chore: import upstream snapshot with attribution

examples/with-langgraph/app/api/[..._path]/route.ts

@@ -0,0 +1,73 @@
+import { type NextRequest, NextResponse } from "next/server";
+
+function getCorsHeaders() {
+  return {
+    "Access-Control-Allow-Origin": "*",
+    "Access-Control-Allow-Methods": "GET, POST, PUT, PATCH, DELETE, OPTIONS",
+    "Access-Control-Allow-Headers": "*",
+  };
+}
+
+async function handleRequest(req: NextRequest, method: string) {
+  try {
+    const path = req.nextUrl.pathname.replace(/^\/?api\//, "");
+    const url = new URL(req.url);
+    const searchParams = new URLSearchParams(url.search);
+    searchParams.delete("_path");
+    searchParams.delete("nxtP_path");
+    const queryString = searchParams.toString()
+      ? `?${searchParams.toString()}`
+      : "";
+
+    const options: RequestInit = {
+      method,
+      headers: {
+        "x-api-key": process.env.LANGCHAIN_API_KEY || "",
+      },
+    };
+
+    if (["POST", "PUT", "PATCH"].includes(method)) {
+      options.body = await req.text();
+    }
+
+    const res = await fetch(
+      `${process.env.LANGGRAPH_API_URL}/${path}${queryString}`,
+      options,
+    );
+
+    const headers = new Headers(res.headers);
+    headers.delete("content-encoding");
+    headers.delete("content-length");
+    headers.delete("transfer-encoding");
+    const corsHeaders = getCorsHeaders();
+    for (const [key, value] of Object.entries(corsHeaders)) {
+      headers.set(key, value);
+    }
+
+    return new NextResponse(res.body, {
+      status: res.status,
+      statusText: res.statusText,
+      headers,
+    });
+  } catch (e: unknown) {
+    if (e instanceof Error) {
+      const typedError = e as Error & { status?: number };
+      return NextResponse.json(
+        { error: typedError.message },
+        { status: typedError.status ?? 500 },
+      );
+    }
+    return NextResponse.json({ error: "Unknown error" }, { status: 500 });
+  }
+}
+
+export const GET = (req: NextRequest) => handleRequest(req, "GET");
+export const POST = (req: NextRequest) => handleRequest(req, "POST");
+export const PUT = (req: NextRequest) => handleRequest(req, "PUT");
+export const PATCH = (req: NextRequest) => handleRequest(req, "PATCH");
+export const DELETE = (req: NextRequest) => handleRequest(req, "DELETE");
+export const OPTIONS = () =>
+  new NextResponse(null, {
+    status: 204,
+    headers: getCorsHeaders(),
+  });