feat: prevent fetch on init (#56)

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.8.0
+
+* Feat: experimental support for skip fetch toggles on start
+
 ## 1.7.0
 
 * Feat: manual control over updateToggles and sendMetrics

README.md

@@ -116,23 +116,24 @@ unleash.setContextFields({'userId': '4141'});
 
 The Unleash SDK takes the following options:
 
-| option            | required | default                   | description                                                                                                                                      |
-|-------------------|----------|---------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|
-| url               | yes | n/a                       | The Unleash Proxy URL to connect to. E.g.: `https://examples.com/proxy`                                                                         |
-| clientKey         | yes | n/a                       | The Unleash Proxy Secret to be used                                                                                                             | 
-| appName           | yes | n/a                       | The name of the application using this SDK. Will be used as part of the metrics sent to Unleash Proxy. Will also be part of the Unleash Context. | 
-| refreshInterval   | no | 30                        | How often, in seconds, the SDK should check for updated toggle configuration. If set to 0 will disable checking for updates                 |
-| disableRefresh    | no | false                     | If set to true, the client will not check for updated toggle configuration                                                                |
-| metricsInterval   | no | 30                        | How often, in seconds, the SDK should send usage metrics back to Unleash Proxy                                                              | 
-| disableMetrics    | no | false                     | Set this option to `true` if you want to disable usage metrics
+| option            | required | default                            | description                                                                                                                                      |
+|-------------------|----------|------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|
+| url               | yes | n/a                                | The Unleash Proxy URL to connect to. E.g.: `https://examples.com/proxy`                                                                         |
+| clientKey         | yes | n/a                                | The Unleash Proxy Secret to be used                                                                                                             | 
+| appName           | yes | n/a                                | The name of the application using this SDK. Will be used as part of the metrics sent to Unleash Proxy. Will also be part of the Unleash Context. | 
+| refreshInterval   | no | 30                                 | How often, in seconds, the SDK should check for updated toggle configuration. If set to 0 will disable checking for updates                 |
+| disableRefresh    | no | false                              | If set to true, the client will not check for updated toggle configuration                                                                |
+| metricsInterval   | no | 30                                 | How often, in seconds, the SDK should send usage metrics back to Unleash Proxy                                                              | 
+| disableMetrics    | no | false                              | Set this option to `true` if you want to disable usage metrics
 | storageProvider   | no | `SharedPreferencesStorageProvider` | Allows you to inject a custom storeProvider                                                                              |
-| bootstrap         | no | `[]`                      | Allows you to bootstrap the cached feature toggle configuration.                                                                               | 
-| bootstrapOverride | no| `true`                    | Should the bootstrap automatically override cached data in the local-storage. Will only be used if bootstrap is not an empty array.     |
-| headerName        | no| `Authorization`           | Provides possiblity to specify custom header that is passed to Unleash / Unleash Proxy with the `clientKey` |
-| customHeaders     | no| `{}`                      | Additional headers to use when making HTTP requests to the Unleash proxy. In case of name collisions with the default headers, the `customHeaders` value will be used. |
-| impressionDataAll | no| `false` | Allows you to trigger "impression" events for **all** `getToggle` and `getVariant` invocations. This is particularly useful for "disabled" feature toggles that are not visible to frontend SDKs. |
+| bootstrap         | no | `null`                             | Allows you to bootstrap the cached feature toggle configuration.                                                                               | 
+| bootstrapOverride | no| `true`                             | Should the bootstrap automatically override cached data in the local-storage. Will only be used if bootstrap is not an empty array.     |
+| headerName        | no| `Authorization`                    | Provides possiblity to specify custom header that is passed to Unleash / Unleash Proxy with the `clientKey` |
+| customHeaders     | no| `{}`                               | Additional headers to use when making HTTP requests to the Unleash proxy. In case of name collisions with the default headers, the `customHeaders` value will be used. |
+| impressionDataAll | no| `false`                            | Allows you to trigger "impression" events for **all** `getToggle` and `getVariant` invocations. This is particularly useful for "disabled" feature toggles that are not visible to frontend SDKs. |
 | fetcher           | no | `http.get`                         | Allows you to define your own **fetcher**. Can be used to add certificate pinning or additional http behavior. |
 | poster            | no | `http.post`                        | Allows you to define your own **poster**. Can be used to add certificate pinning or additional http behavior.  |
+| experimental      | no | `null`                             | Enabling optional experimentation. `togglesStorageTTL` : How long (Time To Live), in seconds, the toggles in storage are considered valid and should not be fetched on start. If set to 0 will disable expiration checking and will be considered always expired.
 ### Listen for updates via the events_emitter
 
 The client is also an event emitter. This means that your code can subscribe to updates from the client.
@@ -174,7 +175,7 @@ This is also useful if you require the toggles to be in a certain state immediat
 
