fix(checksum): return canonical empty checksum

checksum.go

@@ -137,7 +137,7 @@ func ChecksumReader(r io.Reader, pageSize int) (Checksum, error) {
 			chksum = ChecksumFlag | (chksum ^ ChecksumPage(pgno, data))
 		}
 	}
-	return chksum, nil
+	return ChecksumFlag | chksum, nil
 }
 
 // ParseChecksum parses a 16-character hex string into a checksum.

cmd/ltx/apply_test.go

@@ -111,6 +111,38 @@ func TestApplyCommand_SnapshotOverExistingDatabase(t *testing.T) {
 	}
 }
 
+func TestApplyCommand_ChecksumDeletion(t *testing.T) {
+	const pageSize = 512
+
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "db")
+	ltxPath := filepath.Join(dir, "deletion.ltx")
+	initial := bytes.Repeat([]byte{0xbc}, pageSize)
+	if err := os.WriteFile(dbPath, initial, 0o666); err != nil {
+		t.Fatal(err)
+	}
+	writeApplyTestLTX(t, ltxPath, &ltx.FileSpec{
+		Header: ltx.Header{
+			Version:          ltx.Version,
+			PageSize:         pageSize,
+			Commit:           0,
+			MinTXID:          2,
+			MaxTXID:          2,
+			PreApplyChecksum: ltx.ChecksumPage(1, initial),
+		},
+		Trailer: ltx.Trailer{PostApplyChecksum: ltx.ChecksumFlag},
+	})
+
+	if err := NewApplyCommand().Run(context.Background(), []string{"-db", dbPath, ltxPath}); err != nil {
+		t.Fatal(err)
+	}
+	if got, err := os.ReadFile(dbPath); err != nil {
+		t.Fatal(err)
+	} else if len(got) != 0 {
+		t.Fatalf("database size=%d, want 0", len(got))
+	}
+}
+
 func writeApplyTestLTX(t *testing.T, path string, spec *ltx.FileSpec) {
 	t.Helper()
 

ltx_test.go

@@ -403,6 +403,14 @@ func TestParseFilename(t *testing.T) {
 }
 
 func TestChecksumReader(t *testing.T) {
+	t.Run("Empty", func(t *testing.T) {
+		if chksum, err := ltx.ChecksumReader(bytes.NewReader(nil), 512); err != nil {
+			t.Fatal(err)
+		} else if got, want := chksum, ltx.ChecksumFlag; got != want {
+			t.Fatalf("got=%x, want %x", got, want)
+		}
+	})
+
 	t.Run("OK", func(t *testing.T) {
 		r := io.MultiReader(
 			bytes.NewReader(bytes.Repeat([]byte("\x01"), 512)),
@@ -418,8 +426,10 @@ func TestChecksumReader(t *testing.T) {
 
 	t.Run("ErrUnexpectedEOF", func(t *testing.T) {
 		r := bytes.NewReader(bytes.Repeat([]byte("\x01"), 512))
-		if _, err := ltx.ChecksumReader(r, 1024); err != io.ErrUnexpectedEOF {
+		if chksum, err := ltx.ChecksumReader(r, 1024); err != io.ErrUnexpectedEOF {
 			t.Fatal(err)
+		} else if got, want := chksum, ltx.Checksum(0); got != want {
+			t.Fatalf("got=%x, want %x", got, want)
 		}
 	})
 }