aly / cors.js

// We support the GET, POST, HEAD, and OPTIONS methods from any origin, // and allow any header on requests. These headers must be present // on all responses to all CORS preflight 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-Max-Age": "86400", } // The URL for the remote third party API you want to fetch from // but does not implement CORS const API_URL = "/cdn/cors.json" // The endpoint you want the CORS reverse proxy to be on const PROXY_ENDPOINT = "/" async function handleRequest(request) { const url = new URL(request.url) let apiUrl = url.pathname; if (apiUrl == null) { apiUrl = API_URL } apiUrl = "https://p.alyssadev.xyz/file/ads-share" + apiUrl; // Rewrite request to point to API url. This also makes the request mutable // so we can add the correct Origin header to make the API server think // that this request isn't cross-site. request = new Request(apiUrl, request) request.headers.set("Origin", new URL(apiUrl).origin) let response = await fetch(request) // Recreate the response so we can modify the headers response = new Response(response.body, response) // Set CORS headers response.headers.set("Access-Control-Allow-Origin", "*") // Append to/Add Vary header so browser will cache response correctly response.headers.append("Vary", "Origin") return response } function handleOptions(request) { // Make sure the necessary headers are present // for this to be a valid pre-flight request let headers = request.headers; if ( headers.get("Origin") !== null && headers.get("Access-Control-Request-Method") !== null && headers.get("Access-Control-Request-Headers") !== null ){ // Handle CORS pre-flight request. // If you want to check or reject the requested method + headers // you can do that here. let respHeaders = { ...corsHeaders, // Allow all future content Request headers to go back to browser // such as Authorization (Bearer) or X-Client-Name-Version "Access-Control-Allow-Headers": request.headers.get("Access-Control-Request-Headers"), } return new Response(null, { headers: respHeaders, }) } else { // Handle standard OPTIONS request. // If you want to allow other HTTP Methods, you can do that here. return new Response(null, { headers: { Allow: "GET, HEAD, POST, OPTIONS", }, }) } } addEventListener("fetch", event => { const request = event.request const url = new URL(request.url) if(url.pathname.startsWith(PROXY_ENDPOINT)){ if (request.method === "OPTIONS") { // Handle CORS preflight requests event.respondWith(handleOptions(request)) } else if( request.method === "GET" || request.method === "HEAD" || request.method === "POST" ){ // Handle requests to the API server event.respondWith(handleRequest(request)) } else { event.respondWith( new Response(null, { status: 405, statusText: "Method Not Allowed", }), ) } } })