distribution/docs/storage/paths.go

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package storage
import (
"fmt"
"path"
"strings"
"github.com/docker/distribution/digest"
)
const storagePathVersion = "v2"
// 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 is roughly as follows:
//
// <root>/v2
// -> repositories/
// -><name>/
// -> _manifests/
// revisions
// -> <manifest digest path>
// -> link
// -> signatures
// <algorithm>/<digest>/link
// tags/<tag>
// -> current/link
// -> index
// -> <algorithm>/<hex digest>/link
// -> _layers/
// <layer links to blob store>
// -> _uploads/<uuid>
// data
// startedat
// -> blob/<algorithm>
// <split directory content addressable storage>
//
// The storage backend layout is broken up into a content- addressable blob
// store and repositories. The content-addressable blob store holds most data
// throughout the backend, keyed by algorithm and digests of the underlying
// content. Access to the blob store is controled through links from the
// repository to blobstore.
//
// A repository is made up of layers, manifests and tags. The layers component
// is just a directory of layers which are "linked" into a repository. A layer
// can only be accessed through a qualified repository name if it is linked in
// the repository. Uploads of layers are managed in the uploads directory,
// which is key by upload uuid. When all data for an upload is received, the
// data is moved into the blob store and the upload directory is deleted.
// Abandoned uploads can be garbage collected by reading the startedat file
// and removing uploads that have been active for longer than a certain time.
//
// The third component of the repository directory is the manifests store,
// which is made up of a revision store and tag store. Manifests are stored in
// the blob store and linked into the revision store. Signatures are separated
// from the manifest payload data and linked into the blob store, as well.
// While the registry can save all revisions of a manifest, no relationship is
// implied as to the ordering of changes to a manifest. The tag store provides
// support for name, tag lookups of manifests, using "current/link" under a
// named tag directory. An index is maintained to support deletions of all
// revisions of a given manifest tag.
//
// We cover the path formats implemented by this path mapper below.
//
// Manifests:
//
// manifestRevisionPathSpec: <root>/v2/repositories/<name>/_manifests/revisions/<algorithm>/<hex digest>/
// manifestRevisionLinkPathSpec: <root>/v2/repositories/<name>/_manifests/revisions/<algorithm>/<hex digest>/link
// manifestSignaturesPathSpec: <root>/v2/repositories/<name>/_manifests/revisions/<algorithm>/<hex digest>/signatures/
// manifestSignatureLinkPathSpec: <root>/v2/repositories/<name>/_manifests/revisions/<algorithm>/<hex digest>/signatures/<algorithm>/<hex digest>/link
//
// Tags:
//
// manifestTagsPathSpec: <root>/v2/repositories/<name>/_manifests/tags/
// manifestTagPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/
// manifestTagCurrentPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/current/link
// manifestTagIndexPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/index/
// manifestTagIndexEntryPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/index/<algorithm>/<hex digest>/
// manifestTagIndexEntryLinkPathSpec: <root>/v2/repositories/<name>/_manifests/tags/<tag>/index/<algorithm>/<hex digest>/link
//
// Layers:
//
// layerLinkPathSpec: <root>/v2/repositories/<name>/_layers/tarsum/<tarsum version>/<tarsum hash alg>/<tarsum hash>/link
//
// Uploads:
//
// uploadDataPathSpec: <root>/v2/repositories/<name>/_uploads/<uuid>/data
// uploadStartedAtPathSpec: <root>/v2/repositories/<name>/_uploads/<uuid>/startedat
//
// Blob Store:
//
// blobPathSpec: <root>/v2/blobs/<algorithm>/<first two hex bytes of digest>/<hex digest>
// blobDataPathSpec: <root>/v2/blobs/<algorithm>/<first two hex bytes of digest>/<hex digest>/data
//
// 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?
