1 files changed, 111 insertions, 0 deletions
diff --git a/internal/compare/image.go b/internal/compare/image.go
new file mode 100644
index 0000000..fe5fd4c
--- /dev/null
+++ b/internal/compare/image.go
@@ -0,0 +1,111 @@
+// 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"
+	"reflect"
+	"strings"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
+// Images compares the given images to each other and returns an error if they
+// differ.
+func Images(a, b v1.Image) error {
+	digests := []v1.Hash{}
+	manifests := []*v1.Manifest{}
+	cns := []v1.Hash{}
+	sizes := []int64{}
+	mts := []types.MediaType{}
+	layerss := [][]v1.Layer{}
+
+	errs := []string{}
+
+	for _, img := range []v1.Image{a, b} {
+		layers, err := img.Layers()
+		if err != nil {
+			return err
+		}
+		layerss = append(layerss, layers)
+
+		digest, err := img.Digest()
+		if err != nil {
+			return err
+		}
+		digests = append(digests, digest)
+
+		manifest, err := img.Manifest()
+		if err != nil {
+			return err
+		}
+		manifests = append(manifests, manifest)
+
+		cn, err := img.ConfigName()
+		if err != nil {
+			return err
+		}
+		cns = append(cns, cn)
+
+		size, err := img.Size()
+		if err != nil {
+			return err
+		}
+		sizes = append(sizes, size)
+
+		mt, err := img.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 := cns[0], cns[1]; want != got {
+		errs = append(errs, fmt.Sprintf("a.ConfigName() != b.ConfigName(); %s != %s", want, got))
+	}
+	if want, got := manifests[0], manifests[1]; !reflect.DeepEqual(want, got) {
+		errs = append(errs, fmt.Sprintf("a.Manifest() != b.Manifest(); %v != %v", 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(layerss[0]) != len(layerss[1]) {
+		// If we have fewer layers than the first image, abort with an error so we don't panic.
+		return errors.New("len(a.Layers()) != len(b.Layers())")
+	}
+
+	// Compare each layer.
+	for i := 0; i < len(layerss[0]); i++ {
+		if err := Layers(layerss[0][i], layerss[1][i]); err != nil {
+			// Wrap the error in newlines to delineate layer errors.
+			errs = append(errs, fmt.Sprintf("Layers[%d]: %v\n", i, err))
+		}
+	}
+
+	if len(errs) != 0 {
+		return errors.New("Images differ:\n" + strings.Join(errs, "\n"))
+	}
+
+	return nil
+}