Add DNS timeout

[huksley]

When DNS server does not respond, nodemailer timeouts only after 150 seconds on Mac OS X

dev Request --> POST /api/preview

Error: queryA ETIMEOUT smtp.sendgrid.net at QueryReqWrap.onresolve [as oncomplete] (node:dns:279:19) {
 (node:dns:279:19) {
  errno: undefined,
  code: 'EDNS',
  syscall: 'queryA',
  hostname: 'smtp.sendgrid.net',
  command: 'CONN'
}

dev Response <-- 500 POST /api/preview Δ 151071ms

This change adds dnsTimeout which is passed to dns [1] NodeJS module.

• 1: https://nodejs.org/api/dns.html#resolveroptions

[andris9]

In general, I would accept this change. The issue is that Nodemailer has a long-term commitment to backwards compatibility, and your changes do not work with older versions of Node.js. Could you make this conditional so that if there is no Resolver class available, then Nodemailer would not try to use it?

CI does not work with older versions of Node, so you can check if the code works in general like this:

$ nvm use 6
$ export NODE_TLS_REJECT_UNAUTHORIZED="0"
$ node examples/full.js

Currently it ends with

TypeError: dns.Resolver is not a constructor
    at resolver (/root/nodemailer/lib/shared/index.js:51:22)
    at Object.module.exports.resolveHostname (/root/nodemailer/lib/shared/index.js:126:5)

[huksley]

@andris9 Done. Thanks for a test code which is easy to run and test with. Tested on nvm use 6and nvm use 16

[huksley]

🎉 @andris9 Please advise, how to improve types for nodemailer? it is 6.4.6 vs nodemailer@6.7.x, should I find all changes between those two version or I can only bump types to 6.7.x adding dnsTimeout?

[andris9]

Well, I know nothing about typings, these are not part of the Nodemailer project but are fully community-managed. Most of the code in Nodemailer is written years before Typescript was invented 🤷‍♂️

[andris9]

Published changes to npm as nodemailer@6.8.0