dehub/hash.go

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package dehub
import (
"crypto/sha256"
"encoding/binary"
"fmt"
"hash"
"sort"
"gopkg.in/src-d/go-git.v4/plumbing/object"
)
var (
defaultHashHelperAlgo = sha256.New
)
type hashHelper struct {
hash.Hash
varintBuf []byte
}
// if h is nil it then defaultHashHelperAlgo will be used
func newHashHelper(h hash.Hash) *hashHelper {
if h == nil {
h = defaultHashHelperAlgo()
}
s := &hashHelper{
Hash: h,
varintBuf: make([]byte, binary.MaxVarintLen64),
}
return s
}
func (s *hashHelper) sum(prefix []byte) []byte {
out := make([]byte, len(prefix), len(prefix)+s.Hash.Size())
copy(out, prefix)
return s.Hash.Sum(out)
}
func (s *hashHelper) writeUint(i uint64) {
n := binary.PutUvarint(s.varintBuf, i)
if _, err := s.Write(s.varintBuf[:n]); err != nil {
panic(fmt.Sprintf("error writing %x to sha256 sum: %v", s.varintBuf[:n], err))
}
}
func (s *hashHelper) writeStr(str string) {
s.writeUint(uint64(len(str)))
s.Write([]byte(str))
}
func (s *hashHelper) writeTreeDiff(from, to *object.Tree) {
filesChanged, err := calcDiff(from, to)
if err != nil {
panic(err.Error())
}
sort.Slice(filesChanged, func(i, j int) bool {
return filesChanged[i].path < filesChanged[j].path
})
s.writeUint(uint64(len(filesChanged)))
for _, fileChanged := range filesChanged {
s.writeStr(fileChanged.path)
s.Write(fileChanged.fromMode.Bytes())
s.Write(fileChanged.fromHash[:])
s.Write(fileChanged.toMode.Bytes())
s.Write(fileChanged.toHash[:])
}
}
var (
changeHashVersion = []byte{0}
commentHashVersion = []byte{0}
)
// if h is nil it then defaultHashHelperAlgo will be used
func genChangeHash(h hash.Hash, msg string, from, to *object.Tree) []byte {
s := newHashHelper(h)
s.writeStr(msg)
s.writeTreeDiff(from, to)
return s.sum(changeHashVersion)
}
// if h is nil it then defaultHashHelperAlgo will be used
func genCommentHash(h hash.Hash, comment string) []byte {
s := newHashHelper(h)
s.writeStr(comment)
return s.sum(commentHashVersion)
}