internal/format/packrev: Add tests

3 files changed, 370 insertions, 0 deletions

diff --git a/internal/format/packrev/helpers_test.go b/internal/format/packrev/helpers_test.go
new file mode 100644
index 00000000..2ec2f434
--- /dev/null
+++ b/internal/format/packrev/helpers_test.go
@@ -0,0 +1,75 @@
+package packrev_test
+
+import (
+	"cmp"
+	"slices"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packidx"
+	"lindenii.org/go/furgit/internal/testgit"
+	"lindenii.org/go/furgit/object/id"
+	"lindenii.org/go/lgo/intconv"
+)
+
+// makeGitPack seeds a repository,
+// packs the seeded objects with git pack-objects
+// including a reverse index,
+// and returns the artifact path prefix.
+func makeGitPack(t *testing.T, objectFormat id.ObjectFormat) string {
+	t.Helper()
+
+	repo, err := testgit.NewRepo(t, testgit.RepoOptions{ObjectFormat: objectFormat})
+	if err != nil {
+		t.Fatalf("NewRepo: %v", err)
+	}
+
+	seeded, err := repo.SeedHistory(t)
+	if err != nil {
+		t.Fatalf("SeedHistory: %v", err)
+	}
+
+	prefix, err := repo.PackObjects(t, slices.Values(seeded.All()), testgit.PackObjectsOptions{RevIndex: true})
+	if err != nil {
+		t.Fatalf("PackObjects: %v", err)
+	}
+
+	return prefix
+}
+
+// packOrderPositions derives the pack-offset-order index positions
+// from one parsed pack index.
+func packOrderPositions(t *testing.T, idx *packidx.Packidx) []uint32 {
+	t.Helper()
+
+	type pair struct {
+		offset   uint64
+		position uint32
+	}
+
+	pairs := make([]pair, 0, idx.NumObjects())
+
+	for pos := range idx.NumObjects() {
+		offset, err := idx.OffsetAt(pos)
+		if err != nil {
+			t.Fatalf("OffsetAt(%d): %v", pos, err)
+		}
+
+		position, err := intconv.IntToUint32(pos)
+		if err != nil {
+			t.Fatalf("IntToUint32(%d): %v", pos, err)
+		}
+
+		pairs = append(pairs, pair{offset: offset, position: position})
+	}
+
+	slices.SortFunc(pairs, func(a, b pair) int {
+		return cmp.Compare(a.offset, b.offset)
+	})
+
+	positions := make([]uint32, 0, len(pairs))
+	for _, p := range pairs {
+		positions = append(positions, p.position)
+	}
+
+	return positions
+}
diff --git a/internal/format/packrev/packrev_test.go b/internal/format/packrev/packrev_test.go
new file mode 100644
index 00000000..b644e15e
--- /dev/null
+++ b/internal/format/packrev/packrev_test.go
@@ -0,0 +1,160 @@
+package packrev_test
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"os"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packidx"
+	"lindenii.org/go/furgit/internal/format/packrev"
+	"lindenii.org/go/furgit/object/id"
+)
+
+func TestParseGitReverseIndex(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			prefix := makeGitPack(t, objectFormat)
+
+			revData, err := os.ReadFile(prefix + ".rev") //nolint:gosec
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+
+			rev, err := packrev.Parse(revData, objectFormat)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+
+			idxData, err := os.ReadFile(prefix + ".idx") //nolint:gosec
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+
+			idx, err := packidx.Parse(idxData, objectFormat.Size())
+			if err != nil {
+				t.Fatalf("packidx.Parse: %v", err)
+			}
+
+			if rev.NumObjects() != idx.NumObjects() {
+				t.Fatalf("NumObjects = %d, want %d", rev.NumObjects(), idx.NumObjects())
+			}
+
+			packData, err := os.ReadFile(prefix + ".pack") //nolint:gosec
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+
+			packTrailer := packData[len(packData)-objectFormat.Size():]
+			if !bytes.Equal(rev.PackHash(), packTrailer) {
+				t.Fatalf("PackHash does not match pack trailer")
+			}
+
+			want := packOrderPositions(t, &idx)
+
+			for packOrder, wantPosition := range want {
+				position, err := rev.PositionAt(packOrder)
+				if err != nil {
+					t.Fatalf("PositionAt(%d): %v", packOrder, err)
+				}
+
+				if position != int(wantPosition) {
+					t.Fatalf("PositionAt(%d) = %d, want %d", packOrder, position, wantPosition)
+				}
+			}
+		})
+	}
+}
+
+func TestParseMalformed(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			valid := writeSyntheticRev(t, objectFormat, []uint32{2, 0, 1, 3})
+
+			corrupt := func(mutate func(data []byte) []byte) []byte {
+				return mutate(bytes.Clone(valid))
+			}
+
+			cases := []struct {
+				name string
+				data []byte
+			}{
+				{name: "empty", data: []byte{}},
+				{name: "truncated", data: corrupt(func(d []byte) []byte { return d[:10] })},
+				{
+					name: "bad signature",
+					data: corrupt(func(d []byte) []byte {
+						d[0] ^= 0xff
+
+						return d
+					}),
+				},
+				{
+					name: "bad version",
+					data: corrupt(func(d []byte) []byte {
+						d[7] = 2
+
+						return d
+					}),
+				},
+				{
+					name: "hash function mismatch",
+					data: corrupt(func(d []byte) []byte {
+						d[11] ^= 0xff
+
+						return d
+					}),
+				},
+				{
+					name: "position table size not 32-bit multiple",
+					data: corrupt(func(d []byte) []byte { return append(d, 0xde, 0xad) }),
+				},
+			}
+
+			for _, tc := range cases {
+				t.Run(tc.name, func(t *testing.T) {
+					t.Parallel()
+
+					_, err := packrev.Parse(tc.data, objectFormat)
+					if !errors.Is(err, packrev.ErrMalformedReverseIndex) {
+						t.Fatalf("Parse error = %v, want ErrMalformedReverseIndex", err)
+					}
+				})
+			}
+		})
+	}
+}
+
+func TestPositionAtMalformed(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			data := writeSyntheticRev(t, objectFormat, []uint32{2, 0, 1, 3})
+
+			// Corrupt the first stored position to one past the object count.
