code: function addressToKey(address) {
    const protocol = "http";
    const host = iputil.addrToHostname(iputil.normalize(address.address));
    return `${protocol}://${host}:${address.port}`;
  }
docs: Convert an address object ({address: 127.0.0.1, port: 80}, for example) to a string that is suitable for indexing into an object (turns out a URL is pretty good for this). We'll use this to index http.Server objects by host/port combinations.