dns: getServers returns IPv6 addresses without []

[refack]

• Version: v5-v9
• Platform: *
• Subsystem: dns,ceres

dns.getServers mis formats IPv6 addresses

> d.setServers(['192.168.1.1', '[2001:4860:4860::8888]'])
undefined
> d.getServers()
[ '192.168.1.1', '2001:4860:4860::8888' ]

[refack]

Ref: nodejs/node-v0.x-archive#5435

[refack]

I just noticed this, IMHO we should format IPv6 with []:
e.g.

return ret.map(([host, port]) => {
  if (isIP(host) === 6) host = `[${host}]`;
  return (!port || port === 53) host : `${host}:${port}`;
}

Fix will be semver-major

[silverwind]

I think a bare IPv6 without [] is fine as long as it's not in an contained in an URL. Also see rfc5952 which suggests to only use[] when a port is included.

[refack]

I was going by rfc3986, which is ratified while rfc5952 is still "proposed".
IMHO this issue is not urgent and could stay open forever, or closed with known limitation.

[silverwind]

rfc3986 is about URIs, which I think host:port is not (IIRC, a valid URI always requires a protocol). Anyways, If you want to treat it like an URL, you can use the legacy url module to format it (not sure if the same is possible using WHATWG URL, as it doesn't allow calling the constructor without arguments):

> u = new url.Url(); u.hostname = "::1"; u.format()
'[::1]'
> u = new url.Url(); u.hostname = "::1"; u.port = 53; u.format()
'[::1]:53'
> u = new url.Url(); u.hostname = "127.0.0.1"; u.format()
'127.0.0.1'
> u = new url.Url(); u.hostname = "127.0.0.1"; u.port = 53; u.format()
'127.0.0.1:53'

[refack]

As suggested just now #13723 (comment) dns://[addr]:port...

A semver-major fix could return a list of dns:// URLs (even raw not toStringed) 🤷‍♂️

[refack]

 💡
🤓
Or add getServersURLs() as semver-minor (or getServers(true))

[silverwind]

dns://[addr]:port

Declaring a DNS server like this is rather uncommon. Why not require and return [] style IPv6 when port is specified and not 53, e.g.:

2001::db8
[2001::db8]:5353
127.0.0.1
127.0.0.1:5353

[refack]

Declaring a DNS server like this is rather uncommon. Why not require and return [] style IPv6 when port is specified and not 53, e.g.:

(again for context, I think this is of very low priority if at all, I just enjoy the discussion)

Passing URLs (in and out) eliminates hand spun parsing code, by us in setServers and by the user in getServers
We could as well "re-invent" a degenerated URL {addr, port} but even then we'll need to validate that addr is a string representing an IP, and port is a valid port number (0 < port < 2**16-1)

[Trott]

Closing as known limitation. Feel absolutely free to re-open or comment if you feel it should stay open, especially if you think it might be addressed some point in the not-too-distant future.