signal-desktop/ts/textsecure/StringView.ts

// Copyright 2020 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only

/* eslint-disable no-bitwise */
/* eslint-disable no-nested-ternary */

const StringView = {
  /*
   * These functions from the Mozilla Developer Network
   * and have been placed in the public domain.
   * https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding
   * https://developer.mozilla.org/en-US/docs/MDN/About#Copyrights_and_licenses
   */

  // prettier-ignore
  b64ToUint6(nChr: number): number {
    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;
  },

  base64ToBytes(sBase64: string, nBlocksSize: number): ArrayBuffer {
    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 aBBytes = new ArrayBuffer(nOutLen);
    const taBytes = new Uint8Array(aBBytes);

    let nMod3;
    let nMod4;
    let nOutIdx = 0;
    let nInIdx = 0;
    for (let nUint24 = 0; nInIdx < nInLen; nInIdx += 1) {
      nMod4 = nInIdx & 3;
      nUint24 |=
        StringView.b64ToUint6(sB64Enc.charCodeAt(nInIdx)) << (18 - 6 * nMod4);
      if (nMod4 === 3 || nInLen - nInIdx === 1) {
        for (
          nMod3 = 0;
          nMod3 < 3 && nOutIdx < nOutLen;
          nMod3 += 1, nOutIdx += 1
        ) {
          taBytes[nOutIdx] = (nUint24 >>> ((16 >>> nMod3) & 24)) & 255;
        }
        nUint24 = 0;
      }
    }
    return aBBytes;
  },

  // prettier-ignore
  uint6ToB64(nUint6: number): number {
    return nUint6 < 26
      ? nUint6 + 65
      : nUint6 < 52
        ? nUint6 + 71
        : nUint6 < 62
          ? nUint6 - 4
          : nUint6 === 62
            ? 43
            : nUint6 === 63
              ? 47
              : 65;
  },

  bytesToBase64(aBytes: Uint8Array): string {
    let nMod3;
    let sB64Enc = '';
    let nUint24 = 0;
    const nLen = aBytes.length;
    for (let nIdx = 0; nIdx < nLen; nIdx += 1) {
      nMod3 = nIdx % 3;
      if (nIdx > 0 && ((nIdx * 4) / 3) % 76 === 0) {
        sB64Enc += '\r\n';
      }
      nUint24 |= aBytes[nIdx] << ((16 >>> nMod3) & 24);
      if (nMod3 === 2 || aBytes.length - nIdx === 1) {
        sB64Enc += String.fromCharCode(
          StringView.uint6ToB64((nUint24 >>> 18) & 63),
          StringView.uint6ToB64((nUint24 >>> 12) & 63),
          StringView.uint6ToB64((nUint24 >>> 6) & 63),
          StringView.uint6ToB64(nUint24 & 63)
        );
        nUint24 = 0;
      }
    }
    return sB64Enc.replace(/A(?=A$|$)/g, '=');
  },
};

export default StringView;