chore: Add data system configuration. (#193)

Adds a configuration for the data system, this configuration is not yet
in use.

All methods, that will be eventually exposed, are currently set to
internal.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Introduce an internal data system configuration with builders,
predefined modes, and FDv2 polling/streaming data source builders, plus
comprehensive tests.
> 
> - **Configuration**:
> - Add internal `Configuration.DataSystem` and
`ConfigurationBuilder.DataSystem(...)` wiring.
> - Expose `Components.DataSystem()` (internal) returning
`DataSystemModes`.
> - **Data system (internal)**:
> - New builders and types: `DataSystemBuilder`, `DataSystemModes`,
`DataSystemComponents`, `DataSystemConfiguration` (with `Initializers`,
`Synchronizers`, `FDv1FallbackSynchronizer`, and persistent store with
`ReadOnly/ReadWrite` modes).
> - New FDv2 data source builders: `FDv2StreamingDataSourceBuilder` and
`FDv2PollingDataSourceBuilder` with endpoint overrides and tuning
options.
> - **Tests**:
> - Extend `ConfigurationTest` with cases covering
default/streaming/polling/daemon/persistent-store/custom data system
configurations and list replacement/aggregation behaviors.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
8d48a68. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: kinyoklion

pkgs/sdk/server/src/Components.cs

@@ -483,5 +483,14 @@ public static StreamingDataSourceBuilder StreamingDataSource() =>
         /// </remarks>
         /// <returns>a configuration builder</returns>
         public static WrapperInfoBuilder WrapperInfo() => new WrapperInfoBuilder();
+
+        /// <summary>
+        /// Returns a set of builder options for configuring the SDK data system. When the data system configuration
+        /// is used it overrides <see cref="ConfigurationBuilder.DataSource"/> and
+        /// <see cref="ConfigurationBuilder.DataStore"/> in the configuration.
+        /// </summary>
+        /// <returns>a configuration builder</returns>
+        /// TODO: SDK-1678: Internal until ready for use.
+        internal static DataSystemModes DataSystem() => new DataSystemModes();
     }
 }

pkgs/sdk/server/src/Configuration.cs

@@ -116,6 +116,16 @@ public class Configuration
         /// Contains methods for configuring the SDK's 'plugins' to extend or customize SDK behavior.
         /// </summary>
         public PluginConfigurationBuilder Plugins { get; }
+        
+        /// <summary>
+        /// Contains the data system configuration.
+        /// <para>
+        /// This property is not stable, and not subject to any backwards compatibility guarantees or semantic versioning.
+        /// It is not suitable for production usage. Do not use it. You have been warned.
+        /// </para>
+        /// </summary>
+        /// TODO: SDK-1678: Internal until ready for use.
+        internal DataSystemBuilder DataSystem { get; }
 
         #endregion
 
@@ -195,6 +205,7 @@ internal Configuration(ConfigurationBuilder builder)
             WrapperInfo = builder._wrapperInfo;
             Hooks = builder._hooks;
             Plugins = builder._plugins;
+            DataSystem = builder._dataSystem;
         }
 
         #endregion

pkgs/sdk/server/src/ConfigurationBuilder.cs

@@ -32,8 +32,7 @@ public sealed class ConfigurationBuilder
 
         internal static readonly TimeSpan DefaultStartWaitTime = TimeSpan.FromSeconds(10);
 
-        // Let's try to keep these properties and methods alphabetical so they're easy to find. Note that they
-        // are internal rather than private so that they can be read by the Configuration constructor.
+        // Note that these are internal rather than private so that they can be read by the Configuration constructor.
         internal IComponentConfigurer<BigSegmentsConfiguration> _bigSegments = null;
         internal IComponentConfigurer<IDataSource> _dataSource = null;
         internal IComponentConfigurer<IDataStore> _dataStore = null;
@@ -49,6 +48,7 @@ public sealed class ConfigurationBuilder
         internal TimeSpan _startWaitTime = DefaultStartWaitTime;
         internal ApplicationInfoBuilder _applicationInfo;
         internal WrapperInfoBuilder _wrapperInfo;
+        internal DataSystemBuilder _dataSystem;
 
