ROLE_Authority       — owns and can modify this actor (server for replicated actors)
ROLE_AutonomousProxy — client copy of the locally controlled pawn
ROLE_SimulatedProxy  — client copy of another player's actor; engine interpolates state
ROLE_None            — not replicated

ENetRole GetLocalRole() const { return Role; }   // role on current machine
ENetRole GetRemoteRole() const;                   // role the other end sees
bool HasAuthority() const { return (GetLocalRole() == ROLE_Authority); }

UNetDriver* Driver = GetWorld()->GetNetDriver();
// Driver->ClientConnections  — all connected clients (server-side)
// Driver->ServerConnection   — connection to server (client-side)

AMyActor::AMyActor()
{
    bReplicates = true;             // AActor::SetReplicates() also available at runtime
    SetReplicateMovement(true);     // replicates FRepMovement (location/rotation/velocity)
    SetNetUpdateFrequency(10.f);    // checks per second
    SetMinNetUpdateFrequency(2.f);  // floor when nothing changes
    NetPriority = 1.0f;            // higher = preferred when bandwidth is saturated
}

UPROPERTY(Replicated)
int32 Health;

UPROPERTY(ReplicatedUsing = OnRep_State)
EMyState State;

UFUNCTION()
void OnRep_State(EMyState PreviousState); // old value passed as optional parameter

// MyActor.cpp
#include "Net/UnrealNetwork.h"

void AMyActor::GetLifetimeReplicatedProps(
    TArray<FLifetimeProperty>& OutLifetimeProps) const
{
    Super::GetLifetimeReplicatedProps(OutLifetimeProps); // NEVER omit this
    DOREPLIFETIME(AMyActor, Health);
    DOREPLIFETIME_CONDITION(AMyActor, State,        COND_OwnerOnly);
    DOREPLIFETIME_CONDITION(AMyActor, SimData,      COND_SimulatedOnly);
    DOREPLIFETIME_CONDITION(AMyActor, InitData,     COND_InitialOnly);
    DOREPLIFETIME_CONDITION(AMyActor, PublicData,   COND_SkipOwner);
}

// Client calls → server executes. WithValidation is required for state changes.
UFUNCTION(Server, Reliable, WithValidation)
void ServerFireWeapon(FVector_NetQuantize Origin, FVector_NetQuantizeNormal Dir);

// Server calls → owning client executes. No WithValidation needed.
UFUNCTION(Client, Reliable)
void ClientShowKillConfirm();

// Server calls → server + all clients execute.
UFUNCTION(NetMulticast, Unreliable)
void MulticastPlayHitEffect(FVector ImpactPoint);

UFUNCTION(unreliable, server, WithValidation) void ServerSetSpectatorLocation(...);
UFUNCTION(reliable,   server, WithValidation) void ServerAcknowledgePossession(APawn* P);
UFUNCTION(Reliable,   Client)                 void ClientReceiveLocalizedMessage(...);
UFUNCTION(Client,     Unreliable)             void ClientAckTimeDilation(float, int32);

// Server sets owner to control connection routing for RPCs and COND_OwnerOnly
Weapon->SetOwner(PlayerController);

// Relevancy flags (from Actor.h)
bAlwaysRelevant      = true;  // replicate to every connection
bOnlyRelevantToOwner = true;  // replicate only to the owning connection

// Override for custom logic (e.g., team-based relevancy)
virtual bool IsNetRelevantFor(const AActor* RealViewer, const AActor* ViewTarget,
                               const FVector& SrcLocation) const override;

SetNetDormancy(DORM_DormantAll); // stop replication
FlushNetDormancy();              // send one update then return to dormant

ENGINE_API void AddReplicatedSubObject(UObject* SubObject,
                                       ELifetimeCondition NetCondition = COND_None);
ENGINE_API void RemoveReplicatedSubObject(UObject* SubObject);
ENGINE_API void AddActorComponentReplicatedSubObject(UActorComponent* OwnerComponent,
                                                     UObject* SubObject,
                                                     ELifetimeCondition NetCondition = COND_None);

bool AMyActor::ReplicateSubobjects(UActorChannel* Channel,
                                    FOutBunch* Bunch, FReplicationFlags* RepFlags)
{
    bool bWrote = Super::ReplicateSubobjects(Channel, Bunch, RepFlags);
    bWrote |= Channel->ReplicateSubobject(MySubObject, *Bunch, *RepFlags);
    return bWrote;
}

// 1. Client predicts immediately
void AMyCharacter::LocalPredictAbility(int32 AbilityId)
{
    if (IsLocallyControlled())
    {
        ApplyAbilityEffectLocal(AbilityId); // immediate visual/audio
        ServerActivateAbility(AbilityId);   // request server confirmation
    }
}

// 2. Server validates, broadcasts, or corrects
void AMyCharacter::ServerActivateAbility_Implementation(int32 AbilityId)
{
    if (CanActivateAbility(AbilityId))
    {
        ApplyAbilityEffectAuthority(AbilityId);
        MulticastAbilityActivated(AbilityId);
    }
    else
    {
        ClientCorrectionAbilityFailed(AbilityId); // roll back client prediction
    }
}

[ ] bReplicates = true in constructor
[ ] SetNetUpdateFrequency / SetMinNetUpdateFrequency set appropriately
[ ] All UPROPERTY(Replicated) / UPROPERTY(ReplicatedUsing=...) declared
[ ] GetLifetimeReplicatedProps overridden; Super called first
[ ] DOREPLIFETIME / DOREPLIFETIME_CONDITION for each property
[ ] OnRep_ functions declared UFUNCTION() and implemented
[ ] Server RPCs have WithValidation; _Validate implemented
[ ] NetMulticast / Client RPCs guarded with HasAuthority() on call site
[ ] Subobjects registered via AddReplicatedSubObject or ReplicateSubobjects
[ ] SetOwner() called on server after spawning owned actors
[ ] DORM_DormantAll set on actors that rarely update

// Build.cs: "ReplicationGraph"
// Project: set ReplicationDriverClassName in DefaultEngine.ini
// [/Script/OnlineSubsystemUtils.IpNetDriver]
// ReplicationDriverClassName=/Script/MyGame.MyReplicationGraph

UCLASS()
class UMyReplicationGraph : public UReplicationGraph
{
    GENERATED_BODY()
public:
    virtual void InitGlobalActorClassSettings() override;
    virtual void InitGlobalGraphNodes() override;
    virtual void InitConnectionGraphNodes(UNetReplicationGraphConnection* RepGraphConnection) override;
};

// nullptr on local players (server-side); points to the network connection otherwise
UPROPERTY(DuplicateTransient)
TObjectPtr<UNetConnection> NetConnection;