chore: flagd add offline flag source path support through env variables (#647)

Signed-off-by: Kavindu Dodanduwa <[email protected]>
Co-authored-by: Michael Beemer <[email protected]>

Author: Kavindu-Dodan

Diff for: providers/flagd/README.md

@@ -47,6 +47,8 @@ FlagdProvider flagdProvider = new FlagdProvider(
 
 In the above example, in-process handlers attempt to connect to a sync service on address `localhost:8013` to obtain [flag definitions](https://github.com/open-feature/schemas/blob/main/json/flagd-definitions.json).
 
+#### Offline mode
+
 In-process resolvers can also work in an offline mode.
 To enable this mode, you should provide a valid flag configuration file with the option `offlineFlagSourcePath`.
 
@@ -58,9 +60,13 @@ FlagdProvider flagdProvider = new FlagdProvider(
                 .build());
 ```
 
-Provider will not detect file changes nor re-read the file after the initial read.
-This mode is useful for local development, test cases, and offline applications.
-For a full-featured, production-ready file-based implementation, use the RPC evaluator in combination with the flagd standalone application, which can be configured to watch files for changes.
+Provider will attempt to detect file changes using polling. 
+Polling happens at 5 second intervals and this is currently unconfigurable.
+This mode is useful for local development, tests and offline applications.
+
+> [!IMPORTANT]
+> Note that you can only use a single flag source (either gRPC or offline file) for the in-process resolver.
+> If both sources are configured, offline mode will be selected.
 
 ### Configuration options
 
@@ -73,17 +79,18 @@ Given below are the supported configurations:
 
 | Option name           | Environment variable name      | Type & Values          | Default   | Compatible resolver |
 |-----------------------|--------------------------------|------------------------|-----------|---------------------|
-| host                  | FLAGD_HOST                     | String                 | localhost | RPC & in-process    |
-| port                  | FLAGD_PORT                     | int                    | 8013      | RPC & in-process    |
-| tls                   | FLAGD_TLS                      | boolean                | false     | RPC & in-process    |
-| socketPath            | FLAGD_SOCKET_PATH              | String                 | null      | RPC & in-process    |
-| certPath              | FLAGD_SERVER_CERT_PATH         | String                 | null      | RPC & in-process    |
-| deadline              | FLAGD_DEADLINE_MS              | int                    | 500       | RPC & in-process    |
+| host                  | FLAGD_HOST                     | String                 | localhost | rpc & in-process    |
+| port                  | FLAGD_PORT                     | int                    | 8013      | rpc & in-process    |
+| tls                   | FLAGD_TLS                      | boolean                | false     | rpc & in-process    |
+| socketPath            | FLAGD_SOCKET_PATH              | String                 | null      | rpc & in-process    |
+| certPath              | FLAGD_SERVER_CERT_PATH         | String                 | null      | rpc & in-process    |
+| deadline              | FLAGD_DEADLINE_MS              | int                    | 500       | rpc & in-process    |
 | selector              | FLAGD_SOURCE_SELECTOR          | String                 | null      | in-process          |
-| cache                 | FLAGD_CACHE                    | String - lru, disabled | lru       | RPC                 |
-| maxCacheSize          | FLAGD_MAX_CACHE_SIZE           | int                    | 1000      | RPC                 |
-| maxEventStreamRetries | FLAGD_MAX_EVENT_STREAM_RETRIES | int                    | 5         | RPC                 |
-| retryBackoffMs        | FLAGD_RETRY_BACKOFF_MS         | int                    | 1000      | RPC                 |
+| cache                 | FLAGD_CACHE                    | String - lru, disabled | lru       | rpc                 |
+| maxCacheSize          | FLAGD_MAX_CACHE_SIZE           | int                    | 1000      | rpc                 |
+| maxEventStreamRetries | FLAGD_MAX_EVENT_STREAM_RETRIES | int                    | 5         | rpc                 |
+| retryBackoffMs        | FLAGD_RETRY_BACKOFF_MS         | int                    | 1000      | rpc                 |