}
var defaultPathMapper = &pathMapper{
root: "/docker/registry/",
version: storagePathVersion,
}
// 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.
rootPrefix := []string{pm.root, pm.version}
repoPrefix := append(rootPrefix, "repositories")
switch v := spec.(type) {
case manifestRevisionPathSpec:
components, err := digestPathComponents(v.revision, false)
if err != nil {
return "", err
}
return path.Join(append(append(repoPrefix, v.name, "_manifests", "revisions"), components...)...), nil
case manifestRevisionLinkPathSpec:
root, err := pm.path(manifestRevisionPathSpec{
name: v.name,
revision: v.revision,
})
if err != nil {
return "", err
}
return path.Join(root, "link"), nil
case manifestSignaturesPathSpec:
root, err := pm.path(manifestRevisionPathSpec{
name: v.name,
revision: v.revision,
})
if err != nil {
return "", err
}
return path.Join(root, "signatures"), nil
case manifestSignatureLinkPathSpec:
root, err := pm.path(manifestSignaturesPathSpec{
name: v.name,
revision: v.revision,
})
if err != nil {
return "", err
}
signatureComponents, err := digestPathComponents(v.signature, false)
if err != nil {
return "", err
}
return path.Join(root, path.Join(append(signatureComponents, "link")...)), nil
case manifestTagsPathSpec:
return path.Join(append(repoPrefix, v.name, "_manifests", "tags")...), nil
case manifestTagPathSpec:
root, err := pm.path(manifestTagsPathSpec{
name: v.name,
})
if err != nil {
return "", err
}
return path.Join(root, v.tag), nil
case manifestTagCurrentPathSpec:
root, err := pm.path(manifestTagPathSpec{
name: v.name,
tag: v.tag,
})
if err != nil {
return "", err
}
return path.Join(root, "current", "link"), nil
case manifestTagIndexPathSpec:
root, err := pm.path(manifestTagPathSpec{
name: v.name,
tag: v.tag,
})
if err != nil {
return "", err
}
return path.Join(root, "index"), nil
case manifestTagIndexEntryLinkPathSpec:
root, err := pm.path(manifestTagIndexEntryPathSpec{
name: v.name,
tag: v.tag,
revision: v.revision,
})
if err != nil {
return "", err
}
return path.Join(root, "link"), nil
case manifestTagIndexEntryPathSpec:
root, err := pm.path(manifestTagIndexPathSpec{
name: v.name,
tag: v.tag,
})
if err != nil {
return "", err
}
components, err := digestPathComponents(v.revision, false)
if err != nil {
return "", err
}
return path.Join(root, path.Join(components...)), nil
case layerLinkPathSpec:
components, err := digestPathComponents(v.digest, false)
if err != nil {
return "", err
}
layerLinkPathComponents := append(repoPrefix, v.name, "_layers")
return path.Join(path.Join(append(layerLinkPathComponents, components...)...), "link"), nil
case blobDataPathSpec:
components, err := digestPathComponents(v.digest, true)
if err != nil {
return "", err
}
components = append(components, "data")
blobPathPrefix := append(rootPrefix, "blobs")
return path.Join(append(blobPathPrefix, components...)...), nil
case uploadDataPathSpec:
return path.Join(append(repoPrefix, v.name, "_uploads", v.uuid, "data")...), nil
case uploadStartedAtPathSpec:
return path.Join(append(repoPrefix, v.name, "_uploads", v.uuid, "startedat")...), 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()
}
// manifestRevisionPathSpec describes the components of the directory path for
// a manifest revision.
type manifestRevisionPathSpec struct {
name string
revision digest.Digest
}
func (manifestRevisionPathSpec) pathSpec() {}
// manifestRevisionLinkPathSpec describes the path components required to look
// up the data link for a revision of a manifest. If this file is not present,
// the manifest blob is not available in the given repo. The contents of this
// file should just be the digest.
type manifestRevisionLinkPathSpec struct {
name string
revision digest.Digest
}
func (manifestRevisionLinkPathSpec) pathSpec() {}
// manifestSignaturesPathSpec decribes the path components for the directory
// containing all the signatures for the target blob. Entries are named with
// the underlying key id.
type manifestSignaturesPathSpec struct {
name string
revision digest.Digest
}
func (manifestSignaturesPathSpec) pathSpec() {}
// manifestSignatureLinkPathSpec decribes the path components used to look up
// a signature file by the hash of its blob.
