containerd/archive/compression/compression.go

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package compression
import (
"bufio"
"bytes"
"compress/gzip"
"fmt"
"io"
"sync"
)
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
)
var (
bufioReader32KPool = &sync.Pool{
New: func() interface{} { return bufio.NewReaderSize(nil, 32*1024) },
}
)
type readCloserWrapper struct {
io.Reader
closer func() error
}
func (r *readCloserWrapper) Close() error {
if r.closer != nil {
return r.closer()
}
return nil
}
type writeCloserWrapper struct {
io.Writer
closer func() error
}
func (w *writeCloserWrapper) Close() error {
if w.closer != nil {
w.closer()
}
return nil
}
// DetectCompression detects the compression algorithm of the source.
func DetectCompression(source []byte) Compression {
for compression, m := range map[Compression][]byte{
Gzip: {0x1F, 0x8B, 0x08},
} {
if len(source) < len(m) {
// Len too short
continue
}
if bytes.Compare(m, source[:len(m)]) == 0 {
return compression
}
}
return Uncompressed
}
// DecompressStream decompresses the archive and returns a ReaderCloser with the decompressed archive.
func DecompressStream(archive io.Reader) (io.ReadCloser, error) {
buf := bufioReader32KPool.Get().(*bufio.Reader)
buf.Reset(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
}
closer := func() error {
buf.Reset(nil)
bufioReader32KPool.Put(buf)
return nil
}
switch compression := DetectCompression(bs); compression {
case Uncompressed:
readBufWrapper := &readCloserWrapper{buf, closer}
return readBufWrapper, nil
case Gzip:
gzReader, err := gzip.NewReader(buf)
if err != nil {
return nil, err
}
readBufWrapper := &readCloserWrapper{gzReader, closer}
return readBufWrapper, nil
default:
return nil, fmt.Errorf("unsupported compression format %s", (&compression).Extension())
}
}
// CompressStream compresseses 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
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"
}
return ""
}