integration/Plugins/UEWingman/Source/UEWingman/Private/WingServer.cpp

#include "WingServer.h"
#include "WingProperty.h"
#include "WingUtils.h"
#include "UObject/StrongObjectPtr.h"
#include "AssetRegistry/AssetRegistryModule.h"
#include "AssetRegistry/IAssetRegistry.h"
#include "Misc/CoreDelegates.h"
#include "Misc/OutputDeviceRedirector.h"
#include "Serialization/JsonReader.h"
#include "Serialization/JsonSerializer.h"
#include "SocketSubsystem.h"
#include "Sockets.h"
#include "Async/Async.h"

UWingServer* UWingServer::GWingServer = nullptr;

// ============================================================
// Initialization and Shutdown
// ============================================================

void UWingServer::Initialize(FSubsystemCollectionBase& Collection)
{
	Super::Initialize(Collection);
	GWingServer = this;

	// Create TCP listen socket
	ISocketSubsystem* SocketSub = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM);
	ListenSocket = SocketSub->CreateSocket(NAME_Stream, TEXT("WingServer"), false);
	if (!ListenSocket)
	{
		UE_LOG(LogTemp, Error, TEXT("UEWingman: Failed to create listen socket"));
		return;
	}

	ListenSocket->SetReuseAddr(true);
	ListenSocket->SetNonBlocking(true);

	TSharedRef<FInternetAddr> Addr = SocketSub->CreateInternetAddr();
	bool bIsValid = false;
	Addr->SetIp(TEXT("127.0.0.1"), bIsValid);
	Addr->SetPort(Port);

	if (!ListenSocket->Bind(*Addr))
	{
		UE_LOG(LogTemp, Error, TEXT("UEWingman: Failed to bind to port %d"), Port);
		SocketSub->DestroySocket(ListenSocket);
		ListenSocket = nullptr;
		return;
	}

	if (!ListenSocket->Listen(4))
	{
		UE_LOG(LogTemp, Error, TEXT("UEWingman: Failed to listen on port %d"), Port);
		SocketSub->DestroySocket(ListenSocket);
		ListenSocket = nullptr;
		return;
	}

	LoadingPhasesCompleteHandle = FCoreDelegates::OnAllModuleLoadingPhasesComplete.AddUObject(this, &UWingServer::BuildWingHandlerRegistry);
	LogCapture.bEnabled = false;
	GLog->AddOutputDevice(&LogCapture);
	bRunning = true;
	UE_LOG(LogTemp, Display, TEXT("UEWingman: MCP server listening on tcp://localhost:%d"), Port);
}

void UWingServer::Deinitialize()
{
	FCoreDelegates::OnAllModuleLoadingPhasesComplete.Remove(LoadingPhasesCompleteHandle);

	if (!bRunning)
	{
		Super::Deinitialize();
		return;
	}

	ISocketSubsystem* SocketSub = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM);

	// Set shutdown flag and drain pending messages under lock
	{
		FScopeLock Lock(&Mutex);
		bShuttingDown = true;
		for (auto& Msg : PendingMessages)
		{
			Msg->Response.SetValue(FString());
		}
		PendingMessages.Empty();
	}

	// Close all client sockets (unblocks their blocking reads)
	for (auto& Client : Clients)
	{
		if (Client->Socket)
		{
			Client->Socket->Close();
		}
	}

	// Wait for client threads to exit
	for (auto& Client : Clients)
	{
		Client->ThreadFuture.Wait();
		if (Client->Socket)
		{
			SocketSub->DestroySocket(Client->Socket);
		}
	}
	Clients.Empty();

	// Close listen socket
	if (ListenSocket)
	{
		ListenSocket->Close();
		SocketSub->DestroySocket(ListenSocket);
		ListenSocket = nullptr;
	}

	GLog->RemoveOutputDevice(&LogCapture);
	bRunning = false;
	bShuttingDown = false;
	GWingServer = nullptr;
	UE_LOG(LogTemp, Display, TEXT("UEWingman: Server stopped."));
	Super::Deinitialize();
}

// ============================================================
// FTickableEditorObject interface
// ============================================================

void UWingServer::Tick(float DeltaTime)
{
	if (!bRunning) return;

	// Accept new connections (non-blocking)
	AcceptNewConnections();

	// Clean up finished client threads
	CleanupFinishedClients();

	// Dequeue one pending message
	TSharedPtr<FPendingMessage> Request;
	{
		FScopeLock Lock(&Mutex);
		if (PendingMessages.Num() > 0)
		{
			Request = PendingMessages[0];
			PendingMessages.RemoveAt(0);
		}
	}

