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compression.go
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/*
Copyright The containerd Authors.
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
import (
"bufio"
"bytes"
"compress/gzip"
"context"
"encoding/binary"
"fmt"
"io"
"os"
"strconv"
"sync"
"github.com/containerd/containerd/log"
"github.com/klauspost/compress/zstd"
exec "golang.org/x/sys/execabs"
)
type (
// Compression is the state represents if compressed or not.
Compression int
)
const (
// Uncompressed represents the uncompressed.
Uncompressed Compression = iota
// Gzip is gzip compression algorithm.
Gzip
// Zstd is zstd compression algorithm.
Zstd
)
const disablePigzEnv = "CONTAINERD_DISABLE_PIGZ"
var (
initPigz sync.Once
unpigzPath string
)
var (
bufioReader32KPool = &sync.Pool{
New: func() interface{} { return bufio.NewReaderSize(nil, 32*1024) },
}
)
// DecompressReadCloser include the stream after decompress and the compress method detected.
type DecompressReadCloser interface {
io.ReadCloser
// GetCompression returns the compress method which is used before decompressing
GetCompression() Compression
}
type readCloserWrapper struct {
io.Reader
compression Compression
closer func() error
}
func (r *readCloserWrapper) Close() error {
if r.closer != nil {
return r.closer()
}
return nil
}
func (r *readCloserWrapper) GetCompression() Compression {
return r.compression
}
type writeCloserWrapper struct {
io.Writer
closer func() error
}
func (w *writeCloserWrapper) Close() error {
if w.closer != nil {
w.closer()
}
return nil
}
type bufferedReader struct {
buf *bufio.Reader
}
func newBufferedReader(r io.Reader) *bufferedReader {
buf := bufioReader32KPool.Get().(*bufio.Reader)
buf.Reset(r)
return &bufferedReader{buf}
}
func (r *bufferedReader) Read(p []byte) (n int, err error) {
if r.buf == nil {
return 0, io.EOF
}
n, err = r.buf.Read(p)
if err == io.EOF {
r.buf.Reset(nil)
bufioReader32KPool.Put(r.buf)
r.buf = nil
}
return
}
func (r *bufferedReader) Peek(n int) ([]byte, error) {
if r.buf == nil {
return nil, io.EOF
}
return r.buf.Peek(n)
}
const (
zstdMagicSkippableStart = 0x184D2A50
zstdMagicSkippableMask = 0xFFFFFFF0
)
var (
gzipMagic = []byte{0x1F, 0x8B, 0x08}
zstdMagic = []byte{0x28, 0xb5, 0x2f, 0xfd}
)
type matcher = func([]byte) bool
func magicNumberMatcher(m []byte) matcher {
return func(source []byte) bool {
return bytes.HasPrefix(source, m)
}
}
// zstdMatcher detects zstd compression algorithm.
// There are two frame formats defined by Zstandard: Zstandard frames and Skippable frames.
// See https://tools.ietf.org/id/draft-kucherawy-dispatch-zstd-00.html#rfc.section.2 for more details.
func zstdMatcher() matcher {
return func(source []byte) bool {
if bytes.HasPrefix(source, zstdMagic) {
// Zstandard frame
return true
}
// skippable frame
if len(source) < 8 {
return false
}
// magic number from 0x184D2A50 to 0x184D2A5F.
if binary.LittleEndian.Uint32(source[:4])&zstdMagicSkippableMask == zstdMagicSkippableStart {
return true
}
return false
}
}
// DetectCompression detects the compression algorithm of the source.
func DetectCompression(source []byte) Compression {
for compression, fn := range map[Compression]matcher{
Gzip: magicNumberMatcher(gzipMagic),
Zstd: zstdMatcher(),
} {
if fn(source) {
return compression
}
}
return Uncompressed
}
// DecompressStream decompresses the archive and returns a ReaderCloser with the decompressed archive.
func DecompressStream(archive io.Reader) (DecompressReadCloser, error) {
buf := newBufferedReader(archive)
bs, err := buf.Peek(10)
if err != nil && err != io.EOF {
// Note: we'll ignore any io.EOF error because there are some odd
// cases where the layer.tar file will be empty (zero bytes) and
// that results in an io.EOF from the Peek() call. So, in those
// cases we'll just treat it as a non-compressed stream and
// that means just create an empty layer.
// See Issue docker/docker#18170
return nil, err
}
switch compression := DetectCompression(bs); compression {
case Uncompressed:
return &readCloserWrapper{
Reader: buf,
compression: compression,
}, nil
case Gzip:
ctx, cancel := context.WithCancel(context.Background())
gzReader, err := gzipDecompress(ctx, buf)
if err != nil {
cancel()
return nil, err
}
return &readCloserWrapper{
Reader: gzReader,
compression: compression,
closer: func() error {
cancel()
return gzReader.Close()
},
}, nil
case Zstd:
zstdReader, err := zstd.NewReader(buf)
if err != nil {
return nil, err
}
return &readCloserWrapper{
Reader: zstdReader,
compression: compression,
closer: func() error {
zstdReader.Close()
return nil
},
}, nil
default:
return nil, fmt.Errorf("unsupported compression format %s", (&compression).Extension())
}
}
// CompressStream compresses the dest with specified compression algorithm.
func CompressStream(dest io.Writer, compression Compression) (io.WriteCloser, error) {
switch compression {
case Uncompressed:
return &writeCloserWrapper{dest, nil}, nil
case Gzip:
return gzip.NewWriter(dest), nil
case Zstd:
return zstd.NewWriter(dest)
default:
return nil, fmt.Errorf("unsupported compression format %s", (&compression).Extension())
}
}
// Extension returns the extension of a file that uses the specified compression algorithm.
func (compression *Compression) Extension() string {
switch *compression {
case Gzip:
return "gz"
case Zstd:
return "zst"
}
return ""
}
func gzipDecompress(ctx context.Context, buf io.Reader) (io.ReadCloser, error) {
initPigz.Do(func() {
if unpigzPath = detectPigz(); unpigzPath != "" {
log.L.Debug("using pigz for decompression")
}
})
if unpigzPath == "" {
return gzip.NewReader(buf)
}
return cmdStream(exec.CommandContext(ctx, unpigzPath, "-d", "-c"), buf)
}
func cmdStream(cmd *exec.Cmd, in io.Reader) (io.ReadCloser, error) {
reader, writer := io.Pipe()
cmd.Stdin = in
cmd.Stdout = writer
var errBuf bytes.Buffer
cmd.Stderr = &errBuf
if err := cmd.Start(); err != nil {
return nil, err
}
go func() {
if err := cmd.Wait(); err != nil {
writer.CloseWithError(fmt.Errorf("%s: %s", err, errBuf.String()))
} else {
writer.Close()
}
}()
return reader, nil
}
func detectPigz() string {
path, err := exec.LookPath("unpigz")
if err != nil {
log.L.WithError(err).Debug("unpigz not found, falling back to go gzip")
return ""
}
// Check if pigz disabled via CONTAINERD_DISABLE_PIGZ env variable
value := os.Getenv(disablePigzEnv)
if value == "" {
return path
}
disable, err := strconv.ParseBool(value)
if err != nil {
log.L.WithError(err).Warnf("could not parse %s: %s", disablePigzEnv, value)
return path
}
if disable {
return ""
}
return path
}