Handle invalid token responses in FCM

[yanikapitanov]

As per the documentation a token could be invalid if you have two error codes:

• UNREGISTERED (HTTP 404)
• INVALID_ARGUMENT (HTTP 400)

However INVALID_ARGUMENTS can be caused by other errors.

At the moment we receive the content below from the IncomingHttpResponse which is also the error message from the FirebaseMessagingException. What we do is to check the string of the message in order to delete these tokens.

Content: {
  "error": {
    "code": 400,
    "message": "The registration token is not a valid FCM registration token",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.firebase.fcm.v1.FcmError",
        "errorCode": "INVALID_ARGUMENT"
      }
    ]
  }
}

What is the proper way to handle these errors?
Does it make sense to update FirebaseMessagingException to provide more information about which field is invalid or perhaps have a new error code - INVALID_TOKEN? This would remove a lot of unambiguity as to when it is needed to manage the token.

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[tbadalov]

Could it be that mobile clients sent an ill-formed registration token? Could you check what was the token at the time of receiving this error?