plumbing: commitgraph, allow SHA256 commit-graphs

Since the build-tag sha256 was introduced the commit graph code should
be switched to use hash.Size and only use a graph if it has the correct
hash version for the version of go-git that is built.

Signed-off-by: Andrew Thornton <art27@cantab.net>

2 files changed, 31 insertions, 13 deletions

diff --git a/plumbing/format/commitgraph/encoder.go b/plumbing/format/commitgraph/encoder.go
index f61025b..674f52e 100644
--- a/plumbing/format/commitgraph/encoder.go
+++ b/plumbing/format/commitgraph/encoder.go
@@ -1,6 +1,7 @@
 package commitgraph

 

 import (

+	"crypto"

 	"io"

 

 	"github.com/go-git/go-git/v5/plumbing"

@@ -30,7 +31,7 @@ func (e *Encoder) Encode(idx Index) error {
 	hashToIndex, fanout, extraEdgesCount := e.prepare(idx, hashes)

 

 	chunkSignatures := [][]byte{oidFanoutSignature, oidLookupSignature, commitDataSignature}

-	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * hash.Size, uint64(len(hashes)) * 36}

+	chunkSizes := []uint64{4 * 256, uint64(len(hashes)) * hash.Size, uint64(len(hashes)) * (hash.Size + commitDataSize)}

 	if extraEdgesCount > 0 {

 		chunkSignatures = append(chunkSignatures, extraEdgeListSignature)

 		chunkSizes = append(chunkSizes, uint64(extraEdgesCount)*4)

@@ -88,7 +89,11 @@ func (e *Encoder) prepare(idx Index, hashes []plumbing.Hash) (hashToIndex map[pl
 

 func (e *Encoder) encodeFileHeader(chunkCount int) (err error) {

 	if _, err = e.Write(commitFileSignature); err == nil {

-		_, err = e.Write([]byte{1, 1, byte(chunkCount), 0})

+		version := byte(1)

+		if hash.CryptoType == crypto.SHA256 {

+			version = byte(2)

+		}

+		_, err = e.Write([]byte{1, version, byte(chunkCount), 0})

 	}

 	return

 }

diff --git a/plumbing/format/commitgraph/file.go b/plumbing/format/commitgraph/file.go
index 1d25238..17c1c5d 100644
--- a/plumbing/format/commitgraph/file.go
+++ b/plumbing/format/commitgraph/file.go
@@ -2,12 +2,14 @@ package commitgraph
 

 import (

 	"bytes"

+	"crypto"

 	encbin "encoding/binary"

 	"errors"

 	"io"

 	"time"

 

 	"github.com/go-git/go-git/v5/plumbing"

+	"github.com/go-git/go-git/v5/plumbing/hash"

 	"github.com/go-git/go-git/v5/utils/binary"

 )

 

@@ -36,6 +38,8 @@ var (
 	parentLast        = uint32(0x80000000)

 )

 

+const commitDataSize = 16

+

 type fileIndex struct {

 	reader              io.ReaderAt

 	fanout              [256]int

@@ -65,7 +69,7 @@ func OpenFileIndex(reader io.ReaderAt) (Index, error) {
 

 func (fi *fileIndex) verifyFileHeader() error {

 	// Verify file signature

-	var signature = make([]byte, 4)

+	signature := make([]byte, 4)

 	if _, err := fi.reader.ReadAt(signature, 0); err != nil {

 		return err

 	}

@@ -74,22 +78,31 @@ func (fi *fileIndex) verifyFileHeader() error {
 	}

 

 	// Read and verify the file header

-	var header = make([]byte, 4)

+	header := make([]byte, 4)

 	if _, err := fi.reader.ReadAt(header, 4); err != nil {

 		return err

 	}

 	if header[0] != 1 {

 		return ErrUnsupportedVersion

 	}

-	if header[1] != 1 {

-		return ErrUnsupportedHash

+	if hash.CryptoType == crypto.SHA1 {

+		if header[1] != 1 {

+			return ErrUnsupportedVersion

+		}

+	} else if hash.CryptoType == crypto.SHA256 {

+		if header[1] != 2 {

+			return ErrUnsupportedVersion

+		}

+	} else {

+		// Unknown hash type

+		return ErrUnsupportedVersion

 	}

 

 	return nil

 }

 

 func (fi *fileIndex) readChunkHeaders() error {

-	var chunkID = make([]byte, 4)

+	chunkID := make([]byte, 4)

 	for i := 0; ; i++ {

 		chunkHeader := io.NewSectionReader(fi.reader, 8+(int64(i)*12), 12)

 		if _, err := io.ReadAtLeast(chunkHeader, chunkID, 4); err != nil {

@@ -148,7 +161,7 @@ func (fi *fileIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
 	high := fi.fanout[h[0]]

 	for low < high {

 		mid := (low + high) >> 1

-		offset := fi.oidLookupOffset + int64(mid)*20

+		offset := fi.oidLookupOffset + int64(mid)*hash.Size

 		if _, err := fi.reader.ReadAt(oid[:], offset); err != nil {

 			return 0, err

 		}

@@ -170,8 +183,8 @@ func (fi *fileIndex) GetCommitDataByIndex(idx int) (*CommitData, error) {
 		return nil, plumbing.ErrObjectNotFound

 	}

 

-	offset := fi.commitDataOffset + int64(idx)*36

-	commitDataReader := io.NewSectionReader(fi.reader, offset, 36)

+	offset := fi.commitDataOffset + int64(idx)*(hash.Size+commitDataSize)

+	commitDataReader := io.NewSectionReader(fi.reader, offset, hash.Size+commitDataSize)

 

 	treeHash, err := binary.ReadHash(commitDataReader)

 	if err != nil {

@@ -237,7 +250,7 @@ func (fi *fileIndex) getHashesFromIndexes(indexes []int) ([]plumbing.Hash, error
 			return nil, ErrMalformedCommitGraphFile

 		}

 

-		offset := fi.oidLookupOffset + int64(idx)*20

+		offset := fi.oidLookupOffset + int64(idx)*hash.Size

 		if _, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil {

 			return nil, err

 		}

@@ -250,8 +263,8 @@ func (fi *fileIndex) getHashesFromIndexes(indexes []int) ([]plumbing.Hash, error
 func (fi *fileIndex) Hashes() []plumbing.Hash {

 	hashes := make([]plumbing.Hash, fi.fanout[0xff])

 	for i := 0; i < fi.fanout[0xff]; i++ {

-		offset := fi.oidLookupOffset + int64(i)*20

-		if n, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil || n < 20 {

+		offset := fi.oidLookupOffset + int64(i)*hash.Size

+		if n, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil || n < hash.Size {

 			return nil

 		}

 	}