feat(offline-mode): Add support offline mode using json file (#109)

* feat(offline-mode): Add support for offline mode

.github/workflows/go.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Set up Go 1.x
       uses: actions/setup-go@v5
       with:
-        go-version: '1.18'
+        go-version: '1.19'
       id: go
 
     - name: Check out code into the Go module directory

client.go

@@ -27,10 +27,11 @@ type Client struct {
 	analyticsProcessor *AnalyticsProcessor
 	defaultFlagHandler func(string) (Flag, error)
 
-	client       flaghttp.Client
-	ctxLocalEval context.Context
-	ctxAnalytics context.Context
-	log          Logger
+	client         flaghttp.Client
+	ctxLocalEval   context.Context
+	ctxAnalytics   context.Context
+	log            Logger
+	offlineHandler OfflineHandler
 }
 
 // NewClient creates instance of Client with given configuration.
@@ -53,6 +54,19 @@ func NewClient(apiKey string, options ...Option) *Client {
 	}
 	c.client.SetLogger(c.log)
 
+	if c.config.offlineMode && c.offlineHandler == nil {
+		panic("offline handler must be provided to use offline mode.")
+	}
+	if c.defaultFlagHandler != nil && c.offlineHandler != nil {
+		panic("default flag handler and offline handler cannot be used together.")
+	}
+	if c.config.localEvaluation && c.offlineHandler != nil {
+		panic("local evaluation and offline handler cannot be used together.")
+	}
+	if c.offlineHandler != nil {
+		c.environment.Store(c.offlineHandler.GetEnvironment())
+	}
+
 	if c.config.localEvaluation {
 		if !strings.HasPrefix(apiKey, "ser.") {
 			panic("In order to use local evaluation, please generate a server key in the environment settings page.")
@@ -74,7 +88,7 @@ func NewClient(apiKey string, options ...Option) *Client {
 // directly, but instead read the asynchronously updated local environment or
 // use the default flag handler in case it has not yet been updated.
 func (c *Client) GetEnvironmentFlags(ctx context.Context) (f Flags, err error) {
-	if c.config.localEvaluation {
+	if c.config.localEvaluation || c.config.offlineMode {
 		if f, err = c.getEnvironmentFlagsFromEnvironment(); err == nil {
 			return f, nil
 		}
@@ -83,7 +97,9 @@ func (c *Client) GetEnvironmentFlags(ctx context.Context) (f Flags, err error) {
 			return f, nil
 		}
 	}
-	if c.defaultFlagHandler != nil {
+	if c.offlineHandler != nil {
+		return c.getEnvironmentFlagsFromEnvironment()
+	} else if c.defaultFlagHandler != nil {
 		return Flags{defaultFlagHandler: c.defaultFlagHandler}, nil
 	}
 	return Flags{}, &FlagsmithClientError{msg: fmt.Sprintf("Failed to fetch flags with error: %s", err)}
@@ -100,7 +116,7 @@ func (c *Client) GetEnvironmentFlags(ctx context.Context) (f Flags, err error) {
 // directly, but instead read the asynchronously updated local environment or
 // use the default flag handler in case it has not yet been updated.
 func (c *Client) GetIdentityFlags(ctx context.Context, identifier string, traits []*Trait) (f Flags, err error) {
-	if c.config.localEvaluation {
+	if c.config.localEvaluation || c.config.offlineMode {
 		if f, err = c.getIdentityFlagsFromEnvironment(identifier, traits); err == nil {
 			return f, nil
 		}
@@ -109,7 +125,9 @@ func (c *Client) GetIdentityFlags(ctx context.Context, identifier string, traits
 			return f, nil
 		}
 	}
-	if c.defaultFlagHandler != nil {
+	if c.offlineHandler != nil {
+		return c.getIdentityFlagsFromEnvironment(identifier, traits)
+	} else if c.defaultFlagHandler != nil {
 		return Flags{defaultFlagHandler: c.defaultFlagHandler}, nil
 	}
 	return Flags{}, &FlagsmithClientError{msg: fmt.Sprintf("Failed to fetch flags with error: %s", err)}

client_test.go

@@ -23,6 +23,66 @@ func TestClientErrorsIfLocalEvaluationWithNonServerSideKey(t *testing.T) {
 	})
 }
 
