Proxy.js | Next.js 16+ integration for Prerender.io

Proxy.js-Next16+

import { NextResponse, type NextRequest } from "next/server";

export async function proxy(request: NextRequest) {
  const userAgent = request.headers.get("user-agent");

  const bots = [
    "googlebot",
    "yahoo! slurp",
    "bingbot",
    "yandex",
    "baiduspider",
    "facebookexternalhit",
    "twitterbot",
    "rogerbot",
    "linkedinbot",
    "embedly",
    "quora link preview",
    "showyoubot",
    "outbrain",
    "pinterest/0.",
    "developers.google.com/+/web/snippet",
    "slackbot",
    "vkshare",
    "w3c_validator",
    "redditbot",
    "applebot",
    "whatsapp",
    "flipboard",
    "tumblr",
    "bitlybot",
    "skypeuripreview",
    "nuzzel",
    "discordbot",
    "google page speed",
    "qwantify",
    "pinterestbot",
    "bitrix link preview",
    "xing-contenttabreceiver",
    "chrome-lighthouse",
    "telegrambot",
    "oai-searchbot",
    "chatgpt",
    "gptbot",
    "perplexity",
    "claudeBot",
    "amazonbot",
    "integration-test", // Integration testing
  ];

  const IGNORE_EXTENSIONS = [
    ".js", ".css", ".xml", ".less", ".png", ".jpg", ".jpeg", ".gif", ".pdf",
    ".doc", ".txt", ".ico", ".rss", ".zip", ".mp3", ".rar", ".exe", ".wmv",
    ".avi", ".ppt", ".mpg", ".mpeg", ".tif", ".wav", ".mov", ".psd", ".ai",
    ".xls", ".mp4", ".m4a", ".swf", ".dat", ".dmg", ".iso", ".flv", ".m4v",
    ".torrent", ".woff", ".ttf", ".svg", ".webmanifest",
  ];

  const isBot =
    !!userAgent && bots.some((bot) => userAgent.toLowerCase().includes(bot.toLowerCase()));

  const isPrerender = request.headers.get("X-Prerender");
  const pathname = new URL(request.url).pathname;

  const extension = pathname.slice(((pathname.lastIndexOf(".") - 1) >>> 0) + 1);
  const hasExtension = extension.length > 0;
  const dottedExt = hasExtension ? `.${extension}` : "";

  if (isPrerender || !isBot || (hasExtension && IGNORE_EXTENSIONS.includes(dottedExt))) {
    return NextResponse.next();
  }

  // Bot path: proxy to prerender service
  const newURL = `http://service.prerender.io/${request.url}`;
  const newHeaders = new Headers(request.headers);

  newHeaders.set("X-Prerender-Token", process.env.PRERENDER_TOKEN ?? "");
  newHeaders.set("X-Prerender-Int-Type", "NextJS");

  try {
    const res = await fetch(
      new Request(newURL, {
        headers: newHeaders,
        redirect: "manual",
      })
    );

   const responseHeaders = new Headers(res.headers);

    responseHeaders.set("X-Redirected-From", request.url);
    responseHeaders.delete("content-encoding");
    responseHeaders.delete("content-length");
    responseHeaders.delete("transfer-encoding"); // harmless if absent

    // Stream the body through
    const { readable, writable } = new TransformStream();
    if (res.body) {
      res.body.pipeTo(writable);
    }

    return new NextResponse(readable, {
      status: res.status,
      statusText: res.statusText,
      headers: responseHeaders,
    });
  } catch (error) {
    return NextResponse.next();
  }
}