feat: add single evaluation endpoint for OFREP

[thepabloaguilar]

Hi guys, I'm opening this PR to gather opinions around the implementation of this endpoint for OFREP! What I thought was to just translate the protocol to Flipt internals and I did it by declaring an interface which is implemented by evaluation server as all the stuff to evaluate a flag is there, and also the OFREP layer will translate the errors to the expected pattern.

Refs #2980

[thepabloaguilar]

Have you had a chance to check this out @markphelps / @GeorgeMac / @erka?

[markphelps]

looking great @thepabloaguilar !! great approach

just a few comments so far

[markphelps]

@thepabloaguilar can I help with anything here?

[thepabloaguilar]

@markphelps I'm gonna take a look this weekend! Tough week 😆

[codecov]

Codecov Report

Attention: Patch coverage is 78.80795% with 32 lines in your changes missing coverage. Please review.

Project coverage is 64.42%. Comparing base (c005e90) to head (da7e3a6).
Report is 11 commits behind head on main.

Files	Patch %	Lines
internal/server/ofrep/errors.go	62.50%	10 Missing and 5 partials ⚠️
internal/server/ofrep/evaluation.go	82.35%	7 Missing and 2 partials ⚠️
internal/server/evaluation/ofrep_bridge.go	84.90%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3267      +/-   ##
==========================================
+ Coverage   64.26%   64.42%   +0.15%     
==========================================
  Files         168      172       +4     
  Lines       13582    13731     +149     
==========================================
+ Hits         8729     8846     +117     
- Misses       4185     4207      +22     
- Partials      668      678      +10     

Flag	Coverage Δ
unittests	64.42% <78.80%> (+0.15%)	⬆️

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[erka]

Great work @thepabloaguilar!

I tried to use OpenFeature go client for OFREP and somehow it ins't happy with the our metadata in response. It looks like we return null for it and client fails with openfeature: PARSE_ERROR: metadata must be a map of string keys and arbitrary values. Here is what I have with curl

❯ curl -X POST http://localhost:8080/ofrep/v1/evaluate/flags/variant-flag
{"key":"variant-flag","reason":"DEFAULT","variant":"azul","metadata":null,"value":"azul"}

This is my example

package main

import (
	"context"

	"github.com/open-feature/go-sdk-contrib/providers/ofrep"
	"github.com/open-feature/go-sdk/openfeature"
)

func main() {
	ofrepProvider := ofrep.NewProvider("http://localhost:8080")
	openfeature.SetProvider(ofrepProvider)
	client := openfeature.NewClient("default")
	value := client.String(context.Background(), "variant-flag", "", openfeature.EvaluationContext{})
	println("result", value)
}

I have no issue if I add empty metadata in resp := &ofrep.EvaluatedFlag{...} object.

[thepabloaguilar]

@erka the return must be an empty object {}, just fixed it!

[markphelps]

@thepabloaguilar I added support for ofrep targetingKey here: thepabloaguilar#1

[thepabloaguilar]

Done the changes! Sorry @markphelps unconsciously I overrode your changes but I've put them back

[erka]

Looks great! @thepabloaguilar

[markphelps]

looks great! thank you @thepabloaguilar !!