+func TestClientErrorsIfOfflineModeWithoutOfflineHandler(t *testing.T) {
+	// When
+	defer func() {
+		if r := recover(); r != nil {
+			// Then
+			errMsg := fmt.Sprintf("%v", r)
+			expectedErrMsg := "offline handler must be provided to use offline mode."
+			assert.Equal(t, expectedErrMsg, errMsg, "Unexpected error message")
+		}
+	}()
+
+	// Trigger panic
+	_ = flagsmith.NewClient("key", flagsmith.WithOfflineMode())
+}
+
+func TestClientErrorsIfDefaultHandlerAndOfflineHandlerAreBothSet(t *testing.T) {
+	// Given
+	envJsonPath := "./fixtures/environment.json"
+	offlineHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+	assert.NoError(t, err)
+
+	// When
+	defer func() {
+		if r := recover(); r != nil {
+			// Then
+			errMsg := fmt.Sprintf("%v", r)
+			expectedErrMsg := "default flag handler and offline handler cannot be used together."
+			assert.Equal(t, expectedErrMsg, errMsg, "Unexpected error message")
+		}
+	}()
+
+	// Trigger panic
+	_ = flagsmith.NewClient("key",
+		flagsmith.WithOfflineHandler(offlineHandler),
+		flagsmith.WithDefaultHandler(func(featureName string) (flagsmith.Flag, error) {
+			return flagsmith.Flag{IsDefault: true}, nil
+		}))
+}
+func TestClientErrorsIfLocalEvaluationModeAndOfflineHandlerAreBothSet(t *testing.T) {
+	// Given
+	envJsonPath := "./fixtures/environment.json"
+	offlineHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+	assert.NoError(t, err)
+
+	// When
+	defer func() {
+		if r := recover(); r != nil {
+			// Then
+			errMsg := fmt.Sprintf("%v", r)
+			expectedErrMsg := "local evaluation and offline handler cannot be used together."
+			assert.Equal(t, expectedErrMsg, errMsg, "Unexpected error message")
+		}
+	}()
+
+	// Trigger panic
+	_ = flagsmith.NewClient("key",
+		flagsmith.WithOfflineHandler(offlineHandler),
+		flagsmith.WithLocalEvaluation(context.Background()))
+}
+
 func TestClientUpdatesEnvironmentOnStartForLocalEvaluation(t *testing.T) {
 	// Given
 	ctx := context.Background()
@@ -498,3 +558,80 @@ func TestWithProxyClientOption(t *testing.T) {
 	assert.Equal(t, fixtures.Feature1ID, allFlags[0].FeatureID)
 	assert.Equal(t, fixtures.Feature1Value, allFlags[0].Value)
 }
+
+func TestOfflineMode(t *testing.T) {
+	// Given
+	ctx := context.Background()
+
+	envJsonPath := "./fixtures/environment.json"
+	offlineHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+	assert.NoError(t, err)
+
+	client := flagsmith.NewClient(fixtures.EnvironmentAPIKey, flagsmith.WithOfflineMode(), flagsmith.WithOfflineHandler(offlineHandler))
+
+	// Then
+	flags, err := client.GetEnvironmentFlags(ctx)
+	assert.NoError(t, err)
+
+	allFlags := flags.AllFlags()
+
+	assert.Equal(t, 1, len(allFlags))
+
+	assert.Equal(t, fixtures.Feature1Name, allFlags[0].FeatureName)
+	assert.Equal(t, fixtures.Feature1ID, allFlags[0].FeatureID)
+	assert.Equal(t, fixtures.Feature1Value, allFlags[0].Value)
+
+	// And GetIdentityFlags works as well
+	flags, err = client.GetIdentityFlags(ctx, "test_identity", nil)
+	assert.NoError(t, err)
+
+	allFlags = flags.AllFlags()
+
+	assert.Equal(t, 1, len(allFlags))
+
+	assert.Equal(t, fixtures.Feature1Name, allFlags[0].FeatureName)
+	assert.Equal(t, fixtures.Feature1ID, allFlags[0].FeatureID)
+	assert.Equal(t, fixtures.Feature1Value, allFlags[0].Value)
+}
+
+func TestOfflineHandlerIsUsedWhenRequestFails(t *testing.T) {
+	// Given
+	ctx := context.Background()
+
+	envJsonPath := "./fixtures/environment.json"
+	offlineHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+	assert.NoError(t, err)
+
+	server := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	// When
+	client := flagsmith.NewClient(fixtures.EnvironmentAPIKey, flagsmith.WithOfflineHandler(offlineHandler),
+		flagsmith.WithBaseURL(server.URL+"/api/v1/"))
+
+	// Then
+	flags, err := client.GetEnvironmentFlags(ctx)
+	assert.NoError(t, err)
+
+	allFlags := flags.AllFlags()
+
+	assert.Equal(t, 1, len(allFlags))
+
+	assert.Equal(t, fixtures.Feature1Name, allFlags[0].FeatureName)
+	assert.Equal(t, fixtures.Feature1ID, allFlags[0].FeatureID)
+	assert.Equal(t, fixtures.Feature1Value, allFlags[0].Value)
+
+	// And GetIdentityFlags works as well
+	flags, err = client.GetIdentityFlags(ctx, "test_identity", nil)
+	assert.NoError(t, err)
+
+	allFlags = flags.AllFlags()
+
+	assert.Equal(t, 1, len(allFlags))
+
+	assert.Equal(t, fixtures.Feature1Name, allFlags[0].FeatureName)
+	assert.Equal(t, fixtures.Feature1ID, allFlags[0].FeatureID)
+	assert.Equal(t, fixtures.Feature1Value, allFlags[0].Value)
+}

config.go

@@ -22,6 +22,7 @@ type config struct {
 	localEvaluation    bool
 	envRefreshInterval time.Duration
 	enableAnalytics    bool
+	offlineMode        bool
 }
 
