fix: fallback if wasm module failed to load

Author: PhotonQuantum

web/js/main.mjs

@@ -1,6 +1,6 @@
 // This file contains code adapted from https://github.com/TecharoHQ/anubis under the MIT License.
 
-import pow, { supportsWasm } from "./pow.mjs";
+import pow from "./pow.mjs";
 import Messages from "@messageformat/runtime/messages"
 import msgData from "./icu/compiled.mjs"
 import mascotPass from "../img/mascot-pass.png"
@@ -111,8 +111,6 @@ const main = async () => {
   ui.progressMessage('');
   ui.progress(0);
 
-  if (!supportsWasm()) ui.message(t('challenge.wasm_unavailable'));
-
   const t0 = Date.now();
   let lastUpdate = 0;
 
@@ -139,9 +137,13 @@ const main = async () => {
       const speed = totalIters / delta;
       ui.progress(distance);
       ui.metrics(t('challenge.difficulty_speed', { difficulty, speed: speed.toFixed(3) }));
-      ui.progressMessage(probability < 0.01 ? t('challenge.taking_longer') : noWasm ? t('challenge.wasm_unavailable') : undefined);
+      if (probability < 0.01) {
+        ui.progressMessage(t('challenge.taking_longer'));
+      }
       lastUpdate = delta;
     };
+  }, () => {
+    ui.progressMessage(t('challenge.wasm_unavailable'));
   });
   const t1 = Date.now();
 
@@ -160,4 +162,4 @@ const main = async () => {
 
 };
 
-main().catch(handleError);
+main().catch(handleError);

web/js/pow.mjs

@@ -9,8 +9,9 @@ const simdProbeModule = new Uint8Array([
   0, 0, 0, 0, 0, 0, 0, 0, 11,
 ]);
 
-export const supportsWasm = () => {
-  return WebAssembly && [WebAssembly.validate, WebAssembly.instantiate].every(i => typeof i == "function");
+const supportsWasm = () => {
+  return typeof WebAssembly !== "undefined" &&
+    [WebAssembly.validate, WebAssembly.instantiate].every(i => typeof i == "function");
 };
 
 const supportsSimd = () => {
@@ -27,37 +28,44 @@ export default async function process(
   difficulty = 5,
   signal = null,
   progressCallback = null,
+  fallbackCallback = null,
   threads = (navigator.hardwareConcurrency || 1),
 ) {
   const workers = [];
-  try {
-    const useWasm = supportsWasm();
-    let wasmModule = null;
-    let WorkerClass;
-
-    if (useWasm) {
-      const hasSimd = supportsSimd();
-      const wasmUrl = hasSimd ? wasmUrlSimd : wasmUrlMvp;
-      wasmModule = await (await fetch(wasmUrl)).arrayBuffer();
-      WorkerClass = PowWorker;
-    } else {
-      WorkerClass = PowJsWorker;
-    }
-
-    return await Promise.race(Array(threads).fill(0).map((i, idx) => new Promise((resolve, reject) => {
+  const runWorkers = (WorkerClass, message) => Promise.race(
+    Array(threads).fill(0).map((i, idx) => new Promise((resolve, reject) => {
       const worker = new WorkerClass();
       worker.onmessage = ({ data }) => (typeof data === "number" ? progressCallback : resolve)?.(data);
       worker.onerror = reject;
       worker.postMessage({
-        ...(useWasm ? { wasmModule } : {}),
+        ...message,
         data,
         difficulty,
         nonce: idx,
         threads,
       });
       signal?.addEventListener("abort", () => reject(new Error("PoW aborted")), { once: true });
       workers.push(worker);
-    })));
+    }))
+  );
+
+  try {
+    const useWasm = supportsWasm();
+
+    if (useWasm) {
+      try {
+        const hasSimd = supportsSimd();
+        const wasmUrl = hasSimd ? wasmUrlSimd : wasmUrlMvp;
+        const wasmModule = await (await fetch(wasmUrl)).arrayBuffer();
+        return await runWorkers(PowWorker, { wasmModule });
+      } catch (error) {
+        workers.forEach((w) => w.terminate());
+        workers.length = 0;
+        fallbackCallback?.(error);
+      }
+    }
+
+    return await runWorkers(PowJsWorker, {});
   } finally {
     workers.forEach((w) => w.terminate());
   }