+| offlineFlagSourcePath | FLAGD_OFFLINE_FLAG_SOURCE_PATH | String                 | null      | in-process          |
 
 > [!NOTE]  
 > Some configurations are only applicable for RPC resolver.

Diff for: providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/Config.java

@@ -25,6 +25,7 @@ public final class Config {
     static final String BASE_EVENT_STREAM_RETRY_BACKOFF_MS_ENV_VAR_NAME = "FLAGD_RETRY_BACKOFF_MS";
     static final String DEADLINE_MS_ENV_VAR_NAME = "FLAGD_DEADLINE_MS";
     static final String SOURCE_SELECTOR_ENV_VAR_NAME = "FLAGD_SOURCE_SELECTOR";
+    static final String OFFLINE_SOURCE_PATH = "FLAGD_OFFLINE_FLAG_SOURCE_PATH";
 
     public static final String STATIC_REASON = "STATIC";
     public static final String CACHED_REASON = "CACHED";

Diff for: providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/FlagdOptions.java

@@ -5,8 +5,6 @@
 import lombok.Builder;
 import lombok.Getter;
 
-import javax.annotation.Nonnull;
-
 import static dev.openfeature.contrib.providers.flagd.Config.BASE_EVENT_STREAM_RETRY_BACKOFF_MS;
 import static dev.openfeature.contrib.providers.flagd.Config.BASE_EVENT_STREAM_RETRY_BACKOFF_MS_ENV_VAR_NAME;
 import static dev.openfeature.contrib.providers.flagd.Config.CACHE_ENV_VAR_NAME;
@@ -22,6 +20,7 @@
 import static dev.openfeature.contrib.providers.flagd.Config.HOST_ENV_VAR_NAME;
 import static dev.openfeature.contrib.providers.flagd.Config.MAX_CACHE_SIZE_ENV_VAR_NAME;
 import static dev.openfeature.contrib.providers.flagd.Config.MAX_EVENT_STREAM_RETRIES_ENV_VAR_NAME;
+import static dev.openfeature.contrib.providers.flagd.Config.OFFLINE_SOURCE_PATH;
 import static dev.openfeature.contrib.providers.flagd.Config.PORT_ENV_VAR_NAME;
 import static dev.openfeature.contrib.providers.flagd.Config.SERVER_CERT_PATH_ENV_VAR_NAME;
 import static dev.openfeature.contrib.providers.flagd.Config.SOCKET_PATH_ENV_VAR_NAME;
@@ -118,12 +117,8 @@ public class FlagdOptions {
      * File source of flags to be used by offline mode.
      * Setting this enables the offline mode of the in-process provider.
      */
-    private String offlineFlagSourcePath;
-
-    /**
-     * Flagd option to state the offline mode. Only get set with offlineFlagSourcePath.
-     */
-    private boolean isOffline;
+    @Builder.Default
+    private String offlineFlagSourcePath = fallBackToEnvOrDefault(OFFLINE_SOURCE_PATH, null);
 
     /**
      * Inject OpenTelemetry for the library runtime. Providing sdk will initiate distributed tracing for flagd grpc
@@ -135,31 +130,14 @@ public class FlagdOptions {
      * Overload default lombok builder.
      */
     public static class FlagdOptionsBuilder {
-
-        /**
-         * File source of flags to be used by offline mode.
-         * Setting this enables the offline mode of the in-process provider.
-         */
-        public FlagdOptionsBuilder offlineFlagSourcePath(@Nonnull final String offlineFlagSourcePath) {
-            this.isOffline = true;
-            this.offlineFlagSourcePath = offlineFlagSourcePath;
-
-            return this;
-        }
-
-        // Remove the public access as this needs to be connected to offlineFlagSourcePath
-        @SuppressWarnings({"PMD.UnusedFormalParameter", "PMD.UnusedPrivateMethod"})
-        private FlagdOptionsBuilder isOffline(final boolean isOffline) {
-            return this;
-        }
-
         /**
          * Enable OpenTelemetry instance extraction from GlobalOpenTelemetry. Note that, this is only useful if global
          * configurations are registered.
          */
         public FlagdOptionsBuilder withGlobalTelemetry(final boolean b) {
-            this.openTelemetry = GlobalOpenTelemetry.get();
-
+            if (b) {
+                this.openTelemetry = GlobalOpenTelemetry.get();
+            }
             return this;
         }
     }

Diff for: providers/flagd/src/main/java/dev/openfeature/contrib/providers/flagd/resolver/process/InProcessResolver.java

@@ -46,11 +46,7 @@ public class InProcessResolver implements Resolver {
      * Initialize an in-process resolver.
      */
     public InProcessResolver(FlagdOptions options, Consumer<ProviderState> stateConsumer) {
-        final Connector connector = options.isOffline()
-                ? new FileConnector(options.getOfflineFlagSourcePath())
