change: backport server-info to 2.10

[zaunist]

What this PR does / why we need it:

Currently, server-info is refactored, so we should backport to 2.10 release. Because 2.10 is a LTS version.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[zaunist]

cc @tzssangglass @spacewander

[membphis]

remove , nil

[zaunist]

If I don't return nil, how can I be sure there is no err?

[membphis]

the default value is nil in this case

[zaunist]

I checked the other methods in etcd.lua, push, delete, set, etc. all return nil, and I think I'm correct in returning nil here. Shouldn't the code style of a repository be uniform? Even if the default value is nil, it should be explicitly shown in the code, so that the logic of the code is clearer.

[membphis]

, nil is useless, so we should remove it and keep the code simpler

[zaunist]

I checke APISIX repo, other file has the same situation. Example:

• apisix/apisix/balancer/ewma.lua

  Line 93 in cb2ba68

  return ewma, nil

• apisix/apisix/balancer/ewma.lua

  Line 100 in cb2ba68

  return ewma, nil

• apisix/apisix/core/schema.lua

  Line 56 in cb2ba68

  return validator, nil

• apisix/apisix/core/utils.lua

  Line 137 in cb2ba68

  return addr, nil

• apisix/apisix/plugins/basic-auth.lua

  Line 112 in cb2ba68

  return obj, nil

• apisix/apisix/plugins/openid-connect.lua

  Line 159 in cb2ba68

  return false, nil, nil

There are more places where there is a similar situation, where nil is returned when err equals nil, do we need to be uniform for those as well?

[membphis]

we can create a new issue, fix them later

[zaunist]

Got it.

[moonming]

I am not sure why you remove test cases when you add many codes?

[moonming]

So please add more test cases for the added codes

[zaunist]

In this change, we are using keepalive to replace the put operation, and testing keepalive requires verification of revision changes in etcd. However, since test-nginx reloads nginx every time you run a test, this may cause the revision to change, and I have not found a way to verify the keepalive.

[membphis]

LGTM

[zaunist]

I have create an issue for uniform code style #6541. So we can do it in other PRs.