 ### How to use it ?
 Add a `bootstrap` attribute when create a new `UnleashClient`.  
-There's also a `bootstrapOverride` attribute which is by default is `true`.
+There's also a `bootstrapOverride` attribute which by default is `true`.
 
 ```dart
 final unleash = UnleashClient(
@@ -199,6 +200,20 @@ final unleash = UnleashClient(
 You can opt out of the Unleash feature flag auto-refresh mechanism and metrics update by settings the `refreshInterval` and/or `metricsInterval` options to `0`.
 In this case, it becomes your responsibility to call `updateToggles` and/or `sendMetrics` methods.
 
+## Experimental: skip fetching toggles on start
+
+If you start multiple clients sharing the same storage provider (e.g. a default `SharedPreferencesStorageProvider`) you might want to skip fetching toggles on start for all but one of the clients. 
+This can be achieved by setting the `togglesStorageTTL` to a non-zero value. 
+E.g in the example below, the toggles will be considered valid for 60 seconds and will not be fetched on start if they already exist in storage.
+We recommend to set `togglesStorageTTL` to a value greater than the `refreshInterval`.
+
+```dart
+    final anotherUnleash = UnleashClient(
+        // ...
+        experimental: const ExperimentalConfig(togglesStorageTTL: 60)
+    );
+```
+
 ## Release guide
 * Run tests: `flutter test`
 * Format code: `dart format lib test`

lib/last_update_terms.dart

@@ -0,0 +1,25 @@
+class LastUpdateTerms {
+  String key;
+  int timestamp;
+
+  LastUpdateTerms({required this.key, required this.timestamp});
+
+  @override
+  String toString() {
+    return '{key: $key, timestamp: $timestamp}';
+  }
+
+  Map<String, dynamic> toMap() {
+    return {
+      'key': key,
+      'timestamp': timestamp,
+    };
+  }
+
+  factory LastUpdateTerms.fromJson(Map<String, dynamic> json) {
+    return LastUpdateTerms(
+      key: json['key'],
+      timestamp: json['timestamp'],
+    );
+  }
+}

lib/unleash_context.dart

@@ -1,3 +1,5 @@
+import 'dart:convert';
+
 /// https://docs.getunleash.io/reference/unleash-context
 class UnleashContext {
   String? userId;
@@ -30,6 +32,27 @@ class UnleashContext {
     return params;
   }
 
+  String getKey() {
+    final buffer = StringBuffer();
+
+    if (userId != null) {
+      buffer.write('userId=$userId;');
+    }
+    if (sessionId != null) {
+      buffer.write('sessionId=$sessionId;');
+    }
+    if (remoteAddress != null) {
+      buffer.write('remoteAddress=$remoteAddress;');
+    }
+
+    properties.forEach((key, value) {
+      buffer.write('$key=$value;');
+    });
+
+    final bytes = utf8.encode(buffer.toString());
+    return base64.encode(bytes);
+  }
+
   @override
   bool operator ==(Object other) {
     if (identical(this, other)) return true;

lib/unleash_proxy_client_flutter.dart

@@ -1,5 +1,7 @@
 library unleash_proxy_client_flutter;
 
+import 'dart:convert';
+
 import 'package:http/http.dart' as http;
 import 'dart:async';
 import 'package:events_emitter/events_emitter.dart';
@@ -15,6 +17,7 @@ import 'package:unleash_proxy_client_flutter/metrics.dart';
 
 import 'event_id_generator.dart';
 import 'http_toggle_client.dart';
+import 'last_update_terms.dart';
 
 enum ClientState {
   initializing,
@@ -24,11 +27,18 @@ enum ClientState {
 
 const storageKey = '_unleash_repo';
 const sessionStorageKey = '_unleash_sessionId';
+const lastUpdateKey = '_unleash_repoLastUpdateTimestamp';
 
 String storageWithApp(String appName, String key) {
   return '$appName.$key';
 }
 
+class ExperimentalConfig {
+  final int? togglesStorageTTL;
+
+  const ExperimentalConfig({this.togglesStorageTTL});
+}
+
 /// Main entry point to Flutter Unleash Proxy (https://docs.getunleash.io/reference/unleash-proxy) client
 class UnleashClient extends EventEmitter {
   /// Unleash Proxy URL (https://docs.getunleash.io/reference/unleash-proxy)
@@ -113,6 +123,10 @@ class UnleashClient extends EventEmitter {
   /// Internal indicator if the client has been started
   var started = false;
 
+  ExperimentalConfig? experimental;
+
+  int lastRefreshTimestamp = 0;
+
   UnleashClient(
       {required this.url,
       required this.clientKey,
@@ -132,7 +146,8 @@ class UnleashClient extends EventEmitter {
       this.disableRefresh = false,
       this.headerName = 'Authorization',
       this.customHeaders = const {},
