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
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
|
// Copyright 2017 Docker, 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
//
// https://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 digest
import (
"crypto"
"fmt"
"hash"
"io"
"regexp"
)
// Algorithm identifies and implementation of a digester by an identifier.
// Note the that this defines both the hash algorithm used and the string
// encoding.
type Algorithm string
// supported digest types
const (
SHA256 Algorithm = "sha256" // sha256 with hex encoding (lower case only)
SHA384 Algorithm = "sha384" // sha384 with hex encoding (lower case only)
SHA512 Algorithm = "sha512" // sha512 with hex encoding (lower case only)
// Canonical is the primary digest algorithm used with the distribution
// project. Other digests may be used but this one is the primary storage
// digest.
Canonical = SHA256
)
var (
// TODO(stevvooe): Follow the pattern of the standard crypto package for
// registration of digests. Effectively, we are a registerable set and
// common symbol access.
// algorithms maps values to hash.Hash implementations. Other algorithms
// may be available but they cannot be calculated by the digest package.
algorithms = map[Algorithm]crypto.Hash{
SHA256: crypto.SHA256,
SHA384: crypto.SHA384,
SHA512: crypto.SHA512,
}
// anchoredEncodedRegexps contains anchored regular expressions for hex-encoded digests.
// Note that /A-F/ disallowed.
anchoredEncodedRegexps = map[Algorithm]*regexp.Regexp{
SHA256: regexp.MustCompile(`^[a-f0-9]{64}$`),
SHA384: regexp.MustCompile(`^[a-f0-9]{96}$`),
SHA512: regexp.MustCompile(`^[a-f0-9]{128}$`),
}
)
// Available returns true if the digest type is available for use. If this
// returns false, Digester and Hash will return nil.
func (a Algorithm) Available() bool {
h, ok := algorithms[a]
if !ok {
return false
}
// check availability of the hash, as well
return h.Available()
}
func (a Algorithm) String() string {
return string(a)
}
// Size returns number of bytes returned by the hash.
func (a Algorithm) Size() int {
h, ok := algorithms[a]
if !ok {
return 0
}
return h.Size()
}
// Set implemented to allow use of Algorithm as a command line flag.
func (a *Algorithm) Set(value string) error {
if value == "" {
*a = Canonical
} else {
// just do a type conversion, support is queried with Available.
*a = Algorithm(value)
}
if !a.Available() {
return ErrDigestUnsupported
}
return nil
}
// Digester returns a new digester for the specified algorithm. If the algorithm
// does not have a digester implementation, nil will be returned. This can be
// checked by calling Available before calling Digester.
func (a Algorithm) Digester() Digester {
return &digester{
alg: a,
hash: a.Hash(),
}
}
// Hash returns a new hash as used by the algorithm. If not available, the
// method will panic. Check Algorithm.Available() before calling.
func (a Algorithm) Hash() hash.Hash {
if !a.Available() {
// Empty algorithm string is invalid
if a == "" {
panic(fmt.Sprintf("empty digest algorithm, validate before calling Algorithm.Hash()"))
}
// NOTE(stevvooe): A missing hash is usually a programming error that
// must be resolved at compile time. We don't import in the digest
// package to allow users to choose their hash implementation (such as
// when using stevvooe/resumable or a hardware accelerated package).
//
// Applications that may want to resolve the hash at runtime should
// call Algorithm.Available before call Algorithm.Hash().
panic(fmt.Sprintf("%v not available (make sure it is imported)", a))
}
return algorithms[a].New()
}
// Encode encodes the raw bytes of a digest, typically from a hash.Hash, into
// the encoded portion of the digest.
func (a Algorithm) Encode(d []byte) string {
// TODO(stevvooe): Currently, all algorithms use a hex encoding. When we
// add support for back registration, we can modify this accordingly.
return fmt.Sprintf("%x", d)
}
// FromReader returns the digest of the reader using the algorithm.
func (a Algorithm) FromReader(rd io.Reader) (Digest, error) {
digester := a.Digester()
if _, err := io.Copy(digester.Hash(), rd); err != nil {
return "", err
}
return digester.Digest(), nil
}
// FromBytes digests the input and returns a Digest.
func (a Algorithm) FromBytes(p []byte) Digest {
digester := a.Digester()
if _, err := digester.Hash().Write(p); err != nil {
// Writes to a Hash should never fail. None of the existing
// hash implementations in the stdlib or hashes vendored
// here can return errors from Write. Having a panic in this
// condition instead of having FromBytes return an error value
// avoids unnecessary error handling paths in all callers.
panic("write to hash function returned error: " + err.Error())
}
return digester.Digest()
}
// FromString digests the string input and returns a Digest.
func (a Algorithm) FromString(s string) Digest {
return a.FromBytes([]byte(s))
}
// Validate validates the encoded portion string
func (a Algorithm) Validate(encoded string) error {
r, ok := anchoredEncodedRegexps[a]
if !ok {
return ErrDigestUnsupported
}
// Digests much always be hex-encoded, ensuring that their hex portion will
// always be size*2
if a.Size()*2 != len(encoded) {
return ErrDigestInvalidLength
}
if r.MatchString(encoded) {
return nil
}
return ErrDigestInvalidFormat
}
|
