Android GCM - How to remove bad device tokens from my (third party) database?

Question

We have about 900 Android device tokens in our database for GCM push notifications.

I use this PHP function to send the push instruction to the GCM server:

function send_android_push($android_gcm_reg_ids, $title, $message, $activityToLaunch) {

    global $ANDROID_GCM_API_KEY, $TESTING, $TEST_ANDROID_DEVICE_REG_ID;

    if ($TESTING) {
        $android_gcm_reg_ids = [
            $TEST_ANDROID_DEVICE_REG_ID
        ];
    }

    $url = "https://android.googleapis.com/gcm/send";

    $data = array(
        "title" => $title,
        "message" => $message,
        "activityToLaunch" => $activityToLaunch,
    );

    $post = array(
        'registration_ids' => $android_gcm_reg_ids,
        'data' => $data
    );

    $headers = array(
        'Authorization: key=' . $ANDROID_GCM_API_KEY,
        'Content-Type: application/json'
    );

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post));
    $result = curl_exec($ch);

    if (curl_errno($ch)) {
        $result .= "<br />GCM error: " . curl_error($ch);
    }

    curl_close($ch);

    return $result;
}

Here is a snippet of the JSON content returned by that function/GCM:

{
   "multicast_id":5609284883833846123,
   "success":493,
   "failure":401,
   "canonical_ids":20,
   "results":[
      {
         "registration_id":"BPA91bHP29l2j6NPOldcpAvJCJBGk8oQFErfwuh93cxF8ajJJqBlVGqFcxMDEAc2LL2GKwmP86of49UgBTMycB5IdYergWRBETDNUrnzXX_55FgstCZiauPeD7MokIIPOFoOyW9vCRiBqZhlzLCuSnJ1ENFYtIh_PQ",
         "message_id":"0:1462275569015808%814cce86f9fd7ece"
      },
      {
         "registration_id":"BPA91bHP29l2j6NPOldcpAvJCJBGk8oQFErfwuh93cxF8ajJJqBlVGqFcxMDEAc2LL2GKwmP86of49UgBTMycB5IdYergWRBETDNUrnzXX_55FgstCZiauPeD7MokIIPOFoOyW9vCRiBqZhlzLCuSnJ1ENFYtIh_PQ",
         "message_id":"0:1462275569015815%814cce86f9fd7ece"
      },
      {
         "message_id":"0:1462275569014983%814cce86f9fd7ece"
      },
      {
         "error":"NotRegistered"
      },
      {
         "message_id":"0:1462275569017976%814cce86f9fd7ece"
      },
etc., etc.

It seems to be saying I have device tokens in my database that are NotRegistered but, as you can see, it doesn't tell me which device token isn't registered so I am wondering how I can mark it as obsolete in my database?

I thought that maybe the elements of the JSON array returned by the GCM server might correspond to the $android_gcm_reg_ids array I pass into my send_android_push(...) function but that can't be the case because the BPA91bHP29l2j6NPOldcpAvJCJBGk8oQFErfwuh93cxF8ajJJqBlVGqFcxMDEAc2LL2GKwmP86of49UgBTMycB5IdYergWRBETDNUrnzXX_55FgstCZiauPeD7MokIIPOFoOyW9vCRiBqZhlzLCuSnJ1ENFYtIh_PQ registration_id appears numerous times in the GCM JSON array - despite that same token only appearing once in my database.

So presumably there must be some other way of removing obsolete device tokens from my database??

And the reason I am concerned about this is because I have had the situation before (with iOS) where sending bad device tokens (to APNS) resulted in the push notification not being sent to valid devices, and I would obviously like to keep my database in a good state anyway.

I can't find anything to help on the web, so maybe I am missing or getting wrong something obvious?

Answer 1

To know which registration token is causing this, you have to map to the same index in your registration_ids array of your request to GCM.

Here from the docs:

Results: Array of objects representing the status of the messages processed. The objects are listed in the same order as the request (i.e., for each registration ID in the request, its result is listed in the same index in the response).