plugin/template: Add client IP data

[Miouge1]

1. Why is this pull request needed and what does it do?

This PR adds a {{ .Remote }} data in the template module.

I have tested it with the following minimal Corefile (kind of emulating the whoami plugin):

. {
    template IN A {
      answer "{{ .Name }} 60 {{ .Class }} {{ .Type }} {{ .Remote }}"
    }
}

$ dig @127.0.0.1 A example.com +short
127.0.0.1

In terms of use case, the client IP can be useful to make decisions.

2. Which issues (if any) are related?

None

3. Which documentation changes (if any) need to be made?

plugin/template/README.md included in the PR

4. Does this introduce a backward incompatible change or deprecation?

Adding a field should be backwards compatible.

[codecov-commenter]

Codecov Report

Merging #4034 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4034      +/-   ##
==========================================
+ Coverage   57.06%   57.08%   +0.01%     
==========================================
  Files         222      222              
  Lines       11281    11281              
==========================================
+ Hits         6438     6440       +2     
+ Misses       4351     4350       -1     
+ Partials      492      491       -1     

Impacted Files	Coverage Δ
plugin/template/template.go	88.42% <100.00%> (ø)
plugin/file/reload.go	75.00% <0.00%> (+5.55%)	⬆️

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[rtreffer]

Looks cool, although it would be nice to say it might be the IP of an intermediate (at which point it becomes pretty pointless for the original client).

[miekg]

In the log plugin we call this (for better or worse) remote. i think we should have this consistent between plugin, by either renaming it here; or adding {ip} to log. Think the more generic name 'remote' is slightly better

[Miouge1]

Good points. I've replaced .IP to .Remote in the latest commit and re-tested this locally:

. {
    log
    template IN ANY {
      answer "{{ .Name }} 60 {{ .Class }} {{ .Type }} {{ .Remote }}"
    }
}

$ dig @127.0.0.1 TXT example.com +short
"127.0.0.1"
$ dig @::1 TXT example.com +short
"::1"

The log module documents {{remote}} as client's IP address, for IPv6 addresses these are enclosed in brackets: [::1], since the brackets enclosing doesn't happen here I've skipped that from the description in this PR.

[miekg]

[ Quoting <notifications@github.com> in "Re: [coredns/coredns] plugin/templa..." ]

Good points. I've replaced .IP to .Remote in the latest commit and re-tested this locally: . { log template IN ANY { answer "{{ .Name }} 60 {{ .Class }} {{ .Type }} {{ .Remote }}" } } $ dig @127.0.0.1 TXT example.com +short "127.0.0.1" $ dig @::1 TXT example.com +short "::1"

cool

The log module documents {{remote}} as client's IP address, for IPv6 addresses these are enclosed in brackets: [::1], since the brackets enclosing doesn't happen here I've skipped that from the description in this PR.

interesting, should we make it do that? I think we should, because `{{ .Remote }} {{ .Port }}` doesn't allow you to see there is a port number (if .Port even exists - dunno) /Miek

…

-- Miek Gieben

[Miouge1]

{{ .Port }} does not exist, but would not be too hard to add.

Are brackets enclosed IPv6 IPs supported in AAAA records? (I couldn't find an example of that in the codebase).

[miekg]

[ Quoting <notifications@github.com> in "Re: [coredns/coredns] plugin/templa..." ]

{{ .Port }} does not exist, but would not be too hard to add. Are brackets enclosed IPv6 IPs supported in AAAA records? (I couldn't find an example of that in the codebase).

oh sorry, this is aaaa, then no. Thought we where somehow returning a text representation of the record.