From 2251f34f5cbd7fb8a2b54ecd7cd592dbd34e85e2 Mon Sep 17 00:00:00 2001
From: Runxi Yu
Date: Thu, 11 Jun 2026 14:31:21 +0000
Subject: internal/format/packidx: Add lookup tests

---
 internal/format/packidx/lookup_test.go | 99 ++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 internal/format/packidx/lookup_test.go

diff --git a/internal/format/packidx/lookup_test.go b/internal/format/packidx/lookup_test.go
new file mode 100644
index 00000000..514aad7a
--- /dev/null
+++ b/internal/format/packidx/lookup_test.go
@@ -0,0 +1,99 @@
+package packidx_test
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"testing"
+
+	"lindenii.org/go/furgit/internal/format/packidx"
+	"lindenii.org/go/furgit/object/id"
+)
+
+func TestLookupGitIndex(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			repo, prefix, oids := makeGitPack(t, objectFormat)
+			_, idx := parseGitIdxFile(t, prefix, objectFormat)
+
+			wantOffsets := gitPackOffsets(t, repo, prefix+".idx", objectFormat)
+			if len(wantOffsets) != len(oids) {
+				t.Fatalf("verify-pack offsets = %d entries, want %d", len(wantOffsets), len(oids))
+			}
+
+			for _, oid := range oids {
+				offset, found, err := idx.Lookup(oid.RawBytes())
+				if err != nil {
+					t.Fatalf("Lookup(%s): %v", oid, err)
+				}
+
+				if !found {
+					t.Fatalf("Lookup(%s) not found", oid)
+				}
+
+				if offset != wantOffsets[oid.String()] {
+					t.Fatalf("Lookup(%s) = %d, want %d", oid, offset, wantOffsets[oid.String()])
+				}
+			}
+		})
+	}
+}
+
+func TestLookupMissing(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)
+
+			missing := bytes.Clone(oids[0].RawBytes())
+			missing[len(missing)-1] ^= 0xff
+
+			_, found, err := idx.Lookup(missing)
+			if err != nil {
+				t.Fatalf("Lookup: %v", err)
+			}
+
+			if found {
+				t.Fatalf("Lookup of mutated oid unexpectedly found")
+			}
+		})
+	}
+}
+
+func TestOffsetAtMalformedLargeReference(t *testing.T) {
+	t.Parallel()
+
+	for _, objectFormat := range id.SupportedObjectFormats() {
+		t.Run(objectFormat.String(), func(t *testing.T) {
+			t.Parallel()
+
+			hashSize := objectFormat.Size()
+
+			entries := syntheticEntries(3)
+			data := writeSyntheticIndex(t, objectFormat, entries)
+
+			// Mark the first 32-bit offset entry as a 64-bit reference;
+			// the index has no 64-bit offset table.
+			off32Off := 8 + 256*4 + len(entries)*hashSize + len(entries)*4
+			binary.BigEndian.PutUint32(data[off32Off:], 0x80000000)
+
+			idx, err := packidx.Parse(data, hashSize)
+			if err != nil {
+				t.Fatalf("Parse: %v", err)
+			}
+
+			_, err = idx.OffsetAt(0)
+			if !errors.Is(err, packidx.ErrMalformedPackIndex) {
+				t.Fatalf("OffsetAt error = %v, want ErrMalformedPackIndex", err)
+			}
+		})
+	}
+}
-- 
cgit v1.3.1-10-gc9f91