images, services/images: implement image service

Server and Client images of the image store are now provided. We have
created an image metadata interface and converted the bolt functions to
implement that interface over an transaction. A remote client
implementation is provided that implements the same interface.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

images/storage.go

@@ -1,6 +1,7 @@
 package images
 
 import (
+	"context"
 	"encoding/binary"
 	"fmt"
 
@@ -8,12 +9,30 @@ import (
 	"github.com/containerd/containerd/log"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
 )
 
 var (
-	errImageUnknown = fmt.Errorf("image: unknown")
+	ErrExists   = errors.New("images: exists")
+	ErrNotFound = errors.New("images: not found")
 )
 
+type Store interface {
+	Put(ctx context.Context, name string, desc ocispec.Descriptor) error
+	Get(ctx context.Context, name string) (Image, error)
+	List(ctx context.Context) ([]Image, error)
+	Delete(ctx context.Context, name string) error
+}
+
+// IsNotFound returns true if the error is due to a missing image.
+func IsNotFound(err error) bool {
+	return errors.Cause(err) == ErrNotFound
+}
+
+func IsExists(err error) bool {
+	return errors.Cause(err) == ErrExists
+}
+
 var (
 	bucketKeyStorageVersion = []byte("v1")
 	bucketKeyImages         = []byte("images")
@@ -26,6 +45,8 @@ var (
 // "metadata" store. For now, it is bound tightly to the local machine and bolt
 // but we can take this and use it to define a service interface.
 
+// InitDB will initialize the database for use. The database must be opened for
+// write and the caller must not be holding an open transaction.
 func InitDB(db *bolt.DB) error {
 	log.L.Debug("init db")
 	return db.Update(func(tx *bolt.Tx) error {
@@ -34,8 +55,28 @@ func InitDB(db *bolt.DB) error {
 	})
 }
 
-func Register(tx *bolt.Tx, name string, desc ocispec.Descriptor) error {
-	return withImagesBucket(tx, func(bkt *bolt.Bucket) error {
+func NewImageStore(tx *bolt.Tx) Store {
+	return &storage{tx: tx}
+}
+
+type storage struct {
+	tx *bolt.Tx
+}
+
+func (s *storage) Get(ctx context.Context, name string) (Image, error) {
+	var image Image
+	if err := withImageBucket(s.tx, name, func(bkt *bolt.Bucket) error {
+		image.Name = name
+		return readImage(&image, bkt)
+	}); err != nil {
+		return Image{}, err
+	}
+
+	return image, nil
+}
+
+func (s *storage) Put(ctx context.Context, name string, desc ocispec.Descriptor) error {
+	return withImagesBucket(s.tx, func(bkt *bolt.Bucket) error {
 		ibkt, err := bkt.CreateBucketIfNotExists([]byte(name))
 		if err != nil {
 			return err
@@ -65,22 +106,10 @@ func Register(tx *bolt.Tx, name string, desc ocispec.Descriptor) error {
 	})
 }
 
-func Get(tx *bolt.Tx, name string) (Image, error) {
-	var image Image
-	if err := withImageBucket(tx, name, func(bkt *bolt.Bucket) error {
-		image.Name = name
-		return readImage(&image, bkt)
-	}); err != nil {
-		return Image{}, err
-	}
-
-	return image, nil
-}
-
-func List(tx *bolt.Tx) ([]Image, error) {
+func (s *storage) List(ctx context.Context) ([]Image, error) {
 	var images []Image
 
-	if err := withImagesBucket(tx, func(bkt *bolt.Bucket) error {
+	if err := withImagesBucket(s.tx, func(bkt *bolt.Bucket) error {
 		return bkt.ForEach(func(k, v []byte) error {
 			var (
 				image = Image{
@@ -103,8 +132,8 @@ func List(tx *bolt.Tx) ([]Image, error) {
 	return images, nil
 }
 
-func Delete(tx *bolt.Tx, name string) error {
-	return withImagesBucket(tx, func(bkt *bolt.Bucket) error {
+func (s *storage) Delete(ctx context.Context, name string) error {
+	return withImagesBucket(s.tx, func(bkt *bolt.Bucket) error {
 		return bkt.DeleteBucket([]byte(name))
 	})
 }
@@ -119,11 +148,11 @@ func readImage(image *Image, bkt *bolt.Bucket) error {
 		// keys, rather than full arrays.
 		switch string(k) {
 		case string(bucketKeyDigest):
-			image.Descriptor.Digest = digest.Digest(v)
+			image.Target.Digest = digest.Digest(v)
 		case string(bucketKeyMediaType):
-			image.Descriptor.MediaType = string(v)
+			image.Target.MediaType = string(v)
 		case string(bucketKeySize):
-			image.Descriptor.Size, _ = binary.Varint(v)
+			image.Target.Size, _ = binary.Varint(v)
 		}
 
 		return nil
@@ -149,7 +178,7 @@ func createBucketIfNotExists(tx *bolt.Tx, keys ...[]byte) (*bolt.Bucket, error)
 func withImagesBucket(tx *bolt.Tx, fn func(bkt *bolt.Bucket) error) error {
 	bkt := getImagesBucket(tx)
 	if bkt == nil {
-		return errImageUnknown
+		return ErrNotFound
 	}
 
 	return fn(bkt)
@@ -158,7 +187,7 @@ func withImagesBucket(tx *bolt.Tx, fn func(bkt *bolt.Bucket) error) error {
 func withImageBucket(tx *bolt.Tx, name string, fn func(bkt *bolt.Bucket) error) error {
 	bkt := getImageBucket(tx, name)
 	if bkt == nil {
-		return errImageUnknown
+		return ErrNotFound
 	}
 
 	return fn(bkt)