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
|
// Copyright 2022 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 compression abstracts over gzip and zstd.
package compression
import (
"bufio"
"bytes"
"io"
"github.com/google/go-containerregistry/internal/gzip"
"github.com/google/go-containerregistry/internal/zstd"
"github.com/google/go-containerregistry/pkg/compression"
)
// Opener represents e.g. opening a file.
type Opener = func() (io.ReadCloser, error)
// GetCompression detects whether an Opener is compressed and which algorithm is used.
func GetCompression(opener Opener) (compression.Compression, error) {
rc, err := opener()
if err != nil {
return compression.None, err
}
defer rc.Close()
cp, _, err := PeekCompression(rc)
if err != nil {
return compression.None, err
}
return cp, nil
}
// PeekCompression detects whether the input stream is compressed and which algorithm is used.
//
// If r implements Peek, we will use that directly, otherwise a small number
// of bytes are buffered to Peek at the gzip/zstd header, and the returned
// PeekReader can be used as a replacement for the consumed input io.Reader.
func PeekCompression(r io.Reader) (compression.Compression, PeekReader, error) {
pr := intoPeekReader(r)
if isGZip, _, err := checkHeader(pr, gzip.MagicHeader); err != nil {
return compression.None, pr, err
} else if isGZip {
return compression.GZip, pr, nil
}
if isZStd, _, err := checkHeader(pr, zstd.MagicHeader); err != nil {
return compression.None, pr, err
} else if isZStd {
return compression.ZStd, pr, nil
}
return compression.None, pr, nil
}
// PeekReader is an io.Reader that also implements Peek a la bufio.Reader.
type PeekReader interface {
io.Reader
Peek(n int) ([]byte, error)
}
// IntoPeekReader creates a PeekReader from an io.Reader.
// If the reader already has a Peek method, it will just return the passed reader.
func intoPeekReader(r io.Reader) PeekReader {
if p, ok := r.(PeekReader); ok {
return p
}
return bufio.NewReader(r)
}
// CheckHeader checks whether the first bytes from a PeekReader match an expected header
func checkHeader(pr PeekReader, expectedHeader []byte) (bool, PeekReader, error) {
header, err := pr.Peek(len(expectedHeader))
if err != nil {
// https://github.com/google/go-containerregistry/issues/367
if err == io.EOF {
return false, pr, nil
}
return false, pr, err
}
return bytes.Equal(header, expectedHeader), pr, nil
}
|
