Allow trailing dot in valid domains

[yubiuser]

What does this PR aim to accomplish?:

We use validDomain() in several places (e.g. adding a domain to black/whitelist, querying the adlists). So for, domains with a trailing dot (root zone) were marked as invalid, e.g. www.google.com.. However, they are valid.

How does this PR accomplish the above?:

Appends \.? to the validating RegEx

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[DL6ER]

Just as virtually any DNS software (except maybe for bind and its tools such as dig), the final dot is omitted. This makes such domains valid but meaningless in the world of Pi-hole. When you block example.com, you, well, block exactly this domain. When you, however, block example.com., then this will never actually block anything as all internal handling won't see the final dot.

The sole exception from this is the root zone itself . where we intentionally keep . (dnsmasq, however, still treats the root zone internally as zero-length domain).

My suggestion: Don't simply extend the regular expressions. It will just enable users to add domains that will never be blocked, possibly causing more frustration that the mere fact that this is not possible. A proper fix would likely allow them but also adding some internal logic to strip the trailing dot before doing any processing on them.

[dschaper]

marked as invalid, e.g. www.google.com.. However, they are valid.

Are there some examples or an issue that this relates to where we can see how this condition happened in the wild?

Even Windows nslookup will strip off the anchoring . when you nslookup valid.domain.

[yubiuser]

I've not seen this in the wild. The real world stripping is the reason I opened this PR: "Search Adlists" uses validDomain() as well. If users query for flurry.com. it will show "invalid" domain, but usually this domain is blocked as well. This happens on cli as well (no results found), but we do not error because of an invalid domain.

pi@s740:~$ pihole -q flurry.com.
  [i] No results found for flurry.com. within the adlists

If you think we should not change the RegEx I can change the processing of the input on "Search Adlist" to stip a trailing dot before executing the search. This would still prevent users from adding test.com. as black/whitelisted domain.

[rdwebdesign]

I added this to abp_query branch:

Edit:
REMOVED

[dschaper]

I added this to abp_query branch:

Please keep branches and PRs focused on one topic only. Don't bikeshed/goldplate please.

[rdwebdesign]

Please keep branches and PRs focused on one topic only. Don't bikeshed/goldplate please.

I only added this to that branch because yubiuser asked me to do it a few days ago:
pi-hole/pi-hole@273147a#r102882761

My comment was just to show him the code.

My branch is still a WIP and I didn't open a PR. I'll remove the code if this is set on another PR.