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// Copyright 2021 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 (
"compress/gzip"
"encoding/json"
"fmt"
"log"
"github.com/google/go-containerregistry/pkg/crane"
"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/partial"
"github.com/google/go-containerregistry/pkg/v1/remote"
"github.com/google/go-containerregistry/pkg/v1/stream"
"github.com/spf13/cobra"
)
// NewCmdFlatten creates a new cobra.Command for the flatten subcommand.
func NewCmdFlatten(options *[]crane.Option) *cobra.Command {
var dst string
flattenCmd := &cobra.Command{
Use: "flatten",
Short: "Flatten an image's layers into a single layer",
Args: cobra.ExactArgs(1),
Run: func(cmd *cobra.Command, args []string) {
// We need direct access to the underlying remote options because crane
// doesn't expose great facilities for working with an index (yet).
o := crane.GetOptions(*options...)
// Pull image and get config.
src := args[0]
// If the new ref isn't provided, write over the original image.
// If that ref was provided by digest (e.g., output from
// another crane command), then strip that and push the
// mutated image by digest instead.
if dst == "" {
dst = src
}
ref, err := name.ParseReference(src, o.Name...)
if err != nil {
log.Fatalf("parsing %s: %v", src, err)
}
newRef, err := name.ParseReference(dst, o.Name...)
if err != nil {
log.Fatalf("parsing %s: %v", dst, err)
}
repo := newRef.Context()
flat, err := flatten(ref, repo, cmd.Parent().Use, o)
if err != nil {
log.Fatalf("flattening %s: %v", ref, err)
}
digest, err := flat.Digest()
if err != nil {
log.Fatalf("digesting new image: %v", err)
}
if _, ok := ref.(name.Digest); ok {
newRef = repo.Digest(digest.String())
}
if err := push(flat, newRef, o); err != nil {
log.Fatalf("pushing %s: %v", newRef, err)
}
fmt.Println(repo.Digest(digest.String()))
},
}
flattenCmd.Flags().StringVarP(&dst, "tag", "t", "", "New tag to apply to flattened image. If not provided, push by digest to the original image repository.")
return flattenCmd
}
func flatten(ref name.Reference, repo name.Repository, use string, o crane.Options) (partial.Describable, error) {
desc, err := remote.Get(ref, o.Remote...)
if err != nil {
return nil, fmt.Errorf("pulling %s: %w", ref, err)
}
if desc.MediaType.IsIndex() {
idx, err := desc.ImageIndex()
if err != nil {
return nil, err
}
return flattenIndex(idx, repo, use, o)
} else if desc.MediaType.IsImage() {
img, err := desc.Image()
if err != nil {
return nil, err
}
return flattenImage(img, repo, use, o)
}
return nil, fmt.Errorf("can't flatten %s", desc.MediaType)
}
func push(flat partial.Describable, ref name.Reference, o crane.Options) error {
if idx, ok := flat.(v1.ImageIndex); ok {
return remote.WriteIndex(ref, idx, o.Remote...)
} else if img, ok := flat.(v1.Image); ok {
return remote.Write(ref, img, o.Remote...)
}
return fmt.Errorf("can't push %T", flat)
}
type remoteIndex interface {
Manifests() ([]partial.Describable, error)
}
func flattenIndex(old v1.ImageIndex, repo name.Repository, use string, o crane.Options) (partial.Describable, error) {
ri, ok := old.(remoteIndex)
if !ok {
return nil, fmt.Errorf("unexpected index")
}
m, err := old.IndexManifest()
if err != nil {
return nil, err
}
manifests, err := ri.Manifests()
if err != nil {
return nil, err
}
adds := []mutate.IndexAddendum{}
for _, m := range manifests {
// Keep the old descriptor (annotations and whatnot).
desc, err := partial.Descriptor(m)
if err != nil {
return nil, err
}
flattened, err := flattenChild(m, repo, use, o)
if err != nil {
return nil, err
}
desc.Size, err = flattened.Size()
if err != nil {
return nil, err
}
desc.Digest, err = flattened.Digest()
if err != nil {
return nil, err
}
adds = append(adds, mutate.IndexAddendum{
Add: flattened,
Descriptor: *desc,
})
}
idx := mutate.AppendManifests(empty.Index, adds...)
// Retain any annotations from the original index.
if len(m.Annotations) != 0 {
idx = mutate.Annotations(idx, m.Annotations).(v1.ImageIndex)
}
// This is stupid, but some registries get mad if you try to push OCI media types that reference docker media types.
mt, err := old.MediaType()
if err != nil {
return nil, err
}
idx = mutate.IndexMediaType(idx, mt)
return idx, nil
}
func flattenChild(old partial.Describable, repo name.Repository, use string, o crane.Options) (partial.Describable, error) {
if idx, ok := old.(v1.ImageIndex); ok {
return flattenIndex(idx, repo, use, o)
} else if img, ok := old.(v1.Image); ok {
return flattenImage(img, repo, use, o)
}
logs.Warn.Printf("can't flatten %T, skipping", old)
return old, nil
}
func flattenImage(old v1.Image, repo name.Repository, use string, o crane.Options) (partial.Describable, error) {
digest, err := old.Digest()
if err != nil {
return nil, fmt.Errorf("getting old digest: %w", err)
}
m, err := old.Manifest()
if err != nil {
return nil, fmt.Errorf("reading manifest: %w", err)
}
cf, err := old.ConfigFile()
if err != nil {
return nil, fmt.Errorf("getting config: %w", err)
}
cf = cf.DeepCopy()
oldHistory, err := json.Marshal(cf.History)
if err != nil {
return nil, fmt.Errorf("marshal history")
}
// Clear layer-specific config file information.
cf.RootFS.DiffIDs = []v1.Hash{}
cf.History = []v1.History{}
img, err := mutate.ConfigFile(empty.Image, cf)
if err != nil {
return nil, fmt.Errorf("mutating config: %w", err)
}
// TODO: Make compression configurable?
layer := stream.NewLayer(mutate.Extract(old), stream.WithCompressionLevel(gzip.BestCompression))
if err := remote.WriteLayer(repo, layer, o.Remote...); err != nil {
return nil, fmt.Errorf("uploading layer: %w", err)
}
img, err = mutate.Append(img, mutate.Addendum{
Layer: layer,
History: v1.History{
CreatedBy: fmt.Sprintf("%s flatten %s", use, digest),
Comment: string(oldHistory),
},
})
if err != nil {
return nil, fmt.Errorf("appending layers: %w", err)
}
// Retain any annotations from the original image.
if len(m.Annotations) != 0 {
img = mutate.Annotations(img, m.Annotations).(v1.Image)
}
return img, nil
}
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