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mutate.go
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mutate.go
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// 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 mutate
import (
"archive/tar"
"bytes"
"fmt"
"io"
"io/ioutil"
"path/filepath"
"strings"
"time"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/empty"
"github.com/google/go-containerregistry/pkg/v1/tarball"
"github.com/google/go-containerregistry/pkg/v1/types"
"github.com/google/go-containerregistry/pkg/v1/v1util"
)
const whiteoutPrefix = ".wh."
// Addendum contains layers and history to be appended
// to a base image
type Addendum struct {
Layer v1.Layer
History v1.History
URLs []string
Annotations map[string]string
MediaType types.MediaType
}
// AppendLayers applies layers to a base image.
func AppendLayers(base v1.Image, layers ...v1.Layer) (v1.Image, error) {
additions := make([]Addendum, 0, len(layers))
for _, layer := range layers {
additions = append(additions, Addendum{Layer: layer})
}
return Append(base, additions...)
}
// Append will apply the list of addendums to the base image
func Append(base v1.Image, adds ...Addendum) (v1.Image, error) {
if len(adds) == 0 {
return base, nil
}
if err := validate(adds); err != nil {
return nil, err
}
return &image{
base: base,
adds: adds,
}, nil
}
// Appendable is an interface that represents something that can be appended
// to an ImageIndex. We need to be able to construct a v1.Descriptor in order
// to append something, and this is the minimum required information for that.
type Appendable interface {
MediaType() (types.MediaType, error)
Digest() (v1.Hash, error)
Size() (int64, error)
}
// IndexAddendum represents an appendable thing and all the properties that
// we may want to override in the resulting v1.Descriptor.
type IndexAddendum struct {
Add Appendable
v1.Descriptor
}
// AppendManifests appends a manifest to the ImageIndex.
func AppendManifests(base v1.ImageIndex, adds ...IndexAddendum) v1.ImageIndex {
return &index{
base: base,
adds: adds,
}
}
// Config mutates the provided v1.Image to have the provided v1.Config
func Config(base v1.Image, cfg v1.Config) (v1.Image, error) {
cf, err := base.ConfigFile()
if err != nil {
return nil, err
}
cf.Config = cfg
return ConfigFile(base, cf)
}
// ConfigFile mutates the provided v1.Image to have the provided v1.ConfigFile
func ConfigFile(base v1.Image, cfg *v1.ConfigFile) (v1.Image, error) {
m, err := base.Manifest()
if err != nil {
return nil, err
}
image := &image{
base: base,
manifest: m.DeepCopy(),
configFile: cfg,
}
return image, nil
}
// CreatedAt mutates the provided v1.Image to have the provided v1.Time
func CreatedAt(base v1.Image, created v1.Time) (v1.Image, error) {
cf, err := base.ConfigFile()
if err != nil {
return nil, err
}
cfg := cf.DeepCopy()
cfg.Created = created
return ConfigFile(base, cfg)
}
// Extract takes an image and returns an io.ReadCloser containing the image's
// flattened filesystem.
//
// Callers can read the filesystem contents by passing the reader to
// tar.NewReader, or io.Copy it directly to some output.
//
// If a caller doesn't read the full contents, they should Close it to free up
// resources used during extraction.
func Extract(img v1.Image) io.ReadCloser {
pr, pw := io.Pipe()
go func() {
// Close the writer with any errors encountered during
// extraction. These errors will be returned by the reader end
// on subsequent reads. If err == nil, the reader will return
// EOF.
pw.CloseWithError(extract(img, pw))
}()
return pr
}
// Adapted from https://github.com/google/containerregistry/blob/da03b395ccdc4e149e34fbb540483efce962dc64/client/v2_2/docker_image_.py#L816
func extract(img v1.Image, w io.Writer) error {
tarWriter := tar.NewWriter(w)
defer tarWriter.Close()
fileMap := map[string]bool{}
layers, err := img.Layers()
if err != nil {
return fmt.Errorf("retrieving image layers: %v", err)
}
// we iterate through the layers in reverse order because it makes handling
// whiteout layers more efficient, since we can just keep track of the removed
// files as we see .wh. layers and ignore those in previous layers.
