cors-anywhere.js

//
// CORS Anywhere -- Cloudflare Workers edition!
//
// try: https://cors-anywhere.0xhorizon.workers.dev/https://discordapp.com/api/guilds/444586810765475860/widget.json
//

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

async function handleRequest(event, request) {
  // Handle OPTIONS request quickly
  if (request.method === "OPTIONS") {
    return handleCORSPreflight(request)
  } else if (request.method !== "GET" && request.method !== "HEAD") { //&& request.method !== "POST") {
    return new Response(null, {
      status: 405,
      statusText: "Method Not Allowed",
    })
  }

  // Handle normal GET/HEAD request
  let url = new URL(request.url)
  let host = url.host
  let param = url.pathname

  if (param.length >= 1) {
    param = param.substr(1)
  }
  if (param === "") {
    return respondWithText("welcome")
  }
  if (!param.startsWith("http")) {
    return respondWithText("Oops! invalid use, speak to dev team for correct usage.")
  }
  if (param.indexOf("://") < 0) {
    param = param.replace("http:/", "http://")
    param = param.replace("https:/", "https://")
  }

  // Proxy-cache the request (with ttl of 60 seconds)
  let cacheUrl = new URL(param)  
  let cacheKey = new Request(cacheUrl)
  let cache = caches.default

  // Get this request from this zone's cache
  let resp = await cache.match(cacheKey)

  if (!resp) {
    //if not in cache, grab it from the origin
    originResp = await fetch(cacheUrl, {
      method: request.method,
      headers: {
        ...request.headers
      },
      cf: {
        cacheEverything: true,
        cacheTtl: 61,
        scrapeShield: false
      }
    })
    
    // must use Response constructor to inherit all of response's fields
    resp = new Response(originResp.body, {
        status: originResp.status
    })
    
    // copy over certain headers, but we don't want all..
    let v = originResp.headers.get('content-type')
    if (v && v !== '') {
      resp.headers.set('content-type', v)
    }

    // set caching and cors headers
    resp.headers.set('X-Worker', (new Date()).toUTCString())
    resp.headers.set('Cache-Control', 'public, max-age=61')
    resp.headers.set('Access-Control-Allow-Origin', '*')
    resp.headers.set('Access-Control-Allow-Methods', 'GET, HEAD')
    
    // store the fetched response as cacheKey
    await cache.put(cacheKey, resp.clone())
  }

  return resp
}

function respondWithText(text) {
  return new Response(text, { status: 200, headers: { "Content-Type": "text/html" } })
}

// We support the GET, POST, HEAD, and OPTIONS methods from any origin,
// and accept the Content-Type header on requests. These headers must be
// present on all responses to all CORS requests. In practice, this means
// all responses to OPTIONS requests.
const corsHeaders = {
  "Access-Control-Allow-Origin": "*",
  "Access-Control-Allow-Methods": "GET, HEAD, POST, OPTIONS",
  "Access-Control-Allow-Headers": "Content-Type",
}

function handleCORSPreflight(request) {
  if (request.headers.get("Origin") !== null &&
      request.headers.get("Access-Control-Request-Method") !== null) {
    // Handle CORS pre-flight request.
    return new Response(null, {
      headers: corsHeaders
    })
  } else {
    // Handle standard OPTIONS request.
    return new Response(null, {
      headers: {
        "Allow": "GET, HEAD, POST, OPTIONS",
      }
    })
  }
}