UnrealEngineからDifyのボットとチャットしてみる

UnrealEngineでDifyとのAIチャットを実装してみたので内容をメモしておきます。

試した環境

• UE5.5.4
• Dify：1.7.2

試した内容

以下のようなBlueprintノードを用意して、質問してその回答をSSE（Server-Sent Events）で少しずつ受け取れるようにしました。

以下のC++クラスを用意してます。

ChatMessageFunction.h

#pragma once

#include "CoreMinimal.h"
#include "Kismet/BlueprintAsyncActionBase.h"
#include "HttpFwd.h"
#include "ChatMessageFunction.generated.h"

DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(FChatMessageProgress, bool, bResult, FString, ResponseMessage);

/**
 * 
 */
UCLASS()
class DIFYCLIENT_API UChatMessageFunction : public UBlueprintAsyncActionBase
{
	GENERATED_BODY()

public:
	UPROPERTY(BlueprintAssignable, Category = "DifyClient")
	FChatMessageProgress Progress;
	UPROPERTY(BlueprintAssignable, Category = "DifyClient")
	FChatMessageProgress Complete;

public:
	UChatMessageFunction(const FObjectInitializer& ObjectInitializer);

	UFUNCTION(BlueprintCallable, Category = "DifyClient", meta = (worldContext = "WorldContextObject", BlueprintInternalUseOnly = "true"))
	static UChatMessageFunction* SendChatMessage(UObject* WorldContextObject, const FString& Message);

	virtual void Activate() override;

private:
	void OnResponseReceivedComplete(FHttpRequestPtr Request, FHttpResponsePtr Response, bool bWasSuccessful);

	void OnProcessResponse(FHttpRequestPtr Request, uint64 ByteSent, uint64 ByteReceived);

private:
	FString Message;

	int ResponseDataCount;
};

ChatMessageFunction.cpp

#include "ChatMessageFunction.h"
#include "Interfaces/IHttpRequest.h"
#include "Interfaces/IHttpResponse.h"
#include "HttpModule.h"
#include "Misc/Guid.h" // UUID生成用
#include "DifyClientBPLibrary.h"

UChatMessageFunction::UChatMessageFunction(const FObjectInitializer& ObjectInitializer)
	: Super(ObjectInitializer), ResponseDataCount(0)
{
}

UChatMessageFunction* UChatMessageFunction::SendChatMessage(UObject* WorldContextObject, const FString& Message)
{
	UChatMessageFunction* Node = NewObject<UChatMessageFunction>();
	Node->RegisterWithGameInstance(WorldContextObject);
	Node->Message = Message;
	return Node;
}

void UChatMessageFunction::Activate()
{
	TSharedRef<IHttpRequest, ESPMode::ThreadSafe> HttpRequest = FHttpModule::Get().CreateRequest();
	HttpRequest->SetURL(UDifyClientBPLibrary::GetBaseURL()  + TEXT("/chat-messages"));
	HttpRequest->SetVerb(TEXT("POST"));
	HttpRequest->SetHeader(TEXT("Authorization"), TEXT("Bearer ") + UDifyClientBPLibrary::GetApiKey());
	HttpRequest->SetHeader(TEXT("Content-Type"), TEXT("application/json"));

	TSharedPtr<FJsonObject> JsonRoot = MakeShareable(new FJsonObject);
	JsonRoot->SetArrayField(TEXT("inputs"), TArray<TSharedPtr<FJsonValue>>());
	JsonRoot->SetStringField(TEXT("query"), Message);
	JsonRoot->SetStringField(TEXT("response_mode"), TEXT("streaming"));
	JsonRoot->SetStringField(TEXT("user"), TEXT("test"));

	FGuid Guid = FGuid::NewGuid();
	FString GuidString = Guid.ToString(EGuidFormats::DigitsWithHyphens);
	JsonRoot->SetStringField(TEXT("conversation_id"), TEXT(""));

	FString OutPutString;
	TSharedRef<TJsonWriter<>> Writer = TJsonWriterFactory<>::Create(&OutPutString);
	FJsonSerializer::Serialize(JsonRoot.ToSharedRef(), Writer);

	HttpRequest->SetContentAsString(OutPutString);

	HttpRequest->OnProcessRequestComplete().BindUObject(this, &UChatMessageFunction::OnResponseReceivedComplete);
	HttpRequest->OnRequestProgress64().BindUObject(this, &UChatMessageFunction::OnProcessResponse);
	if (!HttpRequest->ProcessRequest())
	{
		Complete.Broadcast(false, TEXT("Failed to ProcessRequest"));
	}
}

void UChatMessageFunction::OnResponseReceivedComplete(FHttpRequestPtr Request, FHttpResponsePtr Response, bool bWasSuccessful)
{
	if (Response.IsValid())
	{
		bool bResult = Response->GetResponseCode() == 200;
		Complete.Broadcast(bResult, bResult ? TEXT("") : Response->GetContentAsString());
	}
	else
	{
		Complete.Broadcast(bWasSuccessful, TEXT(""));
	}


	SetReadyToDestroy();
}

void UChatMessageFunction::OnProcessResponse(FHttpRequestPtr Request, uint64 ByteSent, uint64 ByteReceived)
{
	FHttpResponsePtr Response = Request->GetResponse();
	if (Response.IsValid()) {
		FString ResponseStr = Response->GetContentAsString();
		TArray<FString> ResponseArr;
		const int32 ArrNum = ResponseStr.ParseIntoArray(ResponseArr, TEXT("\n\n"));
		FString ProgressStr;
		bool bReceive = false;
		for (int i = ResponseDataCount; i < ArrNum; i++)
		{
			FString& Line = ResponseArr[i];
			// "data:"を先頭から削除
			if (Line.StartsWith(TEXT("data:"))) 
			{
				Line = Line.RightChop(5).TrimStart();
			}
			else 
			{
				continue;
			}

			// JSONパース
			TSharedPtr<FJsonObject> JsonObject;
			TSharedRef<TJsonReader<>> Reader = TJsonReaderFactory<>::Create(Line);
			if (!FJsonSerializer::Deserialize(Reader, JsonObject) || !JsonObject.IsValid()) {
				continue;
			}

			FString Event = JsonObject->GetStringField("event");
			if (Event == "agent_message") {
				FString Answer = JsonObject->GetStringField("answer");
				ProgressStr = ProgressStr + Answer;
				bReceive = true;
				UE_LOG(LogTemp, Log, TEXT("Progress:%s"), *Answer);
			}
			else
			{
				UE_LOG(LogTemp, Log, TEXT("Progress:%s"), *Line);
			}
		}

		if (bReceive) 
		{
			Progress.Broadcast(true, ProgressStr);
		}

		ResponseDataCount = ArrNum;
	}
}