feat: add FDv2 configuration builder

libs/common/include/launchdarkly/config/shared/builders/data_source_builder.hpp

@@ -69,6 +69,22 @@ class StreamingBuilder {
         return *this;
     }
 
+    /**
+     * Overrides the streaming base URL for this specific source. When unset,
+     * the synchronizer uses the top-level ServiceEndpoints streaming URL.
+     * Intended for FDv2 configurations where individual synchronizers may
+     * target different endpoints.
+     *
+     * @param base_url The base URL to use for this source.
+     * @return Reference to this builder.
+     */
+    template <typename T = SDK>
+    std::enable_if_t<is_server_sdk<T>::value, StreamingBuilder&> BaseUrl(
+        std::string base_url) {
+        config_.base_url_override = std::move(base_url);
+        return *this;
+    }
+
     /**
      * Build the streaming config. Used internal to the SDK.
      * @return The built config.
@@ -119,6 +135,22 @@ class PollingBuilder {
         return *this;
     }
 
+    /**
+     * Overrides the polling base URL for this specific source. When unset,
+     * the synchronizer uses the top-level ServiceEndpoints polling URL.
+     * Intended for FDv2 configurations where individual synchronizers may
+     * target different endpoints.
+     *
+     * @param base_url The base URL to use for this source.
+     * @return Reference to this builder.
+     */
+    template <typename T = SDK>
+    std::enable_if_t<is_server_sdk<T>::value, PollingBuilder&> BaseUrl(
+        std::string base_url) {
+        config_.base_url_override = std::move(base_url);
+        return *this;
+    }
+
     /**
      * Build the polling config. Used internal to the SDK.
      * @return The built config.

libs/common/include/launchdarkly/config/shared/built/data_source_config.hpp

@@ -23,13 +23,15 @@ struct StreamingConfig<ServerSDK> {
     std::chrono::milliseconds initial_reconnect_delay;
     std::string streaming_path;
     std::optional<std::string> filter_key;
+    std::optional<std::string> base_url_override;
 };
 
 inline bool operator==(StreamingConfig<ServerSDK> const& lhs,
                        StreamingConfig<ServerSDK> const& rhs) {
     return lhs.initial_reconnect_delay == rhs.initial_reconnect_delay &&
            lhs.streaming_path == rhs.streaming_path &&
-           lhs.filter_key == rhs.filter_key;
+           lhs.filter_key == rhs.filter_key &&
+           lhs.base_url_override == rhs.base_url_override;
 }
 
 template <typename SDK>
@@ -49,6 +51,7 @@ struct PollingConfig<ServerSDK> {
     std::string polling_get_path;
     std::chrono::seconds min_polling_interval;
     std::optional<std::string> filter_key;
+    std::optional<std::string> base_url_override;
 };
 
 template <typename SDK>

libs/server-sdk/include/launchdarkly/server_side/config/builders/data_system/data_system_builder.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <launchdarkly/server_side/config/builders/data_system/background_sync_builder.hpp>
+#include <launchdarkly/server_side/config/builders/data_system/fdv2_builder.hpp>
 #include <launchdarkly/server_side/config/builders/data_system/lazy_load_builder.hpp>
 #include <launchdarkly/server_side/config/built/data_system/data_system_config.hpp>
 
@@ -13,6 +14,7 @@ class DataSystemBuilder {
     DataSystemBuilder();
     using BackgroundSync = BackgroundSyncBuilder;
     using LazyLoad = LazyLoadBuilder;
+    using FDv2 = FDv2Builder;
 
     /**
      * @brief Alias for Enabled(false).
@@ -46,10 +48,19 @@ class DataSystemBuilder {
      */
     DataSystemBuilder& Method(LazyLoad lazy_load);
 
