All files / base64/src createFromBase64Bin.ts

93.58% Statements 73/78
79.31% Branches 23/29
100% Functions 2/2
100% Lines 63/63

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import {alphabet} from './constants';
 
export const createFromBase64Bin = (chars: string = alphabet, pad: string = '=') => {
  Iif (chars.length !== 64) throw new Error('chars must be 64 characters long');
  let max = 0;
  for (let i = 0; i < chars.length; i++) max = Math.max(max, chars.charCodeAt(i));
  const table: number[] = [];
  for (let i = 0; i <= max; i += 1) table[i] = -1;
  for (let i = 0; i < chars.length; i++) table[chars.charCodeAt(i)] = i;
 
  const doExpectPadding = pad.length === 1;
  const PAD = doExpectPadding ? pad.charCodeAt(0) : 0;
 
  return (view: DataView, offset: number, length: number): Uint8Array => {
    if (!length) return new Uint8Array(0);
    let padding = 0;
    if (length % 4 !== 0) {
      padding = 4 - (length % 4);
      length += padding;
    } else {
      const end = offset + length;
      const last = end - 1;
      if (view.getUint8(last) === PAD) {
        padding = 1;
        if (length > 1 && view.getUint8(last - 1) === PAD) padding = 2;
      }
    }
    Iif (length % 4 !== 0) throw new Error('Base64 string length must be a multiple of 4');
    const mainEnd = offset + length - (padding ? 4 : 0);
    const bufferLength = (length >> 2) * 3 - padding;
    const buf = new Uint8Array(bufferLength);
    let j = 0;
    let i = offset;
    for (; i < mainEnd; i += 4) {
      const word = view.getUint32(i);
      const octet0 = word >>> 24;
      const octet1 = (word >>> 16) & 0xff;
      const octet2 = (word >>> 8) & 0xff;
      const octet3 = word & 0xff;
      const sextet0 = table[octet0];
      const sextet1 = table[octet1];
      const sextet2 = table[octet2];
      const sextet3 = table[octet3];
      Iif (sextet0 < 0 || sextet1 < 0 || sextet2 < 0 || sextet3 < 0) throw new Error('INVALID_BASE64_SEQ');
      buf[j] = (sextet0 << 2) | (sextet1 >> 4);
      buf[j + 1] = (sextet1 << 4) | (sextet2 >> 2);
      buf[j + 2] = (sextet2 << 6) | sextet3;
      j += 3;
    }
    if (!padding) return buf;
    if (padding === 1) {
      const word = view.getUint16(mainEnd);
      const octet0 = word >> 8;
      const octet1 = word & 0xff;
      const octet2 = view.getUint8(mainEnd + 2);
      const sextet0 = table[octet0];
      const sextet1 = table[octet1];
      const sextet2 = table[octet2];
      Iif (sextet0 < 0 || sextet1 < 0 || sextet2 < 0) throw new Error('INVALID_BASE64_SEQ');
      buf[j] = (sextet0 << 2) | (sextet1 >> 4);
      buf[j + 1] = (sextet1 << 4) | (sextet2 >> 2);
      return buf;
    }
    const word = view.getUint16(mainEnd);
    const octet0 = word >> 8;
    const octet1 = word & 0xff;
    const sextet0 = table[octet0];
    const sextet1 = table[octet1];
    Iif (sextet0 < 0 || sextet1 < 0) throw new Error('INVALID_BASE64_SEQ');
    buf[j] = (sextet0 << 2) | (sextet1 >> 4);
    return buf;
  };
};