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base_image.go
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/
base_image.go
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// Copyright 2022, 2023 Chainguard, Inc.
//
// 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 baseimg
import (
"archive/tar"
"bytes"
"compress/gzip"
"fmt"
"os"
"path"
"github.com/chainguard-dev/go-apk/pkg/apk"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/layout"
ocitypes "github.com/google/go-containerregistry/pkg/v1/types"
"chainguard.dev/apko/pkg/build/types"
)
type BaseImage struct {
img v1.Image
apkIndex []byte
installedPackages []*apk.InstalledPackage
materizalizedApkIndexPath string
arch types.Architecture
}
// See https://github.com/opencontainers/image-spec/blob/main/image-index.md#image-index-property-descriptions
// Briefly: index.json can either list manifest of per arch images, or redirect to actual image index (nested case)
func getUnnestedImageIndex(imgPath string) (v1.ImageIndex, error) {
index, err := layout.ImageIndexFromPath(imgPath)
if err != nil {
return nil, err
}
indexManifest, err := index.IndexManifest()
if err != nil {
return nil, err
}
for _, m := range indexManifest.Manifests {
if m.MediaType == ocitypes.OCIImageIndex {
return index.ImageIndex(m.Digest)
}
}
return index, nil
}
func getImageForArch(imgPath string, arch types.Architecture) (v1.Image, error) {
index, err := getUnnestedImageIndex(imgPath)
if err != nil {
return nil, err
}
indexManifest, err := index.IndexManifest()
if err != nil {
return nil, err
}
for _, m := range indexManifest.Manifests {
img, err := index.Image(m.Digest)
if err != nil {
return nil, err
}
config, err := img.ConfigFile()
if err != nil {
return nil, err
}
if config == nil {
return nil, fmt.Errorf("got image without config")
}
if config.Architecture == arch.ToOCIPlatform().Architecture {
return img, nil
}
}
return nil, fmt.Errorf("image for arch not found")
}
// New creates an instance of BaseImage base on provided parameters:
// - imgPath: path to the directory containing OCI layout of the image.
// - apkIndexPath: path to the directory containing per arch APKINDEX files representing
// installed file of the base image.
// - arch: architecture of the base image.
// - materializedApkIndexPath: path where the auxiliary APKINDEX of the base image will be written to in order to
// resolve packages.
func New(imgPath string, apkIndexPath string, arch types.Architecture, materizalizedApkIndexPath string) (*BaseImage, error) {
img, err := getImageForArch(imgPath, arch)
if err != nil {
return nil, err
}
contents, err := os.ReadFile(path.Join(apkIndexPath, arch.ToAPK(), "APKINDEX"))
if err != nil {
return nil, err
}
reader := bytes.NewReader(contents)
installedPackages, err := apk.ParseInstalled(reader)
if err != nil {
return nil, err
}
baseImg := BaseImage{
img: img,
apkIndex: contents,
installedPackages: installedPackages,
materizalizedApkIndexPath: materizalizedApkIndexPath,
arch: arch,
}
err = baseImg.createAPKIndexArchive(baseImg.APKIndexPath())
if err != nil {
return nil, err
}
return &baseImg, nil
}
func (baseImg *BaseImage) Image() v1.Image {
return baseImg.img
}
func (baseImg *BaseImage) InstalledPackages() []*apk.InstalledPackage {
return baseImg.installedPackages
}
func (baseImg *BaseImage) APKIndexPath() string {
return path.Join(baseImg.materizalizedApkIndexPath, "base_image_apkindex")
}
func (baseImg *BaseImage) createAPKIndexArchive(apkIndexTargetPath string) error {
archDir := path.Join(apkIndexTargetPath, baseImg.arch.ToAPK())
if err := os.MkdirAll(archDir, 0777); err != nil {
return err
}
tarFile, err := os.OpenFile(path.Join(archDir, "APKINDEX.tar.gz"), os.O_CREATE|os.O_WRONLY, 0777)
if err != nil {
return err
}
defer tarFile.Close()
gzipWriter := gzip.NewWriter(tarFile)
defer gzipWriter.Close()
tarWriter := tar.NewWriter(gzipWriter)
defer tarWriter.Close()
header := tar.Header{Name: "APKINDEX", Size: int64(len(baseImg.apkIndex)), Mode: 0777}
if err := tarWriter.WriteHeader(&header); err != nil {
return err
}
if _, err := tarWriter.Write(baseImg.apkIndex); err != nil {
return err
}
return nil
}