Version

14.x

Platform

All

Subsystem

dgram

What steps will reproduce the bug?

It appears that UDP/dgram connections perform unnecessary DNS lookups when an IP address is provided as the address to connect to.

The issue is easily demonstrated via this snippet:

const dns = require("dns");

const _lookup = dns.lookup;
dns.lookup = function (...args) {
  console.log("Called lookup", args);
  return _lookup(...arguments);
};

const dgram = require("dgram");

const socket = dgram.createSocket({ type: "udp4" });
console.log("Socket created");

socket.connect(1234, "192.168.1.1", (err) => {
  console.log("Socket connected", { err });
});

Output:

$ node index.js

Socket created
Called lookup [ '0.0.0.0', 4, [Function (anonymous)] ]
Called lookup [ '192.168.1.1', 4, [Function: afterDns] ]
Socket connected { err: undefined }

How often does it reproduce? Is there a required condition?

These lookups appear to happen 100% of the time a UDP socket connects to an address that is a raw IP address.

What is the expected behavior?

DNS lookups only occur when the address is a hostname.

What do you see instead?

No response

Additional information

Note that the net module contains code that bypasses dns.lookup() when the target address is a valid IP address. It seems like we could improve efficiency by adding a similar check to dgram without breaking compatibility.