feat: add EppoClient.Initialized() method to wait for initialization (#72)

Author: rasendubi

eppoclient/bandits_test.go

@@ -54,7 +54,7 @@ func Test_InferContextAttributes(t *testing.T) {
 func Test_bandits_sdkTestData(t *testing.T) {
 	flags := readJsonFile[configResponse]("test-data/ufc/bandit-flags-v1.json")
 	bandits := readJsonFile[banditResponse]("test-data/ufc/bandit-models-v1.json")
-	configStore := newConfigurationStore(configuration{
+	configStore := newConfigurationStoreWithConfig(configuration{
 		flags:   flags,
 		bandits: bandits,
 	})

eppoclient/client.go

@@ -33,6 +33,20 @@ func newEppoClient(
 	}
 }
 
+// Returns a channel that gets closed after client has been
+// *successfully* initialized.
+//
+// It is recommended to apply a timeout to initialization as otherwise
+// it may hang up indefinitely.
+//
+//  select {
+//  case <-client.Initialized():
+//  case <-time.After(5 * time.Second):
+//  }
+func (ec *EppoClient) Initialized() <-chan struct{} {
+	return ec.configurationStore.Initialized()
+}
+
 func (ec *EppoClient) GetBoolAssignment(flagKey string, subjectKey string, subjectAttributes Attributes, defaultValue bool) (bool, error) {
 	variation, err := ec.getAssignment(ec.configurationStore.getConfiguration(), flagKey, subjectKey, subjectAttributes, booleanVariation)
 	if err != nil || variation == nil {

eppoclient/client_test.go

@@ -2,6 +2,7 @@ package eppoclient
 
 import (
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/mock"
@@ -15,15 +16,15 @@ var (
 
 func Test_AssignBlankExperiment(t *testing.T) {
 	var mockLogger = new(mockLogger)
-	client := newEppoClient(newConfigurationStore(configuration{}), nil, nil, mockLogger, applicationLogger)
+	client := newEppoClient(newConfigurationStore(), nil, nil, mockLogger, applicationLogger)
 
 	_, err := client.GetStringAssignment("", "subject-1", Attributes{}, "")
 	assert.Error(t, err)
 }
 
 func Test_AssignBlankSubject(t *testing.T) {
 	var mockLogger = new(mockLogger)
-	client := newEppoClient(newConfigurationStore(configuration{}), nil, nil, mockLogger, applicationLogger)
+	client := newEppoClient(newConfigurationStore(), nil, nil, mockLogger, applicationLogger)
 
 	_, err := client.GetStringAssignment("experiment-1", "", Attributes{}, "")
 	assert.Error(t, err)
@@ -96,7 +97,7 @@ func Test_LogAssignment(t *testing.T) {
 				},
 			}
 
-			client := newEppoClient(newConfigurationStore(configuration{flags: config}), nil, nil, mockLogger, applicationLogger)
+			client := newEppoClient(newConfigurationStoreWithConfig(configuration{flags: config}), nil, nil, mockLogger, applicationLogger)
 
 			assignment, err := client.GetStringAssignment("experiment-key-1", "user-1", Attributes{}, "")
 			expected := "control"
@@ -141,7 +142,7 @@ func Test_client_loggerIsCalledWithProperBanditEvent(t *testing.T) {
 		},
 	}
 
-	client := newEppoClient(newConfigurationStore(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
+	client := newEppoClient(newConfigurationStoreWithConfig(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
 	actions := map[string]ContextAttributes{
 		"action1": {},
 	}
@@ -194,7 +195,7 @@ func Test_GetStringAssignmentHandlesLoggingPanic(t *testing.T) {
 		},
 	}}
 
-	client := newEppoClient(newConfigurationStore(configuration{flags: config}), nil, nil, mockLogger, applicationLogger)
+	client := newEppoClient(newConfigurationStoreWithConfig(configuration{flags: config}), nil, nil, mockLogger, applicationLogger)
 
 	assignment, err := client.GetStringAssignment("experiment-key-1", "user-1", Attributes{}, "")
 	expected := "control"
@@ -236,7 +237,7 @@ func Test_client_handlesBanditLoggerPanic(t *testing.T) {
 		},
 	}
 
-	client := newEppoClient(newConfigurationStore(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
+	client := newEppoClient(newConfigurationStoreWithConfig(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
 	actions := map[string]ContextAttributes{
 		"action1": {},
 	}
@@ -278,7 +279,7 @@ func Test_client_correctActionIsReturnedIfBanditLoggerPanics(t *testing.T) {
 		},
 	}
 
