OFFLINE scenario - recording actual use ?

[PBrunot]

Machines needs to be operated even in OFFLINE scenario. For example, 3D printers may be brought out of the lab for temporary events. Or WiFi may go down.

Currently, the machine remains usable with RFID cards provided that: 1- the user card is in whitelist 2- the user card is in cache (last 10 successfull authentications)

It is possible to instruct users to authenticate on the machine before moving the machine out of the lab so that we are sure that the cache is up to date.

However, the usage data in OFFLINE scenario will be lost.

Possible solution:

• memorize (user card id; duration in sec) in flash memory and, when reconnected to the backend, transmit the data.
• Timestamp will be the time of reconnection, as actual usage datetime is lost (as ESP32 does not have an RTC).

Notes for possible implementation:

• user may power off the machine without logging out, destroying the information. A similar workaround to the one used in ONLINE scenario (i.e. sending inUse message with duration so that the backend can properly close the orphan usage record) is needed. E.g. duration needs to be saved regularly in flash every X minutes.
• space for emulated EEPROM in Arduino on default partition table is limited / not sure we can support two persisted classes. Workaround: Custom partition table / SPIFFS file system may be needed (complexity). On the other hand we only need 12 bytes per event.
• backend already handles "missed" startUse events, so sending "endUse" message with the right duration is enough (simple)
• adding a new dedicated mqtt message (offlineUse with card uid + duration). This would allow the UI to flag the usage record as offline.
• upon connection to MQTT server enumerate persisted messages in flash, and upon successfully playback, delete it.

[PBrunot]

Another use case is bad WiFi coverage in the lab. We can miss events if the network is down at the wrong time. Impact will be limited but still the machine dashboard may show a machine busy for a long time after use.

[PBrunot]

Done from version 0.9 Testcases added.