feat(nextjs-app): 修改 /chat-messages 接口以支持流式响应

重构 Dify 的 chat-messages 接口的 POST 方法，使用 baseRequest 替代 post 方法
新增 response_mode 参数支持
直接透传原始响应给客户端，包括状态码、响应头和流式响应
添加必要的 CORS 头信息

Author: lexmin0412

packages/nextjs-app/app/api/external/dify/[appId]/chat-messages/route.ts

@@ -1,26 +1,43 @@
 import { genDifyRequest } from "@/app/api/utils";
-import { NextRequest, NextResponse } from "next/server";
+import { NextRequest } from "next/server";
 
 const POST = async (
 	_request: NextRequest,
 	{ params }: { params: { appId: string } },
 ) => {
 	const { appId } = await params;
 	// 获取 body 中的参数
-	const { conversation_id, inputs, files, query } = await _request.json();
+	const { conversation_id, inputs, files, query, response_mode } =
+		await _request.json();
 	const difyRequest = await genDifyRequest(appId);
 	const user = _request.headers.get("dc-user") as string;
-	const result = await difyRequest.post(`/chat-messages`, {
-		conversation_id,
-		inputs,
-		files,
-		response_mode: "blocking",
-		user,
-		query,
+	const response = await difyRequest.baseRequest(`/chat-messages`, {
+		method: "POST",
+		body: JSON.stringify({
+			conversation_id,
+			inputs,
+			files,
+			response_mode,
+			user,
+			query,
+		}),
+		headers: {
+			"Content-Type": "application/json",
+		},
 	});
-	return NextResponse.json({
-		code: 200,
-		data: result,
+
+	// 直接将原始响应“透传”给客户端
+	return new Response(response.body, {
+		status: response.status,
+		headers: {
+			// 允许流式响应
+			"Content-Type":
+				response.headers.get("Content-Type") || "application/json",
+			// 允许 CORS 或其他你需要的 header
+			"X-Version": response.headers.get("X-Version") || "",
+			// 允许获取 Dify 版本
+			"Access-Control-Allow-Headers": "X-Version, Authorization, Content-Type",
+		},
 	});
 };