1 files changed, 47 insertions, 0 deletions
diff --git a/pkg/crane/export.go b/pkg/crane/export.go
new file mode 100644
index 0000000..5d6da1d
--- /dev/null
+++ b/pkg/crane/export.go
@@ -0,0 +1,47 @@
+// Copyright 2018 Google LLC All Rights Reserved.
+//
+// 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 crane
+
+import (
+	"io"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
+)
+
+// Export writes the filesystem contents (as a tarball) of img to w.
+// If img has a single layer, just write the (uncompressed) contents to w so
+// that this "just works" for images that just wrap a single blob.
+func Export(img v1.Image, w io.Writer) error {
+	layers, err := img.Layers()
+	if err != nil {
+		return err
+	}
+	if len(layers) == 1 {
+		// If it's a single layer, we don't have to flatten the filesystem.
+		// An added perk of skipping mutate.Extract here is that this works
+		// for non-tarball layers.
+		l := layers[0]
+		rc, err := l.Uncompressed()
+		if err != nil {
+			return err
+		}
+		_, err = io.Copy(w, rc)
+		return err
+	}
+	fs := mutate.Extract(img)
+	_, err = io.Copy(w, fs)
+	return err
+}