 // defaultConfig returns default configuration.

fixtures/environment.json

@@ -0,0 +1,58 @@
+{
+    "api_key": "B62qaMZNwfiqT76p38ggrQ",
+    "project": {
+        "name": "Test project",
+        "organisation": {
+            "feature_analytics": false,
+            "name": "Test Org",
+            "id": 1,
+            "persist_trait_data": true,
+            "stop_serving_flags": false
+        },
+        "id": 1,
+        "hide_disabled_flags": false,
+        "segments": [
+            {
+                "id": 1,
+                "name": "Test Segment",
+                "feature_states": [],
+                "rules": [
+                    {
+                        "type": "ALL",
+                        "conditions": [],
+                        "rules": [
+                            {
+                                "type": "ALL",
+                                "rules": [],
+                                "conditions": [
+                                    {
+                                        "operator": "EQUAL",
+                                        "property_": "foo",
+                                        "value": "bar"
+                                    }
+                                ]
+                            }
+                        ]
+                    }
+                ]
+            }
+        ]
+    },
+    "segment_overrides": [],
+    "id": 1,
+    "feature_states": [
+        {
+            "multivariate_feature_state_values": [],
+            "feature_state_value": "some_value",
+            "id": 1,
+            "featurestate_uuid": "40eb539d-3713-4720-bbd4-829dbef10d51",
+            "feature": {
+                "name": "feature_1",
+                "type": "STANDARD",
+                "id": 1
+            },
+            "segment_id": null,
+            "enabled": true
+        }
+    ]
+}

offline_handler.go

@@ -0,0 +1,40 @@
+package flagsmith
+
+import (
+	"encoding/json"
+	"os"
+
+	"github.com/Flagsmith/flagsmith-go-client/v3/flagengine/environments"
+)
+
+type OfflineHandler interface {
+	GetEnvironment() *environments.EnvironmentModel
+}
+
+type LocalFileHandler struct {
+	environment *environments.EnvironmentModel
+}
+
+// NewLocalFileHandler creates a new LocalFileHandler with the given path.
+func NewLocalFileHandler(environmentDocumentPath string) (*LocalFileHandler, error) {
+	// Read the environment document from the specified path
+	environmentDocument, err := os.ReadFile(environmentDocumentPath)
+	if err != nil {
+		return nil, err
+	}
+	var environment environments.EnvironmentModel
+	if err := json.Unmarshal(environmentDocument, &environment); err != nil {
+		return nil, err
+	}
+
+	// Create and initialize the LocalFileHandler
+	handler := &LocalFileHandler{
+		environment: &environment,
+	}
+
+	return handler, nil
+}
+
+func (handler *LocalFileHandler) GetEnvironment() *environments.EnvironmentModel {
+	return handler.environment
+}

offline_handler_test.go

@@ -0,0 +1,34 @@
+package flagsmith_test
+
+import (
+	"testing"
+
+	flagsmith "github.com/Flagsmith/flagsmith-go-client/v3"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewLocalFileHandler(t *testing.T) {
+	// Given
+	envJsonPath := "./fixtures/environment.json"
+
+	// When
+	offlineHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+
+	// Then
+	assert.NoError(t, err)
+	assert.NotNil(t, offlineHandler)
+}
+
+func TestLocalFileHandlerGetEnvironment(t *testing.T) {
+	// Given
+	envJsonPath := "./fixtures/environment.json"
+	localHandler, err := flagsmith.NewLocalFileHandler(envJsonPath)
+
+	assert.NoError(t, err)
+
+	// When
+	environment := localHandler.GetEnvironment()
+
+	// Then
+	assert.NotNil(t, environment.APIKey)
+}

options.go

@@ -102,3 +102,18 @@ func WithProxy(proxyURL string) Option {
 		c.client.SetProxy(proxyURL)
 	}
 }
+
+// WithOfflineHandler returns an Option function that sets the offline handler.
+func WithOfflineHandler(handler OfflineHandler) Option {
+	return func(c *Client) {
+		c.offlineHandler = handler
+	}
+}
+
+// WithOfflineMode returns an Option function that enables the offline mode.
+// NOTE: before using this option, you should set the offline handler.
+func WithOfflineMode() Option {
+	return func(c *Client) {
+		c.config.offlineMode = true
+	}
+}