1 files changed, 251 insertions, 0 deletions
diff --git a/internal/format/packfile/entry_header_test.go b/internal/format/packfile/entry_header_test.go
new file mode 100644
index 00000000..79dc2740
--- /dev/null
+++ b/internal/format/packfile/entry_header_test.go
@@ -0,0 +1,251 @@
+package packfile_test
+
+import (
+	"bytes"
+	"errors"
+	"math"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packfile"
+	"lindenii.org/go/furgit/object/id"
+)
+
+func TestParseEntryHeaderBase(t *testing.T) {
+	t.Parallel()
+
+	// Commit entry of size 85:
+	// 0x95 has the continuation bit set, type 1, and size low bits 0x5;
+	// 0x05 contributes 5<<4.
+	header, err := packfile.ParseEntryHeader([]byte{0x95, 0x05}, 20)
+	if err != nil {
+		t.Fatalf("ParseEntryHeader: %v", err)
+	}
+
+	if header.Type != packfile.EntryTypeCommit {
+		t.Fatalf("ParseEntryHeader type = %d, want %d", header.Type, packfile.EntryTypeCommit)
+	}
+
+	if header.Size != 85 {
+		t.Fatalf("ParseEntryHeader size = %d, want 85", header.Size)
+	}
+
+	if header.HeaderLen != 2 {
+		t.Fatalf("ParseEntryHeader header len = %d, want 2", header.HeaderLen)
+	}
+}
+
+func TestParseEntryHeaderRefDelta(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			hashSize := objectFormat.Size()
+
+			base := bytes.Repeat([]byte{0xab}, hashSize)
+			data := append([]byte{0x73}, base...)
+
+			header, err := packfile.ParseEntryHeader(data, hashSize)
+			if err != nil {
+				t.Fatalf("ParseEntryHeader: %v", err)
+			}
+
+			if header.Type != packfile.EntryTypeRefDelta {
+				t.Fatalf("ParseEntryHeader type = %d, want %d", header.Type, packfile.EntryTypeRefDelta)
+			}
+
+			if header.Size != 3 {
+				t.Fatalf("ParseEntryHeader size = %d, want 3", header.Size)
+			}
+
+			if header.HeaderLen != 1+hashSize {
+				t.Fatalf("ParseEntryHeader header len = %d, want %d", header.HeaderLen, 1+hashSize)
+			}
+
+			if !bytes.Equal(header.RefBase[:hashSize], base) {
+				t.Fatalf("ParseEntryHeader ref base mismatch")
+			}
+		})
+	}
+}
+
+func TestParseEntryHeaderOfsDelta(t *testing.T) {
+	t.Parallel()
+
+	header, err := packfile.ParseEntryHeader([]byte{0x65, 0x80, 0x00}, 20)
+	if err != nil {
+		t.Fatalf("ParseEntryHeader: %v", err)
+	}
+
+	if header.Type != packfile.EntryTypeOfsDelta {
+		t.Fatalf("ParseEntryHeader type = %d, want %d", header.Type, packfile.EntryTypeOfsDelta)
+	}
+
+	if header.OfsDistance != 128 {
+		t.Fatalf("ParseEntryHeader distance = %d, want 128", header.OfsDistance)
+	}
+
+	if header.HeaderLen != 3 {
+		t.Fatalf("ParseEntryHeader header len = %d, want 3", header.HeaderLen)
+	}
+}
+
+func TestParseEntryHeaderMalformed(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name string
+		data []byte
+	}{
+		{name: "empty", data: []byte{}},
+		{name: "truncated type/size", data: []byte{0x95}},
+		{
+			name: "size overflow",
+			data: append([]byte{0x9f}, bytes.Repeat([]byte{0xff}, 9)...),
+		},
+		{
+			name: "overlong type/size",
+			data: append([]byte{0x95}, append(bytes.Repeat([]byte{0x80}, 9), 0x00)...),
+		},
+		{name: "truncated ref-delta base", data: []byte{0x73, 0xab, 0xab}},
+		{name: "truncated ofs distance", data: []byte{0x65, 0x80}},
+		{name: "type invalid", data: []byte{0x05}},
+		{name: "type future", data: []byte{0x55}},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := packfile.ParseEntryHeader(tc.data, 20)
