Add support for extended error codes in blocklist-v2

[folbricht]

Supports extended errors for blocklists. The text field in the error message is a template that has access to the query and can use that to customize the message.

[groups.cloudflare-blocklist]
type              = "blocklist-v2"
resolvers         = ["cloudflare-dot"]
blocklist-format  = "domain"
edns0-ede = {code = 15, text = "Blocked {{ .Question }} with ID {{ .ID }} because reasons "} # Extended error code
blocklist         = [
  'evil.com',
]

edns0-ede will only be used if the blocklist actually blocks, not when it just spoofs response IPs.

[Anuskuss]

Works but could this be extended to the other block types (i.e. response-blocklist-ip) as well?
Also that syntax looks a bit clunky but as long as it's properly documented, I have no complains.

[folbricht]

Just added the same to response-blocklist-* and static-responder (not tested). As for the syntax, would it be better to simplify to something like {{ .Question }} ? Since it's unlikely anything else is needed from the query.

[Anuskuss]

Just added the same to response-blocklist-*

Works now with response-blocklist-ip but I don't know the right keyword to get the IP address (if that's even possible).

and static-responder (not tested).

Enabling static-responder (without anything) results in a segmentation fault.

As for the syntax, would it be better to simplify

I'd suggest a bash-like syntax like

text = 'Blocked because $qname got caught by "${filter}" ($qtype)'

($filter in my case would be the IP address)

Other (less useful) variables could be

• $date (current date in ISO 8601)
• ${env[]} (array of enviroment variables)
• $version (vX.Y)
• $mtime (static = mtime of config.toml, dynamic = Last-Modified of document)
• $id

[folbricht]

Fixed the nil pointer, missed that one earlier. As for the placeholders, I do want to keep using templating offered by the standard library, so can support syntax like {{ .Question }} and {{ .ID }}.

[Anuskuss]

so can support syntax like {{ .Question }} and {{ .ID }}

This is fine by me. Like I said, I don't care how it looks as long as it's documented. As for the IP address, does that work yet? What's the keyword? Or would that not work with these "templates"?

[folbricht]

Finally found a bit of time to work on this again. I simplified the way templates can access query values. Now it's possible to just use "Blocked {{ .Question }} with ID {{ .ID }}". At this point, this only works for blocklists though, still working on how to get the static-responder to use it (in another PR). Wondering if it'd be better to make a new element like template-responder or dynamic-responder. I should be able to make it support the same template syntax as in the extended error strings.