1 files changed, 72 insertions, 0 deletions
diff --git a/pkg/crane/filemap.go b/pkg/crane/filemap.go
new file mode 100644
index 0000000..36dfc2a
--- /dev/null
+++ b/pkg/crane/filemap.go
@@ -0,0 +1,72 @@
+// 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 (
+	"archive/tar"
+	"bytes"
+	"io"
+	"sort"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
+	"github.com/google/go-containerregistry/pkg/v1/tarball"
+)
+
+// Layer creates a layer from a single file map. These layers are reproducible and consistent.
+// A filemap is a path -> file content map representing a file system.
+func Layer(filemap map[string][]byte) (v1.Layer, error) {
+	b := &bytes.Buffer{}
+	w := tar.NewWriter(b)
+
+	fn := []string{}
+	for f := range filemap {
+		fn = append(fn, f)
+	}
+	sort.Strings(fn)
+
+	for _, f := range fn {
+		c := filemap[f]
+		if err := w.WriteHeader(&tar.Header{
+			Name: f,
+			Size: int64(len(c)),
+		}); err != nil {
+			return nil, err
+		}
+		if _, err := w.Write(c); err != nil {
+			return nil, err
+		}
+	}
+	if err := w.Close(); err != nil {
+		return nil, err
+	}
+
+	// Return a new copy of the buffer each time it's opened.
+	return tarball.LayerFromOpener(func() (io.ReadCloser, error) {
+		return io.NopCloser(bytes.NewBuffer(b.Bytes())), nil
+	})
+}
+
+// Image creates a image with the given filemaps as its contents. These images are reproducible and consistent.
+// A filemap is a path -> file content map representing a file system.
+func Image(filemap map[string][]byte) (v1.Image, error) {
+	y, err := Layer(filemap)
+	if err != nil {
+		return nil, err
+	}
+
+	return mutate.AppendLayers(empty.Image, y)
+}