Add glide.yaml and vendor deps

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

@@ -0,0 +1,61 @@
+package copy
+
+import (
+	"bytes"
+	"compress/bzip2"
+	"compress/gzip"
+	"errors"
+	"io"
+
+	"github.com/Sirupsen/logrus"
+)
+
+// decompressorFunc, given a compressed stream, returns the decompressed stream.
+type decompressorFunc func(io.Reader) (io.Reader, error)
+
+func gzipDecompressor(r io.Reader) (io.Reader, error) {
+	return gzip.NewReader(r)
+}
+func bzip2Decompressor(r io.Reader) (io.Reader, error) {
+	return bzip2.NewReader(r), nil
+}
+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
+}