Consider adding a `mod()` function or similar to OTTL

[bixu]

Component(s)

pkg/ottl

Is your feature request related to a problem? Please describe.

One common use-case for OTTL is making sensitive key values. For example, credit card numbers. Using Regexes alone can be difficult and prone to bugs.

Describe the solution you'd like

Some algorithm like the Luhn algorithm would make OTTL easier to use in the context of redaction or masking of values like credit card numbers.

Describe alternatives you've considered

Regex functions do exist in OTTL, but it's relatively easy to introduce bugs when using "pure" regex. An additional layer of checking using something like Luhn/mod 10 could increase correctness.

[github-actions]

Pinging code owners:

• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley @edmocosta

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[TylerHelmuth]

I wonder if we should build this into OTTL's arithmetic capabilities so you can do 9 % 2

[bixu]

I mentioned the Luhn algorithm specifically only because it's used as part of validation for almost all credit card schemes, but if we can reproduce the Luhn check with a math function, that would be fine. (It would be cool to have an example snippet in the docs, though.)

[edmocosta]

Although adding the reminder operator capability to OTTL would be useful, I think that wouldn't be enough for calculating the Luhn algorithm. If I'm not mistaken, it requires extra steps, such as looping through the number digits, double values, etc. which isn't supported by OTTL. That said, I'd go with a specific function Luhn(), since Mod() might be misinterpreted as normal modulus operation.

[bacherfl]

I could look into implementing this

[bacherfl]

The PR should be ready for review now - I implemented it as a specific Luhn() function now to enable the credit card checksum validation use case, but if needed, I could also follow up with another PR for a Mod() function

[edmocosta]

Hi @bixu, just to double check, do you need validating numbers using the Luhn algorithm or calculating/getting the check digit? I initially thought it was the second option, but I think I misunderstood it. If that's a validation function, I'd name it LuhnCheck, LuhnValidate or something like that.