add option to strip file times to make tarballs more reproducible (#126)

Author: mxey

pkg/content/file.go

@@ -28,6 +28,9 @@ type FileStore struct {
 	DisableOverwrite          bool
 	AllowPathTraversalOnWrite bool
 
+	// Reproducible enables stripping times from added files
+	Reproducible bool
+
 	root       string
 	descriptor *sync.Map // map[digest.Digest]ocispec.Descriptor
 	pathMap    *sync.Map
@@ -109,7 +112,7 @@ func (s *FileStore) descFromDir(name, mediaType, root string) (ocispec.Descripto
 	zw := gzip.NewWriter(io.MultiWriter(file, digester.Hash()))
 	defer zw.Close()
 	tarDigester := digest.Canonical.Digester()
-	if err := tarDirectory(root, name, io.MultiWriter(zw, tarDigester.Hash())); err != nil {
+	if err := tarDirectory(root, name, io.MultiWriter(zw, tarDigester.Hash()), s.Reproducible); err != nil {
 		return ocispec.Descriptor{}, err
 	}
 

pkg/content/utils.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -22,7 +23,7 @@ func ResolveName(desc ocispec.Descriptor) (string, bool) {
 
 // tarDirectory walks the directory specified by path, and tar those files with a new
 // path prefix.
-func tarDirectory(root, prefix string, w io.Writer) error {
+func tarDirectory(root, prefix string, w io.Writer, stripTimes bool) error {
 	tw := tar.NewWriter(w)
 	defer tw.Close()
 	if err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
@@ -56,6 +57,12 @@ func tarDirectory(root, prefix string, w io.Writer) error {
 		header.Uname = ""
 		header.Gname = ""
 
+		if stripTimes {
+			header.ModTime = time.Time{}
+			header.AccessTime = time.Time{}
+			header.ChangeTime = time.Time{}
+		}
+
 		// Write file
 		if err := tw.WriteHeader(header); err != nil {
 			return errors.Wrap(err, "tar")