+    /**
+     * @brief Configures the FDv2 data system, which receives flag delivery
+     * updates over the new changeset-based protocol with built-in fallback
+     * and recovery semantics.
+     * @param fdv2 FDv2 configuration.
+     * @return Reference to this.
+     */
+    DataSystemBuilder& Method(FDv2 fdv2);
+
     [[nodiscard]] tl::expected<built::DataSystemConfig, Error> Build() const;
 
    private:
-    std::optional<std::variant<BackgroundSync, LazyLoad>> method_builder_;
+    std::optional<std::variant<BackgroundSync, LazyLoad, FDv2>> method_builder_;
     built::DataSystemConfig config_;
 };
 

libs/server-sdk/include/launchdarkly/server_side/config/builders/data_system/fdv2_builder.hpp

@@ -0,0 +1,105 @@
+#pragma once
+
+#include <launchdarkly/config/shared/builders/data_source_builder.hpp>
+#include <launchdarkly/config/shared/sdks.hpp>
+#include <launchdarkly/server_side/config/built/data_system/fdv2_config.hpp>
+
+#include <chrono>
+
+namespace launchdarkly::server_side::config::builders {
+
+class FDv2Builder {
+   public:
+    using Streaming = launchdarkly::config::shared::builders::StreamingBuilder<
+        launchdarkly::config::shared::ServerSDK>;
+    using Polling = launchdarkly::config::shared::builders::PollingBuilder<
+        launchdarkly::config::shared::ServerSDK>;
+
+    FDv2Builder();
+
+    /**
+     * @brief Appends a polling initializer to the initializers list. The
+     * first call to this method on a default-constructed builder replaces
+     * the spec-default initializer list; subsequent calls append.
+     * @param source Polling source configuration for the initializer.
+     * @return Reference to this.
+     */
+    FDv2Builder& Initializer(Polling source);
+
+    /**
+     * @brief Appends a streaming synchronizer to the synchronizers list.
+     * Order in the list determines preference: the first entry is the
+     * primary synchronizer, subsequent entries are fallbacks. The first
+     * call to a Synchronizer overload on a default-constructed builder
+     * replaces the spec-default synchronizer list; subsequent calls append.
+     * @param source Streaming source configuration.
+     * @return Reference to this.
+     */
+    FDv2Builder& Synchronizer(Streaming source);
+
+    /**
+     * @brief Appends a polling synchronizer to the synchronizers list. See
+     * Synchronizer(Streaming) for ordering and default-replacement
+     * semantics.
+     * @param source Polling source configuration.
+     * @return Reference to this.
+     */
+    FDv2Builder& Synchronizer(Polling source);
+
+    /**
+     * @brief Configures the FDv1 streaming source used as a last-resort
+     * fallback when the LaunchDarkly service signals (via the
+     * X-LD-FD-Fallback header) that the SDK should switch to FDv1.
+     * Enabled by default with standard streaming settings.
+     * @param source Streaming source configuration to use for the FDv1
+     *     fallback connection.
+     * @return Reference to this.
+     */
+    FDv2Builder& FDv1Fallback(Streaming source);
+
+    /**
+     * @brief Configures the FDv1 polling source used as a last-resort
+     * fallback when the LaunchDarkly service signals (via the
+     * X-LD-FD-Fallback header) that the SDK should switch to FDv1.
+     * @param source Polling source configuration to use for the FDv1
+     *     fallback connection.
+     * @return Reference to this.
+     */
+    FDv2Builder& FDv1Fallback(Polling source);
+
+    /**
+     * @brief Disables the FDv1 fallback. After this call, an FDv1
+     * fallback directive from the service transitions the SDK to
+     * OFFLINE rather than reconnecting via FDv1.
+     * @return Reference to this.
+     */
+    FDv2Builder& DisableFDv1Fallback();
+
+    /**
+     * @brief Sets how long the active synchronizer may remain interrupted
+     * before the orchestrator falls back to the next-preferred synchronizer.
+     * @param timeout Duration the synchronizer must be continuously
+     *     interrupted for before fallback fires.
+     * @return Reference to this.
+     */
+    FDv2Builder& FallbackTimeout(std::chrono::milliseconds timeout);
+
+    /**
+     * @brief Sets how long a fallback synchronizer must run successfully
+     * before the orchestrator attempts to recover to the primary
+     * synchronizer.
+     * @param timeout Duration the fallback synchronizer must run before a
+     *     recovery attempt is made.
+     * @return Reference to this.
+     */
+    FDv2Builder& RecoveryTimeout(std::chrono::milliseconds timeout);
+
+    [[nodiscard]] built::FDv2Config Build() const;
+
+   private:
+    built::FDv2Config config_;
+    bool initializers_explicit_;
+    bool synchronizers_explicit_;
+};
+
+}  // namespace launchdarkly::server_side::config::builders

