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|
package objects
import (
"bytes"
"encoding/hex"
"errors"
"fmt"
"golang.org/x/crypto/sha3"
"hash"
"io"
"strings"
)
type ObjectIdAlgo string
const (
OIdAlgoSHA3_256 ObjectIdAlgo = "sha3-256"
OIdAlgoDefault = OIdAlgoSHA3_256
)
var allowedAlgos = map[ObjectIdAlgo]struct{}{OIdAlgoSHA3_256: {}}
func (algo ObjectIdAlgo) checkAlgo() bool {
_, ok := allowedAlgos[algo]
return ok
}
func (algo ObjectIdAlgo) sumLength() int {
if algo != OIdAlgoSHA3_256 {
panic("Only sha3-256 is implemented!")
}
return 32
}
// ObjectId identifies an object using a cryptogrpahic hash
type ObjectId struct {
Algo ObjectIdAlgo
Sum []byte
}
func (oid ObjectId) wellformed() bool {
return oid.Algo.checkAlgo() && len(oid.Sum) == oid.Algo.sumLength()
}
func (oid ObjectId) String() string {
return fmt.Sprintf("%s:%s", oid.Algo, hex.EncodeToString(oid.Sum))
}
func ParseObjectId(s string) (oid ObjectId, err error) {
parts := strings.SplitN(s, ":", 2)
if len(parts) != 2 {
err = errors.New("Invalid ObjectId format")
return
}
oid.Algo = ObjectIdAlgo(parts[0])
oid.Sum, err = hex.DecodeString(parts[1])
if err != nil {
return
}
if !oid.wellformed() {
err = errors.New("Object ID is malformed")
}
return
}
func MustParseObjectId(s string) ObjectId {
id, err := ParseObjectId(s)
if err != nil {
panic(err)
}
return id
}
func (a ObjectId) Equals(b ObjectId) bool {
return a.Algo == b.Algo && bytes.Equal(a.Sum, b.Sum)
}
// ObjectIdGenerator generates an ObjectId from the binary representation of an object
type ObjectIdGenerator interface {
io.Writer // Must not fail
GetId() ObjectId
}
func (algo ObjectIdAlgo) Generator() ObjectIdGenerator {
if algo != OIdAlgoSHA3_256 {
panic("Only sha3-256 is implemented!")
}
return hashObjectIdGenerator{
algo: algo,
Hash: sha3.New256(),
}
}
type hashObjectIdGenerator struct {
algo ObjectIdAlgo
hash.Hash
}
func (h hashObjectIdGenerator) GetId() ObjectId {
return ObjectId{
Algo: h.algo,
Sum: h.Sum([]byte{}),
}
}
func (oid ObjectId) VerifyObject(o RawObject) bool {
gen := oid.Algo.Generator()
if err := o.Serialize(gen); err != nil {
panic(err)
}
return gen.GetId().Equals(oid)
}
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