Using TransferComponent in a PlayerController example in Unreal Engine.

TestPlayerController.cpp

#include "TestPlayerController.h"
#include "Components/TransferComponent.h"

DEFINE_LOG_CATEGORY_STATIC(TestPlayerControllerSub, Log, All);

ATestPlayerController::ATestPlayerController() {
    _transferComponent = CreateDefaultSubobject<UTransferComponent>(TEXT("TransferComponent"));
    _transferComponent->SetVerboseLoggingEnabled(true);
}

ATestPlayerController::~ATestPlayerController() {
}

void ATestPlayerController::BeginPlay() {
    Super::BeginPlay();

    if (GetNetMode() != ENetMode::NM_Client) {
        int bufferLength = 1000000;
        uint8* buffer = new uint8[bufferLength];
        for (int i = 0; i < bufferLength; i++)
            buffer[i] = i % 16;

        uint64 transferId = _transferComponent->SendBufferToClient(
            buffer,
            bufferLength,
            [this] (uint64 completedTransferId) {
                UE_LOG(TestPlayerControllerSub, Display, TEXT("We finished sending a buffer with id %llu from server to client"), completedTransferId);
                ServerNotifiesClientTransferCompleted(completedTransferId);
            }
        );

        UE_LOG(TestPlayerControllerSub, Display, TEXT("Server started sending a buffer with id %llu"), transferId);
    }
}

void ATestPlayerController::ServerNotifiesClientTransferCompleted_Implementation(uint64 transferId) {
    UE_LOG(TestPlayerControllerSub, Display, TEXT("Client received a buffer with id %llu"), transferId);

    Transfer* transfer = _transferComponent->ClientGetsCompletedTransfer(transferId);

    uint8* buffer = transfer->Buffer;
    int length = transfer->Length;

    _transferComponent->ClientFreesCompletedTransfer(transferId);
}

TestPlayerController.h

#pragma once

#include "CoreMinimal.h"
#include "TestPlayerController.generated.h"

UCLASS()
class ATestPlayerController : public APlayerController {
    GENERATED_BODY()
public:
    ATestPlayerController();
    virtual ~ATestPlayerController();

    virtual void BeginPlay() override;

private: // Network methods
    UFUNCTION(Client, Reliable)
    void ServerNotifiesClientTransferCompleted(uint64 transferId);
    void ServerNotifiesClientTransferCompleted_Implementation(uint64 transferId);

private:
    class UTransferComponent* _transferComponent = nullptr;
};