for i := len(layers) - 1; i >= 0; i-- {
layer := layers[i]
layerReader, err := layer.Uncompressed()
if err != nil {
return fmt.Errorf("reading layer contents: %v", err)
}
defer layerReader.Close()
tarReader := tar.NewReader(layerReader)
for {
header, err := tarReader.Next()
if err == io.EOF {
break
}
if err != nil {
return fmt.Errorf("reading tar: %v", err)
}
basename := filepath.Base(header.Name)
dirname := filepath.Dir(header.Name)
tombstone := strings.HasPrefix(basename, whiteoutPrefix)
if tombstone {
basename = basename[len(whiteoutPrefix):]
}
// check if we have seen value before
// if we're checking a directory, don't filepath.Join names
var name string
if header.Typeflag == tar.TypeDir {
name = header.Name
} else {
name = filepath.Join(dirname, basename)
}
if _, ok := fileMap[name]; ok {
continue
}
// check for a whited out parent directory
if inWhiteoutDir(fileMap, name) {
continue
}
// mark file as handled. non-directory implicitly tombstones
// any entries with a matching (or child) name
fileMap[name] = tombstone || !(header.Typeflag == tar.TypeDir)
if !tombstone {
tarWriter.WriteHeader(header)
if header.Size > 0 {
if _, err := io.Copy(tarWriter, tarReader); err != nil {
return err
}
}
}
}
}
return nil
}
func inWhiteoutDir(fileMap map[string]bool, file string) bool {
for {
if file == "" {
break
}
dirname := filepath.Dir(file)
if file == dirname {
break
}
if val, ok := fileMap[dirname]; ok && val {
return true
}
file = dirname
}
return false
}
// Time sets all timestamps in an image to the given timestamp.
func Time(img v1.Image, t time.Time) (v1.Image, error) {
newImage := empty.Image
layers, err := img.Layers()
if err != nil {
return nil, fmt.Errorf("getting image layers: %v", err)
}
// Strip away all timestamps from layers
var newLayers []v1.Layer
for _, layer := range layers {
newLayer, err := layerTime(layer, t)
if err != nil {
return nil, fmt.Errorf("setting layer times: %v", err)
}
newLayers = append(newLayers, newLayer)
}
newImage, err = AppendLayers(newImage, newLayers...)
if err != nil {
return nil, fmt.Errorf("appending layers: %v", err)
}
ocf, err := img.ConfigFile()
if err != nil {
return nil, fmt.Errorf("getting original config file: %v", err)
}
cf, err := newImage.ConfigFile()
if err != nil {
return nil, fmt.Errorf("setting config file: %v", err)
}
cfg := cf.DeepCopy()
// Copy basic config over
cfg.Architecture = ocf.Architecture
cfg.OS = ocf.OS
cfg.OSVersion = ocf.OSVersion
cfg.Config = ocf.Config
// Strip away timestamps from the config file
cfg.Created = v1.Time{Time: t}
for _, h := range cfg.History {
h.Created = v1.Time{Time: t}
}
return ConfigFile(newImage, cfg)
}
func layerTime(layer v1.Layer, t time.Time) (v1.Layer, error) {
layerReader, err := layer.Uncompressed()
if err != nil {
return nil, fmt.Errorf("getting layer: %v", err)
}
defer layerReader.Close()
w := new(bytes.Buffer)
tarWriter := tar.NewWriter(w)
defer tarWriter.Close()
tarReader := tar.NewReader(layerReader)
for {
header, err := tarReader.Next()
if err == io.EOF {
break
}
if err != nil {
return nil, fmt.Errorf("reading layer: %v", err)
}
header.ModTime = t
if err := tarWriter.WriteHeader(header); err != nil {
return nil, fmt.Errorf("writing tar header: %v", err)
}
if header.Typeflag == tar.TypeReg {
if _, err = io.Copy(tarWriter, tarReader); err != nil {
return nil, fmt.Errorf("writing layer file: %v", err)
}
}
}
if err := tarWriter.Close(); err != nil {
return nil, err
}
b := w.Bytes()
// gzip the contents, then create the layer
opener := func() (io.ReadCloser, error) {
return v1util.GzipReadCloser(ioutil.NopCloser(bytes.NewReader(b))), nil
}
layer, err = tarball.LayerFromOpener(opener)
if err != nil {
return nil, fmt.Errorf("creating layer: %v", err)
}
return layer, nil
}
// Canonical is a helper function to combine Time and configFile
// to remove any randomness during a docker build.
func Canonical(img v1.Image) (v1.Image, error) {
// Set all timestamps to 0
created := time.Time{}
img, err := Time(img, created)
if err != nil {
return nil, err
}
cf, err := img.ConfigFile()
if err != nil {
return nil, err
}
// Get rid of host-dependent random config
cfg := cf.DeepCopy()
cfg.Container = ""
cfg.Config.Hostname = ""
cfg.DockerVersion = ""
return ConfigFile(img, cfg)
}
// MediaType modifies the MediaType() of the given image.
func MediaType(img v1.Image, mt types.MediaType) v1.Image {
return &image{
base: img,
mediaType: &mt,
}
}
// IndexMediaType modifies the MediaType() of the given index.
func IndexMediaType(idx v1.ImageIndex, mt types.MediaType) v1.ImageIndex {
return &index{
base: idx,
mediaType: &mt,
}
}