How to receive Google Push Notifications

[Anders Vincent Lund]

I just managed to call the Google Drive API to enable push notifications for a file.

The code setting up the push notifications look like this:

    public class SampleServlet extends AbstractAppEngineAuthorizationCodeServlet {
        private final static Logger logger = Logger.getLogger(SampleServlet.class.getName());
        private static final long serialVersionUID = 1L;
        // Constants omitted
   
        @Override
        public void doGet(HttpServletRequest req, HttpServletResponse resp)
                throws IOException, ServletException {
   
            AuthorizationCodeFlow authFlow = initializeFlow();
            Credential credential = authFlow.loadCredential(getUserId(req));
   
            StringBuilder resultFromWatch = new StringBuilder();
            Drive drive = new Drive.Builder(Utils.HTTP_TRANSPORT, Utils.JSON_FACTORY, credential).setApplicationName("t").build();
   
            try {
                Optional<Channel> channel = watchFile(drive, FILE_ID, CHANNEL_ID, "web_hook", PUSH_URL);
                String channelStringTmp;
                if (channel.isPresent()) {
                    channelStringTmp = channel.get().toString();
                } else {
                    channelStringTmp = "null...";
                }
                resultFromWatch.append(channelStringTmp);
            } catch (Exception e) {
                resultFromWatch.append(e.getMessage());
            }
   
            final UserService userService = UserServiceFactory.getUserService();
            final String thisUrl = req.getRequestURI();
            // Send the results as the response
            PrintWriter respWriter = resp.getWriter();
            resp.setStatus(200);
            resp.setContentType("text/html");
   
            addLoginLogoutButtons(req, resp, resultFromWatch, userService, thisUrl, respWriter);
        }
   
        private static Optional<Channel> watchFile(Drive service, String fileId,
                                                   String channelId, String channelType, String channelAddress) throws IOException {
            final Channel returnValue;
            Channel channel = new Channel();
            channel.setId(channelId);
            channel.setType(channelType);
            channel.setAddress(channelAddress);
            Drive.Files tmp = service.files();
            returnValue = tmp.watch(fileId, channel).execute();
            return Optional.fromNullable(returnValue);
        }
   
        @Override
        protected AuthorizationCodeFlow initializeFlow() throws ServletException, IOException {
            return Utils.initializeFlow();
        }
   
        @Override
        protected String getRedirectUri(HttpServletRequest req) throws ServletException, IOException {
            return Utils.getRedirectUri(req);
        }
    }

After having called the servlets doGet from my browser and logging in I get this as response:

    {
      "expiration": "1484565747000",
      "id": SAME_ID_AS_DEFINED_IN_SERVLET,
      "kind": "api#channel",
      "resourceId": A_NEW_ID,
      "resourceUri": "https:\/\/www.googleapis.com\/drive\/v3\/files\/FILE_ID?acknowledgeAbuse=false&alt=json"
    }

Next step is to define my controller that receives notifications when the file is modified. Looks like this:

    @RestController
    @RequestMapping(/*PUSH_URL*/)
    public class ConcreteFileWatchController implements FileWatchController {
        private final static Logger logger = Logger.getLogger(ConcreteFileWatchController.class.getName());
   
        @RequestMapping(method = RequestMethod.POST)
        @ResponseStatus(value = HttpStatus.OK)
        @Override
        public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
            logger.info("Received watch call");
        }
    }

Finally I try to modify the file after having deployed the application(it is deployed on Google App Engine) and after looking at the logs in GAE I can see that there has been a call. However, my receiving method is not executed. I only see a 302 in the log with a big json attached to it. Can't really see any error except that I don't notice that my method is called. The path even looks correct in the log. What could I be doing wrong?

[John Boswell]

The only things I can think of are:

- Make sure you're giving the right file id (it's an easy mistake to make).

- Make sure you're following all the instructions here: https://developers.google.com/drive/v3/web/push.

I don't really know a lot about this API, and this forum is more general, so you might get some more specific help asking here: https://developers.google.com/drive/v3/web/support

[mizes...@gmail.com]

After having set-up everything I'm getting error:

    ...
    errors": [
        {
            "domain": "global",
            "reason": "push.webhookUrlUnauthorized",
            "message": "Unauthorized WebHook callback channel: https://app.example.com"
        }
    ],
    ...