HTTP Post Request: Error 400, Firebase Topic Messaging

Question

I'm trying to implement Firebase Topic Messaging in an Android application, and I'm attempting to build a HTTP post request, and I'm receiving a response code of 400. I have looked at various solutions but none of them have seemed to help.

Here is where I call the subclass of AsyncTask:

try{new FirebaseSendMessage().execute("Hello world");}
                catch (Exception e) {
                    Log.d("Exception", e.toString());
                }

Here is my Async Task class's subclass.

class FirebaseSendMessage  extends AsyncTask<String, Integer, Double> {
private final static String USER_AGENT = "Mozilla/5.0";
private final static String AUTH_KEY = "<My firebase authorization key obtained from firebase>";

private Exception exception;

protected Double doInBackground(String... params) {
    try {
        sendRequest(params);
    } catch (Exception e) {
        this.exception = e;
    }
    return null;
}

protected void onPostExecute(Long l) {
    // TODO: check this.exception
    // TODO: do something with the feed
}


public void sendRequest(String... params) {
    try {
        String urlString = "https://fcm.googleapis.com/fcm/send";
        URL url = new URL(urlString);
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        con.setDoOutput(true);
        con.setRequestMethod("POST");
        con.setRequestProperty("Content-Type", "application/json");
        con.setRequestProperty("Authorization", "key=" + AUTH_KEY);
        String postJsonData = "{\"to\": \"/topics/news\"\"data\": {\"message\": \"This is a Firebase Cloud Messaging Topic Message!\"}";
        con.setDoOutput(true);

        DataOutputStream wr = new DataOutputStream(con.getOutputStream());
        wr.writeBytes(postJsonData);
        wr.flush();
        wr.close();

        int responseCode = con.getResponseCode();
        System.out.println("POST Response Code :: " + responseCode);

        if (responseCode == HttpURLConnection.HTTP_OK){
            System.out.println("succeeded");
        }
        /*InputStream is = con.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String line = null;
        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }
        //con.disconnect();*/
    }
    catch(IOException e){
        Log.d("exception thrown: ", e.toString());
    }
}

}

Error: I/System.out: POST Response Code :: 400

Please let me know if there are additional code snippets required to help me debug. Thanks in advance!

Answer 1

Error 400 means an Invalid JSON in your request:

Check that the JSON message is properly formatted and contains valid fields (for instance, making sure the right data type is passed in).

In your sendRequest, you missed a comma (,) between "news\" and \"data\" and a closing bracket (}):

String postJsonData = "{\"to\": \"/topics/news\"\"data\": {\"message\": \"This is a Firebase Cloud Messaging Topic Message!\"}";

which looks like this:

{"to": "/topics/news/""data":{"message":"...."}

Should be:

String postJsonData = "{\"to\": \"/topics/news\", \"data\": {\"message\": \"This is a Firebase Cloud Messaging Topic Message!\"}}";

So that the JSON structure would be correct:

{"to": "/topics/news/",
 "data":{"message":"..."}
}

Answer 2

For those who are willing to use the authentication key in your application.

I suggest to encrypt the key manually by the SHA-1 of your application and the decrypt it at the time of runtime with the SHA-1 code.