distribution/storage/paths.go

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package storage
import (
"strings"
"github.com/docker/docker-registry/digest"
"fmt"
"path"
"github.com/docker/docker-registry/common"
)
const storagePathVersion = "v2"
// TODO(sday): This needs to be changed: all layers for an image will be
// linked under the repository. Lookup from tarsum to name is not necessary,
// so we can remove the layer index. For this to properly work, image push
// must link the images layers under the repo.
// pathMapper maps paths based on "object names" and their ids. The "object
// names" mapped by pathMapper are internal to the storage system.
//
// The path layout in the storage backend will be roughly as follows:
//
// <root>/v2
// -> repositories/
// -><name>/
// -> images/
// <manifests by tag name>
// -> layers/
// -> tarsum/
// -> <tarsum version>/
// -> <tarsum hash alg>/
// <layer links to blob store>
// -> layerindex/
// -> tarsum/
// -> <tarsum version>/
// -> <tarsum hash alg>/
// <repo name links>
// -> blob/sha256
// <split directory sha256 content addressable storage>
//
// There are few important components to this path layout. First, we have the
// repository store identified by name. This contains the image manifests and
// a layer store with links to CAS blob ids. Outside of the named repo area,
// we have the layerindex, which provides lookup from tarsum id to repo
// storage. The blob store contains the actual layer data and any other data
// that can be referenced by a CAS id.
//
// We cover the path formats implemented by this path mapper below.
//
// layerLinkPathSpec: <root>/v2/repositories/<name>/layers/tarsum/<tarsum version>/<tarsum hash alg>/<tarsum hash>
// layerIndexLinkPathSpec: <root>/v2/layerindex/tarsum/<tarsum version>/<tarsum hash alg>/<tarsum hash>
// blobPathSpec: <root>/v2/blob/sha256/<first two hex bytes of digest>/<hex digest>
//
// For more information on the semantic meaning of each path and their
// contents, please see the path spec documentation.
type pathMapper struct {
root string
version string // should be a constant?
}
// TODO(stevvooe): This storage layout currently allows lookup to layer stores
// by repo name via the tarsum. The layer index lookup could come with an
// access control check against the link contents before proceeding. The main
// problem with this comes with a collision in the tarsum algorithm: if party
// A uploads a layer before party B, with an identical tarsum, party B may
// never be able to get access to the tarsum stored under party A. We'll need
// a way for party B to associate with a "unique" version of their image. This
// may be as simple as forcing the client to re-upload images to which they
// don't have access.
// path returns the path identified by spec.
func (pm *pathMapper) path(spec pathSpec) (string, error) {
// Switch on the path object type and return the appropriate path. At
// first glance, one may wonder why we don't use an interface to
// accomplish this. By keep the formatting separate from the pathSpec, we
// keep separate the path generation componentized. These specs could be
// passed to a completely different mapper implementation and generate a
// different set of paths.
//
// For example, imagine migrating from one backend to the other: one could
// build a filesystem walker that converts a string path in one version,
// to an intermediate path object, than can be consumed and mapped by the
// other version.
switch v := spec.(type) {
case layerLinkPathSpec:
if !strings.HasPrefix(v.digest.Algorithm(), "tarsum") {
// Only tarsum is supported, for now
return "", fmt.Errorf("unsupport content digest: %v", v.digest)
}
tsi, err := common.ParseTarSum(v.digest.String())
if err != nil {
// TODO(sday): This will return an InvalidTarSumError from
// ParseTarSum but we may want to wrap this. This error should
// never be encountered in production, since the tarsum should be
// validated by this point.
return "", err
}
p := path.Join(append([]string{pm.root, pm.version, "repositories", v.name, "layers"}, tarSumInfoPathComponents(tsi)...)...)
return p, nil
case layerIndexLinkPathSpec:
if !strings.HasPrefix(v.digest.Algorithm(), "tarsum") {
// Only tarsum is supported, for now
return "", fmt.Errorf("unsupport content digest: %v", v.digest)
}
tsi, err := common.ParseTarSum(v.digest.String())
if err != nil {
// TODO(sday): This will return an InvalidTarSumError from
// ParseTarSum but we may want to wrap this. This error should
// never be encountered in production, since the tarsum should be
// validated by this point.
return "", err
}
p := path.Join(append([]string{pm.root, pm.version, "layerindex"}, tarSumInfoPathComponents(tsi)...)...)
return p, nil
case blobPathSpec:
p := path.Join([]string{pm.root, pm.version, "blob", v.alg, v.digest[:2], v.digest}...)
return p, nil
default:
// TODO(sday): This is an internal error. Ensure it doesn't escape (panic?).
return "", fmt.Errorf("unknown path spec: %#v", v)
}
}
// pathSpec is a type to mark structs as path specs. There is no
// implementation because we'd like to keep the specs and the mappers
// decoupled.
type pathSpec interface {
pathSpec()
}
// layerLink specifies a path for a layer link, which is a file with a blob
// id. The layer link will contain a content addressable blob id reference
// into the blob store. The format of the contents is as follows:
//
// <algorithm>:<hex digest of layer data>
//
// The following example of the file contents is more illustrative:
//
// sha256:96443a84ce518ac22acb2e985eda402b58ac19ce6f91980bde63726a79d80b36
//
// This says indicates that there is a blob with the id/digest, calculated via
// sha256 that can be fetched from the blob store.
type layerLinkPathSpec struct {
name string
digest digest.Digest
}
func (layerLinkPathSpec) pathSpec() {}
// layerIndexLinkPath provides a path to a registry global layer store,
// indexed by tarsum. The target file will contain the repo name of the
// "owner" of the layer. An example name link file follows:
//
// library/ubuntu
// foo/bar
//
// The above file has the tarsum stored under the foo/bar repository and the
// library/ubuntu repository. The storage layer should access the tarsum from
// the first repository to which the client has access.
type layerIndexLinkPathSpec struct {
digest digest.Digest
}
func (layerIndexLinkPathSpec) pathSpec() {}
// blobPath contains the path for the registry global blob store. For now,
// this contains layer data, exclusively.
type blobPathSpec struct {
// TODO(stevvooe): Port this to make better use of Digest type.
alg string
digest string
}
func (blobPathSpec) pathSpec() {}
// tarSumInfoPath generates storage path components for the provided
// TarSumInfo.
func tarSumInfoPathComponents(tsi common.TarSumInfo) []string {
version := tsi.Version
if version == "" {
version = "v0"
}
return []string{"tarsum", version, tsi.Algorithm, tsi.Digest}
}