Unpack filesystem and whitelist from /proc/self/mountinfo

vendor/github.com/containers/image/pkg/compression/compression.go

@@ -0,0 +1,67 @@
+package compression
+
+import (
+	"bytes"
+	"compress/bzip2"
+	"compress/gzip"
+	"io"
+
+	"github.com/pkg/errors"
+
+	"github.com/sirupsen/logrus"
+)
+
+// DecompressorFunc returns the decompressed stream, given a compressed stream.
+type DecompressorFunc func(io.Reader) (io.Reader, error)
+
+// GzipDecompressor is a DecompressorFunc for the gzip compression algorithm.
+func GzipDecompressor(r io.Reader) (io.Reader, error) {
+	return gzip.NewReader(r)
+}
+
+// Bzip2Decompressor is a DecompressorFunc for the bzip2 compression algorithm.
+func Bzip2Decompressor(r io.Reader) (io.Reader, error) {
+	return bzip2.NewReader(r), nil
+}
+
+// XzDecompressor is a DecompressorFunc for the xz compression algorithm.
+func XzDecompressor(r io.Reader) (io.Reader, error) {
+	return nil, errors.New("Decompressing xz streams is not supported")
+}
+
+// compressionAlgos is an internal implementation detail of DetectCompression
+var compressionAlgos = map[string]struct {
+	prefix       []byte
+	decompressor DecompressorFunc
+}{
+	"gzip":  {[]byte{0x1F, 0x8B, 0x08}, GzipDecompressor},                 // gzip (RFC 1952)
+	"bzip2": {[]byte{0x42, 0x5A, 0x68}, Bzip2Decompressor},                // bzip2 (decompress.c:BZ2_decompress)
+	"xz":    {[]byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, XzDecompressor}, // xz (/usr/share/doc/xz/xz-file-format.txt)
+}
+
+// DetectCompression returns a DecompressorFunc if the input is recognized as a compressed format, nil otherwise.
+// Because it consumes the start of input, other consumers must use the returned io.Reader instead to also read from the beginning.
+func DetectCompression(input io.Reader) (DecompressorFunc, io.Reader, error) {
+	buffer := [8]byte{}
+
+	n, err := io.ReadAtLeast(input, buffer[:], len(buffer))
+	if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
+		// This is a “real” error. We could just ignore it this time, process the data we have, and hope that the source will report the same error again.
+		// Instead, fail immediately with the original error cause instead of a possibly secondary/misleading error returned later.
+		return nil, nil, err
+	}
+
+	var decompressor DecompressorFunc
+	for name, algo := range compressionAlgos {
+		if bytes.HasPrefix(buffer[:n], algo.prefix) {
+			logrus.Debugf("Detected compression format %s", name)
+			decompressor = algo.decompressor
+			break
+		}
+	}
+	if decompressor == nil {
+		logrus.Debugf("No compression detected")
+	}
+
+	return decompressor, io.MultiReader(bytes.NewReader(buffer[:n]), input), nil
+}