libs/server-sdk/include/launchdarkly/server_side/config/built/data_system/data_system_config.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <launchdarkly/server_side/config/built/data_system/background_sync_config.hpp>
+#include <launchdarkly/server_side/config/built/data_system/fdv2_config.hpp>
 #include <launchdarkly/server_side/config/built/data_system/lazy_load_config.hpp>
 
 #include <variant>
@@ -9,7 +10,7 @@ namespace launchdarkly::server_side::config::built {
 
 struct DataSystemConfig {
     bool disabled;
-    std::variant<LazyLoadConfig, BackgroundSyncConfig> system_;
+    std::variant<LazyLoadConfig, BackgroundSyncConfig, FDv2Config> system_;
 };
 
 }  // namespace launchdarkly::server_side::config::built

libs/server-sdk/include/launchdarkly/server_side/config/built/data_system/fdv2_config.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <launchdarkly/config/shared/built/data_source_config.hpp>
+#include <launchdarkly/config/shared/sdks.hpp>
+
+#include <chrono>
+#include <optional>
+#include <variant>
+#include <vector>
+
+namespace launchdarkly::server_side::config::built {
+
+struct FDv2Config {
+    using StreamingConfig =
+        launchdarkly::config::shared::built::StreamingConfig<
+            launchdarkly::config::shared::ServerSDK>;
+    using PollingConfig = launchdarkly::config::shared::built::PollingConfig<
+        launchdarkly::config::shared::ServerSDK>;
+
+    std::vector<PollingConfig> initializers;
+    std::vector<std::variant<StreamingConfig, PollingConfig>> synchronizers;
+    std::optional<std::variant<StreamingConfig, PollingConfig>> fdv1_fallback;
+    std::chrono::milliseconds fallback_timeout;
+    std::chrono::milliseconds recovery_timeout;
+};
+
+}  // namespace launchdarkly::server_side::config::built

libs/server-sdk/src/CMakeLists.txt

@@ -29,6 +29,7 @@ target_sources(${LIBNAME}
         config/builders/data_system/background_sync_builder.cpp
         config/builders/data_system/bootstrap_builder.cpp
         config/builders/data_system/data_system_builder.cpp
+        config/builders/data_system/fdv2_builder.cpp
         config/builders/data_system/lazy_load_builder.cpp
         config/builders/data_system/data_destination_builder.cpp
         config/builders/big_segments_builder.cpp
@@ -73,6 +74,10 @@ target_sources(${LIBNAME}
         data_systems/fdv2/fdv2_data_system.cpp
         data_systems/fdv2/fdv1_adapter_synchronizer.hpp
         data_systems/fdv2/fdv1_adapter_synchronizer.cpp
+        data_systems/fdv2/synchronizer_factories.hpp
+        data_systems/fdv2/synchronizer_factories.cpp
+        data_systems/fdv2/initializer_factories.hpp
+        data_systems/fdv2/initializer_factories.cpp
         data_systems/background_sync/sources/streaming/streaming_data_source.hpp
         data_systems/background_sync/sources/streaming/streaming_data_source.cpp
         data_systems/background_sync/sources/streaming/event_handler.hpp