	// If we have a request, process it.
	if (Request.IsValid())
	{
		FString Response = HandleRequest(Request->Line);
		Request->Response.SetValue(Response);
	}
}

void UWingServer::TickServer(float DeltaTime)
{
	if (GWingServer) GWingServer->Tick(DeltaTime);
}

TStatId UWingServer::GetStatId() const
{
	RETURN_QUICK_DECLARE_CYCLE_STAT(UWingServer, STATGROUP_Tickables);
}

// ============================================================
// HandleRequest — Given a command, execute it.
// ============================================================

FString UWingServer::HandleRequest(const FString& Line)
{
	// Parse the request as JSON before doing anything else.
	TSharedPtr<FJsonValue> Value;
	TSharedRef<TJsonReader<>> Reader = TJsonReaderFactory<>::Create(Line);
	if (!FJsonSerializer::Deserialize(Reader, Value))
		return PackageResponses({TEXT("Invalid Json")});
	
	const TSharedPtr<FJsonObject>* RequestPtr = nullptr;
	if (!Value->TryGetObject(RequestPtr))
		return PackageResponses({TEXT("Json must be an object")});
	TSharedPtr<FJsonObject> Request = *RequestPtr;

	FString Command;
	Request->TryGetStringField(TEXT("command"), Command);
	if (Command == TEXT("Sequence"))
	{
		const TArray<TSharedPtr<FJsonValue>>* Subcommands = nullptr;
		if (!Request->TryGetArrayField(TEXT("subcommands"), Subcommands))
			return PackageResponses({TEXT("Sequence requires a 'subcommands' array.")});

		TArray<FString> Responses;
		Responses.Reserve(Subcommands->Num());
		for (const TSharedPtr<FJsonValue>& Sub : *Subcommands)
		{
			const TSharedPtr<FJsonObject>* SubObjPtr = nullptr;
			if (!Sub->TryGetObject(SubObjPtr))
				Responses.Add(TEXT("Subcommand must be a JSON object."));
			else
				Responses.Add(HandleJsonRequest(*SubObjPtr));
		}
		return PackageResponses(Responses);
	}

	return PackageResponses({HandleJsonRequest(Request)});
}

FString UWingServer::PackageResponses(const TArray<FString>& Responses)
{
	TArray<TSharedPtr<FJsonValue>> Blocks;
	Blocks.Reserve(Responses.Num());
	for (const FString& Response : Responses)
	{
		// Unreal's JSON writer terminates string serialization at the first
		// embedded null byte rather than escaping it, which would silently
		// truncate output. Sanitize null bytes to spaces.
		FString Sanitized = Response;
		for (int32 i = 0; i < Sanitized.Len(); ++i)
		{
			if (Sanitized[i] == TEXT('\0')) Sanitized[i] = TEXT(' ');
		}

		TSharedPtr<FJsonObject> Block = MakeShared<FJsonObject>();
		Block->SetStringField(TEXT("type"), TEXT("text"));
		Block->SetStringField(TEXT("text"), Sanitized);
		Blocks.Add(MakeShared<FJsonValueObject>(Block));
	}

	FString OutJson;
	TSharedRef<TJsonWriter<>> Writer = TJsonWriterFactory<>::Create(&OutJson);
	FJsonSerializer::Serialize(Blocks, Writer);
	return OutJson;
}

FString UWingServer::HandleJsonRequest(TSharedPtr<FJsonObject> Request)
{
	LogCapture.CapturedErrors.Empty();
	LogCapture.bEnabled = true;
	WingOut::StdoutBuffer.Reset();
	SuggestedManualSections.Empty();
	bSuggestHandlerHelp = false;
	LastHandler = nullptr;

	TryCallHandler(Request);

	Notifier.SendNotifications();
	LogCapture.bEnabled = false;
	for (const FString& Msg : LogCapture.CapturedErrors)
	{
		WingOut::Stdout.Printf(TEXT("UE_LOG: %s\n"), *Msg);
	}
	LogCapture.CapturedErrors.Empty();
	if (bSuggestHandlerHelp || (!SuggestedManualSections.IsEmpty()))
	{
		if (LastHandler) WingManual::PrintHandlerHelp(*LastHandler);
		if ((LastHandler == nullptr) || (LastHandler->Name != TEXT("Documentation_Manual")))
		{
			WingOut::Stdout.Print(TEXT("To see manual: command=Documentation_Manual\n"));
		}
		if (!SuggestedManualSections.IsEmpty())
		{
			WingManual::PrintSectionNames(TEXT("Suggested manual sections: "),
				SuggestedManualSections, WingOut::Stdout);
		}
	}
	FString Result = WingOut::StdoutBuffer.ToString();
	WingOut::StdoutBuffer.Reset();
	return Result;
}

void UWingServer::TryCallHandler(TSharedPtr<FJsonObject> Request)
{
	// Extract the command from the request.
	FString Command;
	if (!Request->TryGetStringField(TEXT("command"), Command))
	{
		WingOut::Stdout.Printf(TEXT("Request does not contain 'command' parameter"));
		WingOut::Stdout.Printf(TEXT("We recommend sending command='Documentation_Manual'."));
		return;
	}
	Request->RemoveField(TEXT("command"));

