Start of making QueueCreator optional for replication sources.

Change-Id: I82290991208c6e8953bdc63424760b378437674d

pkg/server/sync.go

@@ -43,7 +43,8 @@ const (
 // TODO: expose copierPoolSize as tunable
 type SyncHandler struct {
 	fromName, fromqName, toName string
-	from, fromq, to             blobserver.Storage
+	from, fromq                 blobserver.Storage
+	to                          blobserver.BlobReceiver
 
 	idle bool // if true, the handler does nothing other than providing the discovery.
 
@@ -63,14 +64,15 @@ func init() {
 	blobserver.RegisterHandlerConstructor("sync", newSyncFromConfig)
 }
 
-func newSyncFromConfig(ld blobserver.Loader, conf jsonconfig.Obj) (h http.Handler, err error) {
+func newSyncFromConfig(ld blobserver.Loader, conf jsonconfig.Obj) (http.Handler, error) {
 	from := conf.RequiredString("from")
 	to := conf.RequiredString("to")
 	fullSync := conf.OptionalBool("fullSyncOnStart", false)
 	blockFullSync := conf.OptionalBool("blockingFullSyncOnStart", false)
 	idle := conf.OptionalBool("idle", false)
-	if err = conf.Validate(); err != nil {
-		return
+	queueDir := conf.OptionalString("queueDir", "")
+	if err := conf.Validate(); err != nil {
+		return nil, err
 	}
 	if idle {
 		synch, err := createIdleSyncHandler(from, to)
@@ -81,19 +83,26 @@ func newSyncFromConfig(ld blobserver.Loader, conf jsonconfig.Obj) (h http.Handle
 	}
 	fromBs, err := ld.GetStorage(from)
 	if err != nil {
-		return
+		return nil, err
 	}
 	toBs, err := ld.GetStorage(to)
 	if err != nil {
-		return
+		return nil, err
 	}
 	fromQsc, ok := fromBs.(blobserver.StorageQueueCreator)
 	if !ok {
+		if queueDir != "" {
+			// TODO(bradfitz): finish implementing.
+			// Should create a a localdisk target on the
+			// queueDir and setup sync from that.  Be sure
+			// to remove item from top-level TODO too.
+		}
 		return nil, fmt.Errorf("Prefix %s (type %T) does not support being efficient replication source (queueing)", from, fromBs)
 	}
+
 	synch, err := createSyncHandler(from, to, fromQsc, toBs)
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	if fullSync || blockFullSync {
@@ -136,7 +145,7 @@ type timestampedError struct {
 	err error
 }
 
-func createSyncHandler(fromName, toName string, from blobserver.StorageQueueCreator, to blobserver.Storage) (*SyncHandler, error) {
+func createSyncHandler(fromName, toName string, from blobserver.StorageQueueCreator, to blobserver.BlobReceiver) (*SyncHandler, error) {
 	h := &SyncHandler{
 		copierPoolSize: 3,
 		from:           from,