Add validate function to crd resource and do validate before creation/update (#580)

types.go

@@ -99,6 +99,7 @@ type (
 		// package update, making it possible to cache the function based on its metadata.
 		ResourceVersion string `json:"resourceversion,omitempty"`
 	}
+
 	FunctionPackageRef struct {
 		PackageRef PackageRef `json:"packageref"`
 
@@ -289,11 +290,13 @@ type (
 		FunctionReference FunctionReference `json:"functionref"`
 	}
 
+	MessageQueueType string
+
 	// MessageQueueTriggerSpec defines a binding from a topic in a
 	// message queue to a function.
 	MessageQueueTriggerSpec struct {
 		FunctionReference FunctionReference `json:"functionref"`
-		MessageQueueType  string            `json:"messageQueueType"`
+		MessageQueueType  MessageQueueType  `json:"messageQueueType"`
 		Topic             string            `json:"topic"`
 		ResponseTopic     string            `json:"respTopic,omitempty"`
 		ContentType       string            `json:"contentType"`
@@ -387,6 +390,11 @@ const (
 	SharedVolumeConfigmaps = "configmaps"
 )
 
+const (
+	MessageQueueTypeNats = "nats-streaming"
+	MessageQueueTypeASQ  = "azure-storage-queue"
+)
+
 const (
 	// FunctionReferenceFunctionName means that the function
 	// reference is simply by function name.