Start to flesh out crane optimize.

This is a hidden command, which roundtrips a remote image to a target image through `tarball.LayerFromOpener(layer.Uncompressed)`.

Right now this does nothing to force estargz (still need `GGCR_EXPERIMENT_ESTARGZ=1`) or prioritize files (need `estargz.WithPrioritizedFiles(foo)`), but want to start the convo.

Fixes: #878

cmd/crane/cmd/optimize.go

@@ -0,0 +1,39 @@
+// 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 cmd
+
+import (
+	"log"
+
+	"github.com/google/go-containerregistry/pkg/crane"
+	"github.com/spf13/cobra"
+)
+
+// NewCmdOptimize creates a new cobra.Command for the optimize subcommand.
+func NewCmdOptimize(options *[]crane.Option) *cobra.Command {
+	return &cobra.Command{
+		Use:     "optimize SRC DST",
+		Hidden:  true,
+		Aliases: []string{"opt"},
+		Short:   "Optimize a remote container image from src to dst",
+		Args:    cobra.ExactArgs(2),
+		Run: func(_ *cobra.Command, args []string) {
+			src, dst := args[0], args[1]
+			if err := crane.Optimize(src, dst, *options...); err != nil {
+				log.Fatal(err)
+			}
+		},
+	}
+}

cmd/crane/cmd/root.go

@@ -86,6 +86,7 @@ func New(use, short string, options []crane.Option) *cobra.Command {
 		NewCmdExport(&options),
 		NewCmdList(&options),
 		NewCmdManifest(&options),
+		NewCmdOptimize(&options),
 		NewCmdPull(&options),
 		NewCmdPush(&options),
 		NewCmdRebase(&options),

pkg/crane/optimize.go

@@ -0,0 +1,176 @@
+// 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 (
+	"errors"
+	"fmt"
+
+	"github.com/google/go-containerregistry/pkg/logs"
+	"github.com/google/go-containerregistry/pkg/name"
+	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/remote"
+	"github.com/google/go-containerregistry/pkg/v1/tarball"
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
+// Optimize optimizes a remote image or index from src to dst.
+func Optimize(src, dst string, opt ...Option) error {
+	o := makeOptions(opt...)
+	srcRef, err := name.ParseReference(src, o.name...)
+	if err != nil {
+		return fmt.Errorf("parsing reference %q: %v", src, err)
+	}
+
+	dstRef, err := name.ParseReference(dst, o.name...)
+	if err != nil {
+		return fmt.Errorf("parsing reference for %q: %v", dst, err)
+	}
+
+	logs.Progress.Printf("Optimizing from %v to %v", srcRef, dstRef)
+	desc, err := remote.Get(srcRef, o.remote...)
+	if err != nil {
+		return fmt.Errorf("fetching %q: %v", src, err)
+	}
+
+	switch desc.MediaType {
+	case types.OCIImageIndex, types.DockerManifestList:
+		// Handle indexes separately.
+		if o.platform != nil {
+			// If platform is explicitly set, don't optimize the whole index, just the appropriate image.
+			if err := optimizeAndPushImage(desc, dstRef, o); err != nil {
+				return fmt.Errorf("failed to optimize image: %v", err)
+			}
+		} else {
+			if err := optimizeAndPushIndex(desc, dstRef, o); err != nil {
+				return fmt.Errorf("failed to optimize index: %v", err)
+			}
+		}
+
+	case types.DockerManifestSchema1, types.DockerManifestSchema1Signed:
+		return errors.New("docker schema 1 images are not supported")
+
+	default:
+		// Assume anything else is an image, since some registries don't set mediaTypes properly.
+		if err := optimizeAndPushImage(desc, dstRef, o); err != nil {
+			return fmt.Errorf("failed to optimize image: %v", err)
+		}
+	}
+
+	return nil
+}
+
+func optimizeAndPushImage(desc *remote.Descriptor, dstRef name.Reference, o options) error {
+	img, err := desc.Image()
+	if err != nil {
+		return err
+	}
+
+	oimg, err := optimizeImage(img, o)
+	if err != nil {
+		return err
+	}
+
+	return remote.Write(dstRef, oimg, o.remote...)
+}
+
+func optimizeImage(img v1.Image, o options) (v1.Image, error) {
+	cfg, err := img.ConfigFile()
+	if err != nil {
+		return nil, err
+	}
+	ocfg := cfg.DeepCopy()
+	ocfg.History = nil
+	ocfg.RootFS.DiffIDs = nil
+
+	oimg, err := mutate.ConfigFile(empty.Image, ocfg)
+	if err != nil {
+		return nil, err
+	}
+
+	layers, err := img.Layers()
+	if err != nil {
+		return nil, err
+	}
+
+	olayers := make([]mutate.Addendum, 0, len(layers))
+	for i, layer := range layers {
+		olayer, err := tarball.LayerFromOpener(layer.Uncompressed)
+		if err != nil {
+			return nil, err
+		}
+
+		olayers = append(olayers, mutate.Addendum{
+			Layer:     olayer,
+			History:   cfg.History[i],
+			MediaType: types.DockerLayer,
+		})
+	}
+
+	return mutate.Append(oimg, olayers...)
+}
+
+func optimizeAndPushIndex(desc *remote.Descriptor, dstRef name.Reference, o options) error {
+	idx, err := desc.ImageIndex()
+	if err != nil {
+		return err
+	}
+
+	oidx, err := optimizeIndex(idx, o)
+	if err != nil {
+		return err
+	}
+
+	return remote.WriteIndex(dstRef, oidx, o.remote...)
+}
+
+func optimizeIndex(idx v1.ImageIndex, o options) (v1.ImageIndex, error) {
+	im, err := idx.IndexManifest()
+	if err != nil {
+		return nil, err
+	}
+
+	// Build an image for each child from the base and append it to a new index to produce the result.
+	adds := make([]mutate.IndexAddendum, 0, len(im.Manifests))
+	for _, desc := range im.Manifests {
+		img, err := idx.Image(desc.Digest)
+		if err != nil {
+			return nil, err
+		}
+
+		oimg, err := optimizeImage(img, o)
+		if err != nil {
+			return nil, err
+		}
+		adds = append(adds, mutate.IndexAddendum{
+			Add: oimg,
+			Descriptor: v1.Descriptor{
+				URLs:        desc.URLs,
+				MediaType:   desc.MediaType,
+				Annotations: desc.Annotations,
+				Platform:    desc.Platform,
+			},
+		})
+	}
+
+	idxType, err := idx.MediaType()
+	if err != nil {
+		return nil, err
+	}
+
+	return mutate.IndexMediaType(mutate.AppendManifests(empty.Index, adds...), idxType), nil
+}