fix: introduced RWMutex to flag state to prevent concurrent r/w of map (

#370)

## This PR
<!-- add the description of the PR here -->

- Introduces RWMutex on flag state to prevent concurrent read/write of
map.

### Related Issues
<!-- add here the GitHub issue that this PR resolves if applicable -->

Fixes #368 

### Notes
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### Follow-up Tasks
<!-- anything that is related to this PR but not done here should be
noted under this section -->
<!-- if there is a need for a new issue, please link it here -->

### How to test
<!-- if applicable, add testing instructions under this section -->

---------

Signed-off-by: Skye Gill <gill.skye95@gmail.com>

pkg/eval/fractional_evaluation_test.go

@@ -1,6 +1,7 @@
 package eval
 
 import (
+	"sync"
 	"testing"
 
 	"github.com/open-feature/flagd/pkg/logger"
@@ -10,6 +11,7 @@ import (
 
 func TestFractionalEvaluation(t *testing.T) {
 	flags := Flags{
+		mx: &sync.RWMutex{},
 		Flags: map[string]Flag{
 			"headerColor": {
 				State:          "ENABLED",
@@ -113,6 +115,7 @@ func TestFractionalEvaluation(t *testing.T) {
 		},
 		"non even split": {
 			flags: Flags{
+				mx: &sync.RWMutex{},
 				Flags: map[string]Flag{
 					"headerColor": {
 						State:          "ENABLED",
@@ -164,6 +167,7 @@ func TestFractionalEvaluation(t *testing.T) {
 		},
 		"fallback to default variant if no email provided": {
 			flags: Flags{
+				mx: &sync.RWMutex{},
 				Flags: map[string]Flag{
 					"headerColor": {
 						State:          "ENABLED",
@@ -206,6 +210,7 @@ func TestFractionalEvaluation(t *testing.T) {
 		},
 		"fallback to default variant if invalid variant as result of fractional evaluation": {
 			flags: Flags{
+				mx: &sync.RWMutex{},
 				Flags: map[string]Flag{
 					"headerColor": {
 						State:          "ENABLED",
@@ -240,6 +245,7 @@ func TestFractionalEvaluation(t *testing.T) {
 		},
 		"fallback to default variant if percentages don't sum to 100": {
 			flags: Flags{
+				mx: &sync.RWMutex{},
 				Flags: map[string]Flag{
 					"headerColor": {
 						State:          "ENABLED",

pkg/eval/json_evaluator.go

@@ -8,6 +8,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	mxSync "sync"
 
 	"github.com/open-feature/flagd/pkg/sync"
 
@@ -47,6 +48,7 @@ func NewJSONEvaluator(logger *logger.Logger) *JSONEvaluator {
 		),
 		state: Flags{
 			Flags: map[string]Flag{},
+			mx:    &mxSync.RWMutex{},
 		},
 	}
 	jsonlogic.AddOperator("fractionalEvaluation", ev.fractionalEvaluation)
@@ -110,6 +112,8 @@ func (je *JSONEvaluator) ResolveAllValues(reqID string, context *structpb.Struct
 	var variant string
 	var reason string
 	var err error
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	for flagKey, flag := range je.state.Flags {
 		defaultValue := flag.Variants[flag.DefaultVariant]
 		switch defaultValue.(type) {
@@ -161,6 +165,8 @@ func (je *JSONEvaluator) ResolveBooleanValue(reqID string, flagKey string, conte
 	reason string,
 	err error,
 ) {
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	je.Logger.DebugWithID(reqID, fmt.Sprintf("evaluating boolean flag: %s", flagKey))
 	return resolve[bool](reqID, flagKey, context, je.evaluateVariant, je.state.Flags[flagKey].Variants)
 }
@@ -171,6 +177,8 @@ func (je *JSONEvaluator) ResolveStringValue(reqID string, flagKey string, contex
 	reason string,
 	err error,
 ) {
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	je.Logger.DebugWithID(reqID, fmt.Sprintf("evaluating string flag: %s", flagKey))
 	return resolve[string](reqID, flagKey, context, je.evaluateVariant, je.state.Flags[flagKey].Variants)
 }
@@ -181,6 +189,8 @@ func (je *JSONEvaluator) ResolveFloatValue(reqID string, flagKey string, context
 	reason string,
 	err error,
 ) {
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	je.Logger.DebugWithID(reqID, fmt.Sprintf("evaluating float flag: %s", flagKey))
 	value, variant, reason, err = resolve[float64](
 		reqID, flagKey, context, je.evaluateVariant, je.state.Flags[flagKey].Variants)
@@ -193,6 +203,8 @@ func (je *JSONEvaluator) ResolveIntValue(reqID string, flagKey string, context *
 	reason string,
 	err error,
 ) {
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	je.Logger.DebugWithID(reqID, fmt.Sprintf("evaluating int flag: %s", flagKey))
 	var val float64
 	val, variant, reason, err = resolve[float64](
@@ -207,6 +219,8 @@ func (je *JSONEvaluator) ResolveObjectValue(reqID string, flagKey string, contex
 	reason string,
 	err error,
 ) {
+	je.state.mx.RLock()
+	defer je.state.mx.RUnlock()
 	je.Logger.DebugWithID(reqID, fmt.Sprintf("evaluating object flag: %s", flagKey))
 	return resolve[map[string]any](reqID, flagKey, context, je.evaluateVariant, je.state.Flags[flagKey].Variants)
 }
@@ -256,7 +270,7 @@ func (je *JSONEvaluator) evaluateVariant(
 		variant = strings.ReplaceAll(strings.TrimSpace(result.String()), "\"", "")
 
