From b1f08819620a238ba09f8f7199e67cf0c13afc97 Mon Sep 17 00:00:00 2001
From: Runxi Yu
Date: Thu, 11 Jun 2026 08:21:21 +0000
Subject: internal/format/packfile: Return ErrInvalidHashSize on
 ParseEntryHeader

---
 internal/format/packfile/entry_header.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/internal/format/packfile/entry_header.go b/internal/format/packfile/entry_header.go
index 04d529d5..1428600b 100644
--- a/internal/format/packfile/entry_header.go
+++ b/internal/format/packfile/entry_header.go
@@ -13,6 +13,12 @@ import (
 // or declares a size that overflows uint64.
 var ErrMalformedEntryHeader = errors.New("internal/format/packfile: malformed entry header")
 
+// ErrInvalidHashSize reports that
+// a supplied hash size is not a plausible object ID size.
+// This indicates a caller bug,
+// not malformed pack data.
+var ErrInvalidHashSize = errors.New("internal/format/packfile: invalid hash size")
+
 // MaxTypeSizeLen is the maximum encoded length
 // of the type/size prefix of an entry header.
 // Every uint64 size is encodable within this bound,
@@ -77,7 +83,7 @@ func ParseEntryHeader(data []byte, hashSize int) (EntryHeader, error) {
 	var zero EntryHeader
 
 	if hashSize <= 0 || hashSize > id.MaxObjectIDSize {
-		return zero, fmt.Errorf("internal/format/packfile: invalid hash size %d", hashSize)
+		return zero, fmt.Errorf("%w: %d", ErrInvalidHashSize, hashSize)
 	}
 
 	if len(data) == 0 {
-- 
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