	// Find the handler for the specified command.
	FWingHandlerConfig* Found = FindHandler(Command);
	if (!Found)
	{
		WingOut::Stdout.Printf(TEXT("Unknown command: %s\n"), *Command);
		UWingServer::SuggestManual(GET_FUNCTION_NAME_CHECKED(UWingManualSections, ImportantCommands));
		return;
	}
	LastHandler = Found;

	// Make an object of the handler class.
	TStrongObjectPtr<UObject> HandlerObj(NewObject<UObject>(GetTransientPackage(), Found->HandlerClass.Get()));
	UWingHandler* Handler = Cast<UWingHandler>(HandlerObj.Get());
	Handler->Configuration = Found;

	// Populate the handler object with the request parameters.
	TArray<FWingProperty> Props = FWingProperty::GetVisible(Handler, true);
	if (!FWingProperty::PopulateFromJson(Props, *Request, false, WingOut::Stdout))
	{
		UWingServer::SuggestHandlerHelp();
		return;
	}

	// MCP handlers must not run inside an undo transaction.
	check(GUndo == nullptr);

	// Invoke the handler.
	Handler->Handle();
}

// ============================================================
// Connection Maintenance
// ============================================================

void UWingServer::AcceptNewConnections()
{
	if (!ListenSocket) return;

	bool bHasPending = false;
	if (!ListenSocket->HasPendingConnection(bHasPending) || !bHasPending) return;

	FSocket* ClientSocket = ListenSocket->Accept(TEXT("MCPClient"));
	if (!ClientSocket) return;

	ClientSocket->SetNonBlocking(false); // client threads use blocking I/O

	TSharedPtr<FClientConnection> Client = MakeShared<FClientConnection>();
	Client->Socket = ClientSocket;
	Client->ThreadFuture = Async(EAsyncExecution::Thread, [this, Client]() { ClientThreadFunc(this, Client); });
	Clients.Add(Client);
}

void UWingServer::CleanupFinishedClients()
{
	ISocketSubsystem* SocketSub = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM);

	for (int32 i = Clients.Num() - 1; i >= 0; --i)
	{
		if (!Clients[i]->bDone) continue;

		Clients[i]->ThreadFuture.Wait();
		if (Clients[i]->Socket)
		{
			SocketSub->DestroySocket(Clients[i]->Socket);
		}
		Clients.RemoveAt(i);
	}
}

// ============================================================
// Stuff Performed on the Client Thread
// ============================================================

void UWingServer::ClientThreadFunc(UWingServer* Server, TSharedPtr<FClientConnection> Client)
{
	constexpr int32 MaxRecvBufBytes = 1024 * 1024;
	constexpr int32 MinUnusedRecvSpace = 4096;

	FSocket* Socket = Client->Socket;
	TArray<uint8> RecvBuf;
	RecvBuf.SetNumUninitialized(MinUnusedRecvSpace);
	int32 RecvLen = 0;

	WaitForAssetRegistry();

	while (true)
	{
		FString Request;
		if (ExtractRequestFromBuffer(RecvBuf, RecvLen, Request))
		{
			FString Response;
			if (!ProcessRequestOnGameThread(Request, Response))
			{
				Client->bDone = true;
				return;
			}

			// Write the response back, null-terminated (blocking)
			FTCHARToUTF8 Utf8(*Response);
			if (!SendAll(Socket, reinterpret_cast<const uint8*>(Utf8.Get()),
				Utf8.Length() + 1))
			{
				Client->bDone = true;
				return;
			}
			continue;
		}

		if (!ReceiveMoreBytesIntoBuffer(Socket, RecvBuf, RecvLen))
		{
			break;
		}
	}

	Client->bDone = true;
}

bool UWingServer::ExtractRequestFromBuffer(
	TArray<uint8>& RecvBuf, int32& RecvLen, FString& OutRequest)
{
	const uint8* EndOfRequest = static_cast<const uint8*>(
		memchr(RecvBuf.GetData(), '\0', RecvLen));
	if (EndOfRequest == nullptr)
	{
		return false;
	}

