use multiple workers for PoW

src/main/resources/web/index.html

@@ -35,9 +35,6 @@ script-src 'self' https://*.cloudflare.com/ https://alcdn.msauth.net/ https://*.
     <script crossorigin="anonymous"
             integrity="sha512-UNM1njAgOFUa74Z0bADwAq8gbTcqZC8Ej4xPSzpnh0l6KMevwvkBvbldF9uR++qKeJ+MOZHRjV1HZjoRvjDfNQ=="
             src="https://cdnjs.cloudflare.com/ajax/libs/uuid/8.3.2/uuid.min.js"></script>
-    <script crossorigin="anonymous"
-            integrity="sha512-/yIGjYJZIXZx10ig0yhbK41OiwcqBUxIj0xQJe+NwkMIdS/u07b6Mwo0nvXB4o7A6WiKnKOf92JwE5Ezo27u9Q=="
-            src="https://cdnjs.cloudflare.com/ajax/libs/jsSHA/3.2.0/sha.min.js"></script>
     <script src="https://alcdn.msauth.net/browser/2.14.2/js/msal-browser.min.js"
             integrity="sha384-ggh+EF1aSqm+Y4yvv2n17KpurNcZTeYtUZUvhPziElsstmIEubyEB6AIVpKLuZgr"
             crossorigin="anonymous"></script>

src/main/resources/web/js/page.js

@@ -4,6 +4,7 @@ var listening = document.getElementById("listening");
 var actions = document.getElementById("actions");
 var accounts = document.getElementById("accounts-list");
 var listenVisible = false;
+var workers = new Array(navigator.hardwareConcurrency).fill(null).map(() => new Worker("js/worker.js"));
 
 // On load
 $(() => {
@@ -20,10 +21,9 @@ $(() => {
     $("#form_ws_url").on("submit", e => setWsUrl($("#ws-url").val()));
     $("#form_cors_proxy").on("submit", e => setCorsProxy($("#cors-proxy").val()));
 
-
+    workers.forEach(it => it.onmessage = onWorkerMsg);
     refreshAccountList();
-    // Heroku sleeps in 30 minutes, let's call it every 10 minutes to keep the same address, so Mojang see it as less suspect
-    setInterval(refreshCorsStatus, 10 * 60 * 1000);
+    setInterval(refreshCorsStatus, 10 * 60 * 1000); // Heroku auto sleeps in 30 min
     refreshCorsStatus();
     resetHtml();
 
@@ -99,20 +99,23 @@ function renderActions() {
         addAction("Listen to offline login in VIAaaS instance", () => {
             let user = prompt("Offline username (case-sensitive):", "");
             if (!user) return;
-            let msg = null;
-            do {
-                msg = JSON.stringify({
-                    action: "offline_login",
-                    username: user,
-                    date: Date.now(),
-                    rand: Math.random()
-                });
-            } while (!sha512(msg).startsWith("00000"));
-            socket.send(msg);
+            workers.forEach(it => it.postMessage({action: "listen_pow", user: user, id: Math.random()}));
+            addToast("Offline username", "Please wait a minute...");
         });
     }
 }
 
+function onWorkerMsg(e) {
+    console.log(e);
+    if (e.data.action == "completed_pow") onCompletedPoW(e);
+}
+
+function onCompletedPoW(e) {
+    addToast("Offline username", "Completed proof of work");
+    workers.forEach(it => it.postMessage({action: "cancel", id: e.data.id}));
+    socket.send(e.data.msg);
+}
+
 function addAction(text, onClick) {
     let p = document.createElement("p");
     let link = document.createElement("a");

src/main/resources/web/js/util.js

@@ -15,9 +15,3 @@ function icanhazip(cors) {
         .then(r => r.text())
         .then(it => it.trim());
 }
-
-function sha512(s) {
-    const shaObj = new jsSHA("SHA-512", "TEXT", { encoding: "UTF8" });
-    shaObj.update(s);
-    return shaObj.getHash("HEX");
-}

src/main/resources/web/js/worker.js

@@ -0,0 +1,47 @@
+importScripts("https://cdnjs.cloudflare.com/ajax/libs/jsSHA/3.2.0/sha.min.js");
+
+var pending = [];
+
+onmessage = function(e) {
+  if (e.data.action == "listen_pow") startPoW(e);
+  if (e.data.action == "cancel") removePending(e.data.id);
+}
+
+function removePending(id) {
+  console.log("removing task" + id);
+  pending = pending.filter(it => it != id);
+}
+
+function startPoW(e) {
+  pending.push(e.data.id);
+  listenPoW(e);
+}
+
+function listenPoW(e) {
+  var user = e.data.user;
+  let msg = null;
+  var endTime = Date.now() + 1000;
+  do {
+    if (!pending.includes(e.data.id)) return; // cancelled
+
+    msg = JSON.stringify({
+      action: "offline_login",
+      username: user,
+      date: Date.now(),
+      rand: Math.random()
+    });
+
+    if (Date.now() >= endTime) {
+        setTimeout(() => listenPoW(e), 1);
+        return;
+    }
+  } while (!sha512(msg).startsWith("00000"));
+
+  postMessage({id: e.data.id, action: "completed_pow", msg: msg});
+}
+
+function sha512(s) {
+    const shaObj = new jsSHA("SHA-512", "TEXT", { encoding: "UTF8" });
+    shaObj.update(s);
+    return shaObj.getHash("HEX");
+}