fix: Init WASM modules using Base64 (#2913)

This PR changes the WASM loader slightly to package the WASM source code
using Base64 and decode it at runtime. This has multiple effects:
- Fixes an obscure OOM bug in Firefox that would only occur on Mac OS
(possibly due to extremely large arrays?)
- Reduces bundle size for Snaps that leverage WASM
- Prevents bundler slowdown due to large arrays needing to be parsed by
Babel

This adds minor overhead to initializing WASM bundles, but this seems
worth it given the effects above.

packages/examples/packages/wasm/snap.manifest.json

@@ -7,7 +7,7 @@
     "url": "https://github.com/MetaMask/snaps.git"
   },
   "source": {
-    "shasum": "1LptzjDvA6o8jrzA9XsE7NYdhh7kx3alSd7pLwiUq0w=",
+    "shasum": "t4uK/pnTJODpftadTGKumNIEqmSCTP0zb87aMLMqFt8=",
     "location": {
       "npm": {
         "filePath": "dist/bundle.js",

packages/snaps-cli/src/webpack/loaders/wasm.test.ts

@@ -73,7 +73,18 @@ describe('loader', () => {
       "
           import { add } from "../src/bindings.ts";
 
-          const bytes = new Uint8Array([0,97,115,109,1,0,0,0,1,12,2,96,2,127,127,1,127,96,1,127,1,127,2,26,1,18,46,46,47,115,114,99,47,98,105,110,100,105,110,103,115,46,116,115,3,97,100,100,0,0,3,2,1,1,5,3,1,0,0,7,22,2,9,102,105,98,111,110,97,99,99,105,0,1,6,109,101,109,111,114,121,2,0,10,54,1,52,1,3,127,65,1,33,1,32,0,65,0,74,4,64,3,64,32,0,65,1,107,34,0,4,64,32,2,32,1,16,0,33,3,32,1,33,2,32,3,33,1,12,1,11,11,32,1,15,11,65,0,11]);
+          const b64 = "AGFzbQEAAAABDAJgAn9/AX9gAX8BfwIaARIuLi9zcmMvYmluZGluZ3MudHMDYWRkAAADAgEBBQMBAAAHFgIJZmlib25hY2NpAAEGbWVtb3J5AgAKNgE0AQN/QQEhASAAQQBKBEADQCAAQQFrIgAEQCACIAEQACEDIAEhAiADIQEMAQsLIAEPC0EACw==";
+
+          function decode(encoded) {
+            const str = atob(encoded);
+            const bytes = new Uint8Array(str.length);
+            for (let i = 0; i < str.length; i++) {
+              bytes[i] = str.charCodeAt(i);
+            }
+            return bytes;
+          }
+
+          const bytes = decode(b64);
           const module = new WebAssembly.Module(bytes);
           const instance = new WebAssembly.Instance(module, {
             "../src/bindings.ts": { add },

packages/snaps-cli/src/webpack/loaders/wasm.ts

@@ -1,6 +1,6 @@
 /* eslint-disable no-restricted-globals */
 
-import { assert } from '@metamask/utils';
+import { assert, bytesToBase64 } from '@metamask/utils';
 import { dirname, resolve } from 'path';
 import type { LoaderDefinitionFunction } from 'webpack';
 
@@ -80,8 +80,7 @@ const loader: LoaderDefinitionFunction = async function loader(
 ) {
   assert(source instanceof Uint8Array, 'Expected source to be a Uint8Array.');
 
-  const bytes = new Uint8Array(source);
-  const wasmModule = await WebAssembly.compile(bytes);
+  const wasmModule = await WebAssembly.compile(source);
 
   // eslint-disable-next-line @typescript-eslint/no-shadow
   const exports = WebAssembly.Module.exports(wasmModule);
@@ -104,7 +103,18 @@ const loader: LoaderDefinitionFunction = async function loader(
   return `
     ${getImports(imports)}
 
-    const bytes = new Uint8Array(${JSON.stringify(Array.from(source))});
+    const b64 = ${JSON.stringify(bytesToBase64(source))};
+
+    function decode(encoded) {
+      const str = atob(encoded);
+      const bytes = new Uint8Array(str.length);
+      for (let i = 0; i < str.length; i++) {
+        bytes[i] = str.charCodeAt(i);
+      }
+      return bytes;
+    }
+
+    const bytes = decode(b64);
     const module = new WebAssembly.Module(bytes);
     const instance = new WebAssembly.Instance(module, {
       ${getModuleImports(imports)}