ref: bd9519b464f919f2ca174a45c3c19c9a8a1fe3d1
parent: c0d1cc442031c8200df4a3a499c07081fab40553
author: Runxi Yu <me@runxiyu.org>
date: Tue Mar 3 13:26:57 EST 2026
objectstore/packed: Check pack/idx checksums here. We previously had helpers in format/pack/checksum that checks .pack/.idx-related checksums with []byte-based APIs. But it only really makes sense to use those []byte-based APIs on mmap's (otherwise it'd be horribly inefficient). Since the packed object-store only needs to check that the .pack and .idx trailer match, we move the relevant part into objectstore/packed. The rest are deleted for now; we'll definitely need a streaming version for the pack verification (when ingesting packfiles from the network) (though we might just make it a streaming API (writer? reader? not decided yet) that *produces* a hash, then verify it in the caller; this way we could reuse the function in the pack-producing routines). The others might get the []byte-based APIs back, or perhaps they too get streaming APIs. Remember that "reading objects from a packed object store", "creating/writing packfiles", and "ingesting an incoming pack (which usually involves creating an .idx for it)", are all very different tasks.
--- a/format/pack/checksum/checksum.go
+++ /dev/null
@@ -1,108 +1,0 @@
-// Package checksum provides Git pack/index checksum primitives.
-package checksum
-
-import (
- "bytes"
- "fmt"
-
- "codeberg.org/lindenii/furgit/objectid"
-)
-
-// VerifyPackTrailer verifies one pack trailer hash against the pack payload.
-//
-// This computes the object hash over all bytes except the trailing hash, so it
-// is O(pack size).
-func VerifyPackTrailer(data []byte, algo objectid.Algorithm) error {- hashSize := algo.Size()
- if hashSize <= 0 {- return objectid.ErrInvalidAlgorithm
- }
- if len(data) < hashSize {- return fmt.Errorf("format/pack/checksum: pack too short for trailer hash")- }
-
- hash, err := algo.New()
- if err != nil {- return err
- }
- if _, err := hash.Write(data[:len(data)-hashSize]); err != nil {- return err
- }
- computed := hash.Sum(nil)
- trailer := data[len(data)-hashSize:]
- if !bytes.Equal(computed, trailer) {- return fmt.Errorf("format/pack/checksum: pack trailer hash mismatch")- }
- return nil
-}
-
-// PackTrailerHash returns the trailer hash bytes from one pack file.
-func PackTrailerHash(data []byte, algo objectid.Algorithm) ([]byte, error) {- hashSize := algo.Size()
- if hashSize <= 0 {- return nil, objectid.ErrInvalidAlgorithm
- }
- if len(data) < hashSize {- return nil, fmt.Errorf("format/pack/checksum: pack too short for trailer hash")- }
- return data[len(data)-hashSize:], nil
-}
-
-// ParseIdxTrailer parses one idx v2 trailer and returns (packHash, idxHash).
-func ParseIdxTrailer(data []byte, algo objectid.Algorithm) ([]byte, []byte, error) {- hashSize := algo.Size()
- if hashSize <= 0 {- return nil, nil, objectid.ErrInvalidAlgorithm
- }
- if len(data) < hashSize*2 {- return nil, nil, fmt.Errorf("format/pack/checksum: idx too short for trailer hashes")- }
- packHashOff := len(data) - hashSize*2
- idxHashOff := len(data) - hashSize
- return data[packHashOff:idxHashOff], data[idxHashOff:], nil
-}
-
-// VerifyIdxTrailer verifies one idx trailer checksum against preceding bytes.
-func VerifyIdxTrailer(data []byte, algo objectid.Algorithm) error {- hashSize := algo.Size()
- if hashSize <= 0 {- return objectid.ErrInvalidAlgorithm
- }
- if len(data) < hashSize*2 {- return fmt.Errorf("format/pack/checksum: idx too short for trailer hashes")- }
-
- _, idxHash, err := ParseIdxTrailer(data, algo)
- if err != nil {- return err
- }
- hash, err := algo.New()
- if err != nil {- return err
- }
- if _, err := hash.Write(data[:len(data)-hashSize]); err != nil {- return err
- }
- computed := hash.Sum(nil)
- if !bytes.Equal(computed, idxHash) {- return fmt.Errorf("format/pack/checksum: idx trailer hash mismatch")- }
- return nil
-}
-
-// VerifyPackMatchesIdx compares a pack trailer hash with one idx-recorded pack
-// hash.
-func VerifyPackMatchesIdx(packData, idxData []byte, algo objectid.Algorithm) error {- packTrailerHash, err := PackTrailerHash(packData, algo)
- if err != nil {- return err
- }
- idxPackHash, _, err := ParseIdxTrailer(idxData, algo)
- if err != nil {- return err
- }
- if !bytes.Equal(packTrailerHash, idxPackHash) {- return fmt.Errorf("format/pack/checksum: pack hash does not match idx")- }
- return nil
-}
--- /dev/null
+++ b/objectstore/packed/pack_idx_checksum.go
@@ -1,0 +1,30 @@
+package packed
+
+import (
+ "bytes"
+ "fmt"
+
+ "codeberg.org/lindenii/furgit/objectid"
+)
+
+// verifyMappedPackMatchesMappedIdx compares one mapped pack trailer hash with
+// the pack hash recorded in one mapped idx trailer.
+func verifyMappedPackMatchesMappedIdx(packData, idxData []byte, algo objectid.Algorithm) error {+ hashSize := algo.Size()
+ if hashSize <= 0 {+ return objectid.ErrInvalidAlgorithm
+ }
+ if len(packData) < hashSize {+ return fmt.Errorf("objectstore/packed: pack too short for trailer hash")+ }
+ if len(idxData) < hashSize*2 {+ return fmt.Errorf("objectstore/packed: idx too short for trailer hashes")+ }
+
+ packTrailerHash := packData[len(packData)-hashSize:]
+ idxPackHash := idxData[len(idxData)-hashSize*2 : len(idxData)-hashSize]
+ if !bytes.Equal(packTrailerHash, idxPackHash) {+ return fmt.Errorf("objectstore/packed: pack hash does not match idx")+ }
+ return nil
+}
--- a/objectstore/packed/store.go
+++ b/objectstore/packed/store.go
@@ -7,7 +7,6 @@
"os"
"sync"
- packchecksum "codeberg.org/lindenii/furgit/format/pack/checksum"
"codeberg.org/lindenii/furgit/objectid"
"codeberg.org/lindenii/furgit/objectstore"
)
@@ -195,7 +194,7 @@
if err != nil {return err
}
- if err := packchecksum.VerifyPackMatchesIdx(pack.data, index.data, store.algo); err != nil {+ if err := verifyMappedPackMatchesMappedIdx(pack.data, index.data, store.algo); err != nil { return fmt.Errorf("objectstore/packed: pack %q does not match idx %q: %w", pack.name, index.idxName, err)}
return nil
--
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