discordeno/util/base64.ts

/**
 * CREDIT: https://gist.github.com/enepomnyaschih/72c423f727d395eeaa09697058238727
 * Encodes a given Uint8Array, ArrayBuffer or string into RFC4648 base64 representation
 * @param data
 */
export function encode(data: ArrayBuffer | string): string {
  const uint8 = typeof data === "string"
    ? new TextEncoder().encode(data)
    : data instanceof Uint8Array
    ? data
    : new Uint8Array(data);
  let result = "",
    i;
  const l = uint8.length;
  for (i = 2; i < l; i += 3) {
    result += base64abc[uint8[i - 2] >> 2];
    result += base64abc[((uint8[i - 2] & 0x03) << 4) | (uint8[i - 1] >> 4)];
    result += base64abc[((uint8[i - 1] & 0x0f) << 2) | (uint8[i] >> 6)];
    result += base64abc[uint8[i] & 0x3f];
  }
  if (i === l + 1) {
    // 1 octet yet to write
    result += base64abc[uint8[i - 2] >> 2];
    result += base64abc[(uint8[i - 2] & 0x03) << 4];
    result += "==";
  }
  if (i === l) {
    // 2 octets yet to write
    result += base64abc[uint8[i - 2] >> 2];
    result += base64abc[((uint8[i - 2] & 0x03) << 4) | (uint8[i - 1] >> 4)];
    result += base64abc[(uint8[i - 1] & 0x0f) << 2];
    result += "=";
  }
  return result;
}

/**
 * CREDIT: https://gist.github.com/enepomnyaschih/72c423f727d395eeaa09697058238727
 * Decodes RFC4648 base64 string into an Uint8Array
 * @param data
 */
export function decode(data: string): Uint8Array {
  if (data.length % 4 !== 0) {
    throw new Error("Unable to parse base64 string.");
  }
  const index = data.indexOf("=");
  if (index !== -1 && index < data.length - 2) {
    throw new Error("Unable to parse base64 string.");
  }
  let missingOctets = data.endsWith("==") ? 2 : data.endsWith("=") ? 1 : 0,
    n = data.length,
    result = new Uint8Array(3 * (n / 4)),
    buffer;
  for (let i = 0, j = 0; i < n; i += 4, j += 3) {
    buffer = getBase64Code(data.charCodeAt(i)) << 18 |
      getBase64Code(data.charCodeAt(i + 1)) << 12 |
      getBase64Code(data.charCodeAt(i + 2)) << 6 |
      getBase64Code(data.charCodeAt(i + 3));
    result[j] = buffer >> 16;
    result[j + 1] = (buffer >> 8) & 0xFF;
    result[j + 2] = buffer & 0xFF;
  }
  return result.subarray(0, result.length - missingOctets);
}

/**
 * CREDIT: https://gist.github.com/enepomnyaschih/72c423f727d395eeaa09697058238727
 * @param charCode
 */
function getBase64Code(charCode: number): number {
  if (charCode >= base64codes.length) {
    throw new Error("Unable to parse base64 string.");
  }
  const code = base64codes[charCode];
  if (code === 255) {
    throw new Error("Unable to parse base64 string.");
  }
  return code;
}

// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
const base64abc = [
  "A",
  "B",
  "C",
  "D",
  "E",
  "F",
  "G",
  "H",
  "I",
  "J",
  "K",
  "L",
  "M",
  "N",
  "O",
  "P",
  "Q",
  "R",
  "S",
  "T",
  "U",
  "V",
  "W",
  "X",
  "Y",
  "Z",
  "a",
  "b",
  "c",
  "d",
  "e",
  "f",
  "g",
  "h",
  "i",
  "j",
  "k",
  "l",
  "m",
  "n",
  "o",
  "p",
  "q",
  "r",
  "s",
  "t",
  "u",
  "v",
  "w",
  "x",
  "y",
  "z",
  "0",
  "1",
  "2",
  "3",
  "4",
  "5",
  "6",
  "7",
  "8",
  "9",
  "+",
  "/",
];

// CREDIT: https://gist.github.com/enepomnyaschih/72c423f727d395eeaa09697058238727
const base64codes = [
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  255,
  62,
  255,
  255,
  255,
  63,
  52,
  53,
  54,
  55,
  56,
  57,
  58,
  59,
  60,
  61,
  255,
  255,
  255,
  0,
  255,
  255,
  255,
  0,
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9,
  10,
  11,
  12,
  13,
  14,
  15,
  16,
  17,
  18,
  19,
  20,
  21,
  22,
  23,
  24,
  25,
  255,
  255,
  255,
  255,
  255,
  255,
  26,
  27,
  28,
  29,
  30,
  31,
  32,
  33,
  34,
  35,
  36,
  37,
  38,
  39,
  40,
  41,
  42,
  43,
  44,
  45,
  46,
  47,
  48,
  49,
  50,
  51,
];