node-ssl-certificates/lib/parser/asn1/hex.js

a node.js library for fetching, parsing and validating ssl-certificates

// Hex JavaScript decoder
// Copyright (c) 2008-2022 Lapo Luchini <lapo@lapo.it>

// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

(typeof define != "undefined" ? define : function(factory) {
  "use strict";
  if (typeof module == "object") module.exports = factory();
  else window.hex = factory();
})(function() {
  "use strict";

  const Hex = {};
  let decoder; // populated on first usage
  const haveU8 = (typeof Uint8Array == "function");

  /**
 * Decodes an hexadecimal value.
 * @param {string|Array|Uint8Array} a - a string representing hexadecimal data, or an array representation of its charcodes
 */
  Hex.decode = function(a) {
    const isString = (typeof a == "string");
    let i;
    if (decoder === undefined) {
      let hex = "0123456789ABCDEF";
      const ignore = " \f\n\r\t\u00A0\u2028\u2029";
      decoder = [];
      for (i = 0; i < 16; ++i) {
        decoder[hex.charCodeAt(i)] = i;
      }
      hex = hex.toLowerCase();
      for (i = 10; i < 16; ++i) {
        decoder[hex.charCodeAt(i)] = i;
      }
      for (i = 0; i < ignore.length; ++i) {
        decoder[ignore.charCodeAt(i)] = -1;
      }
    }
    let out = haveU8 ? new Uint8Array(a.length >> 1) : [];
    let bits = 0;
    let char_count = 0;
    let len = 0;
    for (i = 0; i < a.length; ++i) {
      let c = isString ? a.charCodeAt(i) : a[i];
      c = decoder[c];
      if (c == -1) {
        continue;
      }
      if (c === undefined) {
        throw "Illegal character at offset " + i;
      }
      bits |= c;
      if (++char_count >= 2) {
        out[len++] = bits;
        bits = 0;
        char_count = 0;
      } else {
        bits <<= 4;
      }
    }
    if (char_count) {
      throw "Hex encoding incomplete: 4 bits missing";
    }
    if (haveU8 && out.length > len) // in case it was originally longer because of ignored characters
    {
      out = out.subarray(0, len);
    }
    return out;
  };

  return Hex;
});