+			binary.BigEndian.PutUint32(data[12:], 4)
+
+			rev, err := packrev.Parse(data, objectFormat)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+
+			_, err = rev.PositionAt(0)
+			if !errors.Is(err, packrev.ErrMalformedReverseIndex) {
+				t.Fatalf("PositionAt error = %v, want ErrMalformedReverseIndex", err)
+			}
+		})
+	}
+}
diff --git a/internal/format/packrev/write_test.go b/internal/format/packrev/write_test.go
new file mode 100644
index 00000000..b5c1fcb9
--- /dev/null
+++ b/internal/format/packrev/write_test.go
@@ -0,0 +1,135 @@
+package packrev_test
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packidx"
+	"lindenii.org/go/furgit/internal/format/packrev"
+	"lindenii.org/go/furgit/object/id"
+)
+
+// writeSyntheticRev writes one reverse index over positions
+// with a fixed fake pack hash.
+func writeSyntheticRev(t *testing.T, objectFormat id.ObjectFormat, positions []uint32) []byte {
+	t.Helper()
+
+	packHash := bytes.Repeat([]byte{0x5a}, objectFormat.Size())
+
+	var buf bytes.Buffer
+
+	err := packrev.Write(&buf, objectFormat, positions, packHash)
+	if err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+
+	return buf.Bytes()
+}
+
+func TestWriteRoundTrip(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			positions := []uint32{8, 6, 7, 5, 3, 0, 4, 1, 2}
+			data := writeSyntheticRev(t, objectFormat, positions)
+
+			rev, err := packrev.Parse(data, objectFormat)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+
+			if rev.NumObjects() != len(positions) {
+				t.Fatalf("NumObjects = %d, want %d", rev.NumObjects(), len(positions))
+			}
+
+			if !bytes.Equal(rev.PackHash(), bytes.Repeat([]byte{0x5a}, objectFormat.Size())) {
+				t.Fatalf("PackHash mismatch")
+			}
+
+			for packOrder, want := range positions {
+				position, err := rev.PositionAt(packOrder)
+				if err != nil {
+					t.Fatalf("PositionAt(%d): %v", packOrder, err)
+				}
+
+				if position != int(want) {
+					t.Fatalf("PositionAt(%d) = %d, want %d", packOrder, position, want)
+				}
+			}
+		})
+	}
+}
+
+func TestWriteMatchesGit(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			prefix := makeGitPack(t, objectFormat)
+
+			gitData, err := os.ReadFile(prefix + ".rev") //nolint:gosec
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+
+			idxData, err := os.ReadFile(prefix + ".idx") //nolint:gosec
+			if err != nil {
+				t.Fatalf("ReadFile: %v", err)
+			}
+
+			idx, err := packidx.Parse(idxData, objectFormat.Size())
+			if err != nil {
+				t.Fatalf("packidx.Parse: %v", err)
+			}
+
+			positions := packOrderPositions(t, &idx)
+
+			var buf bytes.Buffer
+
+			err = packrev.Write(&buf, objectFormat, positions, idx.PackHash())
+			if err != nil {
+				t.Fatalf("Write: %v", err)
+			}
+
+			if !bytes.Equal(buf.Bytes(), gitData) {
+				t.Fatalf("Write output differs from git's reverse index (%d vs %d bytes)", buf.Len(), len(gitData))
+			}
+		})
+	}
+}
+
+func TestWriteInvalidPositions(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			packHash := bytes.Repeat([]byte{0x5a}, objectFormat.Size())
+
+			err := packrev.Write(&bytes.Buffer{}, objectFormat, []uint32{0, 5}, packHash)
+			if !errors.Is(err, packrev.ErrInvalidPositions) {
+				t.Fatalf("Write error = %v, want ErrInvalidPositions", err)
+			}
+		})
+	}
+}
+
+func TestWriteBadPackHashPanics(t *testing.T) {
+	t.Parallel()
+
+	defer func() {
+		if recover() == nil {
+			t.Fatalf("Write with short pack hash: expected panic")
+		}
+	}()
+
+	_ = packrev.Write(&bytes.Buffer{}, id.ObjectFormatSHA256, nil, []byte{0x01})
+}