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oci_layout_package.go
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/
oci_layout_package.go
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package buildpackage
import (
"archive/tar"
"compress/gzip"
"encoding/json"
"io"
"path"
"strings"
"github.com/docker/docker/pkg/ioutils"
v1 "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
"github.com/buildpacks/pack/internal/archive"
blob2 "github.com/buildpacks/pack/internal/blob"
"github.com/buildpacks/pack/internal/dist"
"github.com/buildpacks/pack/internal/style"
)
// IsOCILayoutBlob checks whether a blob is in OCI layout format.
func IsOCILayoutBlob(blob blob2.Blob) (bool, error) {
readCloser, err := blob.Open()
if err != nil {
return false, err
}
defer readCloser.Close()
_, _, err = archive.ReadTarEntry(readCloser, "/oci-layout")
if err != nil {
if archive.IsEntryNotExist(err) {
return false, nil
}
return false, err
}
return true, nil
}
// BuildpackFromOCILayoutBlob constructs buildpacks from a blob in OCI layout format.
func BuildpacksFromOCILayoutBlob(blob dist.Blob) (mainBP dist.Buildpack, dependencies []dist.Buildpack, err error) {
layoutPackage, err := newOCILayoutPackage(blob)
if err != nil {
return nil, nil, err
}
return ExtractBuildpacks(layoutPackage)
}
func ConfigFromOCILayoutBlob(blob dist.Blob) (config v1.ImageConfig, err error) {
layoutPackage, err := newOCILayoutPackage(blob)
if err != nil {
return v1.ImageConfig{}, err
}
return layoutPackage.imageInfo.Config, nil
}
type ociLayoutPackage struct {
imageInfo v1.Image
manifest v1.Manifest
blob dist.Blob
}
func newOCILayoutPackage(blob dist.Blob) (*ociLayoutPackage, error) {
index := &v1.Index{}
if err := unmarshalJSONFromBlob(blob, "/index.json", index); err != nil {
return nil, err
}
var manifestDescriptor *v1.Descriptor
for _, m := range index.Manifests {
if m.MediaType == "application/vnd.docker.distribution.manifest.v2+json" {
manifestDescriptor = &m // nolint:scopelint
break
}
}
if manifestDescriptor == nil {
return nil, errors.New("unable to find manifest")
}
manifest := &v1.Manifest{}
if err := unmarshalJSONFromBlob(blob, pathFromDescriptor(*manifestDescriptor), manifest); err != nil {
return nil, err
}
imageInfo := &v1.Image{}
if err := unmarshalJSONFromBlob(blob, pathFromDescriptor(manifest.Config), imageInfo); err != nil {
return nil, err
}
layersLabel := imageInfo.Config.Labels[dist.BuildpackLayersLabel]
if layersLabel == "" {
return nil, errors.Errorf("label %s not found", style.Symbol(dist.BuildpackLayersLabel))
}
bpLayers := dist.BuildpackLayers{}
if err := json.Unmarshal([]byte(layersLabel), &bpLayers); err != nil {
return nil, errors.Wrap(err, "unmarshaling layers label")
}
return &ociLayoutPackage{
imageInfo: *imageInfo,
manifest: *manifest,
blob: blob,
}, nil
}
func (o *ociLayoutPackage) Label(name string) (value string, err error) {
return o.imageInfo.Config.Labels[name], nil
}
func (o *ociLayoutPackage) GetLayer(diffID string) (io.ReadCloser, error) {
index := -1
for i, dID := range o.imageInfo.RootFS.DiffIDs {
if dID.String() == diffID {
index = i
break
}
}
if index == -1 {
return nil, errors.Errorf("layer %s not found in rootfs", style.Symbol(diffID))
}
layerDescriptor := o.manifest.Layers[index]
layerPath := pathFromDescriptor(layerDescriptor)
blobReader, err := o.blob.Open()
if err != nil {
return nil, err
}
tr := tar.NewReader(blobReader)
for {
header, err := tr.Next()
if err == io.EOF {
break
}
if err != nil {
return nil, errors.Wrap(err, "failed to get next tar entry")
}
if path.Clean(header.Name) == path.Clean(layerPath) {
finalReader := blobReader
if strings.HasSuffix(layerDescriptor.MediaType, ".gzip") {
finalReader, err = gzip.NewReader(tr)
if err != nil {
return nil, err
}
}
return ioutils.NewReadCloserWrapper(finalReader, func() error {
if err := finalReader.Close(); err != nil {
return err
}
return blobReader.Close()
}), nil
}
}
if err := blobReader.Close(); err != nil {
return nil, err
}
return nil, errors.Errorf("layer blob %s not found", style.Symbol(layerPath))
}
func pathFromDescriptor(descriptor v1.Descriptor) string {
return path.Join("/blobs", descriptor.Digest.Algorithm().String(), descriptor.Digest.Encoded())
}
func unmarshalJSONFromBlob(blob dist.Blob, path string, obj interface{}) error {
reader, err := blob.Open()
if err != nil {
return err
}
defer reader.Close()
_, contents, err := archive.ReadTarEntry(reader, path)
if err != nil {
return err
}
if err = json.Unmarshal(contents, obj); err != nil {
return err
}
return nil
}