	const int32 MessageLen =
		static_cast<int32>(EndOfRequest - RecvBuf.GetData());
	OutRequest = FString::ConstructFromPtrSize(
		reinterpret_cast<const UTF8CHAR*>(RecvBuf.GetData()), MessageLen);
	const int32 RemainingBytes = RecvLen - (MessageLen + 1);
	if (RemainingBytes > 0)
	{
		FMemory::Memmove(
			RecvBuf.GetData(),
			RecvBuf.GetData() + MessageLen + 1,
			RemainingBytes);
	}
	RecvLen = RemainingBytes;
	return true;
}

bool UWingServer::ReceiveMoreBytesIntoBuffer(
	FSocket* Socket, TArray<uint8>& RecvBuf, int32& RecvLen)
{
	constexpr int32 MaxRecvBufBytes = 1024 * 1024;
	constexpr int32 MinUnusedRecvSpace = 4096;

	int32 UnusedSpace = RecvBuf.Num() - RecvLen;
	if (UnusedSpace < MinUnusedRecvSpace)
	{
		if (RecvBuf.Num() >= MaxRecvBufBytes)
		{
			return false;
		}
		RecvBuf.SetNumUninitialized(RecvBuf.Num() * 2);
		UnusedSpace = RecvBuf.Num() - RecvLen;
	}

	int32 BytesRead = 0;
	if (!Socket->Recv(RecvBuf.GetData() + RecvLen, UnusedSpace, BytesRead))
	{
		return false;
	}
	if (BytesRead <= 0)
	{
		return false;
	}

	RecvLen += BytesRead;
	return true;
}

bool UWingServer::SendAll(FSocket* Socket, const uint8* Data, int32 BytesToSend)
{
	while (BytesToSend > 0)
	{
		int32 BytesSent = 0;
		if (!Socket->Send(Data, BytesToSend, BytesSent) || (BytesSent <= 0))
		{
			return false;
		}
		Data += BytesSent;
		BytesToSend -= BytesSent;
	}
	return true;
}

bool UWingServer::ProcessRequestOnGameThread(
	const FString& Request, FString& Response)
{
	// Enqueue the message for game-thread processing.
	TSharedPtr<UWingServer::FPendingMessage> Msg =
		MakeShared<UWingServer::FPendingMessage>();
	Msg->Line = Request;
	TFuture<FString> Future = Msg->Response.GetFuture();

	{
		FScopeLock Lock(&GWingServer->Mutex);
		if (GWingServer->bShuttingDown)
		{
			return false;
		}
		GWingServer->PendingMessages.Add(Msg);
	}

	// Block until the game thread processes this message.
	Response = Future.Get();
	return true;
}

void UWingServer::WaitForAssetRegistry()
{
	IAssetRegistry& AR =
		FModuleManager::LoadModuleChecked<FAssetRegistryModule>(
			"AssetRegistry").Get();
	while (AR.IsLoadingAssets()) FPlatformProcess::Sleep(0.25f);
}

// ============================================================
// BuildWingHandlerRegistry
// ============================================================

void UWingServer::AddHandler(UObject* Obj, const FString& Documentation)
{
	AddHandler(Obj, WingUtils::GetHandlerName(Obj->GetClass()), nullptr, EWingHandlerKind::Normal, nullptr, Documentation);
}

void UWingServer::AddHandler(UObject* Obj, const FString& Name, UObject* Config, EWingHandlerKind Kind, UClass* FactoryClass, const FString& Documentation)
{
	FWingHandlerConfig H;
	H.Name = Name;
	H.Documentation = Documentation;
	H.HandlerClass = TStrongObjectPtr<UClass>(Obj->GetClass());
	H.Config = TStrongObjectPtr<UObject>(Config);
	H.FactoryClass = TStrongObjectPtr<UClass>(FactoryClass);
	H.Kind = Kind;

	GWingServer->WingHandlerRegistry.Add(MoveTemp(H));
}

void UWingServer::BuildWingHandlerRegistry()
{
	WingHandlerRegistry.Empty();
	for (UClass* Class : WingUtils::CollectHandlerClasses())
	{
		UWingHandler* CDO = Cast<UWingHandler>(Class->GetDefaultObject());
		CDO->Register();
	}
	WingHandlerRegistry.Sort([](const FWingHandlerConfig& A, const FWingHandlerConfig& B) { return A.Name < B.Name; });
}

FWingHandlerConfig* UWingServer::FindHandler(const FString& Name)
{
	int32 Index = Algo::LowerBoundBy(WingHandlerRegistry, Name, [](const FWingHandlerConfig& H) { return H.Name; });
	if (Index < WingHandlerRegistry.Num() && WingHandlerRegistry[Index].Name == Name)
	{
		return &WingHandlerRegistry[Index];
	}
	return nullptr;
}

TStringBuilder<65536> WingOut::StdoutBuffer;
WingOut WingOut::Stdout(&WingOut::StdoutBuffer);
WingOut WingOut::None(nullptr);