string, sequence, keep uint64) (purged uint6
 		}
 		last := ss.Last
 		if sequence > 0 {
-			last = sequence + 1
+			last = sequence - 1
 		}
 		ms.mu.Lock()
 		for seq := ss.First; seq <= last; seq++ {