fix: Record 0 for headerSize if transferSize is 0 (#496)

Author: limhjgrace

src/plugins/event-plugins/NavigationPlugin.ts

@@ -253,7 +253,10 @@ export class NavigationPlugin extends InternalPlugin {
 
             duration: entryData.duration,
 
-            headerSize: entryData.transferSize - entryData.encodedBodySize,
+            headerSize:
+                entryData.transferSize > 0
+                    ? entryData.transferSize - entryData.encodedBodySize
+                    : 0,
             transferSize: entryData.transferSize,
             compressionRatio:
                 entryData.encodedBodySize > 0

src/plugins/event-plugins/__tests__/NavigationPlugin.test.ts

@@ -46,6 +46,23 @@ describe('NavigationPlugin tests', () => {
         );
     });
 
+    test('When transferSize is 0 then headerSize is 0', async () => {
+        const plugin: NavigationPlugin = buildNavigationPlugin();
+        // Run
+        plugin.load(context);
+        window.dispatchEvent(new Event('load'));
+        plugin.disable();
+
+        expect(record.mock.calls[0][0]).toEqual(
+            PERFORMANCE_NAVIGATION_EVENT_TYPE
+        );
+        expect(record.mock.calls[0][1]).toEqual(
+            expect.objectContaining({
+                headerSize: 0
+            })
+        );
+    });
+
     test('When navigation timing level 2 API is not present then navigation timing level 1 API is recorded', async () => {
         jest.useFakeTimers();
         mockPerformanceObjectWith([putRumEventsDocument], [], []);

src/test-utils/mock-data.ts

@@ -41,7 +41,7 @@ export const navigationEvent = {
     secureConnectionStart: 6.495000001450535,
     serverTiming: [],
     startTime: 0,
-    transferSize: 36525,
+    transferSize: 0,
     type: 'navigate',
     unloadEventEnd: 0,
     unloadEventStart: 0,