prepareUrls.js

const url = require('url');
const color = require('colors-cli');
const address = require('address');

module.exports = function prepareUrls(protocol, host, port) {
  const formatUrl = hostname =>
    url.format({
      protocol,
      hostname,
      port,
      pathname: '/',
    });
  const prettyPrintUrl = hostname =>
    url.format({
      protocol,
      hostname,
      port: color.bold(port),
      pathname: '/',
    });

  const isUnspecifiedHost = host === '0.0.0.0' || host === '::';
  let prettyHost, lanUrlForConfig, lanUrlForTerminal;
  if (isUnspecifiedHost) {
    prettyHost = 'localhost';
    try {
      // This can only return an IPv4 address
      lanUrlForConfig = address.ip();
      if (lanUrlForConfig) {
        // Check if the address is a private ip
        // https://en.wikipedia.org/wiki/Private_network#Private_IPv4_address_spaces
        if (
          /^10[.]|^172[.](1[6-9]|2[0-9]|3[0-1])[.]|^192[.]168[.]/.test(
            lanUrlForConfig
          )
        ) {
          // Address is private, format it for later use
          lanUrlForTerminal = prettyPrintUrl(lanUrlForConfig);
        } else {
          // Address is not private, so we will discard it
          lanUrlForConfig = undefined;
        }
      }
    } catch (_e) {
      // ignored
    }
  } else {
    prettyHost = host;
  }
  const localUrlForTerminal = prettyPrintUrl(prettyHost);
  const localUrlForBrowser = formatUrl(prettyHost);
  return {
    lanUrlForConfig,
    lanUrlForTerminal,
    localUrlForTerminal,
    localUrlForBrowser,
  };
}