Authority transfer

Overview

Authority over state changes to an Entity is transferrable, so it is possible to move the authority over simulation of an Entity between Clients and Simulation Servers. This is useful for things such as balancing the simulation load, or exchanging items. It is possible for an Entity to have no Client or Simulator as the authority - these Entities are considered orphaned and are not simulated.

Types of authority transfer

In the design phase, CoherenceSync objects can be configured to handle authority transfer in different ways:

• Request. Authority transfer may be requested, but it may be rejected by the current authority.

• Steal. Authority will always be given to the requesting party on a FCFS ("first come first serve") basis.

• Disabled. Authority cannot be transferred.

Note that you need to set up Auto-adopt Orphan if you want orphans to be adopted automatically when an Entity's authority disconnects, otherwise an orphaned Entity is not simulated. Auto-adopt is only allowed for persistent entities.

When using Request, an optional callback OnAuthorityRequested can be set on the CoherenceSync behaviour. If the callback is set, then the results of the callback will override the Approve Requests setting in the behaviour.

The request can be approved or rejected in the callback.

// connectionID is the network connection ID of the requesting client.
// sync is the CoherenceSync behaviour of the object the other client is
// requesting authority over.
public bool OnRequest(ushort connectionID, CoherenceSync sync)
{
    return (sync == theRightSync && connectionID == goodConnectionID);
}

Support for requests based on CoherenceClientConnection.ClientID is coming soon.

Requesting authority in code

Requesting authority is very straight-forward.

var coherenceSync = target.GetComponent<CoherenceSync>();
bool requestSuccess = coherenceSync.RequestAuthority(AuthorityType.Full);

RequestAuthority returns false if the request was not sent. This can be because of the following reasons:

1. The sync is not ready yet.

2. The entity is not allowed to be transferred becauseauthorityTransferType is set to NonTransferable.

3. There is already a request underway.

4. The entity is orphaned, in which case you must call Adopt instead to request authority.

The request itself might fail depending on the response of the current authority.

As the transfer is asynchronous, we have to subscribe to one or more Unity Events in CoherenceSync to learn the result.

The request will first go to the Replication Server and be passed onto the receiving Simulator or Game Client, so it may take a few frames to get a response.

// There Unity Events in CoherenceSync help us understand 
// what happened with authority requests and act accordingly.

// called when the CoherenceSync entity becomes the simulation authority
public UnityEvent OnStateAuthority;

// called when the CoherenceSync entity loses simulatino authority
public UnityEvent OnStateRemote;

// called when a request to assume authority over the CoherenceSync entity
// is rejected
public UnityEvent OnAuthorityRequestRejected;

These events are also exposed in the Custom Events section of the CoherenceSync inspector.