How to call Server function from client on a level placed Actor?

Development Programming & Scripting C++
1

I have an Actor placed on a level, and I would like to be able to call a Server function from a client.

I know that Server functions can be called only on client-owning actors, that’s why I’m doing this in the BeginPlay() of the actor:



 void AMyActor::BeginPlay()
{    
    Super::BeginPlay();
    SetOwner(UGameplayStatics::GetPlayerController(GetWorld(), 0));
}

And then I try to call a Server function when something happens in the Tick() method. The server function only prints something in the log, and looks like this:




// In the .h:
UFUNCTION(Server, Reliable, WithValidation)
void ServerDoSomething();

// In the .cpp
void AMyActor::ServerDoSomething_Implementation()
{
    UE_LOG(LogTemp, Warning, TEXT("I made it"));
}

bool AMyActor::ServerDoSomething_Validate()
{        
     return true;
}

By setting the owner in the BeginPlay() the error about “owning connections” goes away, but the actual method is NEVER called in the server. It just does nothing. So, how can I call a server function from an Actor placed in a level?

2

Unless the server also has your player set as owner, it will ignore the call.

Do you need to be able to use this from multiple players? Then I don’t think there’s a way other than adding a proxy function to the player controller (with a ptr to the actor) and have that call the actual function.

3

Yes, this object is “shared” among the players.It’s not the “cleanest” solution, but if there is no other way that should work :slight_smile:

Thanks!

4

If you do go that way, make sure the actor is actually valid on the server side, otherwise malicious client could crash the server by sending a nullptr

5

Thanks for the tip!

6

Could you please elaborate on how to do this? I’m working on a board for my RPG System and I need all players to be able to move the pieces.

7

You will need a start and end function and your server functions you made.
Example code, but it should work



/*
MoveYourPiece() CLIENT MOVES YOUR PIECE Start functon from button or what ever trigers it
*/
void AYourClass::MoveYourPiece()
{
     ENetMode NetMode = GetNetMode();

     SetThePiece();

     if (NetMode == NM_Client)
     {
        ServerDoSomething();
      }
}

// In the .cpp
void AMyActor::ServerDoSomething_Implementation()
{
    UE_LOG(LogTemp, Warning, TEXT("I made it"));
    SetThePiece();
}

bool AMyActor::ServerDoSomething_Validate()
{
    return true;
}

/*
SetThePiece(); end function to actually move the piece
*/
void AYourClass::SetThePiece()
{
     bMovePiece = !bMovePiece;//you will want to replicate this to everyone but yourself, if you need this

     //rest of your code to actually move your piece
}
3 Likes
8

Thank you!!

I checked your reply a few days ago and you pointed me into the right direction!! Just replying to thank you for taking the time to help!!
It worked!!

1 Like