Tracing Remote Procedure Call Execution Flows

In this lesson, you will learn how to implement custom logging and visual debugging markers to track the lifecycle and execution success of RPCs as they traverse the client-server boundary.

The Challenge of "Invisible" RPCs

When a Remote Procedure Call is fired, it disappears into the networking layer, making it difficult to know if it was dropped, executed successfully, or blocked by authority restrictions. Because RPCs are asynchronous, simple breakpoints often fail to capture the context of the network state.

Implementing Diagnostic Tracing

To gain visibility, wrap your RPCs in a diagnostic pattern. Instead of calling a function directly, pass the intent through a logging decorator that captures the Role, RemoteRole, and HasAuthority() state at the exact moment of invocation.

void AMyActor::Server_PerformAction_Implementation(int32 ActionID)
{
    // Visual and Console feedback for tracing
    UE_LOG(LogTemp, Warning, TEXT("RPC Received: Server_PerformAction | ID: %d | Authority: %s"), 
        ActionID, HasAuthority() ? TEXT("True") : TEXT("False"));

    DrawDebugSphere(GetWorld(), GetActorLocation(), 50.0f, 12, FColor::Green, false, 2.0f);
    
    // Execute logic...
}

Visualizing Execution Flows

Beyond logs, use DrawDebug utilities tied to your RPC entry points. By spawning a DrawDebugLine or Sphere only when an RPC executes on the server, you create a real-time visual heartbeat of your network traffic. If you call an RPC from a client and the sphere fails to appear on the server’s display, you have immediate visual confirmation that the packet failed or the ownership hierarchy is misconfigured.

Best Practices for Tracing

1. Conditional Filtering: Only log when GetNetMode() != NM_Standalone to avoid cluttering your output during local testing.
2. Execution Context: Include the GetOwner()->GetName() in your trace logs to ensure the RPC is being routed through the expected connection channel.
3. Transient Markers: Always pair your DrawDebug calls with a short duration (e.g., 2.0s) to keep the viewport clean while actively debugging high-frequency calls.

Key Takeaway: By augmenting RPC implementations with contextual logs and transient visual markers, you transform opaque network calls into observable events, allowing you to instantly diagnose ownership conflicts or packet delivery failures.