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"
)
var (
// ErrUnsupportedVersion is returned by OpenFileIndex when the commit graph
// file version is not supported.
ErrUnsupportedVersion = errors.New("unsupported version")
// ErrUnsupportedHash is returned by OpenFileIndex when the commit graph
// hash function is not supported. Currently only SHA-1 is defined and
// supported
ErrUnsupportedHash = errors.New("unsupported hash algorithm")
// ErrMalformedCommitGraphFile is returned by OpenFileIndex when the commit
// graph file is corrupted.
ErrMalformedCommitGraphFile = errors.New("malformed commit graph file")
commitFileSignature = []byte{'C', 'G', 'P', 'H'}
oidFanoutSignature = []byte{'O', 'I', 'D', 'F'}
oidLookupSignature = []byte{'O', 'I', 'D', 'L'}
commitDataSignature = []byte{'C', 'D', 'A', 'T'}
extraEdgeListSignature = []byte{'E', 'D', 'G', 'E'}
lastSignature = []byte{0, 0, 0, 0}
parentNone = uint32(0x70000000)
parentOctopusUsed = uint32(0x80000000)
parentOctopusMask = uint32(0x7fffffff)
parentLast = uint32(0x80000000)
)
const commitDataSize = 16
type fileIndex struct {
reader io.ReaderAt
fanout [256]int
oidFanoutOffset int64
oidLookupOffset int64
commitDataOffset int64
extraEdgeListOffset int64
}
// OpenFileIndex opens a serialized commit graph file in the format described at
// https://github.com/git/git/blob/master/Documentation/technical/commit-graph-format.txt
func OpenFileIndex(reader io.ReaderAt) (Index, error) {
fi := &fileIndex{reader: reader}
if err := fi.verifyFileHeader(); err != nil {
return nil, err
}
if err := fi.readChunkHeaders(); err != nil {
return nil, err
}
if err := fi.readFanout(); err != nil {
return nil, err
}
return fi, nil
}
func (fi *fileIndex) verifyFileHeader() error {
// Verify file signature
signature := make([]byte, 4)
if _, err := fi.reader.ReadAt(signature, 0); err != nil {
return err
}
if !bytes.Equal(signature, commitFileSignature) {
return ErrMalformedCommitGraphFile
}
// Read and verify the file header
header := make([]byte, 4)
if _, err := fi.reader.ReadAt(header, 4); err != nil {
return err
}
if header[0] != 1 {
return ErrUnsupportedVersion
}
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 {
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 {
return err
}
chunkOffset, err := binary.ReadUint64(chunkHeader)
if err != nil {
return err
}
if bytes.Equal(chunkID, oidFanoutSignature) {
fi.oidFanoutOffset = int64(chunkOffset)
} else if bytes.Equal(chunkID, oidLookupSignature) {
fi.oidLookupOffset = int64(chunkOffset)
} else if bytes.Equal(chunkID, commitDataSignature) {
fi.commitDataOffset = int64(chunkOffset)
} else if bytes.Equal(chunkID, extraEdgeListSignature) {
fi.extraEdgeListOffset = int64(chunkOffset)
} else if bytes.Equal(chunkID, lastSignature) {
break
}
}
if fi.oidFanoutOffset <= 0 || fi.oidLookupOffset <= 0 || fi.commitDataOffset <= 0 {
return ErrMalformedCommitGraphFile
}
return nil
}
func (fi *fileIndex) readFanout() error {
fanoutReader := io.NewSectionReader(fi.reader, fi.oidFanoutOffset, 256*4)
for i := 0; i < 256; i++ {
fanoutValue, err := binary.ReadUint32(fanoutReader)
if err != nil {
return err
}
if fanoutValue > 0x7fffffff {
return ErrMalformedCommitGraphFile
}
fi.fanout[i] = int(fanoutValue)
}
return nil
}
func (fi *fileIndex) GetIndexByHash(h plumbing.Hash) (int, error) {
var oid plumbing.Hash
// Find the hash in the oid lookup table
var low int
if h[0] == 0 {
low = 0
} else {
low = fi.fanout[h[0]-1]
}
high := fi.fanout[h[0]]
for low < high {
mid := (low + high) >> 1
offset := fi.oidLookupOffset + int64(mid)*hash.Size
if _, err := fi.reader.ReadAt(oid[:], offset); err != nil {
return 0, err
}
cmp := bytes.Compare(h[:], oid[:])
if cmp < 0 {
high = mid
} else if cmp == 0 {
return mid, nil
} else {
low = mid + 1
}
}
return 0, plumbing.ErrObjectNotFound
}
func (fi *fileIndex) GetCommitDataByIndex(idx int) (*CommitData, error) {
if idx >= fi.fanout[0xff] {
return nil, plumbing.ErrObjectNotFound
}
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 {
return nil, err
}
parent1, err := binary.ReadUint32(commitDataReader)
if err != nil {
return nil, err
}
parent2, err := binary.ReadUint32(commitDataReader)
if err != nil {
return nil, err
}
genAndTime, err := binary.ReadUint64(commitDataReader)
if err != nil {
return nil, err
}
var parentIndexes []int
if parent2&parentOctopusUsed == parentOctopusUsed {
// Octopus merge
parentIndexes = []int{int(parent1 & parentOctopusMask)}
offset := fi.extraEdgeListOffset + 4*int64(parent2&parentOctopusMask)
buf := make([]byte, 4)
for {
_, err := fi.reader.ReadAt(buf, offset)
if err != nil {
return nil, err
}
parent := encbin.BigEndian.Uint32(buf)
offset += 4
parentIndexes = append(parentIndexes, int(parent&parentOctopusMask))
if parent&parentLast == parentLast {
break
}
}
} else if parent2 != parentNone {
parentIndexes = []int{int(parent1 & parentOctopusMask), int(parent2 & parentOctopusMask)}
} else if parent1 != parentNone {
parentIndexes = []int{int(parent1 & parentOctopusMask)}
}
parentHashes, err := fi.getHashesFromIndexes(parentIndexes)
if err != nil {
return nil, err
}
return &CommitData{
TreeHash: treeHash,
ParentIndexes: parentIndexes,
ParentHashes: parentHashes,
Generation: int(genAndTime >> 34),
When: time.Unix(int64(genAndTime&0x3FFFFFFFF), 0),
}, nil
}
func (fi *fileIndex) getHashesFromIndexes(indexes []int) ([]plumbing.Hash, error) {
hashes := make([]plumbing.Hash, len(indexes))
for i, idx := range indexes {
if idx >= fi.fanout[0xff] {
return nil, ErrMalformedCommitGraphFile
}
offset := fi.oidLookupOffset + int64(idx)*hash.Size
if _, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil {
return nil, err
}
}
return hashes, nil
}
// Hashes returns all the hashes that are available in the index
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)*hash.Size
if n, err := fi.reader.ReadAt(hashes[i][:], offset); err != nil || n < hash.Size {
return nil
}
}
return hashes
}