         #endregion
 
@@ -87,6 +87,7 @@ internal ConfigurationBuilder(Configuration copyFrom)
             _serviceEndpointsBuilder = new ServiceEndpointsBuilder(copyFrom.ServiceEndpoints);
             _startWaitTime = copyFrom.StartWaitTime;
             _applicationInfo = copyFrom.ApplicationInfo;
+            _dataSystem = copyFrom.DataSystem;
         }
 
         #endregion
@@ -339,6 +340,7 @@ public ConfigurationBuilder SdkKey(string sdkKey)
             SetSdkKeyIfValid(sdkKey);
             return this;
         }
+
         /// <summary>
         /// Sets the SDK's service URIs, using a configuration builder obtained from
         /// <see cref="Components.ServiceEndpoints"/>.
@@ -401,6 +403,30 @@ public ConfigurationBuilder WrapperInfo(WrapperInfoBuilder wrapperInfo)
             return this;
         }
 
+        /// <summary>
+        /// Configure the data system.
+        /// <para>
+        /// This class is not stable, and not subject to any backwards compatibility guarantees or semantic versioning.
+        /// It is not suitable for production usage. Do not use it. You have been warned.
+        /// </para>
+        /// </summary>
+        /// <remarks>
+        /// <example>
+        /// <code>
+        /// var config = Configuration.Builder("my-sdk-key")
+        ///   .DataSystem(Components.DataSystem().Default());
+        /// </code>
+        /// </example>
+        /// </remarks>
+        /// <param name="dataSystemBuilder">the data system builder</param>
+        /// <returns>the same builder</returns>
+        /// TODO: SDK-1678: Internal until ready for use.
+        internal ConfigurationBuilder DataSystem(DataSystemBuilder dataSystemBuilder)
+        {
+            _dataSystem = dataSystemBuilder;
+            return this;
+        }
+
         #endregion
     }
 }

