Add error return to Repository method on Registry

The method (Registry).Repository may now return an error. This is too allow
certain implementationt to validate the name or opt to not return a repository
under certain conditions.

In conjunction with this change, error declarations have been moved into a
single file in the distribution package. Several error declarations that had
remained in the storage package have been moved into distribution, as well. The
declarations for Layer and LayerUpload have also been moved into the main
registry file, as a result.

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

docs/handlers/app.go

@@ -227,10 +227,30 @@ func (app *App) dispatcher(dispatch dispatchFunc) http.Handler {
 			return
 		}
 
-		// decorate the authorized repository with an event bridge.
-		context.Repository = notifications.Listen(
-			app.registry.Repository(context, getName(context)),
-			app.eventBridge(context, r))
+		if app.nameRequired(r) {
+			repository, err := app.registry.Repository(context, getName(context))
+
+			if err != nil {
+				ctxu.GetLogger(context).Errorf("error resolving repository: %v", err)
+
+				switch err := err.(type) {
+				case distribution.ErrRepositoryUnknown:
+					context.Errors.Push(v2.ErrorCodeNameUnknown, err)
+				case distribution.ErrRepositoryNameInvalid:
+					context.Errors.Push(v2.ErrorCodeNameInvalid, err)
+				}
+
+				w.WriteHeader(http.StatusBadRequest)
+				serveJSON(w, context.Errors)
+				return
+			}
+
+			// assign and decorate the authorized repository with an event bridge.
+			context.Repository = notifications.Listen(
+				repository,
+				app.eventBridge(context, r))
+		}
+
 		handler := dispatch(context, r)
 
 		ssrw := &singleStatusResponseWriter{ResponseWriter: w}
@@ -318,9 +338,7 @@ func (app *App) authorized(w http.ResponseWriter, r *http.Request, context *Cont
 		}
 	} else {
 		// Only allow the name not to be set on the base route.
-		route := mux.CurrentRoute(r)
-
-		if route == nil || route.GetName() != v2.RouteNameBase {
+		if app.nameRequired(r) {
 			// For this to be properly secured, repo must always be set for a
 			// resource that may make a modification. The only condition under
 			// which name is not set and we still allow access is when the
@@ -378,6 +396,12 @@ func (app *App) eventBridge(ctx *Context, r *http.Request) notifications.Listene
 	return notifications.NewBridge(ctx.urlBuilder, app.events.source, actor, request, app.events.sink)
 }
 
+// nameRequired returns true if the route requires a name.
+func (app *App) nameRequired(r *http.Request) bool {
+	route := mux.CurrentRoute(r)
+	return route == nil || route.GetName() != v2.RouteNameBase
+}
+
 // apiBase implements a simple yes-man for doing overall checks against the
 // api. This can support auth roundtrips to support docker login.
 func apiBase(w http.ResponseWriter, r *http.Request) {