Add support for splitting strings to CEL expressions.

[bigkevmcd]

Changes

This adds an additional CEL function for splitting strings on a separator.

e.g. body.ref.split('/') would split the ref on '/' and return a list of strings.

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Release Notes

This adds a CEL expression function for splitting strings.

e.g. to extract the tag or branch from a hook event in an overlay:

            overlays:
            - key: intercepted.branch_name
              expression: "body.ref.split('/')[2]"

[bigkevmcd]

This could easily be flipped to become split(body.ref, '/') instead of body.ref.split('/')

[dibyom]

This could easily be flipped to become split(body.ref, '/') instead of body.ref.split('/')

Yeah, I think I like split(body.ref, '/') slightly better since it also matches the pattern from truncate

[bitsofinfo]

really, really need this function to be able to mutate values and capture them as new fields (overlay) in the body. Please merge at least into the master so I can start playing with it. thanks!

[bobcatfish]

Thanks for adding this, complete with tests cases and docs @bigkevmcd !!

This seems fine but I think it would be worth a larger conversation about how many of these custom functions we want to support.

Shameless plug for Rego, looks like it comes with a number of string manipulation functions built in: https://www.openpolicyagent.org/docs/latest/policy-reference/#strings

Related: @wlynch feature request for string splitting google/cel-go#306

/approve
/lgtm

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[bitsofinfo]

@bobcatfish I agree, would be great if some bridge could be developed to just expose functions available in other libraries that would not have to be directly maintained by tekton. i.e. like how helm exposes all the go template functions provided by sprig (http://masterminds.github.io/sprig/) greatly enhancing the capabilities.

if another lib like you suggested could be added to expose much more CEL string manipulation functions that would be awesome!

[bigkevmcd]

@bobcatfish yes, I'd like to deprecate match in favour of canonical as there's less ambiguity (there's a matches function in CEL already).

Other than that, I can't see many more items being added, splitting strings, decoding base64 and trimming strings are the things that I wanna do in my pipelines, but clearly, there might be other useful things, we're dealing with broadly the same data across different environments.

I currently have no plans for further functions, but it's fairly easy to add them... :-)

[dibyom]

Agreed. I think we need base64 (for things like pub/sub events that are base64 encoded); trimming strings (tags, commits, refs). The header one is interesting...mainly due to how go represents header values as a array of strings. Other than these 3, I don't see any new ones in the short term!

[bitsofinfo]

is there a nightly release I can point to that has this? or i'll have to build it all and deploy locally?

[TristonianJones]

Hey everyone, awesome to see CEL being embraced in the wild. I am totally open to reviewing PRs for google/cel-go#306 if that would help accelerate your project.

[bitsofinfo]

is this not possible?

apiVersion: tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: deploy
spec:
  params:

    - name: appName
      value: "$(split(body.action_values[0],'_')[1])"

[bigkevmcd]

is this not possible?

No, see #367

But, you can use the CEL interceptor, without actually intercepting, and use the overlay function there.

Something like this should work:

apiVersion: tekton.dev/v1alpha1
kind: EventListener
metadata:
  name: listener-interceptor
spec:
  triggers:
    - name: demo-trigger
      interceptors:
        - cel:
            overlays:
            - key: intercepted.appName
              expression: "split(body.action_values[0],'_')[1]"
      bindings:
        - name: deploy
      template:
        name: deploy-template

Then you could use the value like this:

apiVersion: tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: deploy
spec:
  params:
    - name: appName
      value: $(body.intercepted.appName)

[TristonianJones]

BTW, I created google/cel-go#316, so if your favorite string function isn't there, just let me know and I'll see if I can get it in.

[bitsofinfo]

@bigkevmcd yep thats what i ended up doing, thanks!

[bitsofinfo]

@TristonianJones would be great to have a replace function. or... can anyone point me to an example of how to essentially do a string replace w/ CEL? I've looked but can't think of anything.

i need to take a value and replace . with - so I can use that value in meta-data names in a pipelinerun.

looks like it will be in go-cel eventually w/ google/cel-go#316