cloudflare worker CORS proxy

cors-proxy.js

/**
 * Usage:
 * https://worker-name.myusername.workers.dev/?url=http://google.com
 */

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

/**
 * Respond to the request
 * @param {Request} request
 */
async function handleRequest(request) {
  if (request.method === "OPTIONS") {
    return new Response('ok', {headers: {
      "access-control-allow-origin": request.headers.get('origin'),
      "access-control-allow-methods": "GET",
      "access-control-allow-headers": request.headers.get("access-control-request-headers"),
    }})
  }

  const url = new URL(request.url)
  const requested_url = url.searchParams.get('url')
  const userAgent = url.searchParams.get('userAgent')
  const headers = {...request.headers}
  if (userAgent) {
    headers["User-Agent"] = userAgent
  }

  const res = await fetch(requested_url, {
    headers: headers})
  const body = await res.arrayBuffer()
  const resHeaders = {}
  for (let [k, v] of res.headers.entries()) {
    resHeaders[k] = v
  }
  return new Response(body, {
    status: res.status,
    headers: {
      ...resHeaders,
      "access-control-allow-origin": request.headers.get('origin'),
    }
  })
}