Encode the WASM as base64

Some nasty hackery to get around the nastiness of the JS ecosystem

bindings/matrix-sdk-crypto-js/package.json

@@ -37,12 +37,9 @@
         "node": ">= 10"
     },
     "scripts": {
-        "build": "cross-env RUSTFLAGS='-C opt-level=z' WASM_BINDGEN_WEAKREF=1 wasm-pack build --release --target nodejs --scope matrix-org --out-dir ./pkg",
+        "build": "./scripts/build.sh",
         "test": "jest --verbose",
         "doc": "typedoc --tsconfig .",
-        "prepack": "npm run build && npm run test",
-        "pack": "wasm-pack pack",
-        "prepublish": "npm run pack",
-        "publish": "wasm-pack publish"
+        "prepack": "npm run build && npm run test"
     }
 }

bindings/matrix-sdk-crypto-js/scripts/build.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+#
+# Build the javascript modules
+#
+# This script is really a workaround for https://github.com/rustwasm/wasm-pack/issues/1074.
+#
+# Currently, the only reliable way to load webassembly in all the JS
+# environments we want to target (web-via-webpack, web-via-browserify, jest)
+# seems to be to pack the WASM into base64, and then unpack it and instantiate
+# it at runtime.
+#
+# Hopefully one day, https://github.com/rustwasm/wasm-pack/issues/1074 will be
+# fixed and this will be unnecessary.
+
+set -e
+
+RUSTFLAGS='-C opt-level=z' WASM_BINDGEN_WEAKREF=1 wasm-pack build --release --target nodejs --scope matrix-org --out-dir ./pkg
+
+# convert the wasm into a js file that exports the b64'ed wasm
+{
+    echo 'module.exports = `'
+    base64 pkg/matrix_sdk_crypto_js_bg.wasm
+    echo '`;'
+} > pkg/matrix_sdk_crypto_js_bg.wasm.js
+
+# In the javascript:
+#  1. replace the lines that load the wasm
+#  2. remove the imports of TextDecoder and TextEncoder. We rely on the global defaults.
+loadwasm='const bytes = require("../unbase64.js")(require("./matrix_sdk_crypto_js_bg.wasm.js"));'
+sed -i -e "/^const path = /,+1 c$loadwasm" \
+    -e '/= require(`util`)/d' \
+    pkg/matrix_sdk_crypto_js.js

bindings/matrix-sdk-crypto-js/unbase64.js

@@ -0,0 +1,48 @@
+// Javascript module which exports a function which will un-base64 a string
+//
+// From the code at https://developer.mozilla.org/en-US/docs/Glossary/Base64#solution_2_%E2%80%93_rewriting_atob_and_btoa_using_typedarrays_and_utf-8
+
+function b64ToUint6(nChr) {
+  return nChr > 64 && nChr < 91
+    ? nChr - 65
+    : nChr > 96 && nChr < 123
+    ? nChr - 71
+    : nChr > 47 && nChr < 58
+    ? nChr + 4
+    : nChr === 43
+    ? 62
+    : nChr === 47
+    ? 63
+    : 0;
+}
+
+function base64DecToArr(sBase64, nBlocksSize) {
+  const sB64Enc = sBase64.replace(/[^A-Za-z0-9+/]/g, "");
+  const nInLen = sB64Enc.length;
+  const nOutLen = nBlocksSize
+    ? Math.ceil(((nInLen * 3 + 1) >> 2) / nBlocksSize) * nBlocksSize
+    : (nInLen * 3 + 1) >> 2;
+  const taBytes = new Uint8Array(nOutLen);
+
+  let nMod3;
+  let nMod4;
+  let nUint24 = 0;
+  let nOutIdx = 0;
+  for (let nInIdx = 0; nInIdx < nInLen; nInIdx++) {
+    nMod4 = nInIdx & 3;
+    nUint24 |= b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << (6 * (3 - nMod4));
+    if (nMod4 === 3 || nInLen - nInIdx === 1) {
+      nMod3 = 0;
+      while (nMod3 < 3 && nOutIdx < nOutLen) {
+        taBytes[nOutIdx] = (nUint24 >>> ((16 >>> nMod3) & 24)) & 255;
+        nMod3++;
+        nOutIdx++;
+      }
+      nUint24 = 0;
+    }
+  }
+
+  return taBytes;
+}
+
+module.exports = base64DecToArr;