feat: add lookup option to Client, Pool and Agent (#2440)

[hjr3]

We add an optional custom lookup function to that has the same interface as the lookup option in TCP/UDP socket.connect. This allows users of this library to implement their own DNS caching implementation.

This does not preclude the future possibility of including a DNS caching implementation by default.

This relates to...

• Add dns caching by default #2440

Rationale

PR #2552 is attempting to add a default dns caching implementation to undici. Instead of trying to first add a default implementation, which is a lot of work, this PR adds the standard lookup option which allows a user to bring their own DNS lookup implementation.

I believe this is a better place to start from because:

• avoids committing to a default DNS caching implementation
  • there is no one-size DNS caching implementation that fits all use cases
• users may have other DNS implementation requirement beyond caching
• this is a smaller change to the undici public interface
• this follows existing Node.js convention of providing a lookup option

Adding DNS caching is now as easy as:

import CacheableLookup from 'cacheable-lookup';

const cacheable = new CacheableLookup();

new Agent({
  lookup: cacheable.lookup
});

Changes

Features

• adds an optional lookup option to Client, Pool and Agent

Bug Fixes

N/A

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[ronag]

This is already possible. Pass lookup in the connect option.

[hjr3]

For anyone else wading through the docs:

import * as dns from 'dns';


const agent = new Agent({
  connect: {
    lookup: dns.lookup,
  },
});