 		// if this is a valid variant, return it
-		if _, ok := je.state.Flags[flagKey].Variants[variant]; ok {
+		if _, ok := flag.Variants[variant]; ok {
 			return variant, model.TargetingMatchReason, nil
 		}
 
@@ -266,7 +280,7 @@ func (je *JSONEvaluator) evaluateVariant(
 		reason = model.StaticReason
 	}
 
-	return je.state.Flags[flagKey].DefaultVariant, reason, nil
+	return flag.DefaultVariant, reason, nil
 }
 
 // configToFlags convert string configurations to flags and store them to pointer newFlags

pkg/eval/json_evaluator_model.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"sync"
 
 	"github.com/open-feature/flagd/pkg/logger"
 )
@@ -21,6 +22,7 @@ type Evaluators struct {
 }
 
 type Flags struct {
+	mx    *sync.RWMutex
 	Flags map[string]Flag `json:"flags"`
 }
 
@@ -29,7 +31,10 @@ func (f Flags) Add(logger *logger.Logger, source string, ff Flags) map[string]in
 	notifications := map[string]interface{}{}
 
 	for k, newFlag := range ff.Flags {
-		if storedFlag, ok := f.Flags[k]; ok && storedFlag.Source != source {
+		f.mx.RLock()
+		storedFlag, ok := f.Flags[k]
+		f.mx.RUnlock()
+		if ok && storedFlag.Source != source {
 			logger.Warn(fmt.Sprintf(
 				"flag with key %s from source %s already exist, overriding this with flag from source %s",
 				k,
@@ -45,7 +50,9 @@ func (f Flags) Add(logger *logger.Logger, source string, ff Flags) map[string]in
 
 		// Store the new version of the flag
 		newFlag.Source = source
+		f.mx.Lock()
 		f.Flags[k] = newFlag
+		f.mx.Unlock()
 	}
 
 	return notifications
@@ -56,14 +63,18 @@ func (f Flags) Update(logger *logger.Logger, source string, ff Flags) map[string
 	notifications := map[string]interface{}{}
 
 	for k, flag := range ff.Flags {
-		if storedFlag, ok := f.Flags[k]; !ok {
+		f.mx.RLock()
+		storedFlag, ok := f.Flags[k]
+		f.mx.RUnlock()
+		if !ok {
 			logger.Warn(
-				fmt.Sprintf("failed to update the flag, flag with key %s from source %s does not exisit.",
+				fmt.Sprintf("failed to update the flag, flag with key %s from source %s does not exist.",
 					k,
 					source))
 
 			continue
-		} else if storedFlag.Source != source {
+		}
+		if storedFlag.Source != source {
 			logger.Warn(fmt.Sprintf(
 				"flag with key %s from source %s already exist, overriding this with flag from source %s",
 				k,
@@ -78,7 +89,9 @@ func (f Flags) Update(logger *logger.Logger, source string, ff Flags) map[string
 		}
 
 		flag.Source = source
+		f.mx.Lock()
 		f.Flags[k] = flag
+		f.mx.Unlock()
 	}
 
 	return notifications
@@ -89,13 +102,18 @@ func (f Flags) Delete(logger *logger.Logger, source string, ff Flags) map[string
 	notifications := map[string]interface{}{}
 
 	for k := range ff.Flags {
-		if _, ok := f.Flags[k]; ok {
+		f.mx.RLock()
+		_, ok := f.Flags[k]
+		f.mx.RUnlock()
+		if ok {
 			notifications[k] = map[string]interface{}{
 				"type":   string(NotificationDelete),
 				"source": source,
 			}
 
+			f.mx.Lock()
 			delete(f.Flags, k)
+			f.mx.Unlock()
 		} else {
 			logger.Warn(
 				fmt.Sprintf("failed to remove flag, flag with key %s from source %s does not exisit.",
@@ -111,6 +129,7 @@ func (f Flags) Delete(logger *logger.Logger, source string, ff Flags) map[string
 func (f Flags) Merge(logger *logger.Logger, source string, ff Flags) map[string]interface{} {
 	notifications := map[string]interface{}{}
 
+	f.mx.Lock()
 	for k, v := range f.Flags {
 		if v.Source == source {
 			if _, ok := ff.Flags[k]; !ok {
@@ -124,11 +143,14 @@ func (f Flags) Merge(logger *logger.Logger, source string, ff Flags) map[string]
 			}
 		}
 	}
+	f.mx.Unlock()
 
 	for k, newFlag := range ff.Flags {
 		newFlag.Source = source
 
+		f.mx.RLock()
 		storedFlag, ok := f.Flags[k]
+		f.mx.RUnlock()
 		if !ok {
 			notifications[k] = map[string]interface{}{
 				"type":   string(NotificationCreate),
@@ -151,8 +173,10 @@ func (f Flags) Merge(logger *logger.Logger, source string, ff Flags) map[string]
 			}
 		}
 
+		f.mx.Lock()
 		// Store the new version of the flag
 		f.Flags[k] = newFlag
+		f.mx.Unlock()
 	}
 
 	return notifications