ip.js

'use strict'
var ip = exports;

var ipv4Regex = /^(\d{1,3}\.){3,3}\d{1,3}$/;
var ipv6Regex =
  /^(::)?(((\d{1,3}\.){3}(\d{1,3}){1})?([0-9a-f]){0,4}:{0,2}){1,8}(::)?$/i;

function isV4Format (ip) {
  return ipv4Regex.test(ip);
};

function isV6Format (ip) {
  return ipv6Regex.test(ip);
};

ip.toString = function (buff, offset, length) {
  offset = ~~offset;
  length = length || (buff.length - offset);

  var result = [];
  if (length === 4) {
    // IPv4
    for (var i = 0; i < length; i++) {
      result.push(buff[offset + i]);
    }
    result = result.join('.');
  } else if (length === 16) {
    // IPv6
    for (var i = 0; i < length; i += 2) {
      result.push(buff.readUInt16BE(offset + i).toString(16));
    }
    result = result.join(':');
    result = result.replace(/(^|:)0(:0)*:0(:|$)/, '$1::$3');
    result = result.replace(/:{3,4}/, '::');
  }

  return result;
};

ip.toBuffer = function (ip, buff, offset) {
  offset = ~~offset;

  var result;

  if (this.isV4Format(ip)) {
    result = buff || new Buffer(offset + 4);
    ip.split(/\./g).map(function (byte) {
      result[offset++] = parseInt(byte, 10) & 0xff;
    });
  } else if (this.isV6Format(ip)) {
    var sections = ip.split(':', 8);

    var i;
    for (i = 0; i < sections.length; i++) {
      var isv4 = this.isV4Format(sections[i]);
      var v4Buffer;

      if (isv4) {
        v4Buffer = this.toBuffer(sections[i]);
        sections[i] = v4Buffer.slice(0, 2).toString('hex');
      }

      if (v4Buffer && ++i < 8) {
        sections.splice(i, 0, v4Buffer.slice(2, 4).toString('hex'));
      }
    }

    if (sections[0] === '') {
      while (sections.length < 8) sections.unshift('0');
    } else if (sections[sections.length - 1] === '') {
      while (sections.length < 8) sections.push('0');
    } else if (sections.length < 8) {
      for (i = 0; i < sections.length && sections[i] !== ''; i++);
      var argv = [i, 1];
      for (i = 9 - sections.length; i > 0; i--) {
        argv.push('0');
      }
      sections.splice.apply(sections, argv);
    }

    result = buff || new Buffer(offset + 16);
    for (i = 0; i < sections.length; i++) {
      var word = parseInt(sections[i], 16);
      result[offset++] = (word >> 8) & 0xff;
      result[offset++] = word & 0xff;
    }
  }

  if (!result) {
    throw Error('Invalid ip address: ' + ip);
  }

  return result;
};