feat(extension): Add flattenEvent parsing to RestEventParser and conv…

…ert Groovy to Java in echo-rest (#708)

echo-api/README.md

@@ -0,0 +1,12 @@
+# echo-api
+
+A module for defining plugin extension interfaces.
+
+WARNING: This is an Alpha module and is not stable.  Consider this an experiment.
+
+Currently there is one extension point `RestEventParser` which is limited to parsing events 
+in echo's `RestEventListener`.  This is primarily for early iteration and testing purposes.
+
+The more powerful extension point for Echo is likely to be `EchoEventListener` - this would enable a plugin
+ecosystem for Echo and also allow us to break existing implementations of `EchoEventListener` 
+(echo-rest, echo-notifications, echo-telemetry, etc) up into discrete plugins.

echo-api/src/main/java/com/netflix/spinnaker/echo/extension/rest/RestEventParser.java

@@ -28,12 +28,20 @@
 public interface RestEventParser extends ExtensionPoint {
 
   /**
-   * Parse an Event prior to POST to the configured URL
+   * Parse an event prior to POST to the configured URL
    *
    * @param event {@link Event}
    * @return Map, which conforms to the RestEventListener API
    */
-  Map parse(Event event);
+  Map<String, Object> parseEvent(Event event);
+
+  /**
+   * Flatten an event prior to POST to configured URL
+   *
+   * @param event
+   * @return FlatEvent, which conforms to the RestEventListener API for flattened events
+   */
+  FlatEvent flattenEvent(Event event);
 
   @Data
   class Event {
@@ -58,4 +66,12 @@ class Metadata {
     private Map<String, List> requestHeaders;
     private Map<String, String> attributes;
   }
+
+  @Data
+  @AllArgsConstructor
+  @NoArgsConstructor
+  class FlatEvent {
+    private String details;
+    private String content;
+  }
 }