Host

Host means that you are running as both the server and the client.

This is the main thing to keep in mind when working with host logic in PurrNet. A host is not a special third side. It is a server side and a client side running on the same machine.

Because of that, anything in PurrNet that gives you an asServer parameter can run twice on a host. This applies to callbacks, ticks, events, and other hooks where PurrNet gives you that bool:

protected override void OnSpawned(bool asServer)
{
    base.OnSpawned(asServer);

    if (asServer)
        return;
}

One call is for the server side. The other call is for the client side. The asServer value tells you which side that specific call belongs to.

asServer does not mean "is this machine a host?". It means "is this call currently running as the server side?".

On a dedicated server, that same callback only runs as server. On a normal remote client, it only runs as client. On a host, you get both, because the host is both.

This is why host bugs often show up as logic running twice, inputs being sent twice, events being subscribed twice, or visual/audio logic also running on the server side.

Use asServer to split the work:

protected override void OnSpawned(bool asServer)
{
    base.OnSpawned(asServer);

    if (asServer)
        SetupServerSide();
    else
        SetupClientSide();
}

For server-authoritative gameplay, spawning, validation, damage, score, inventory changes, and similar state changes, you usually want the server side.

For input, camera, UI, audio, local VFX, and other player-facing logic, you usually want the client side.

If the same code should run on both sides, that is also fine. Just make sure it is intentional, because on a host that means it will run twice.