Add Koa middleware

.env.example

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+PRERENDER_TOKEN=
+PRERENDER_SERVICE_URL=

.gitignore

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+node_modules/
+.env

README.md

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+# prerender-koa
+
+Koa middleware for [Prerender.io](https://prerender.io). Intercepts requests from bots and crawlers and serves prerendered HTML, so your JavaScript-rendered app is fully indexable by search engines and social media scrapers.
+
+Compatible with **Koa v2+** and **Node.js 18+**.
+
+## Installation
+
+```bash
+npm install prerender-koa
+```
+
+## Usage
+
+```javascript
+const Koa = require('koa');
+const prerender = require('prerender-koa');
+
+const app = new Koa();
+
+app.use(prerender({
+  token: 'YOUR_PRERENDER_TOKEN'
+}));
+
+// your other middleware and routes
+```
+
+The middleware intercepts bot requests and proxies them to Prerender.io, returning prerendered HTML. Regular browser requests pass through unaffected. All responses include an `X-Prerender: true/false` header.
+
+## Options
+
+| Option | Type | Default | Description |
+|--------|------|---------|-------------|
+| `token` | `string` | `process.env.PRERENDER_TOKEN` | Your Prerender.io token |
+| `serviceUrl` | `string` | `process.env.PRERENDER_SERVICE_URL` or `https://service.prerender.io/` | Prerender service URL (use this for self-hosted Prerender) |
+| `protocol` | `string` | `null` | Force a protocol (`http` or `https`). Defaults to the request's protocol |
+
+## Environment variables
+
+```bash
+PRERENDER_TOKEN=your_token_here
+PRERENDER_SERVICE_URL=https://service.prerender.io/  # optional
+```
+
+## Self-hosted Prerender
+
+```javascript
+app.use(prerender({
+  serviceUrl: 'http://your-prerender-server:3000'
+}));
+```
+
+## How it works
+
+Requests are prerendered when **all** of the following are true:
+
+- The HTTP method is `GET`
+- The `User-Agent` matches a known bot/crawler (Googlebot, Bingbot, Twitterbot, GPTBot, ClaudeBot, etc.)  
+  — OR the URL contains `_escaped_fragment_`  
+  — OR the `X-Bufferbot` header is present
+- The URL does not end with a static asset extension (`.js`, `.css`, `.png`, etc.)
+
+Everything else passes through to your normal Koa middleware.
+
+## License
+
+MIT

index.js

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+'use strict';
+
+const internals = {};
+
+internals.crawlerUserAgents = [
+  'googlebot', 'yahoo', 'bingbot', 'baiduspider',
+  'facebookexternalhit', 'twitterbot', 'rogerbot', 'linkedinbot',
+  'embedly', 'quora link preview', 'showyoubot', 'outbrain',
+  'pinterest', 'slackbot', 'developers.google.com/+/web/snippet',
+  'w3c_validator', 'perplexity', 'oai-searchbot', 'chatgpt-user',
+  'gptbot', 'claudebot', 'amazonbot'
+];
+
+internals.extensionsToIgnore = [
+  '.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', '.ttf', '.woff', '.svg'
+];
+
+internals.defaults = {
+  serviceUrl: process.env.PRERENDER_SERVICE_URL || 'https://service.prerender.io/',
+  token: process.env.PRERENDER_TOKEN || null,
+  protocol: null
+};
+
+function isBot(userAgent) {
+  const ua = userAgent.toLowerCase();
+  return internals.crawlerUserAgents.some((bot) => ua.includes(bot));
+}
+
+function isStaticAsset(path) {
+  return internals.extensionsToIgnore.some((ext) => path.endsWith(ext));
+}
+
+function shouldPrerender(ctx) {
+  const userAgent = ctx.get('user-agent');
+  if (!userAgent || ctx.method !== 'GET') return false;
+  if (isStaticAsset(ctx.path)) return false;
+
+  return '_escaped_fragment_' in ctx.query
+    || isBot(userAgent)
+    || !!ctx.get('x-bufferbot');
+}
+
+function buildApiUrl(ctx, settings) {
+  const protocol = settings.protocol || ctx.protocol;
+  const base = settings.serviceUrl.endsWith('/')
+    ? settings.serviceUrl
+    : settings.serviceUrl + '/';
+  return `${base}${protocol}://${ctx.host}${ctx.url}`;
+}
+
+async function fetchPrerendered(apiUrl, ctx, settings) {
+  const headers = { 'User-Agent': ctx.get('user-agent') };
+  if (settings.token) {
+    headers['X-Prerender-Token'] = settings.token;
+  }
+  const response = await fetch(apiUrl, { headers, redirect: 'manual' });
+  const body = await response.text();
+  return { status: response.status, body };
+}
+
+module.exports = function prerenderMiddleware(options = {}) {
+  const settings = { ...internals.defaults, ...options };
+
+  return async function prerender(ctx, next) {
+    if (!shouldPrerender(ctx)) {
+      ctx.set('X-Prerender', 'false');
+      return next();
+    }
+
+    try {
+      const apiUrl = buildApiUrl(ctx, settings);
+      const prerendered = await fetchPrerendered(apiUrl, ctx, settings);
+      ctx.status = prerendered.status;
+      ctx.body = prerendered.body;
+      ctx.set('X-Prerender', 'true');
+    } catch (err) {
+      console.error('Prerender error, falling back:', err.message);
+      ctx.set('X-Prerender', 'false');
+      return next();
+    }
+  };
+};