Bot silently stops receiving updates when it gets a message that fails to parse

Well, that’s not funny anymore. It happened again, one more time, and it happened countless times before. The bot just got another message with slightly modified JSON markup (games this time) that it failed to parse. And it again just stopped processing all updates, even those that were correct.

Bot was in polling mode.

Failing message

{
  "update_id": 16538441,
  "edited_message": {
    "message_id": 1015764,
    "from": {
      "id": 1599103365,
      "is_bot": false,
      "first_name": "m0unteni [block toxic]",
      "username": "m0unteni"
    },
    "chat": {
      "id": -1000123456,
      "title": "Group title",
      "username": "group_username",
      "type": "supergroup"
    },
    "date": 1637011117,
    "edit_date": 1637011143,
    "game": {
      "title": "Keep it UP",
      "text": "Top Players\n1. m0unteni [block toxic] – 3",
      "text_entities": [
        {
          "offset": 0,
          "length": 11,
          "type": "bold"
        },
        {
          "offset": 40,
          "length": 1,
          "type": "bold"
        }
      ],
      "description": "Time for some football freestyle! Keep it UP!",
      "photo": [
        {
          "file_id": "AgACAgQAAxUAAWGSzsc6ls4XQ4kPR49ns9fbCbp8AAIKrTEbtmhxUSW6OTezqSMYAQADAgADcwADIgQ",
          "file_unique_id": "AQADCq0xG7ZocVF4",
          "file_size": 1360,
          "width": 90,
          "height": 51
        },
        {
          "file_id": "AgACAgQAAxUAAWGSzsc6ls4XQ4kPR49ns9fbCbp8AAIKrTEbtmhxUSW6OTezqSMYAQADAgADbQADIgQ",
          "file_unique_id": "AQADCq0xG7ZocVFy",
          "file_size": 12556,
          "width": 320,
          "height": 180
        },
        {
          "file_id": "AgACAgQAAxUAAWGSzsc6ls4XQ4kPR49ns9fbCbp8AAIKrTEbtmhxUSW6OTezqSMYAQADAgADeAADIgQ",
          "file_unique_id": "AQADCq0xG7ZocVF9",
          "file_size": 26959,
          "width": 640,
          "height": 360
        }
      ],
      "animation": {
        "file_name": "animation.mp4",
        "mime_type": "video/mp4",
        "duration": 5,
        "width": 320,
        "height": 180,
        "thumb": {
          "file_id": "AAMCBAADFQABYZLOx2VPMYUFnXKujlkcc_fU7r0AAtUEAAK2aHFRaML43E0g8oUBAAdzAAMiBA",
          "file_unique_id": "AQAD1QQAArZocVF4",
          "file_size": 1569,
          "width": 90,
          "height": 50
        },
        "file_id": "CgACAgQAAxUAAWGSzsdlTzGFBZ1yro5ZHHP31O69AALVBAACtmhxUWjC-NxNIPKFIgQ",
        "file_unique_id": "AgAD1QQAArZocVE",
        "file_size": 95370
      }
    },
    "reply_markup": {
      "inline_keyboard": [
        [
          {
            "text": "Play Keep it UP!",
            "callback_game": {}
          }
        ]
      ]
    },
    "via_bot": {
      "id": 280713127,
      "is_bot": true,
      "first_name": "Gamee",
      "username": "gamee"
    }
  }
}

Serialization mechanism where one failing message could block all update queue is a huge problem and can lead to silent denial-of-service scenarios.

[ex0ns]

5.1.0 published with the fix, closing this for now. Feel free to re-open an issue if this is still a problem

[makkarpov]

Looks good!

Typing can be made clearer by introducing custom sealed trait instead of doing 4-th level of generics, like that:

sealed trait ParsedUpdate
object ParsedUpdate {
  case class Failure(updateId: Long, cause: DecodingFailure) extends ParsedUpdate
  case class Success(update: Update) extends ParsedUpdate
}

Conversion from raw update type to wrapped should be rather straightforward and can be done by wrapping a decoder object.

As for that assert: if assertion failure would result in circe DecodingFailure - I don’t think that there is a need for removal. Anyway update with an unknown event (so that every field is None) is a malformed update from library’s perspective.

If decoder is unable to decode even updateId - I think that whole request should fail because something really bad is happening.