events: decouple events package from grpc

By defining a concrete, non-protobuf type for the events interface, we
can completely decouple it from the grpc packages that are expensive at
runtime. This does requires some allocation cost for converting between
types, but the saving for the size of the shim are worth it.

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

services/events/service.go

@@ -3,6 +3,7 @@ package events
 import (
 	api "github.com/containerd/containerd/api/services/events/v1"
 	"github.com/containerd/containerd/errdefs"
+	"github.com/containerd/containerd/events"
 	"github.com/containerd/containerd/events/exchange"
 	"github.com/containerd/containerd/plugin"
 	ptypes "github.com/gogo/protobuf/types"
@@ -44,7 +45,7 @@ func (s *service) Publish(ctx context.Context, r *api.PublishRequest) (*ptypes.E
 }
 
 func (s *service) Forward(ctx context.Context, r *api.ForwardRequest) (*ptypes.Empty, error) {
-	if err := s.events.Forward(ctx, r.Envelope); err != nil {
+	if err := s.events.Forward(ctx, fromProto(r.Envelope)); err != nil {
 		return nil, errdefs.ToGRPC(err)
 	}
 
@@ -59,7 +60,7 @@ func (s *service) Subscribe(req *api.SubscribeRequest, srv api.Events_SubscribeS
 	for {
 		select {
 		case ev := <-eventq:
-			if err := srv.Send(ev); err != nil {
+			if err := srv.Send(toProto(ev)); err != nil {
 				return errors.Wrapf(err, "failed sending event to subscriber")
 			}
 		case err := <-errq:
@@ -71,3 +72,21 @@ func (s *service) Subscribe(req *api.SubscribeRequest, srv api.Events_SubscribeS
 		}
 	}
 }
+
+func toProto(env *events.Envelope) *api.Envelope {
+	return &api.Envelope{
+		Timestamp: env.Timestamp,
+		Namespace: env.Namespace,
+		Topic:     env.Topic,
+		Event:     env.Event,
+	}
+}
+
+func fromProto(env *api.Envelope) *events.Envelope {
+	return &events.Envelope{
+		Timestamp: env.Timestamp,
+		Namespace: env.Namespace,
+		Topic:     env.Topic,
+		Event:     env.Event,
+	}
+}