Verify stored Firebase FCM tokens

Question

We have developed an app in iOS and Android which stores the FCM tokens in a database in order to send PUSH notifications depending on the user configuration.

Users

Answer 1

I recently noticed that step 9 in the Cloud Functions codelab uses the response it gets from the FCM API to remove invalid registration tokens from its database.

The relevant code from there:

// Get the list of device tokens.
return admin.database().ref('fcmTokens').once('value').then(allTokens => {
  if (allTokens.val()) {
    // Listing all tokens.
    const tokens = Object.keys(allTokens.val());

    // Send notifications to all tokens.
    return admin.messaging().sendToDevice(tokens, payload).then(response => {
      // For each message check if there was an error.
      const tokensToRemove = [];
      response.results.forEach((result, index) => {
        const error = result.error;
        if (error) {
          console.error('Failure sending notification to', tokens[index], error);
          // Cleanup the tokens who are not registered anymore.
          if (error.code === 'messaging/invalid-registration-token' ||
              error.code === 'messaging/registration-token-not-registered') {
            tokensToRemove.push(allTokens.ref.child(tokens[index]).remove());
          }
        }
      });
      return Promise.all(tokensToRemove);
    });
  }
});

I quickly checked and this same approach is also used in the Cloud Functions sample for sending notifications.