prepare for public link thumbnails

- Implement a CS3 image source handler
 - Use checksum instead of etag for unique check
 - Simplify storage layout

thumbnails/pkg/server/grpc/server.go

@@ -1,6 +1,7 @@
 package grpc
 
 import (
+	"github.com/cs3org/reva/pkg/rgrpc/todo/pool"
 	"github.com/owncloud/ocis/ocis-pkg/service/grpc"
 	"github.com/owncloud/ocis/thumbnails/pkg/proto/v0"
 	svc "github.com/owncloud/ocis/thumbnails/pkg/service/v0"
@@ -23,19 +24,26 @@ func NewService(opts ...Option) grpc.Service {
 		grpc.Flags(options.Flags...),
 		grpc.Version(options.Config.Server.Version),
 	)
-
+	tconf := options.Config.Thumbnail
+	gc, err := pool.GetGatewayServiceClient(tconf.RevaGateway)
+	if err != nil {
+		options.Logger.Error().Err(err).Msg("could not get gateway client")
+		return grpc.Service{}
+	}
 	var thumbnail proto.ThumbnailServiceHandler
 	{
 		thumbnail = svc.NewService(
 			svc.Config(options.Config),
 			svc.Logger(options.Logger),
-			svc.ThumbnailSource(imgsource.NewWebDavSource(options.Config.Thumbnail.WebDavSource)),
+			svc.ThumbnailSource(imgsource.NewWebDavSource(tconf)),
 			svc.ThumbnailStorage(
 				storage.NewFileSystemStorage(
-					options.Config.Thumbnail.FileSystemStorage,
+					tconf.FileSystemStorage,
 					options.Logger,
 				),
 			),
+			svc.CS3Source(imgsource.NewCS3Source(gc)),
+			svc.CS3Client(gc),
 		)
 		thumbnail = svc.NewInstrument(thumbnail, options.Metrics)
 		thumbnail = svc.NewLogging(thumbnail, options.Logger)