+			if !errors.Is(err, packfile.ErrMalformedEntryHeader) {
+				t.Fatalf("ParseEntryHeader error = %v, want ErrMalformedEntryHeader", err)
+			}
+		})
+	}
+}
+
+func TestParseEntryHeaderBadHashSize(t *testing.T) {
+	t.Parallel()
+
+	for _, hashSize := range []int{-1, 0, id.MaxObjectIDSize + 1} {
+		func() {
+			defer func() {
+				if recover() == nil {
+					t.Fatalf("ParseEntryHeader hash size %d: expected panic", hashSize)
+				}
+			}()
+
+			_, _ = packfile.ParseEntryHeader([]byte{0x95, 0x05}, hashSize)
+		}()
+	}
+}
+
+func TestTypeSizeRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	baseTypes := []packfile.EntryType{
+		packfile.EntryTypeCommit,
+		packfile.EntryTypeTree,
+		packfile.EntryTypeBlob,
+		packfile.EntryTypeTag,
+	}
+
+	sizes := []uint64{
+		0, 1, 15, 16, 127, 128, 1 << 20, 1 << 57, math.MaxUint64,
+	}
+
+	for _, entryType := range baseTypes {
+		for _, size := range sizes {
+			data := packfile.AppendTypeSize(nil, entryType, size)
+			if len(data) > packfile.MaxTypeSizeLen {
+				t.Fatalf("AppendTypeSize(%d, %d) length = %d, want <= %d",
+					entryType, size, len(data), packfile.MaxTypeSizeLen)
+			}
+
+			header, err := packfile.ParseEntryHeader(data, 20)
+			if err != nil {
+				t.Fatalf("ParseEntryHeader: %v", err)
+			}
+
+			if header.Type != entryType {
+				t.Fatalf("round trip type = %d, want %d", header.Type, entryType)
+			}
+
+			if header.Size != size {
+				t.Fatalf("round trip size = %d, want %d", header.Size, size)
+			}
+
+			if header.HeaderLen != len(data) {
+				t.Fatalf("round trip header len = %d, want %d", header.HeaderLen, len(data))
+			}
+		}
+	}
+}
+
+func TestRefDeltaHeaderRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			hashSize := objectFormat.Size()
+
+			base := bytes.Repeat([]byte{0xcd}, hashSize)
+			data := packfile.AppendTypeSize(nil, packfile.EntryTypeRefDelta, 42)
+			data = append(data, base...)
+
+			header, err := packfile.ParseEntryHeader(data, hashSize)
+			if err != nil {
+				t.Fatalf("ParseEntryHeader: %v", err)
+			}
+
+			if !bytes.Equal(header.RefBase[:hashSize], base) {
+				t.Fatalf("round trip ref base mismatch")
+			}
+
+			if header.HeaderLen != len(data) {
+				t.Fatalf("round trip header len = %d, want %d", header.HeaderLen, len(data))
+			}
+		})
+	}
+}
+
+func TestOfsDeltaHeaderRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	data := packfile.AppendTypeSize(nil, packfile.EntryTypeOfsDelta, 7)
+	data = packfile.AppendOfsDeltaDistance(data, 123456)
+
+	header, err := packfile.ParseEntryHeader(data, 20)
+	if err != nil {
+		t.Fatalf("ParseEntryHeader: %v", err)
+	}
+
+	if header.OfsDistance != 123456 {
+		t.Fatalf("round trip distance = %d, want 123456", header.OfsDistance)
+	}
+
+	if header.HeaderLen != len(data) {
+		t.Fatalf("round trip header len = %d, want %d", header.HeaderLen, len(data))
+	}
+}
+
+func TestMaxEntryHeaderLenBounds(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		hashSize := objectFormat.Size()
+
+		maxLen := packfile.MaxEntryHeaderLen(hashSize)
+		if maxLen < packfile.MaxTypeSizeLen+hashSize {
+			t.Fatalf("MaxEntryHeaderLen(%d) = %d cannot fit a ref-delta header", hashSize, maxLen)
+		}
+
+		if maxLen < packfile.MaxTypeSizeLen+packfile.MaxOfsDeltaDistanceLen {
+			t.Fatalf("MaxEntryHeaderLen(%d) = %d cannot fit an ofs-delta header", hashSize, maxLen)
+		}
+	}
+}