-      this.impressionDataAll = false}) {
+      this.impressionDataAll = false,
+      this.experimental}) {
     _init();
     metrics = Metrics(
         appName: appName,
@@ -147,6 +162,12 @@ class UnleashClient extends EventEmitter {
     if (bootstrap != null) {
       toggles = bootstrap;
     }
+    if (experimental != null) {
+      final ttl = experimental?.togglesStorageTTL;
+      if (ttl != null && ttl > 0) {
+        experimental = ExperimentalConfig(togglesStorageTTL: ttl * 1000);
+      }
+    }
   }
 
   Future<void> _init() async {
@@ -167,6 +188,12 @@ class UnleashClient extends EventEmitter {
       toggles = togglesInStorage;
     }
 
+    if (bootstrap != null) {
+      await _storeLastRefreshTimestamp();
+    } else {
+      lastRefreshTimestamp = await _getLastRefreshTimestamp();
+    }
+
     clientState = ClientState.initialized;
     emit(initializedEvent);
 
@@ -212,8 +239,12 @@ class UnleashClient extends EventEmitter {
         await actualStorageProvider.save(
             storageWithApp(appName, storageKey), response.body);
         toggles = parseToggles(response.body);
+        await _storeLastRefreshTimestamp();
         emit(updateEvent);
       }
+      if (response.statusCode == 304) {
+        await _storeLastRefreshTimestamp();
+      }
       if (response.statusCode > 399) {
         emit(errorEvent, {
           "type": 'HttpError',
@@ -345,6 +376,50 @@ class UnleashClient extends EventEmitter {
     }
   }
 
+  bool _isTogglesStorageTTLEnabled() {
+    return experimental?.togglesStorageTTL != null &&
+        experimental!.togglesStorageTTL! > 0;
+  }
+
+  bool _isUpToDate() {
+    if (!_isTogglesStorageTTLEnabled()) {
+      return false;
+    }
+
+    final now = clock().millisecondsSinceEpoch;
+    final ttl = experimental?.togglesStorageTTL ?? 0;
+
+    return lastRefreshTimestamp > 0 &&
+        (lastRefreshTimestamp <= now) &&
+        (now - lastRefreshTimestamp < ttl);
+  }
+
+  Future<int> _getLastRefreshTimestamp() async {
+    if (_isTogglesStorageTTLEnabled()) {
+      final lastRefresh = await actualStorageProvider
+          .get(storageWithApp(appName, lastUpdateKey));
+      final lastRefreshDecoded = lastRefresh != null
+          ? LastUpdateTerms.fromJson(jsonDecode(lastRefresh))
+          : null;
+      final contextHash = context.getKey();
+      if (lastRefreshDecoded != null && lastRefreshDecoded.key == contextHash) {
+        return lastRefreshDecoded.timestamp;
+      }
+      return 0;
+    }
+    return 0;
+  }
+
+  Future<void> _storeLastRefreshTimestamp() async {
+    if (_isTogglesStorageTTLEnabled()) {
+      lastRefreshTimestamp = clock().millisecondsSinceEpoch;
+      final lastUpdateValue = LastUpdateTerms(
+          key: context.getKey(), timestamp: lastRefreshTimestamp);
+      await actualStorageProvider.save(storageWithApp(appName, lastUpdateKey),
+          jsonEncode(lastUpdateValue.toMap()));
+    }
+  }
+
   Future<void> _waitForEvent(String eventName) async {
     final completer = Completer<void>();
     void listener(dynamic value) async {
@@ -363,7 +438,10 @@ class UnleashClient extends EventEmitter {
     }
 
     metrics.start();
-    await _fetchToggles();
+
+    if (!_isUpToDate()) {
+      await _fetchToggles();
+    }
 
     if (clientState != ClientState.ready) {
       clientState = ClientState.ready;

pubspec.yaml

@@ -3,7 +3,7 @@ description: A Flutter/Dart client that can be used together with the unleash-pr
 homepage: https://github.com/Unleash/unleash_proxy_client_flutter
 repository: https://github.com/Unleash/unleash_proxy_client_flutter
 issue_tracker: https://github.com/Unleash/unleash_proxy_client_flutter
-version: 1.7.0
+version: 1.8.0
 
 environment:
   sdk: ">=2.18.0 <4.0.0"

test/unleash_context_test.dart

@@ -0,0 +1,15 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:unleash_proxy_client_flutter/unleash_context.dart';
+
+void main() {
+  test('returns consistent key for same values', () {
+    final context1 = UnleashContext(
+        userId: 'user1',
+        sessionId: 'session1',
+        remoteAddress: '192.168.1.1',
+        properties: {'key1': 'value1'});
+
+    expect(context1.getKey(),
+        "dXNlcklkPXVzZXIxO3Nlc3Npb25JZD1zZXNzaW9uMTtyZW1vdGVBZGRyZXNzPTE5Mi4xNjguMS4xO2tleTE9dmFsdWUxOw==");
+  });
+}