fix containerd config generation

[vflaux]

This is proposal to fix #549.
This is a bit complicated in my opinion but I couldn't figure out a better way.
Except by writing a toml file without a toml lib which should be simpler and maybe preferable?

Map are output as toml table sorted by the key, which is not what we expect.
This patch dynamically build a struct with a field for each host (and a toml tag).
This allow us to control the order of hosts in the toml file as go-toml output struct as toml tables while preserving the order of the fields in the struct.

[phillebaba]

Thank you for reporting the problem and proposing a solution. I dont really know why I never thought about this being a problem. It is slightly weird that the order of maps actually matter. There is something about your solution that I feel makes things more complicated than it has to be. I will dig a bit and see if there is a easier solution, if not we will merge yours for the time being.

The good thing is that we have tests that validate this for future changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files	Coverage Δ
pkg/oci/containerd.go	63.80% <100.00%> (+4.21%)	⬆️

[vflaux]

I opened a new PR with an alternative implementation using go template : #557.
It's less complicated than this one.

It is slightly weird that the order of maps actually matter.

That's quite unexpected and a bad choice IMO, they should have used an array instead. Containerd also need to parse the file a second time to get the order : https://github.com/containerd/containerd/blob/7f707b5e7970105723257d483394454049eabe47/core/remotes/docker/config/hosts.go#L519.