1 files changed, 80 insertions, 0 deletions
diff --git a/internal/compare/layer.go b/internal/compare/layer.go
new file mode 100644
index 0000000..01e63aa
--- /dev/null
+++ b/internal/compare/layer.go
@@ -0,0 +1,80 @@
+// Copyright 2019 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 compare
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
+// Layers compares the given layers to each other and returns an error if they
+// differ.  Note that this does not compare the actual contents (by calling
+// Compressed or Uncompressed).
+func Layers(a, b v1.Layer) error {
+	digests := []v1.Hash{}
+	diffids := []v1.Hash{}
+	sizes := []int64{}
+	mts := []types.MediaType{}
+	errs := []string{}
+
+	for _, layer := range []v1.Layer{a, b} {
+		digest, err := layer.Digest()
+		if err != nil {
+			return err
+		}
+		digests = append(digests, digest)
+
+		diffid, err := layer.DiffID()
+		if err != nil {
+			return err
+		}
+		diffids = append(diffids, diffid)
+
+		size, err := layer.Size()
+		if err != nil {
+			return err
+		}
+		sizes = append(sizes, size)
+
+		mt, err := layer.MediaType()
+		if err != nil {
+			return err
+		}
+		mts = append(mts, mt)
+	}
+
+	if want, got := digests[0], digests[1]; want != got {
+		errs = append(errs, fmt.Sprintf("a.Digest() != b.Digest(); %s != %s", want, got))
+	}
+	if want, got := diffids[0], diffids[1]; want != got {
+		errs = append(errs, fmt.Sprintf("a.DiffID() != b.DiffID(); %s != %s", want, got))
+	}
+	if want, got := sizes[0], sizes[1]; want != got {
+		errs = append(errs, fmt.Sprintf("a.Size() != b.Size(); %d != %d", want, got))
+	}
+	if want, got := mts[0], mts[1]; want != got {
+		errs = append(errs, fmt.Sprintf("a.MediaType() != b.MediaType(); %s != %s", want, got))
+	}
+
+	if len(errs) != 0 {
+		return errors.New("Layers differ:\n" + strings.Join(errs, "\n"))
+	}
+
+	return nil
+}