Add webhome validator

[DL6ER]

What does this implement/fix?

Add specific validator for webserver.paths.webhome ensuring there are slashes both at the beginning and the end of the string

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Related issue or feature (if applicable): Fixes #2274

Pull request in docs with documentation (if applicable): N/A

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[PromoFaux]

Computer says no:

[rdwebdesign]

The check fails and the value is used.

I tried with:

  FTLCONF_webserver_paths_webroot: '/home/root/www'
  FTLCONF_webserver_paths_webhome: '/adm'   # (missing the last slash)

and the web interface is redirected to:
http://192.168.0.208/admlogin

[rdwebdesign]

The validator is not used when the env vars are used.

But if you try to add an invalid webhome via web interface or using pihole-FTL --config it will correctly fail:

2830143614c3:/# pihole-FTL --config webserver.paths.webhome '/admin'
Invalid value: webserver.paths.webhome: file path does not start and end with a slash ("/admin")

[DL6ER]

Yes, but that is because the validators cannot be used when using either the config file directly (or via env vars) because there is no way to communicate the warning/error to the user. What should we do in this case? Revert the config and overwrite what users have done? Ignore then env variable and use the default? It was unclear to me but rethinking this yesterday seems to make this a clear strategy.

Note: This is a problem of general scope and not limited to the webhome setting. The validators are never used for config file and env var values so far. If we want to change this, we should do it in a separate PR for cleanness. (#2294)

I think enforcing the validators on env vars (and falling back to ignoring the env var) is still somewhat doable as this will be in the container logs, I do find this more of an issue for direct config file changes. Your feelings may change, hence, I would like to talk about this.

[rdwebdesign]

The validators are never used for config file and env var values so far.

Yeah... I noticed that when I was checking the code.

I agree with your PR suggestion, to validate env vars and send error messages to the log.

Note:

Not sure how to do it when the config file is directly edited.

We can enforce the validation even in this case. If invalid, we set the value to default and send the errors to FTL.log (not sure if this is very user friendly). Or we simply don't validate in this case and leave the "user input" there. At least, the wrong value will be on the debug log to help us understand the issue.