Delay UID change after loop start

[nim-odoo]

What do these changes do?

Listening to a port < 1024 without --nosetuid leads to a permission error.

The UID change is done too early: we should first open the port, then change the UID.

Are there changes in behavior for the user?

Users can now drop privileges while listening to port < 1024.

Related issue number

Fixes #304

Checklist

• I think the code is well written
• Unit tests for the changes exist
• tox testenvs have been executed in the following environments:
  • Linux (Ubuntu 18.04, Ubuntu 20.04, Arch): {py36,py37,py38,py39}-{nocov,cov,diffcov}, qa, docs
  • Windows (7, 10): {py36,py37,py38,py39}-{nocov,cov,diffcov}
  • WSL 1.0 (Ubuntu 18.04): {py36,py37,py38,py39}-{nocov,cov,diffcov}, pypy3-{nocov,cov}, qa, docs
  • FreeBSD (12.2, 12.1, 11.4): {py36,pypy3}-{nocov,cov,diffcov}, qa
  • Cygwin: py36-{nocov,cov,diffcov}, qa, docs
• Documentation reflects the changes
• Add a news fragment into the NEWS.rst file
  • Add under the "aiosmtpd-next" section, creating one if necessary
    • You may create subsections to group the changes, if you like
  • Use full sentences with correct case and punctuation
  • Refer to relevant Issue if applicable

[waynew]

I'm not particularly sure how to test for this aside from an integration test (at least using the definition I used on the Salt Project).

I went ahead and implemented my own little sample python asyncio server on my Test Clinic tonight, and verified that setuid to nobody before server creation like we were doing will throw the permissions error.

I'm not 100% positive about any security implications, I'm assuming that the correct thing happens here once we hit the setuid line, but... not positive.

It would be nice if we could have some automated tests for this, but... I am OK with it. FWIW #370 would have a conflict here if we end out merging that one first.

Or vice versa 🙃

[waynew]

Note that there is a QA issue with comment line being a little too long.

[nim-odoo]

Hello @pepoluan , is there a chance this can be looked at? Thanks

[pepoluan]

Hello @pepoluan , is there a chance this can be looked at? Thanks

I'll see what I can do this weekend.