Persistent Vehicles

[Manason]

The problem

There is a bug in FiveM that makes it so server spawned vehicles can be deleted. This can happen even when a player is driving it.

Ideal solution

When a vehicle is deleted, it is respawned at the position it was deleted, with the same vehicle properties.

Using the server side entityRemoved event, we can intercept the entity deletion to cache some data about the vehicle, such as the vehicleId, plate, and coords. Then, we can lookup the vehicle in the database to determine whether it is an owned vehicle and respawn it. This could result in stale vehicle properties however, as the database may not have been recently updated.

Therefore, in addition to the above solution, we should also save vehicle properties to the database on an on-demand basis. That is, whenever it changes. Only a client can read the vehicle properties, and would need to send this to the server when it changed. Therefore I propose that when a client is occupying the driver seat of a vehicle, regardless of whether it is the entity owner or not it should do the following:

1. cache the vehicle properties
2. every few seconds, check if the vehicle properties have changed
3. send the diff (if there is one) to the server

The server will then

1. receive the diff from the client
2. read the vehicle from the database
3. overwrite diffed fields
4. save the vehicle properties back

If this proves to be too much of a performance cost, the server could save to a buffer, and flush the buffer on a less regular cadence, but this should only be done if there proves to be an issue, not before as it adds its own complications, drawbacks, and edge cases.

Exploits in this solution aren't entirely preventable, as the client is the source of truth for the vehicle property data. To prevent exploits to the extent possible, the following can be done:

• Only fields changed outside of other events need be accepted by the server. Changing the owner of a vehicle, or its mods for example should result in a separate event on its own rather than be changed through a regular properties detection solution. The vehicles the server could accept would be limited to damage and fuel fields.
• if there is a non RPC server native to get the data, the server will use it rather than trust the value sent by the client
• anomalous diffs could be detected. i.e. if a vehicle is repaired, we might expect the event to be sent by the script that did the repairing, and so a regular client diff would point to lua injection. This isn't recommended however, as it would assume that all scripts which repair vehicles would be sending property update events to the server.

Alternative solutions

No response

Additional context

No response