Question

It took me some time, but I managed to get to the last point in real time updates, the challenge.

I know that when subscribing Facebook should ping my server, the problem is that it never happens, I always get the same response back:

{“error”:{“type”:”OAuthException”,”message”:”(#2201) response does not match challenge, expected value = ‘1506372182’, received=””}}

It looks like it is able to connect to my server (every other callback url fails with address not available), however I don’t see it calling me in the logs.

I’m using app engine:

public void doGet(HttpServletRequest req, HttpServletResponse resp)
    throws IOException {
...

else if (parameters.containsKey("hub.mode")) {
            log.info("doing hub.mode");
            // Check that challenge is valid.
            if (parameters.get("hub_verify_token").equals(Constants.FACEBOOK_VERIFY_TOKEN)) {
                log.info("hub.mode test is valid");
                resp.setContentType("text/plain");
                resp.getWriter().print(req.getParameter("hub.challenge"));
            }

        }
...


// I want real time information on a specific user, on its feeds.
        String data = URLEncoder.encode("object", "UTF-8") + "="
                + URLEncoder.encode("user", "UTF-8");
        data += "&" + URLEncoder.encode("fields", "UTF-8") + "="
                + URLEncoder.encode("feed", "UTF-8");
        // Send real time updates to this URL.
        data += "&" + URLEncoder.encode("callback_url", "UTF-8") + "="
                + URLEncoder.encode(reconstructedURL.toString(), "UTF-8");
        // A token used to verify that it is actually me who is running the verification process.
        data += "&" + URLEncoder.encode("verify_token", "UTF-8") + "="
                + URLEncoder.encode(Constants.FACEBOOK_VERIFY_TOKEN, "UTF-8");
        data += "&"
                + URLEncoder.encode("access_token", "UTF-8")
                + "="
                +Constants.FACEBOOK_APP_CODE + "|"
                        + Constants.FACEBOOK_APP_SECRET;
        // Subscribe by doing a post.
        URL url = new URL(String.format(
                "https://graph.facebook.com/%s/subscriptions?access_token=%s",
                Constants.FACEBOOK_APP_CODE, accessToken));
        URLConnection conn = url.openConnection();
        conn.setDoOutput(true);
        conn.setDoInput(true);
        OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());
        log.info(String.format("Sent the following data '%s'", data));
        wr.write(data);
        wr.flush();

I’m handling both the user authentication and real time subscription in the same servlet.

When reading back the response I’m getting the above error and I don’t see any call to my servlet (in the app engine logs).
I’m sure I’m missing something.

Any help will be appreciated.

Answer 1

Ok, solved. The problem was with the permissions in web.xml, Facebook couldn’t reach my page.