From d8b9a921b8fb0a18887699fc398216daa9edb910 Mon Sep 17 00:00:00 2001
From: Seebs <seebs@molecula.com>
Date: Fri, 4 Mar 2022 13:50:22 -0600
Subject: [PATCH] handle BitN when updating an existing bitmap pointer cell

We have code to correctly fill in cell.BitN when a leaf cell already
exists but isn't of the correct sort, but not to handle the case where
it already exists and *is* a BitmapPtr, but doesn't necessarily have
the right BitN value.
---
 rbf/cursor.go      |  4 ++--
 rbf/cursor_test.go | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/rbf/cursor.go b/rbf/cursor.go
index b0fb50df5..dea006e95 100644
--- a/rbf/cursor.go
+++ b/rbf/cursor.go
@@ -411,10 +411,10 @@ func (c *Cursor) putLeafCell(in leafCell) (err error) {
 				}
 				cell.Type = ContainerTypeBitmapPtr
 				cell.Data = fromPgno(bitmapPgno)
-				// update the BitN too
-				cell.BitN = in.BitN
 				cell.ElemN = in.ElemN
 			}
+			// update the BitN regardless
+			cell.BitN = in.BitN
 		}
 	}
 
diff --git a/rbf/cursor_test.go b/rbf/cursor_test.go
index 7de5f7d77..7859a9efa 100644
--- a/rbf/cursor_test.go
+++ b/rbf/cursor_test.go
@@ -557,6 +557,44 @@ func TestCursor_RLETesting(t *testing.T) {
 	})
 }
 
+func TestCursor_BitmapBitN(t *testing.T) {
+	db := MustOpenDB(t)
+	defer MustCloseDB(t, db)
+	tx := MustBegin(t, db, true)
+	defer tx.Rollback()
+	if err := tx.CreateBitmap("x"); err != nil {
+		t.Fatal(err)
+	}
+	bmData := make([]uint64, 1024)
+	for i := range bmData {
+		bmData[i] = 0x5555555555555555
+	}
+	ct := roaring.NewContainerBitmap(-1, bmData)
+	err := tx.PutContainer("x", 0, ct)
+	if err != nil {
+		t.Fatalf("error writing container: %v", err)
+	}
+	// Putting a container to the same slot, which is also a bitmap
+	// (rather than a BitmapPtr), while the existing cell is a BitmapPtr,
+	// may not update BitN correctly.
+	ct, _ = ct.Add(1)
+	err = tx.PutContainer("x", 0, ct)
+	if err != nil {
+		t.Fatalf("rewriting container: %v", err)
+	}
+	v, err := tx.Container("x", 0)
+	if err != nil {
+		t.Fatalf("getting container: %v", err)
+	}
+	c1 := v.N()
+	v.Repair()
+	c2 := v.N()
+	if c1 != c2 {
+		t.Fatalf("expected count %d, got %d", c2, c1)
+	}
+	tx.Commit()
+}
+
 func TestCursor_RLEConversion(t *testing.T) {
 	db := MustOpenDB(t)
 	defer MustCloseDB(t, db)