-
Notifications
You must be signed in to change notification settings - Fork 7
/
hash.go
106 lines (95 loc) · 2.92 KB
/
hash.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
// Copyright 2022 Google LLC
//
// 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 snapshot
import (
"crypto/sha256"
"encoding/hex"
"fmt"
"hash"
"io"
"strings"
)
var (
defaultHashFunction = "sha256"
supportedHashFunctions = map[string]func() hash.Hash{
"sha256": sha256.New,
}
)
// Hash represents a hash/fingerprint of a blob.
type Hash struct {
// function is the name of the hash function used (e.g. `sha256`, etc).
function string
// hexContents is the hash value serialized as a hexadecimal string.
hexContents string
}
// NewHash constructs a new hash by calculating the checksum of the provided reader.
//
// The caller is responsible for closing the reader.
func NewHash(reader io.Reader) (*Hash, error) {
sum := supportedHashFunctions[defaultHashFunction]()
if _, err := io.Copy(sum, reader); err != nil {
return nil, fmt.Errorf("failure hashing an object: %v", err)
}
return &Hash{
function: defaultHashFunction,
hexContents: fmt.Sprintf("%x", sum.Sum(nil)),
}, nil
}
// ParseHash parses the string encoding of a hash.
func ParseHash(str string) (*Hash, error) {
if len(str) == 0 {
return nil, nil
}
if !strings.Contains(str, ":") {
return nil, fmt.Errorf("malformed hash string %q", str)
}
parts := strings.SplitN(str, ":", 2)
if len(parts) != 2 {
return nil, fmt.Errorf("internal programming error in snapshot.ParseHash(%q)", str)
}
if _, ok := supportedHashFunctions[parts[0]]; !ok {
return nil, fmt.Errorf("unsupported hash function %q", parts[0])
}
if _, err := hex.DecodeString(parts[1]); err != nil {
return nil, fmt.Errorf("malformed hash contents %q: %v", parts[1], err)
}
return &Hash{
function: parts[0],
hexContents: parts[1],
}, nil
}
// Function returns the name of the hash function used (e.g. `sha256`, etc).
func (h *Hash) Function() string {
return h.function
}
// HexContents returns the hash value serialized as a hexadecimal string.
func (h *Hash) HexContents() string {
return h.hexContents
}
// Equal reports whether or not two hash objects are equal.
func (h *Hash) Equal(other *Hash) bool {
if h == nil || other == nil {
return h == nil && other == nil
}
return h.function == other.function && h.hexContents == other.hexContents
}
// String implements the `fmt.Stringer` interface.
//
// The resulting value is used when serializing objects holding a hash.
func (h *Hash) String() string {
if h == nil {
return ""
}
return h.function + ":" + h.hexContents
}