From 454a3f8e491f84ce19aab0d3873062f5ccc2330e Mon Sep 17 00:00:00 2001
From: Runxi Yu
Date: Thu, 11 Jun 2026 14:23:49 +0000
Subject: internal/format/packidx: Add pack index parse tests

---
 internal/format/packidx/packidx_test.go | 124 ++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 internal/format/packidx/packidx_test.go

(limited to 'internal/format')

diff --git a/internal/format/packidx/packidx_test.go b/internal/format/packidx/packidx_test.go
new file mode 100644
index 00000000..d225a993
--- /dev/null
+++ b/internal/format/packidx/packidx_test.go
@@ -0,0 +1,124 @@
+package packidx_test
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"os"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packidx"
+	"lindenii.org/go/furgit/object/id"
+)
+
+func TestParseGitIndex(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			_, prefix, oids := makeGitPack(t, objectFormat)
+			_, idx := parseGitIdxFile(t, prefix, objectFormat)
+
+			if idx.NumObjects() != len(oids) {
+				t.Fatalf("NumObjects = %d, want %d", idx.NumObjects(), len(oids))
+			}
+
+			for pos := 1; pos < idx.NumObjects(); pos++ {
+				if bytes.Compare(idx.OIDAt(pos-1), idx.OIDAt(pos)) >= 0 {
+					t.Fatalf("OIDAt(%d) not sorted after predecessor", pos)
+				}
+			}
+
+			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(idx.PackHash(), packTrailer) {
+				t.Fatalf("PackHash does not match pack trailer")
+			}
+		})
+	}
+}
+
+func TestParseMalformed(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			hashSize := objectFormat.Size()
+
+			valid := writeSyntheticIndex(t, objectFormat, syntheticEntries(8))
+
+			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[:20] })},
+				{
+					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] = 3
+
+						return d
+					}),
+				},
+				{
+					name: "non-monotonic fanout",
+					data: corrupt(func(d []byte) []byte {
+						binary.BigEndian.PutUint32(d[8:], 0xffffffff)
+
+						return d
+					}),
+				},
+				{
+					name: "tables exceed index size",
+					data: corrupt(func(d []byte) []byte {
+						binary.BigEndian.PutUint32(d[8+255*4:], 0x00ffffff)
+
+						return d
+					}),
+				},
+				{
+					name: "trailing size not 64-bit multiple",
+					data: corrupt(func(d []byte) []byte { return append(d, 0xde, 0xad, 0xbe, 0xef) }),
+				},
+				{
+					name: "more 64-bit offsets than objects",
+					data: corrupt(func(d []byte) []byte {
+						return append(d, bytes.Repeat([]byte{0x00}, 9*8)...)
+					}),
+				},
+			}
+
+			for _, tc := range cases {
+				t.Run(tc.name, func(t *testing.T) {
+					t.Parallel()
+
+					_, err := packidx.Parse(tc.data, hashSize)
+					if !errors.Is(err, packidx.ErrMalformedPackIndex) {
+						t.Fatalf("Parse error = %v, want ErrMalformedPackIndex", err)
+					}
+				})
+			}
+		})
+	}
+}
-- 
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