-                : new GrpcStreamConnector(options);
-
-        this.flagStore = new FlagStore(connector);
+        this.flagStore = new FlagStore(getConnector(options));
         this.deadline = options.getDeadline();
         this.stateConsumer = stateConsumer;
         this.operator = new Operator();
@@ -153,6 +149,12 @@ public ProviderEvaluation<Value> objectEvaluation(String key, Value defaultValue
                 .build();
     }
 
+    static Connector getConnector(final FlagdOptions options) {
+        return options.getOfflineFlagSourcePath() != null && !options.getOfflineFlagSourcePath().isEmpty()
+                ? new FileConnector(options.getOfflineFlagSourcePath())
+                : new GrpcStreamConnector(options);
+    }
+
     private <T> ProviderEvaluation<T> resolve(Class<T> type, String key,
             EvaluationContext ctx) {
         final FeatureFlag flag = flagStore.getFlag(key);

Diff for: providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/FeatureFlagProviderBuilderTest.java renamed to providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/FlagdOptionsTest.java

@@ -14,7 +14,7 @@
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-public class FeatureFlagProviderBuilderTest {
+public class FlagdOptionsTest {
 
     @Test
     public void TestDefaults() {
@@ -31,7 +31,6 @@ public void TestDefaults() {
         assertNull(builder.getSelector());
         assertNull(builder.getOpenTelemetry());
         assertNull(builder.getOfflineFlagSourcePath());
-        assertFalse(builder.isOffline());
     }
 
     @Test
@@ -59,7 +58,6 @@ public void TestBuilderOptions() {
         assertEquals(flagdOptions.getMaxCacheSize(), 100);
         assertEquals(flagdOptions.getMaxEventStreamRetries(), 1);
         assertEquals(flagdOptions.getSelector(), "app=weatherApp");
-        assertTrue(flagdOptions.isOffline());
         assertEquals("some-path", flagdOptions.getOfflineFlagSourcePath());
         assertEquals(flagdOptions.getOpenTelemetry(), openTelemetry);
     }

Diff for: providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/e2e/reconnect/steps/StepDefinitions.java

@@ -45,7 +45,7 @@ public class StepDefinitions {
      * Tests run one at a time, but just in case, a lock is used to make sure the
      * client is not updated mid-test.
      * 
-     * @param client client to inject into test.
+     * @param provider client to inject into test.
      */
     public static void setProvider(FeatureProvider provider) {
         StepDefinitions.provider = provider;

Diff for: providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/resolver/process/InProcessResolverTest.java

@@ -1,8 +1,11 @@
 package dev.openfeature.contrib.providers.flagd.resolver.process;
 
+import dev.openfeature.contrib.providers.flagd.Config;
 import dev.openfeature.contrib.providers.flagd.FlagdOptions;
 import dev.openfeature.contrib.providers.flagd.resolver.process.model.FeatureFlag;
 import dev.openfeature.contrib.providers.flagd.resolver.process.storage.StorageState;
+import dev.openfeature.contrib.providers.flagd.resolver.process.storage.connector.file.FileConnector;
+import dev.openfeature.contrib.providers.flagd.resolver.process.storage.connector.grpc.GrpcStreamConnector;
 import dev.openfeature.sdk.ImmutableContext;
 import dev.openfeature.sdk.ImmutableMetadata;
 import dev.openfeature.sdk.MutableContext;
@@ -35,12 +38,26 @@
 import static dev.openfeature.contrib.providers.flagd.resolver.process.MockFlags.OBJECT_FLAG;
 import static dev.openfeature.contrib.providers.flagd.resolver.process.MockFlags.VARIANT_MISMATCH_FLAG;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTimeoutPreemptively;
 
 class InProcessResolverTest {
 
+    @Test
+    public void connectorSetup(){
+        // given
+        FlagdOptions forGrpcOptions =
+                 FlagdOptions.builder().resolverType(Config.Evaluator.IN_PROCESS).host("localhost").port(8080).build();
+        FlagdOptions forOfflineOptions =
+                FlagdOptions.builder().resolverType(Config.Evaluator.IN_PROCESS).offlineFlagSourcePath("path").build();
+
+        // then
+        assertInstanceOf(GrpcStreamConnector.class, InProcessResolver.getConnector(forGrpcOptions));
+        assertInstanceOf(FileConnector.class, InProcessResolver.getConnector(forOfflineOptions));
+    }
+
     @Test
     public void eventHandling() throws Throwable {
         // given