cel expression to match list items?

[Rucha Deshpande]

Hello All,

 I am looking to find an optimized way of matching items in  2 lists. For example:
User                                           Data 

   Group1                                     Group1

   Group2                                     Group5

   Group3                                     Group6

I want to evaluate whether an element from  User Groups List has a matching element in Data Groups list.

Here Group1 matches, so result would be true.

Is there an optimized CEL way of doing this?

or do I have to write an iterator?

Thank you!

[Jim Larson]

Hi, Rucha!

If you don't mind a quadratic-time solution, i.e. if your lists are small or if your performance expectations are loose, you can use nested macros.

    user.exists(u, data.exists(d, u == d))

Otherwise, if you want a more efficient algorithm (e.g. pre-sorting both lists and using a linear-time match finder), you'd have to implement it yourself.

Jim

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[Rucha Deshpande]

Awesome! That works...

The list is going to be fairly small ... 7 to 8 elements in both the list so this will work for now.

This is working when I pass the list in the request:

decisions, err := enforcer.Evaluate(map[string]interface{}{
                                           "User":"srihari",
                                           "Service":"Storage",
                                           "Resource":"/Get",
                                           "Usergroups": []string{"service.storage.admin","data.default.admin"},
                                           })

and my rule is:

Usergroups.exists(u,groups_to_match_storage_get.exists(d,u==d))

However, if the usergroups list is dynamic which I need to retrieve from a datastore by using  a rule such as:

getUserGroups(User).exists(u,groups_to_match_storage_get.exists(d,u==d))

and
(right now only returning static list)

getUserGroups = policy.Functions(&functions.Overload{
              Operator: "get_usergroups_string",
              Unary: func(User ref.Val) interface{} {
                 list:= []string{"A","B"}
                 return list

              },
           })

This does not work.

I did not find examples with custom functions returning lists. Can you help?

On Monday, May 4, 2020 at 1:54:58 PM UTC-5, Jim Larson wrote:

Hi, Rucha!

If you don't mind a quadratic-time solution, i.e. if your lists are small or if your performance expectations are loose, you can use nested macros.

    user.exists(u, data.exists(d, u == d))

Otherwise, if you want a more efficient algorithm (e.g. pre-sorting both lists and using a linear-time match finder), you'd have to implement it yourself.

Jim

On Mon, May 4, 2020 at 8:27 AM Rucha Deshpande <rborg...@gmail.com> wrote:

Hello All,

 I am looking to find an optimized way of matching items in  2 lists. For example:
User                                           Data 

   Group1                                     Group1

   Group2                                     Group5

   Group3                                     Group6

I want to evaluate whether an element from  User Groups List has a matching element in Data Groups list.

Here Group1 matches, so result would be true.

Is there an optimized CEL way of doing this?

or do I have to write an iterator?

Thank you!

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[Tristan Swadell]

Hi Rucha, the `ext/strings.go` in cel-go is a pretty good example of how to do what you're looking for:

https://github.com/google/cel-go/blob/3023710f92aa1469e7c0734514b080e15fbcb6a5/ext/strings.go#L274 

-Tristan

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[Rucha Deshpande]

Thank you Tristan.. that helped!

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