salt.js

const crypto = require('crypto');

const Salt = {
    /**
     * Length.
     * @const int
     */
    LENGTH: 128,

    /**
     * Characters.
     * @const string
     */
    CHARACTERS: '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+/',

    /**
     * Generate.
     * @param  {Int}  length?
     * @param  {Int}  bitsPerChar?
     * @param  {Bool} opt_translate?
     * @return {String}
     * @see    https://github.com/php/php-src/blob/master/ext/session/session.c#L267,#L326
     */
    generate: function(length, bitsPerChar, opt_translate)
    {
        let len = length || this.LENGTH; // output length
        let bpc = bitsPerChar || 6; // 4=hex chars, 5=base36 chars, 6=base64 chars

        let bytes = crypto.randomBytes(parseInt(Math.ceil(len * bpc / 8)));

        let p = 0, q = bytes.length;
        let w = 0, have = 0, mask = (1 << bpc) - 1, byte;
        let out = '';

        while (len--) {
            if (have < bpc) {
                if (p < q) {
                    byte = bytes[p++];
                    w |= (byte << have);
                    have += 8;
                } else {
                    break;
                }
            }

            // consume bpc bits
            out += this.CHARACTERS[w & mask];
            w >>= bpc;
            have -= bpc;
        }

        if (opt_translate) {
            out = out.replace(/\+/g, '-').replace(/\//g, '_');
        }

        return out;
    }
};

module.exports = Salt;