distribution/storage/paths.go
Stephen J Day 83d62628fc Refactor storage to use new backend layout
This change refactors the storage backend to use the new path layout. To
facilitate this, manifest storage has been separated into a revision store and
tag store, supported by a more general blob store. The blob store is a hybrid
object, effectively providing both small object access, keyed by content
address, as well as methods that can be used to manage and traverse links to
underlying blobs. This covers common operations used in the revision store and
tag store, such as linking and traversal. The blob store can also be updated to
better support layer reading but this refactoring has been left for another
day.

The revision store and tag store support the manifest store's compound view of
data. These underlying stores provide facilities for richer access models, such
as content-addressable access and a richer tagging model. The highlight of this
change is the ability to sign a manifest from different hosts and have the
registry merge and serve those signatures as part of the manifest package.

Various other items, such as the delegate layer handler, were updated to more
directly use the blob store or other mechanism to fit with the changes.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2015-01-15 10:32:18 -08:00

458 lines
14 KiB
Go

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>/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 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(append(components, "link")...)), nil
case layerLinkPathSpec:
components, err := digestPathComponents(v.digest, false)
if err != nil {
return "", err
}
// For now, only map tarsum paths.
if components[0] != "tarsum" {
// Only tarsum is supported, for now
return "", fmt.Errorf("unsupported content digest: %v", v.digest)
}
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 describes the link to a revisions of a
// manifest with given tag within the index.
type manifestTagIndexEntryPathSpec struct {
name string
tag string
revision digest.Digest
}
func (manifestTagIndexEntryPathSpec) 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
}