1 files changed, 88 insertions, 0 deletions
diff --git a/internal/format/packfile/delta/header_test.go b/internal/format/packfile/delta/header_test.go
new file mode 100644
index 00000000..8d97674f
--- /dev/null
+++ b/internal/format/packfile/delta/header_test.go
@@ -0,0 +1,88 @@
+package delta_test
+
+import (
+	"bytes"
+	"errors"
+	"math"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packfile/delta"
+)
+
+func TestParseHeaderSizesRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name       string
+		baseSize   uint64
+		resultSize uint64
+	}{
+		{name: "zero", baseSize: 0, resultSize: 0},
+		{name: "small", baseSize: 5, resultSize: 130},
+		{name: "boundaries", baseSize: 127, resultSize: 128},
+		{name: "large", baseSize: 1 << 32, resultSize: 1 << 57},
+		{name: "max", baseSize: math.MaxUint64, resultSize: math.MaxUint64},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			data := delta.AppendHeaderSizes(nil, tc.baseSize, tc.resultSize)
+
+			wantConsumed := len(data)
+
+			data = append(data, 0xde, 0xad)
+
+			baseSize, resultSize, consumed, err := delta.ParseHeaderSizes(data)
+			if err != nil {
+				t.Fatalf("ParseHeaderSizes: %v", err)
+			}
+
+			if baseSize != tc.baseSize {
+				t.Fatalf("ParseHeaderSizes base size = %d, want %d", baseSize, tc.baseSize)
+			}
+
+			if resultSize != tc.resultSize {
+				t.Fatalf("ParseHeaderSizes result size = %d, want %d", resultSize, tc.resultSize)
+			}
+
+			if consumed != wantConsumed {
+				t.Fatalf("ParseHeaderSizes consumed = %d, want %d", consumed, wantConsumed)
+			}
+		})
+	}
+}
+
+func TestParseHeaderSizesMalformed(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name string
+		data []byte
+	}{
+		{name: "empty", data: []byte{}},
+		{name: "truncated first varint", data: []byte{0x80}},
+		{name: "missing second varint", data: []byte{0x05}},
+		{name: "truncated second varint", data: []byte{0x05, 0x80}},
+		{
+			name: "overflow",
+			data: append(bytes.Repeat([]byte{0xff}, 9), 0x7f),
+		},
+		{
+			name: "overlong",
+			data: append(bytes.Repeat([]byte{0x80}, 10), 0x00),
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, _, _, err := delta.ParseHeaderSizes(tc.data)
+			if !errors.Is(err, delta.ErrMalformedDelta) {
+				t.Fatalf("ParseHeaderSizes error = %v, want ErrMalformedDelta", err)
+			}
+		})
+	}
+}