Add service plugin and support in process integration.

Signed-off-by: Lantao Liu <lantaol@google.com>

services/content/service.go

@@ -20,14 +20,12 @@ import (
 	"io"
 	"sync"
 
-	eventstypes "github.com/containerd/containerd/api/events"
 	api "github.com/containerd/containerd/api/services/content/v1"
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/errdefs"
-	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/log"
-	"github.com/containerd/containerd/metadata"
 	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/services"
 	ptypes "github.com/gogo/protobuf/types"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
@@ -39,8 +37,7 @@ import (
 )
 
 type service struct {
-	store     content.Store
-	publisher events.Publisher
+	store content.Store
 }
 
 var bufPool = sync.Pool{
@@ -57,26 +54,29 @@ func init() {
 		Type: plugin.GRPCPlugin,
 		ID:   "content",
 		Requires: []plugin.Type{
-			plugin.MetadataPlugin,
+			plugin.ServicePlugin,
 		},
 		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
-			m, err := ic.Get(plugin.MetadataPlugin)
+			plugins, err := ic.GetByType(plugin.ServicePlugin)
 			if err != nil {
 				return nil, err
 			}
-
-			s, err := NewService(m.(*metadata.DB).ContentStore(), ic.Events)
-			return s, err
+			p, ok := plugins[services.ContentService]
+			if !ok {
+				return nil, errors.New("content store service not found")
+			}
+			cs, err := p.Instance()
+			if err != nil {
+				return nil, err
+			}
+			return newService(cs.(content.Store)), nil
 		},
 	})
 }
 
-// NewService returns the content GRPC server
-func NewService(cs content.Store, publisher events.Publisher) (api.ContentServer, error) {
-	return &service{
-		store:     cs,
-		publisher: publisher,
-	}, nil
+// newService returns the content GRPC server
+func newService(cs content.Store) api.ContentServer {
+	return &service{store: cs}
 }
 
 func (s *service) Register(server *grpc.Server) error {
@@ -166,12 +166,6 @@ func (s *service) Delete(ctx context.Context, req *api.DeleteContentRequest) (*p
 		return nil, errdefs.ToGRPC(err)
 	}
 
-	if err := s.publisher.Publish(ctx, "/content/delete", &eventstypes.ContentDelete{
-		Digest: req.Digest,
-	}); err != nil {
-		return nil, err
-	}
-
 	return &ptypes.Empty{}, nil
 }
 

services/content/store.go

@@ -0,0 +1,71 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package content
+
+import (
+	"context"
+
+	eventstypes "github.com/containerd/containerd/api/events"
+	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/events"
+	"github.com/containerd/containerd/metadata"
+	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/services"
+	digest "github.com/opencontainers/go-digest"
+)
+
+// store wraps content.Store with proper event published.
+type store struct {
+	content.Store
+	publisher events.Publisher
+}
+
+func init() {
+	plugin.Register(&plugin.Registration{
+		Type: plugin.ServicePlugin,
+		ID:   services.ContentService,
+		Requires: []plugin.Type{
+			plugin.MetadataPlugin,
+		},
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			m, err := ic.Get(plugin.MetadataPlugin)
+			if err != nil {
+				return nil, err
+			}
+
+			s, err := newContentStore(m.(*metadata.DB).ContentStore(), ic.Events)
+			return s, err
+		},
+	})
+}
+
+func newContentStore(cs content.Store, publisher events.Publisher) (content.Store, error) {
+	return &store{
+		Store:     cs,
+		publisher: publisher,
+	}, nil
+}
+
+func (s *store) Delete(ctx context.Context, dgst digest.Digest) error {
+	if err := s.Store.Delete(ctx, dgst); err != nil {
+		return err
+	}
+	// TODO: Consider whether we should return error here.
+	return s.publisher.Publish(ctx, "/content/delete", &eventstypes.ContentDelete{
+		Digest: dgst,
+	})
+}