type manifestSignatureLinkPathSpec struct {
name string
revision digest.Digest
signature digest.Digest
}
func (manifestSignatureLinkPathSpec) pathSpec() {}
// manifestTagsPathSpec describes the path elements required to point to the
// manifest tags directory.
type manifestTagsPathSpec struct {
name string
}
func (manifestTagsPathSpec) pathSpec() {}
// manifestTagPathSpec describes the path elements required to point to the
// manifest tag links files under a repository. These contain a blob id that
// can be used to look up the data and signatures.
type manifestTagPathSpec struct {
name string
tag string
}
func (manifestTagPathSpec) pathSpec() {}
// manifestTagCurrentPathSpec describes the link to the current revision for a
// given tag.
type manifestTagCurrentPathSpec struct {
name string
tag string
}
func (manifestTagCurrentPathSpec) pathSpec() {}
// manifestTagCurrentPathSpec describes the link to the index of revisions
// with the given tag.
type manifestTagIndexPathSpec struct {
name string
tag string
}
func (manifestTagIndexPathSpec) pathSpec() {}
// manifestTagIndexEntryPathSpec contains the entries of the index by revision.
type manifestTagIndexEntryPathSpec struct {
name string
tag string
revision digest.Digest
}
func (manifestTagIndexEntryPathSpec) pathSpec() {}
// manifestTagIndexEntryLinkPathSpec describes the link to a revisions of a
// manifest with given tag within the index.
type manifestTagIndexEntryLinkPathSpec struct {
name string
tag string
revision digest.Digest
}
func (manifestTagIndexEntryLinkPathSpec) 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() {}
// blobAlgorithmReplacer does some very simple path sanitization for user
// input. Mostly, this is to provide some heirachry for tarsum digests. Paths
// should be "safe" before getting this far due to strict digest requirements
// but we can add further path conversion here, if needed.
var blobAlgorithmReplacer = strings.NewReplacer(
"+", "/",
".", "/",
";", "/",
)
// // blobPathSpec contains the path for the registry global blob store.
// type blobPathSpec struct {
// digest digest.Digest
// }
// func (blobPathSpec) pathSpec() {}
// blobDataPathSpec contains the path for the registry global blob store. For
// now, this contains layer data, exclusively.
type blobDataPathSpec struct {
digest digest.Digest
}
func (blobDataPathSpec) pathSpec() {}
// uploadDataPathSpec defines the path parameters of the data file for
// uploads.
type uploadDataPathSpec struct {
name string
uuid string
}
func (uploadDataPathSpec) pathSpec() {}
// uploadDataPathSpec defines the path parameters for the file that stores the
// start time of an uploads. If it is missing, the upload is considered
// unknown. Admittedly, the presence of this file is an ugly hack to make sure
// we have a way to cleanup old or stalled uploads that doesn't rely on driver
// FileInfo behavior. If we come up with a more clever way to do this, we
// should remove this file immediately and rely on the startetAt field from
// the client to enforce time out policies.
type uploadStartedAtPathSpec struct {
name string
uuid string
}
func (uploadStartedAtPathSpec) pathSpec() {}
// digestPathComponents provides a consistent path breakdown for a given
// digest. For a generic digest, it will be as follows:
//
// <algorithm>/<hex digest>
//
// Most importantly, for tarsum, the layout looks like this:
//
// tarsum/<version>/<digest algorithm>/<full digest>
//
// If multilevel is true, the first two bytes of the digest will separate
// groups of digest folder. It will be as follows:
//
// <algorithm>/<first two bytes of digest>/<full digest>
//
func digestPathComponents(dgst digest.Digest, multilevel bool) ([]string, error) {
if err := dgst.Validate(); err != nil {
return nil, err
}
algorithm := blobAlgorithmReplacer.Replace(dgst.Algorithm())
hex := dgst.Hex()
prefix := []string{algorithm}
var suffix []string
if multilevel {
suffix = append(suffix, hex[:2])
}
suffix = append(suffix, hex)
if tsi, err := digest.ParseTarSum(dgst.String()); err == nil {
// We have a tarsum!
version := tsi.Version
if version == "" {
version = "v0"
}
prefix = []string{
"tarsum",
version,
tsi.Algorithm,
}
}
return append(prefix, suffix...), nil
}