[Feature Request] Negation of <check>?

[DopeforHope]

Hello,

nice work with this plugin. Makes working with Fluentd and JSON much easier. May it be possible to get a <exclude> (just like on the grep filter plugin) which just does the opposite of <check>?

Thank you very much

[iamazeem]

Hi @DopeforHope,

Glad the plugin was helpful!
Thank you for the feature request!
Yes, the exclusion/negation could be implemented.

But, did you try to negate via regex with negative lookahead (?!) and inversion (^)?

(?!pat) - Negative lookahead assertion: ensures that the following characters do not match pat, but doesn't include those characters in the matched text

For example:

  <check>
    pointer   /log/user     # point to { "log": { "user": "test", ... } }
    pattern   /^(?!test)/   # check it against the value of username except `test`
  </check>

---

Apart from that, please add some test examples for exclusion/negations.
This is a nice feature to have for a straightforward negation instead of fiddling with regex a lot.
Thought about it a little and it seems like that a flag e.g. negate or invert would be much better and concise instead of having a new tag.

Example:

  <check>
    pointer   /log/user
    pattern   /test/i
    negate    true        # default: false
  </check>

[DopeforHope]

Yeah, the negative lookahead and inversion should suffice for most cases as well as for me.

The flag seems convenient. I will try creating some test cases but I'm no ruby expert.

[iamazeem]

@DopeforHope : Would you be able to review and test the negation support (#8) on your side?

[DopeforHope]

Test have passed and seems fine.

[nmaupu]

Hi, it would be very nice to be able to negate the entire filter configuration. I mean, instead of letting an event pass if all checks match, I would like my event to NOT pass if all checks pass. Does that make sense ?

Now I don't seem to be able to do it because there is no support for or operator.
Because:

a && b && c == !a || !b || !c

So either I have to negate the entire filter (!(a && b && c)) or support or operator and negate each check (either by using the negate function - not merged - or negate all regex myself). I can't do that with the actual code if I am not mistaken.

What do you think ?

[iamazeem]

Hi @nmaupu,

IIUC, by "negating the entire filter configuration", you meant to introduce a global flag e.g. negate_all true (default: false).
Is that correct?

Apart from that, if the existing PR #8 is merged then that'll serve your purpose too, right?
But, in that case, you'll have to negate each check which might be cumbersome to do if it's a frequent occurrence. 🤔

[nmaupu]

Yes, that is correct
The PR #8 is not ok for me because negating every check is not sufficient, I would also need to be able to ORing them instead of ANDing them.
By the way, I succeeded in doing what I needed with the regexp filter with something like this:

<filter test>
  @type grep
  <and>
    <exclude>
      key $.properties.log.verb
      pattern ^get$
    </exclude>
    <exclude>
      key $.properties.log.kind
      pattern ^Event$
    </exclude>
    <exclude>
      key $['properties'].['log'].['annotations'].['authorization.k8s.io/reason']
      pattern ^$
    </exclude>
  </and>
</filter>

[iamazeem]

Good to hear that, @nmaupu! Looks good! 👍
A little bit of fiddling with the existing plugins solves almost all the cases.