Getting more detailed errors from FCM back-end service (#217)

CHANGELOG.md

@@ -1,7 +1,10 @@
 # Unreleased
 
 - [fixed] Fixing error handling in FCM. The SDK now checks the key
-  type.googleapis.com/google.firebase.fcm.v1.FcmError to set error code.
+  `type.googleapis.com/google.firebase.fcm.v1.FcmError` to set error
+  code.
+- [fixed] FCM errors sent by the back-end now include more details
+  that are helpful when debugging problems.
 
 # v6.5.0
 

src/main/java/com/google/firebase/messaging/FirebaseMessaging.java

@@ -249,6 +249,7 @@ protected String execute() throws FirebaseMessagingException {
         try {
           HttpRequest request = requestFactory.buildPostRequest(
               new GenericUrl(url), new JsonHttpContent(jsonFactory, payload.build()));
+          request.getHeaders().set("X-GOOG-API-FORMAT-VERSION", "2");
           request.setParser(new JsonObjectParser(jsonFactory));
           request.setResponseInterceptor(interceptor);
           response = request.execute();

src/test/java/com/google/firebase/messaging/FirebaseMessagingTest.java

@@ -512,6 +512,7 @@ private static HttpRequest checkRequestHeader(TestResponseInterceptor intercepto
     assertEquals("POST", request.getRequestMethod());
     assertEquals(TEST_FCM_URL, request.getUrl().toString());
     assertEquals("Bearer test-token", request.getHeaders().getAuthorization());
+    assertEquals("2", request.getHeaders().get("X-GOOG-API-FORMAT-VERSION"));
     return request;
   }