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// Copyright 2018 Google LLC All Rights Reserved.
//
// 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 v1
import (
"crypto"
"encoding/hex"
"encoding/json"
"fmt"
"hash"
"io"
"strconv"
"strings"
)
// Hash is an unqualified digest of some content, e.g. sha256:deadbeef
type Hash struct {
// Algorithm holds the algorithm used to compute the hash.
Algorithm string
// Hex holds the hex portion of the content hash.
Hex string
}
// String reverses NewHash returning the string-form of the hash.
func (h Hash) String() string {
return fmt.Sprintf("%s:%s", h.Algorithm, h.Hex)
}
// NewHash validates the input string is a hash and returns a strongly type Hash object.
func NewHash(s string) (Hash, error) {
h := Hash{}
if err := h.parse(s); err != nil {
return Hash{}, err
}
return h, nil
}
// MarshalJSON implements json.Marshaler
func (h Hash) MarshalJSON() ([]byte, error) {
return json.Marshal(h.String())
}
// UnmarshalJSON implements json.Unmarshaler
func (h *Hash) UnmarshalJSON(data []byte) error {
s, err := strconv.Unquote(string(data))
if err != nil {
return err
}
return h.parse(s)
}
// MarshalText implements encoding.TextMarshaler. This is required to use
// v1.Hash as a key in a map when marshalling JSON.
func (h Hash) MarshalText() (text []byte, err error) {
return []byte(h.String()), nil
}
// UnmarshalText implements encoding.TextUnmarshaler. This is required to use
// v1.Hash as a key in a map when unmarshalling JSON.
func (h *Hash) UnmarshalText(text []byte) error {
return h.parse(string(text))
}
// Hasher returns a hash.Hash for the named algorithm (e.g. "sha256")
func Hasher(name string) (hash.Hash, error) {
switch name {
case "sha256":
return crypto.SHA256.New(), nil
default:
return nil, fmt.Errorf("unsupported hash: %q", name)
}
}
func (h *Hash) parse(unquoted string) error {
parts := strings.Split(unquoted, ":")
if len(parts) != 2 {
return fmt.Errorf("cannot parse hash: %q", unquoted)
}
rest := strings.TrimLeft(parts[1], "0123456789abcdef")
if len(rest) != 0 {
return fmt.Errorf("found non-hex character in hash: %c", rest[0])
}
hasher, err := Hasher(parts[0])
if err != nil {
return err
}
// Compare the hex to the expected size (2 hex characters per byte)
if len(parts[1]) != hasher.Size()*2 {
return fmt.Errorf("wrong number of hex digits for %s: %s", parts[0], parts[1])
}
h.Algorithm = parts[0]
h.Hex = parts[1]
return nil
}
// SHA256 computes the Hash of the provided io.Reader's content.
func SHA256(r io.Reader) (Hash, int64, error) {
hasher := crypto.SHA256.New()
n, err := io.Copy(hasher, r)
if err != nil {
return Hash{}, 0, err
}
return Hash{
Algorithm: "sha256",
Hex: hex.EncodeToString(hasher.Sum(make([]byte, 0, hasher.Size()))),
}, n, nil
}
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