datagram socket send on 127.0.0.1 invokes dns.lookup()

[naseemkullah]

What steps will reproduce the bug?

> const dgram = require('dgram');
undefined
> const server = dgram.createSocket('udp4');
undefined
> server.send('hi', 0, 2, 8125, '127.0.0.1', console.log)
undefined
> null 2

This results in a dns.lookup(), provided that an address is being passed to it, it should not have to.

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

Always

What is the expected behavior?

As per https://nodejs.org/api/dgram.html#dgram_socket_send_msg_offset_length_port_address_callback

The address argument is a string. If the value of address is a host name, DNS will be used to resolve the address of the host.

Implies that if it is not a host name, DNS will not be used. I.e. I would not expect dns to be used if not a host name.

What do you see instead?

dns.lookup() being called

Additional information

I was able to observe dns trace by instrumenting with https://github.com/open-telemetry/opentelemetry-js-contrib/tree/master/plugins/node/opentelemetry-plugin-dns

[bnoordhuis]

There is no bug here. dns.lookup() has a fast path for IP addresses, hence there's no need for the dgram module to perform any special casing.

Closing but thanks anyway for the report.

[naseemkullah]

There is no bug here. dns.lookup() has a fast path for IP addresses, hence there's no need for the dgram module to perform any special casing.

Closing but thanks anyway for the report.

Thanks for explaining! It may be worthwhile to mention that in docs.

[bnoordhuis]

You can send a documentation pull request if you want.

[naseemkullah]

Okidokie