RPC — Remote Procedure Calls

One-shot replicated function calls. Three kinds:

RPC	Caller	Executed on
Server	Client	Server
Client	Server	Owning client
NetMulticast	Server	All clients (and server)

Declaration (C++)

UFUNCTION(Server, Reliable, WithValidation)
void Server_Fire(FVector AimDirection);
void Server_Fire_Implementation(FVector AimDirection);
bool Server_Fire_Validate(FVector AimDirection);

UFUNCTION(Client, Reliable)
void Client_ShowKillFeed(FString Killer, FString Killed);

UFUNCTION(NetMulticast, Unreliable)
void NetMulticast_PlayHitFX(FVector_NetQuantize Loc);

Specifier	Meaning
Reliable	Resend until ACK; bandwidth cost
Unreliable	Best-effort; lost packets dropped
WithValidation	Adds _Validate overload — server kicks client if returns false

Reliable vs Unreliable

• Reliable for game-state-critical events (kill, score, ability cast).
• Unreliable for cosmetic events (footstep, particle).
• NetMulticast must be unreliable in most cases — reliable multicast costs N × bandwidth.

Calling pattern

void AMyChar::OnFireButtonPressed()
{
    if (HasAuthority())
        Server_Fire_Implementation(AimDir);  // local server call
    else
        Server_Fire(AimDir);                 // RPC to server
}

Validation

_Validate is your anti-cheat hook. Sanity-check inputs:

bool AMyChar::Server_Fire_Validate(FVector Dir)
{
    return Dir.IsNormalized() && AmmoCount > 0;
}

Returning false kicks the client.

NetMulticast best practice

Prefer replicated property + OnRep over multicast for state. Use multicast for transient events that need to fire on all clients (e.g. one-shot VFX).

See also

• Replication