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digest.go
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digest.go
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// Copyright 2020-2023 Buf Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package manifest
import (
"bytes"
"encoding/hex"
"errors"
"fmt"
"io"
"strings"
"golang.org/x/crypto/sha3"
)
// DigestType is the type for digests in this package.
type DigestType string
const (
DigestTypeShake256 DigestType = "shake256"
shake256Length = 64
)
// Digest represents a hash function's value.
type Digest struct {
dtype DigestType
digest []byte
hexstr string
}
// NewDigestFromBytes builds a digest from a type and the digest bytes.
func NewDigestFromBytes(dtype DigestType, digest []byte) (*Digest, error) {
if dtype == "" {
return nil, errors.New("digest type cannot be empty")
}
if dtype != DigestTypeShake256 {
return nil, fmt.Errorf("unsupported digest type: %q", dtype)
}
if len(digest) != shake256Length {
return nil, fmt.Errorf(
"invalid digest: got %d bytes, expected %d bytes for type %q",
len(digest), shake256Length, dtype,
)
}
return &Digest{
dtype: dtype,
digest: digest,
hexstr: hex.EncodeToString(digest),
}, nil
}
// NewDigestFromHex builds a digest from a type and the hexadecimal string of
// the bytes. It returns an error if the received string is not a valid hex.
func NewDigestFromHex(dtype DigestType, hexstr string) (*Digest, error) {
digest, err := hex.DecodeString(hexstr)
if err != nil {
return nil, err
}
return NewDigestFromBytes(dtype, digest)
}
// NewDigestFromString build a digest from a string representation of it.
func NewDigestFromString(typedDigest string) (*Digest, error) {
dtype, hexstr, found := strings.Cut(typedDigest, ":")
if !found {
return nil, errors.New("malformed digest string")
}
return NewDigestFromHex(DigestType(dtype), hexstr)
}
// String returns the hash in a manifest's string format: "<type>:<hex>".
func (d *Digest) String() string {
return string(d.dtype) + ":" + d.hexstr
}
// Type returns the digest type.
func (d *Digest) Type() DigestType {
return d.dtype
}
// Bytes returns the digest bytes.
func (d *Digest) Bytes() []byte {
return d.digest
}
// Hex returns the digest bytes in its hexadecimal string representation.
func (d *Digest) Hex() string {
return d.hexstr
}
// Equal compares the digest type and bytes with other digest.
func (d *Digest) Equal(other Digest) bool {
return d.dtype == other.dtype && bytes.Equal(d.digest, other.digest)
}
// Digester is something that can digest a content into a digest.
type Digester interface {
Digest(content io.Reader) (*Digest, error)
}
type shake256Digester struct {
hash sha3.ShakeHash
}
// NewDigester returns a digester of the requested type.
func NewDigester(dtype DigestType) (Digester, error) {
if dtype != DigestTypeShake256 {
return nil, fmt.Errorf("not supported digest type %q", dtype)
}
return &shake256Digester{hash: sha3.NewShake256()}, nil
}
func (d *shake256Digester) Digest(content io.Reader) (*Digest, error) {
d.hash.Reset()
if _, err := io.Copy(d.hash, content); err != nil {
return nil, err
}
digest := make([]byte, shake256Length)
if _, err := d.hash.Read(digest); err != nil {
// sha3.ShakeHash never errors or short reads. Something horribly wrong
// happened if your computer ended up here.
return nil, err
}
return NewDigestFromBytes(DigestTypeShake256, digest)
}