Implement the CORS proxy in a cloudflare worker

This should help with #337

cloudflare-worker-proxy.js

@@ -0,0 +1,39 @@
+/**
+ * This is a cloudflare worker for dezoomify
+ */
+
+/**
+ * Respond to the request
+ * @param {Request} request
+ */
+async function handleRequest(request) {
+    const url = new URL(request.url);
+    const target_url = new URL(url.searchParams.get("url"));
+    let target_request = new Request(target_url, request);
+    target_request.headers.set("Origin", target_url.origin);
+    target_request.headers.set("Referer", target_url.toString());
+    const cookies = url.searchParams.get("cookies");
+    if (cookies) target_request.headers.set("Cookie", cookies);
+    let response = await fetch(target_request);
+    response = new Response(response.body, response);
+    const response_cookie = response.headers.get("Set-Cookie");
+    if (response_cookie) response.headers.set("X-Set-Cookie", response_cookie);
+    response.headers.delete("Set-Cookie");
+    return response;
+}
+
+/**
+ * Handle a fetch event
+ * @param {Error} error
+ */
+async function handleError(error) {
+    console.error(error);
+    return new Response(error.toString(), { status: 500 });
+}
+
+addEventListener('fetch', evt => {
+    const req = evt.request;
+    console.log(req.url);
+    let response = handleRequest(req).catch(handleError);
+    evt.respondWith(response);
+});