-	client := newEppoClient(newConfigurationStore(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
+	client := newEppoClient(newConfigurationStoreWithConfig(configuration{flags: flags, bandits: bandits}), nil, nil, logger, applicationLogger)
 	actions := map[string]ContextAttributes{
 		"action1": {},
 	}
@@ -290,3 +291,39 @@ func Test_client_correctActionIsReturnedIfBanditLoggerPanics(t *testing.T) {
 		Action:    &expectedAction,
 	}, result)
 }
+
+func Test_Initialized_timeout(t *testing.T) {
+	var mockLogger = new(mockLogger)
+	client := newEppoClient(newConfigurationStore(), nil, nil, mockLogger, applicationLogger)
+
+	timedOut := false
+	select {
+	case <-client.Initialized():
+		timedOut = false
+	case <-time.After(1 * time.Millisecond):
+		timedOut = true
+	}
+
+	assert.True(t, timedOut)
+}
+
+func Test_Initialized_success(t *testing.T) {
+	var mockLogger = new(mockLogger)
+	configurationStore := newConfigurationStore()
+	client := newEppoClient(configurationStore, nil, nil, mockLogger, applicationLogger)
+
+	go func() {
+		<-time.After(1 * time.Microsecond)
+		configurationStore.setConfiguration(configuration{})
+	}()
+
+	timedOut := false
+	select {
+	case <-client.Initialized():
+		timedOut = false
+	case <-time.After(1 * time.Millisecond):
+		timedOut = true
+	}
+
+	assert.False(t, timedOut)
+}

eppoclient/configuration.go

@@ -0,0 +1,57 @@
+package eppoclient
+
+type configuration struct {
+	flags   configResponse
+	bandits banditResponse
+	// flag key -> variation value -> banditVariation.
+	//
+	// This is cached from `flags` field for easier access in
+	// evaluation.
+	banditFlagAssociations map[string]map[string]banditVariation
+}
+
+func (c *configuration) precompute() {
+	associations := make(map[string]map[string]banditVariation)
+
+	c.flags.precompute()
+
+	for _, banditVariations := range c.flags.Bandits {
+		for _, bandit := range banditVariations {
+			byVariation, ok := associations[bandit.FlagKey]
+			if !ok {
+				byVariation = make(map[string]banditVariation)
+				associations[bandit.FlagKey] = byVariation
+			}
+			byVariation[bandit.VariationValue] = bandit
+		}
+	}
+
+	c.banditFlagAssociations = associations
+}
+
+func (c configuration) getBanditVariant(flagKey, variation string) (result banditVariation, ok bool) {
+	byVariation, ok := c.banditFlagAssociations[flagKey]
+	if !ok {
+		return result, false
+	}
+	result, ok = byVariation[variation]
+	return result, ok
+}
+
+func (c configuration) getFlagConfiguration(key string) (*flagConfiguration, error) {
+	flag, ok := c.flags.Flags[key]
+	if !ok {
+		return nil, ErrFlagConfigurationNotFound
+	}
+
+	return flag, nil
+}
+
+func (c configuration) getBanditConfiguration(key string) (banditConfiguration, error) {
+	bandit, ok := c.bandits.Bandits[key]
+	if !ok {
+		return bandit, ErrBanditConfigurationNotFound
+	}
+
+	return bandit, nil
+}

eppoclient/configurationrequestor_test.go

@@ -17,7 +17,7 @@ func Test_configurationRequestor_requestBandits(t *testing.T) {
 
 	sdkParams := SDKParams{sdkKey: "blah", sdkName: "go", sdkVersion: __version__}
 	httpClient := newHttpClient(server.URL, &http.Client{Timeout: REQUEST_TIMEOUT_SECONDS}, sdkParams)
-	configurationStore := newConfigurationStore(configuration{})
+	configurationStore := newConfigurationStore()
 	configurationRequestor := newConfigurationRequestor(*httpClient, configurationStore, applicationLogger)
 
 	configurationRequestor.FetchAndStoreConfigurations()
@@ -36,7 +36,7 @@ func Test_configurationRequestor_shouldNotRequestBanditsIfNotPresentInFlags(t *t
 
 	sdkParams := SDKParams{sdkKey: "blah", sdkName: "go", sdkVersion: __version__}
 	httpClient := newHttpClient(server.URL, &http.Client{Timeout: REQUEST_TIMEOUT_SECONDS}, sdkParams)
-	configurationStore := newConfigurationStore(configuration{})
+	configurationStore := newConfigurationStore()
 	configurationRequestor := newConfigurationRequestor(*httpClient, configurationStore, applicationLogger)
 
 	configurationRequestor.FetchAndStoreConfigurations()

eppoclient/configurationstore.go

@@ -4,82 +4,59 @@ import (
 	"sync/atomic"
 )
 
