proxy.js

export default {
  async fetch(request) {
    const corsHeaders = {
      "Access-Control-Allow-Origin": "*",
      "Access-Control-Allow-Methods": "GET",
      "Access-Control-Max-Age": "86400",
      "Access-Control-Allow-Headers": "X-Proxy-URL, X-Proxy-Method, X-Proxy-Header",
    };

    if (request.method === "OPTIONS") {
      if (request.headers.get("Origin") && 
          request.headers.get("Access-Control-Request-Method") && 
          request.headers.get("Access-Control-Request-Headers")) {
        return new Response(null, { headers: corsHeaders });
      } else {
        return new Response(null, { headers: { Allow: "GET" } });
      }
    }

    const url = new URL(request.url)
    var pathurl = "";
    if (url.pathname == "/" && url.searchParams) {
      pathurl = url.search.slice(1);
    }
    const originalHeaders = request.headers;
    const proxyUrl = request.headers.get('X-Proxy-URL') || pathurl;
    const proxyMethod = originalHeaders.get('X-Proxy-Method') || 'GET';
    const proxyHeaders = originalHeaders.get('X-Proxy-Header') || null;
    if (!proxyUrl) {
      return new Response(null, {headers: {...corsHeaders}})
    }
    if (!isValidHttpUrl(proxyUrl)) {
      return new Response('Error URL invalid', { status: 500, headers: corsHeaders });
    }
    let parsedProxyHeaders = new Headers();
    if (proxyHeaders) {
      try {
        const headerObj = JSON.parse(proxyHeaders);
        for (const key in headerObj) {
          parsedProxyHeaders.append(key, headerObj[key]);
        }
      } catch (err) {
        return new Response('X-Proxy-Headers must be valid JSON', { status: 400 });
      }
    }
    try {
      const proxiedRequest = new Request(proxyUrl, {
        method: proxyMethod,
        headers: parsedProxyHeaders,
      });

      const response = await fetch(proxiedRequest);
      const headers = new Headers(response.headers);
      headers.set('Access-Control-Allow-Origin', "*");
      headers.set('Cache-Control', "max-age=1800");
      headers.set('Vary', "x-proxy-url, x-proxy-method, x-proxy-header");

      return new Response(response.body, {
        status: response.status,
        statusText: response.statusText,
        headers: headers,
      });
    } catch (error) {
      console.error('Error fetching proxied URL:', error);
      return new Response('Error fetching proxied URL', { status: 500, headers: corsHeaders });
    }
  },
}

function isValidHttpUrl(string) {
  let url;
  
  try {
    url = new URL(string);
  } catch (_) {
    return false;  
  }

  return url.protocol === "http:" || url.protocol === "https:";
}