fix: Fix missing fields in message events

Closes #27

Change-Id: I6691c8678555efb090266b7e58ef4c1856434c24

eme-trace-config.js

@@ -34,13 +34,10 @@ function emeLogger(log) {
       log.eventName == 'message') {
     // You can't (and shouldn't, to avoid breaking the app) modify the event
     // object here.  So clone it, and replace the message field of that.
-    log.event = {
-      // The spread operator reads the fields and values (shallow clone) of the
-      // object named here.
-      ...log.event,
-      // This overrides on of those fields with a new value.
+    log.event = cloneEvent(log.event, {
+      // This overrides the message field with a new value from the formatter.
       message: formatEmeRequest(log.event.message),
-    };
+    });
   } else if (log.type == TraceAnything.LogTypes.Method &&
       log.className == 'MediaKeys' &&
       log.methodName == 'setServerCertificate' &&
@@ -62,6 +59,41 @@ function emeLogger(log) {
   window.postMessage({type: 'emeTraceLog', log: prepLogForMessage(log)}, '*');
 }
 
+/**
+ * Clone an event.  The clone will have the same type and values, except for the
+ * values overridden by the overrides parameter.
+ *
+ * The spread operator and Object.assign can only read "own" properties of an
+ * object, so this custom cloning method must be used for Events instead.
+ *
+ * @param {!Event} original
+ * @param {Object=} overrides
+ * @return {!Event}
+ */
+function cloneEvent(original, overrides) {
+  const clone = {};
+
+  // When reading the original, we must use a for-in loop to see all fields.
+  // Static fields from Event and methods are skipped, but everything else is
+  // copied into a plain object.
+  for (const key in original) {
+    if (!(key in Event) && (typeof original[key] != 'function')) {
+      clone[key] = original[key];
+    }
+  }
+
+  // Overrides are applied all at once using Object.assign.
+  if (overrides) {
+    Object.assign(clone, overrides);
+  }
+
+  // Setting the prototype of the clone gives the clone the same type as the
+  // original.
+  Object.setPrototypeOf(clone, original.constructor.prototype);
+
+  return clone;
+}
+
 /**
  * @param {BufferSource} response
  * @return {(string|!Object|BufferSource)}

spec/eme-trace-tests.js

@@ -18,13 +18,15 @@
 
 describe('EME tracing', () => {
   beforeEach(() => {
-    spyOn(window, 'emeLogger').and.callFake((log) => {
+    spyOn(window, 'emeLogger').and.callThrough();
+
+    spyOn(window, 'postMessage').and.callFake((log) => {
+      expect(log.type).toEqual('emeTraceLog');
+
       // Validate that the logs can always be serialized.  We don't care about
       // the output at this level.
-      delete log.instance;
-
       try {
-        JSON.stringify(prepLogForMessage(log));
+        JSON.stringify(log);
       } catch (exception) {
         fail(exception);
       }
@@ -262,6 +264,32 @@ describe('EME tracing', () => {
             'value': session.keyStatuses,
           }));
     });
+
+    // Regression test for https://github.com/google/eme_logger/issues/27
+    it('Message events with all fields', async () => {
+      await session.generateRequest('cenc', initData);
+      // Wait for the message event to come through, with a generous timeout.
+      await delay(2);
+
+      // Cloning of Events happens at the emeLogger level, so we have to
+      // validate the results of that at the level of postMessage instead.
+      // Both message and messageType fields should be present.
+      const expectedMessage = jasmine.objectContaining({
+          log: jasmine.objectContaining({
+	          type: TraceAnything.LogTypes.Event,
+            event: {
+              __type__: 'message Event',
+              __fields__: jasmine.objectContaining({
+                message: jasmine.objectContaining({
+                  __type__: 'Uint8Array',
+                }),
+                messageType: 'license-request',
+              }),
+            },
+          }),
+        });
+      expect(postMessage).toHaveBeenCalledWith(expectedMessage, '*');
+    });
   });
 
   describe('logs HTML media elements', () => {