Simplify base64 bytes decoding (#239)

CHANGELOG.md

@@ -5,6 +5,7 @@
 Changes:
 
 - Adjust and optimize WASM function JS interface construction
+- Simplify base64 bytes decoding
 
 
 ## 4.4.1 Nov 22, 2021

packages/wasm-crypto-wasm/src/base64.ts

@@ -1,86 +1,22 @@
 // Copyright 2019-2021 @polkadot/wasm-crypto authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-// MIT License
-//
-// Copyright (c) 2014 Jameson Little
-//
-// https://github.com/beatgammit/base64-js/blob/88957c9943c7e2a0f03cdf73e71d579e433627d3/index.js
-// This only contains the toByteArray function (no encoding)
-//
-// Only tweaks make here are some TS adjustments (we use strict null checks), the code is otherwise as-is with
-// only the single required function provided
+const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
 
-const CODE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+export function base64Decode (data: string): Uint8Array {
+  const bytes = [];
+  let byte = 0;
+  let bits = 0;
 
-const lookup: string[] = [];
-const revLookup: number[] = [];
+  for (let i = 0; i < data.length && data[i] !== '='; i++) {
+    // each character represents 6 bits
+    byte = (byte << 6) | chars.indexOf(data[i]);
 
-for (let i = 0; i < CODE.length; ++i) {
-  lookup[i] = CODE[i];
-  revLookup[CODE.charCodeAt(i)] = i;
-}
-
-// Support decoding URL-safe base64 strings, as Node.js does.
-// See: https://en.wikipedia.org/wiki/Base64#URL_applications
-revLookup['-'.charCodeAt(0)] = 62;
-revLookup['_'.charCodeAt(0)] = 63;
-
-function getLens (b64: string): [number, number] {
-  const len = b64.length;
-
-  if (len % 4 > 0) {
-    throw new Error('Invalid string. Length must be a multiple of 4');
+    // each byte needs to contain 8 bits
+    if ((bits += 6) >= 8) {
+      bytes.push((byte >>> (bits -= 8)) & 0xff);
+    }
   }
 
-  // Trim off extra bytes after placeholder bytes are found
-  // See: https://github.com/beatgammit/base64-js/issues/42
-  const validLen = b64.indexOf('=');
-
-  return validLen === -1
-    ? [len, 0]
-    : [validLen, 4 - (validLen % 4)];
-}
-
-export function toByteArray (b64: string): Uint8Array {
-  const [validLen, placeHoldersLen] = getLens(b64);
-  const arr = new Uint8Array(((validLen + placeHoldersLen) * 3 / 4) - placeHoldersLen);
-  let curByte = 0;
-  let i: number;
-  let tmp: number;
-
-  // if there are placeholders, only get up to the last complete 4 chars
-  const len = placeHoldersLen > 0
-    ? validLen - 4
-    : validLen;
-
-  for (i = 0; i < len; i += 4) {
-    tmp =
-      (revLookup[b64.charCodeAt(i)] << 18) |
-      (revLookup[b64.charCodeAt(i + 1)] << 12) |
-      (revLookup[b64.charCodeAt(i + 2)] << 6) |
-      revLookup[b64.charCodeAt(i + 3)];
-
-    arr[curByte++] = (tmp >> 16) & 0xFF;
-    arr[curByte++] = (tmp >> 8) & 0xFF;
-    arr[curByte++] = tmp & 0xFF;
-  }
-
-  if (placeHoldersLen === 2) {
-    tmp =
-      (revLookup[b64.charCodeAt(i)] << 2) |
-      (revLookup[b64.charCodeAt(i + 1)] >> 4);
-
-    arr[curByte++] = tmp & 0xFF;
-  } else if (placeHoldersLen === 1) {
-    tmp =
-      (revLookup[b64.charCodeAt(i)] << 10) |
-      (revLookup[b64.charCodeAt(i + 1)] << 4) |
-      (revLookup[b64.charCodeAt(i + 2)] >> 2);
-
-    arr[curByte++] = (tmp >> 8) & 0xFF;
-    arr[curByte++] = tmp & 0xFF;
-  }
-
-  return arr;
+  return Uint8Array.from(bytes);
 }

packages/wasm-crypto-wasm/src/data.ts

@@ -1,8 +1,8 @@
 // Copyright 2019-2021 @polkadot/wasm-crypto-wasm authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
-import { toByteArray } from './base64';
+import { base64Decode } from './base64';
 import { bytes, sizeUncompressed } from './bytes';
 import { unzlibSync } from './fflate';
 
-export const wasmBytes = unzlibSync(toByteArray(bytes), new Uint8Array(sizeUncompressed));
+export const wasmBytes = unzlibSync(base64Decode(bytes), new Uint8Array(sizeUncompressed));