Send error payload with MQTT, especially when NTP/RTC is out of sync

[3rwww1]

THIS IS A DRAFT

We are lacking an error reporting funnel.

When we have a Big Problem™, we should record it somewhere, or send it somewhere, if possible. Flashing a LED just doesn't cut it. Here is a proposed solution:

What to to when we detect an error:

• obviously flash the LED and log an error message (already working somehow)
• prepare an MQTT message with an error payload and possibly error properties
• if we can send it, send it
• if we can't send it, record it (and then replay it)

How to format the error message:
we SHALL have a global errors object, with one entry per error type.

• the entry key MUST be the error code, so that the latest error of that type remains in the shadow
• the entry value CAN be an object with nested properties. Properties differ with respect to the error type.

Example

"state" : {
  "reported" : {
    "errors" : {
      "ntp": {
        "lastNtpSync": "date_or_null",
      },
      "spiffs": null,
      "rtc" : {
        "stopped": {
          "lastSyncOffset": "diff_between_rtc_time_and_last_ntp_sync"
        }
      }
    }
  }
}

[Kameeno]

can be right to get also a timestamp ?