(bug) Nil pointer dereference when calling a variation without Init

[joshm91]

Observed behavior

When calling a variation (e.g., ffclient.BoolVariation("test", ffUser, false) without first calling ffclient.Init(), a panic happens due to a nil pointer dereference.

This is happening due to directly referencing ff here:

go-feature-flag/variation.go

Lines 22 to 27 in d6dd663

	// BoolVariation return the value of the flag in boolean.
	// An error is return if you don't have init the library before calling the function.
	// If the key does not exist we return the default value.
	func BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error) {
	return ff.BoolVariation(flagKey, user, defaultValue)
	}

where ff is a pointer type:

go-feature-flag/feature_flag.go

Line 49 in d6dd663

var ff *GoFeatureFlag

that is only set when calling Init():

go-feature-flag/feature_flag.go

Lines 26 to 32 in d6dd663

	func Init(config Config) error {
	var err error
	onceFF.Do(func() {
	ff, err = New(config)
	})
	return err
	}

Expected Behavior

I expect the variation call to return an error, and set the return value to the default specified in the call. This behaviour is expected based on the existing documentation, both in function docs:

go-feature-flag/variation.go

Lines 22 to 25 in d6dd663

	// BoolVariation return the value of the flag in boolean.
	// An error is return if you don't have init the library before calling the function.
	// If the key does not exist we return the default value.
	func BoolVariation(flagKey string, user ffuser.User, defaultValue bool) (bool, error) {

and in the documentation site:

go-feature-flag/docs/users.md

Line 70 in d6dd663

The default value is return when an error is encountered _(`ffclient` not initialized, variation with wrong type, flag does not exist ...)._

I do not expect a panic/nil pointer dereference.

Steps to reproduce

package main

import (
	"fmt"

	ffclient "github.com/thomaspoignant/go-feature-flag"
	"github.com/thomaspoignant/go-feature-flag/ffuser"
)

func main() {
	res, err := ffclient.BoolVariation("test", ffuser.NewUser("test"), false) // <-- This results in nil pointer dereference
	fmt.Println(res)
	fmt.Println(err)
}

Results in:

➜ go run .
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x99 pc=0x102cc2230]

goroutine 1 [running]:
github.com/thomaspoignant/go-feature-flag.(*GoFeatureFlag).boolVariation(0x12a2bbfff?, {0x102cc30e3?, 0x14000066da8?}, {{0x102cc30e3?, 0x12a3f2e40?}, 0x1?, 0x14000112780?}, 0x8?)
	/Users/josh/go/pkg/mod/github.com/thomaspoignant/[email protected]/variation.go:217 +0x40
github.com/thomaspoignant/go-feature-flag.(*GoFeatureFlag).BoolVariation(0x14000159f28?, {0x102cc30e3, 0x4}, {{0x102cc30e3?, 0x0?}, 0xa0?, 0x14000112780?}, 0x44?)
	/Users/josh/go/pkg/mod/github.com/thomaspoignant/[email protected]/variation.go:84 +0x48
github.com/thomaspoignant/go-feature-flag.BoolVariation(...)
	/Users/josh/go/pkg/mod/github.com/thomaspoignant/[email protected]/variation.go:26
main.main()
	/var/folders/f4/dlqjqljs70dbl279lrbdcdjc0000gn/T/tmp.6GuEmS7X/main.go:11 +0x58
exit status 2

[thomaspoignant]

@joshm91 thanks for this super details issue 🙏 this is much appreciated.
I am sorry that this bug was introduced.

I have opened a PR #361 to fix the issue.
I will create a new version soon with the fix.

[thomaspoignant]

The fix is available in the version v0.28.1.

[joshm91]

Wow, thank you so much for the quick fix, and for this great library in general!

[thomaspoignant]

Wow, thank you so much for the quick fix, and for this great library in general!

Thanks a lot for your feedback this is much appreciated.