Allow clients to determine the difference between create or update on PUT

PUT allows an object to be created (http 201).  This allows REST code to
indicate an object has been created and clients to react to it.

APIServer now deals with <-chan RESTResult instead of <-chan runtime.Object,
allowing more data to be passed through.

pkg/apiserver/async.go

@@ -28,13 +28,38 @@ type WorkFunc func() (result runtime.Object, err error)
 
 // MakeAsync takes a function and executes it, delivering the result in the way required
 // by RESTStorage's Update, Delete, and Create methods.
-func MakeAsync(fn WorkFunc) <-chan runtime.Object {
-	channel := make(chan runtime.Object)
+func MakeAsync(fn WorkFunc) <-chan RESTResult {
+	channel := make(chan RESTResult)
 	go func() {
 		defer util.HandleCrash()
 		obj, err := fn()
 		if err != nil {
-			channel <- errToAPIStatus(err)
+			channel <- RESTResult{Object: errToAPIStatus(err)}
+		} else {
+			channel <- RESTResult{Object: obj}
+		}
+		// 'close' is used to signal that no further values will
+		// be written to the channel. Not strictly necessary, but
+		// also won't hurt.
+		close(channel)
+	}()
+	return channel
+}
+
+// WorkFunc is used to perform any time consuming work for an api call, after
+// the input has been validated. Pass one of these to MakeAsync to create an
+// appropriate return value for the Update, Delete, and Create methods.
+type WorkResultFunc func() (result RESTResult, err error)
+
+// MakeAsync takes a function and executes it, delivering the result in the way required
+// by RESTStorage's Update, Delete, and Create methods.
+func MakeAsyncResult(fn WorkResultFunc) <-chan RESTResult {
+	channel := make(chan RESTResult)
+	go func() {
+		defer util.HandleCrash()
+		obj, err := fn()
+		if err != nil {
+			channel <- RESTResult{Object: errToAPIStatus(err)}
 		} else {
 			channel <- obj
 		}