-type configuration struct {
-	flags   configResponse
-	bandits banditResponse
-	// flag key -> variation value -> banditVariation.
-	//
-	// This is cached from `flags` field for easier access in
-	// evaluation.
-	banditFlagAssociations map[string]map[string]banditVariation
-}
-
-func (c *configuration) precompute() {
-	associations := make(map[string]map[string]banditVariation)
-
-	c.flags.precompute()
-
-	for _, banditVariations := range c.flags.Bandits {
-		for _, bandit := range banditVariations {
-			byVariation, ok := associations[bandit.FlagKey]
-			if !ok {
-				byVariation = make(map[string]banditVariation)
-				associations[bandit.FlagKey] = byVariation
-			}
-			byVariation[bandit.VariationValue] = bandit
-		}
-	}
-
-	c.banditFlagAssociations = associations
-}
-
-func (c configuration) getBanditVariant(flagKey, variation string) (result banditVariation, ok bool) {
-	byVariation, ok := c.banditFlagAssociations[flagKey]
-	if !ok {
-		return result, false
-	}
-	result, ok = byVariation[variation]
-	return result, ok
-}
-
-func (c configuration) getFlagConfiguration(key string) (*flagConfiguration, error) {
-	flag, ok := c.flags.Flags[key]
-	if !ok {
-		return nil, ErrFlagConfigurationNotFound
-	}
-
-	return flag, nil
-}
-
-func (c configuration) getBanditConfiguration(key string) (banditConfiguration, error) {
-	bandit, ok := c.bandits.Bandits[key]
-	if !ok {
-		return bandit, ErrBanditConfigurationNotFound
-	}
-
-	return bandit, nil
-}
-
 // `configurationStore` is a thread-safe in-memory storage. It stores
 // the currently active configuration and provides access to multiple
 // readers (e.g., flag/bandit evaluation) and writers (e.g.,
 // configuration requestor).
 type configurationStore struct {
 	configuration atomic.Pointer[configuration]
+
+	// `initializedCh` is closed when we receive a proper
+	// configuration.
+	initializedCh chan struct{}
+	// `isInitialized` is used to protect `initializedCh`, so we
+	// don’t double-close it (which is an error in Go).
+	isInitialized atomic.Bool
+}
+
+func newConfigurationStore() *configurationStore {
+	return &configurationStore{
+		initializedCh: make(chan struct{}),
+	}
 }
 
-func newConfigurationStore(configuration configuration) *configurationStore {
-	store := &configurationStore{}
+func newConfigurationStoreWithConfig(configuration configuration) *configurationStore {
+	store := newConfigurationStore()
 	store.setConfiguration(configuration)
 	return store
 }
 
 // Returns a snapshot of the currently active configuration.
 func (cs *configurationStore) getConfiguration() configuration {
-	return *cs.configuration.Load()
+	if config := cs.configuration.Load(); config != nil {
+		return *config
+	} else {
+		return configuration{}
+	}
 }
 
 func (cs *configurationStore) setConfiguration(configuration configuration) {
 	configuration.precompute()
 	cs.configuration.Store(&configuration)
+	cs.setInitialized()
+}
+
+// Set `initialized` flag to `true` notifying anyone waiting on it.
+func (cs *configurationStore) setInitialized() {
+	if cs.isInitialized.CompareAndSwap(false, true) {
+		// Channels can only be closed once, so we protect the
+		// call to `close` with a CAS.
+		close(cs.initializedCh)
+	}
+}
+
+// Returns a channel that gets closed after configuration store is
+// successfully initialized.
+func (cs *configurationStore) Initialized() <-chan struct{} {
+	return cs.initializedCh
 }

eppoclient/configurationstore_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 func Test_GetConfiguration_unknownKey(t *testing.T) {
-	var store = newConfigurationStore(configuration{})
+	store := newConfigurationStore()
 
 	config := store.getConfiguration()
 	result, err := config.getFlagConfiguration("unknown_exp")
@@ -26,7 +26,7 @@ func Test_GetConfiguration_knownKey(t *testing.T) {
 			},
 		},
 	}
-	var store = newConfigurationStore(configuration{flags: flags})
+	store := newConfigurationStoreWithConfig(configuration{flags: flags})
 
 	config := store.getConfiguration()
 	result, err := config.getFlagConfiguration("experiment-key-1")

eppoclient/initclient.go

@@ -15,7 +15,7 @@ func InitClient(config Config) (*EppoClient, error) {
 	applicationLogger := config.ApplicationLogger
 
 	httpClient := newHttpClient(config.BaseUrl, &http.Client{Timeout: REQUEST_TIMEOUT_SECONDS}, sdkParams)
-	configStore := newConfigurationStore(configuration{})
+	configStore := newConfigurationStore()
 	requestor := newConfigurationRequestor(*httpClient, configStore, applicationLogger)
 
 	assignmentLogger := config.AssignmentLogger

eppoclient/version.go

@@ -1,3 +1,3 @@
 package eppoclient
 
-var __version__ = "6.0.0"
+var __version__ = "6.1.0"