API to retrive tag's digests

Add an interface alongside TagStore that provides API to retreive
digests of all manifests that a tag historically pointed to. It also
includes currently linked tag.

Signed-off-by: Manish Tomar <manish.tomar@docker.com>

registry/storage/tagstore.go

@@ -196,3 +196,37 @@ func (ts *tagStore) Lookup(ctx context.Context, desc distribution.Descriptor) ([
 
 	return tags, nil
 }
+
+func (ts *tagStore) Indexes(ctx context.Context, tag string) ([]digest.Digest, error) {
+	var tagLinkPath = func(name string, dgst digest.Digest) (string, error) {
+		return pathFor(manifestTagIndexEntryLinkPathSpec{
+			name:     name,
+			tag:      tag,
+			revision: dgst,
+		})
+	}
+	lbs := &linkedBlobStore{
+		blobStore: ts.blobStore,
+		blobAccessController: &linkedBlobStatter{
+			blobStore:   ts.blobStore,
+			repository:  ts.repository,
+			linkPathFns: []linkPathFunc{manifestRevisionLinkPath},
+		},
+		repository:  ts.repository,
+		ctx:         ctx,
+		linkPathFns: []linkPathFunc{tagLinkPath},
+		linkDirectoryPathSpec: manifestTagIndexPathSpec{
+			name: ts.repository.Named().Name(),
+			tag:  tag,
+		},
+	}
+	var dgsts []digest.Digest
+	err := lbs.Enumerate(ctx, func(dgst digest.Digest) error {
+		dgsts = append(dgsts, dgst)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return dgsts, nil
+}

registry/storage/tagstore_test.go

@@ -2,15 +2,22 @@ package storage
 
 import (
 	"context"
+	"reflect"
 	"testing"
 
 	"github.com/docker/distribution"
+	"github.com/docker/distribution/manifest"
+	"github.com/docker/distribution/manifest/schema2"
 	"github.com/docker/distribution/reference"
 	"github.com/docker/distribution/registry/storage/driver/inmemory"
+	digest "github.com/opencontainers/go-digest"
 )
 
 type tagsTestEnv struct {
 	ts  distribution.TagService
+	bs  distribution.BlobStore
+	ms  distribution.ManifestService
+	gbs distribution.BlobStatter
 	ctx context.Context
 }
 
@@ -27,10 +34,17 @@ func testTagStore(t *testing.T) *tagsTestEnv {
 	if err != nil {
 		t.Fatal(err)
 	}
+	ms, err := repo.Manifests(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	return &tagsTestEnv{
 		ctx: ctx,
 		ts:  repo.Tags(ctx),
+		bs:  repo.Blobs(ctx),
+		gbs: reg.BlobStatter(),
+		ms:  ms,
 	}
 }
 
@@ -205,5 +219,75 @@ func TestTagLookup(t *testing.T) {
 	if len(tags) != 2 {
 		t.Errorf("Lookup of descB returned %d tags, expected 2", len(tags))
 	}
-
+}
+
+func TestTagIndexes(t *testing.T) {
+	env := testTagStore(t)
+	tagStore := env.ts
+	ctx := env.ctx
+
+	indexes, ok := tagStore.(distribution.TagIndexes)
+	if !ok {
+		t.Fatal("tagStore does not implement TagIndexes interface")
+	}
+
+	conf, err := env.bs.Put(ctx, "application/octet-stream", []byte{0})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dgstsSet := make(map[digest.Digest]bool)
+	for i := 0; i < 3; i++ {
+		layer, err := env.bs.Put(ctx, "application/octet-stream", []byte{byte(i + 1)})
+		if err != nil {
+			t.Fatal(err)
+		}
+		m := schema2.Manifest{
+			Versioned: manifest.Versioned{
+				SchemaVersion: 2,
+				MediaType:     schema2.MediaTypeManifest,
+			},
+			Config: distribution.Descriptor{
+				Digest:    conf.Digest,
+				Size:      1,
+				MediaType: schema2.MediaTypeImageConfig,
+			},
+			Layers: []distribution.Descriptor{
+				{
+					Digest:    layer.Digest,
+					Size:      1,
+					MediaType: schema2.MediaTypeLayer,
+				},
+			},
+		}
+		dm, err := schema2.FromStruct(m)
+		if err != nil {
+			t.Fatal(err)
+		}
+		dgst, err := env.ms.Put(ctx, dm)
+		if err != nil {
+			t.Fatal(err)
+		}
+		desc, err := env.gbs.Stat(ctx, dgst)
+		if err != nil {
+			t.Fatal(err)
+		}
+		err = tagStore.Tag(ctx, "t", desc)
+		if err != nil {
+			t.Fatal(err)
+		}
+		dgstsSet[dgst] = true
+	}
+
+	gotDgsts, err := indexes.Indexes(ctx, "t")
+	if err != nil {
+		t.Fatal(err)
+	}
+	gotDgstsSet := make(map[digest.Digest]bool)
+	for _, dgst := range gotDgsts {
+		gotDgstsSet[dgst] = true
+	}
+	if !reflect.DeepEqual(dgstsSet, gotDgstsSet) {
+		t.Fatalf("Expected digests: %v but got digests: %v", dgstsSet, gotDgstsSet)
+	}
 }

tags.go

@@ -2,6 +2,8 @@ package distribution
 
 import (
 	"context"
+
+	digest "github.com/opencontainers/go-digest"
 )
 
 // TagService provides access to information about tagged objects.
@@ -25,3 +27,10 @@ type TagService interface {
 	// Lookup returns the set of tags referencing the given digest.
 	Lookup(ctx context.Context, digest Descriptor) ([]string, error)
 }
+
+// TagIndexes proves method to retreive all the digests that a tag historically pointed to
+type TagIndexes interface {
+	// Indexes returns set of digests that this tag historically pointed to. This also includes
+	// currently linked digest. There is no ordering guaranteed
+	Indexes(ctx context.Context, tag string) ([]digest.Digest, error)
+}