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// Package objectid provides utilities around object IDs and hash algorithms.
package objectid
import (
"crypto/sha1"
"crypto/sha256"
"encoding/hex"
"errors"
"fmt"
"hash"
)
var (
// ErrInvalidAlgorithm indicates an unsupported object ID algorithm.
ErrInvalidAlgorithm = errors.New("objectid: invalid algorithm")
// ErrInvalidObjectID indicates malformed object ID data.
ErrInvalidObjectID = errors.New("objectid: invalid object id")
)
// maxObjectIDSize MUST be >= the largest supported algorithm size.
const maxObjectIDSize = sha256.Size
// Algorithm identifies the hash algorithm used for Git object IDs.
type Algorithm uint8
const (
AlgorithmUnknown Algorithm = iota
AlgorithmSHA1
AlgorithmSHA256
)
type algorithmDetails struct {
name string
size int
sum func([]byte) ObjectID
new func() hash.Hash
}
var algorithmTable = [...]algorithmDetails{
AlgorithmUnknown: {},
AlgorithmSHA1: {
name: "sha1",
size: sha1.Size,
sum: func(data []byte) ObjectID {
sum := sha1.Sum(data)
var id ObjectID
copy(id.data[:], sum[:])
id.algo = AlgorithmSHA1
return id
},
new: func() hash.Hash {
return sha1.New()
},
},
AlgorithmSHA256: {
name: "sha256",
size: sha256.Size,
sum: func(data []byte) ObjectID {
sum := sha256.Sum256(data)
var id ObjectID
copy(id.data[:], sum[:])
id.algo = AlgorithmSHA256
return id
},
new: func() hash.Hash {
return sha256.New()
},
},
}
var algorithmByName = map[string]Algorithm{}
var supportedAlgorithms []Algorithm
func init() {
for algo, info := range algorithmTable {
if info.name == "" {
continue
}
parsed := Algorithm(algo)
algorithmByName[info.name] = parsed
supportedAlgorithms = append(supportedAlgorithms, parsed)
}
}
func (algo Algorithm) info() algorithmDetails {
return algorithmTable[algo]
}
// SupportedAlgorithms returns all object ID algorithms supported by furgit.
// Do not mutate.
func SupportedAlgorithms() []Algorithm {
return supportedAlgorithms
}
// ParseAlgorithm parses a canonical algorithm name (e.g. "sha1", "sha256").
func ParseAlgorithm(s string) (Algorithm, bool) {
algo, ok := algorithmByName[s]
return algo, ok
}
// Size returns the hash size in bytes.
func (algo Algorithm) Size() int {
return algo.info().size
}
// String returns the canonical algorithm name.
func (algo Algorithm) String() string {
inf := algo.info()
if inf.name == "" {
return "unknown"
}
return inf.name
}
// HexLen returns the encoded hexadecimal length.
func (algo Algorithm) HexLen() int {
return algo.Size() * 2
}
// Sum computes an object ID from raw data using the selected algorithm.
func (algo Algorithm) Sum(data []byte) ObjectID {
return algo.info().sum(data)
}
// New returns a new hash.Hash for this algorithm.
func (algo Algorithm) New() (hash.Hash, error) {
newFn := algo.info().new
if newFn == nil {
return nil, ErrInvalidAlgorithm
}
return newFn(), nil
}
// ObjectID represents a Git object ID.
type ObjectID struct {
algo Algorithm
data [maxObjectIDSize]byte
}
// Algorithm returns the object ID's hash algorithm.
func (id ObjectID) Algorithm() Algorithm {
return id.algo
}
// Size returns the object ID size in bytes.
func (id ObjectID) Size() int {
return id.algo.Size()
}
// String returns the canonical hex representation.
func (id ObjectID) String() string {
size := id.Size()
return hex.EncodeToString(id.data[:size])
}
// Bytes returns a copy of the object ID bytes.
func (id ObjectID) Bytes() []byte {
size := id.Size()
return append([]byte(nil), id.data[:size]...)
}
// RawBytes returns a direct byte slice view of the object ID bytes.
//
// The returned slice aliases the object ID's internal storage. Callers MUST
// treat it as read-only and MUST NOT modify its contents.
//
// Use Bytes when an independent copy is required.
func (id *ObjectID) RawBytes() []byte {
size := id.Size()
return id.data[:size:size]
}
// ParseHex parses an object ID from hex for the specified algorithm.
func ParseHex(algo Algorithm, s string) (ObjectID, error) {
var id ObjectID
if algo.Size() == 0 {
return id, ErrInvalidAlgorithm
}
if len(s)%2 != 0 {
return id, fmt.Errorf("%w: odd hex length %d", ErrInvalidObjectID, len(s))
}
if len(s) != algo.HexLen() {
return id, fmt.Errorf("%w: got %d chars, expected %d", ErrInvalidObjectID, len(s), algo.HexLen())
}
decoded, err := hex.DecodeString(s)
if err != nil {
return id, fmt.Errorf("%w: decode: %v", ErrInvalidObjectID, err)
}
copy(id.data[:], decoded)
id.algo = algo
return id, nil
}
// FromBytes builds an object ID from raw bytes for the specified algorithm.
func FromBytes(algo Algorithm, b []byte) (ObjectID, error) {
var id ObjectID
if algo.Size() == 0 {
return id, ErrInvalidAlgorithm
}
if len(b) != algo.Size() {
return id, fmt.Errorf("%w: got %d bytes, expected %d", ErrInvalidObjectID, len(b), algo.Size())
}
copy(id.data[:], b)
id.algo = algo
return id, nil
}
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