pkgs/sdk/server/src/Integrations/DataSystemBuilder.cs

@@ -0,0 +1,112 @@
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using LaunchDarkly.Sdk.Server.Subsystems;
+
+namespace LaunchDarkly.Sdk.Server.Integrations
+{
+    /// <summary>
+    /// Configuration builder for the SDK's data acquisition and storage strategy.
+    /// <para>
+    /// This class is not stable, and not subject to any backwards compatibility guarantees or semantic versioning.
+    /// It is not suitable for production usage. Do not use it. You have been warned.
+    /// </para>
+    /// </summary>
+    internal sealed class DataSystemBuilder
+    {
+        // TODO: SDK-1678: Internal until ready for use.
+
+        private readonly List<IComponentConfigurer<IDataSource>> _initializers =
+            new List<IComponentConfigurer<IDataSource>>();
+
+        private readonly List<IComponentConfigurer<IDataSource>> _synchronizers =
+            new List<IComponentConfigurer<IDataSource>>();
+
+        private IComponentConfigurer<IDataSource> _fdV1FallbackSynchronizer;
+
+        private IComponentConfigurer<IDataStore> _persistentStore;
+
+        private DataSystemConfiguration.DataStoreMode _persistentDataStoreMode;
+        
+        /// <summary>
+        /// Add one or more initializers to the builder.
+        /// To replace initializers, please refer to <see cref="DataSystemBuilder.ReplaceInitializers"/>.
+        /// </summary>
+        /// <param name="initializers">the initializers to add</param>
+        /// <returns>a reference to the builder</returns>
+        public DataSystemBuilder Initializers(params IComponentConfigurer<IDataSource>[] initializers)
+        {
+            _initializers.AddRange(initializers);
+            return this;
+        }
+
+        /// <summary>
+        /// Replaces any existing initializers with the given initializers.
+        /// To add initializers, please refer to <see cref="Initializers"/>.
+        /// </summary>
+        /// <param name="initializers">the initializers to replace the current initializers with</param>
+        /// <returns>a reference to this builder</returns>
+        public DataSystemBuilder ReplaceInitializers(params IComponentConfigurer<IDataSource>[] initializers)
+        {
+            _initializers.Clear();
+            _initializers.AddRange(initializers);
+            return this;
+        }
+
+        /// <summary>
+        /// Add one or more synchronizers to the builder.
+        /// To replace synchronizers, please refer to <see cref="DataSystemBuilder.ReplaceSynchronizers"/>.
+        /// </summary>
+        /// <param name="synchronizers">the synchronizers to add</param>
+        /// <returns>a reference to the builder</returns>
+        public DataSystemBuilder Synchronizers(params IComponentConfigurer<IDataSource>[] synchronizers)
+        {
+            _synchronizers.AddRange(synchronizers);
+            return this;
+        }
+
+        /// <summary>
+        /// Replaces any existing synchronizers with the given synchronizers.
+        /// To add synchronizers, please refer to <see cref="Synchronizers"/>.
+        /// </summary>
+        /// <param name="synchronizers">the synchronizers to replace the current synchronizers with</param>
+        /// <returns>a reference to this builder</returns>
+        public DataSystemBuilder ReplaceSynchronizers(params IComponentConfigurer<IDataSource>[] synchronizers)
+        {
+            _synchronizers.Clear();
+            _synchronizers.AddRange(synchronizers);
+            return this;
+        }
+
+        /// <summary>
+        /// Configured the FDv1 fallback synchronizer.
+        /// <remarks>LaunchDarkly can instruct the SDK to fall back to this synchronizer.</remarks>
+        /// </summary>
+        /// <param name="fdv1FallbackSynchronizer">the FDv1 fallback synchronizer</param>
+        /// <returns>a reference to the builder</returns>
+        public DataSystemBuilder FDv1FallbackSynchronizer(IComponentConfigurer<IDataSource> fdv1FallbackSynchronizer)
+        {
+            _fdV1FallbackSynchronizer = fdv1FallbackSynchronizer;
+            return this;
+        }
+
+        public DataSystemBuilder PersistentStore(IComponentConfigurer<IDataStore> persistentStore,
+            DataSystemConfiguration.DataStoreMode mode)
+        {
+            _persistentStore = persistentStore;
+            _persistentDataStoreMode = mode;
+            return this;
+        }
+
+        internal DataSystemConfiguration Build()
+        {
+            // This function should remain internal.
+
+            return new DataSystemConfiguration(
+                _initializers.ToImmutableList(),
+                _synchronizers.ToImmutableList(),
+                _fdV1FallbackSynchronizer,
+                _persistentStore,
+                _persistentDataStoreMode);
+        }
+    }
+}

pkgs/sdk/server/src/Integrations/DataSystemComponents.cs

@@ -0,0 +1,47 @@
+using System;
+using LaunchDarkly.Sdk.Server.Subsystems;
+
+namespace LaunchDarkly.Sdk.Server.Integrations
+{
+    /// <summary>
+    /// Components for use with the data system.
+    /// <para>
+    /// This class is not stable, and not subject to any backwards compatibility guarantees or semantic versioning.
+    /// It is not suitable for production usage. Do not use it. You have been warned.
+    /// </para>
+    /// </summary>
+    internal static class DataSystemComponents
+    {
+        // TODO: SDK-1678: Internal until ready for use.
+        
+        /// <summary>
+        /// Get a builder for a polling data source.
+        /// </summary>
+        /// <returns>the polling data source builder</returns>
+        public static FDv2PollingDataSourceBuilder Polling()
+        {
+            return new FDv2PollingDataSourceBuilder();
+        }
+
+        /// <summary>
+        /// Get a builder for a streaming data source.
+        /// </summary>
+        /// <returns>the streaming data source builder</returns>
+        public static FDv2StreamingDataSourceBuilder Streaming()
+        {
+            return new FDv2StreamingDataSourceBuilder();
+        }
+
+        /// <summary>
+        /// Get a builder for a FDv1 compatible polling data source.
+        /// <remarks>
+        /// This is intended for use as a fallback.
+        /// </remarks>
+        /// </summary>
+        /// <returns>the FDv1 compatible polling data source.</returns>
+        public static PollingDataSourceBuilder FDv1Polling()
+        {
+            return new PollingDataSourceBuilder();
+        }
+    }
+}