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feat: add FDv2 configuration builder (#545)
Adds a public `FDv2Builder` and wires the FDv2 data system into `MakeDataSystem`, so end users can opt into the FDv2 protocol via the existing config-builder pattern. ```cpp // Default FDv2 stack (streaming primary, polling fallback, // FDv1 streaming last-resort) auto config = ConfigBuilder("sdk-key-123") .DataSystem().Method(DataSystemBuilder::FDv2()) /* ... */; // Customised: payload filter + shorter fallback timeout, no FDv1 fallback auto config = ConfigBuilder("sdk-key-123") .DataSystem().Method( DataSystemBuilder::FDv2() .Streaming(FDv2Builder::StreamingSource().Filter("mobile-flags")) .FallbackTimeout(std::chrono::seconds{30}) .DisableFDv1Fallback()) /* ... */; ``` ## Test plan - [x] 5 new FDv2 builder tests in `config_builder_test.cpp` - [x] Full server suite green (503 tests) <!-- CURSOR_SUMMARY --> --- > [!NOTE] > **Medium Risk** > Changes how the server SDK selects and connects its data source (new public API and client construction path); default remains Background Sync unless FDv2 is configured. > > **Overview** > Introduces **`FDv2Builder`** and **`FDv2Config`** so apps can select the FDv2 changeset protocol via `DataSystemBuilder::Method(FDv2::Default())` or a custom stack (ordered initializers/synchronizers, optional FDv1 streaming/polling fallback, fallback/recovery timeouts, per-source **`BaseUrl`** overrides). > > **`MakeDataSystem`** in `client_impl.cpp` now constructs **`FDv2DataSystem`** from config: polling initializer factories plus streaming/polling synchronizer factories and optional FDv1 adapter factories, with shared fallback/recovery condition factories. > > FDv2 poll/stream implementations take a resolved **base URL string** (override or service endpoints) instead of full `ServiceEndpoints`. New **initializer/synchronizer factory** types build runtime sources from built config. > > **`config_builder_test.cpp`** adds FDv2 builder coverage; existing FDv2 HTTP tests updated for the new request API. > > <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit afe78d6. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).</sup> <!-- /CURSOR_SUMMARY -->
1 parent c5fd239 commit 43850ce

24 files changed

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

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

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#pragma once
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#include <launchdarkly/config/shared/builders/data_source_builder.hpp>
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#include <launchdarkly/config/shared/sdks.hpp>
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#include <launchdarkly/server_side/config/built/data_system/fdv2_config.hpp>
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#include <chrono>
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#include <optional>
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#include <string>
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namespace launchdarkly::server_side::config::builders {
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class FDv2Builder {
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public:
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class Streaming {
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public:
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Streaming& InitialReconnectDelay(std::chrono::milliseconds delay);
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Streaming& BaseUrl(std::string base_url);
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[[nodiscard]] built::FDv2Config::StreamingConfig Build() const;
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private:
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std::chrono::milliseconds initial_reconnect_delay_{1000};
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std::optional<std::string> filter_key_;
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std::optional<std::string> base_url_override_;
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};
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class Polling {
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public:
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Polling& PollInterval(std::chrono::seconds interval);
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Polling& BaseUrl(std::string base_url);
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[[nodiscard]] built::FDv2Config::PollingConfig Build() const;
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private:
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std::chrono::seconds poll_interval_{30};
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std::optional<std::string> filter_key_;
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std::optional<std::string> base_url_override_;
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};
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/**
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* @return A builder pre-populated with the spec-recommended initializers,
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* synchronizers, and FDv1 fallback. Equivalent to calling
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* Initializer(), Synchronizer(), and FDv1Fallback() with the
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* standard sources.
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*/
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static FDv2Builder Default();
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/**
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* @return A builder with no initializers, no synchronizers, and no
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* FDv1 fallback. Callers must add sources explicitly.
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*/
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static FDv2Builder Custom();
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/**
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* @brief Appends a polling initializer to the initializers list.
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* @param source Polling source configuration for the initializer.
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* @return Reference to this.
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*/
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FDv2Builder& Initializer(Polling source);
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/**
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* @brief Appends a streaming synchronizer to the synchronizers list.
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* Order in the list determines preference: the first entry is the
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* primary synchronizer, subsequent entries are fallbacks.
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* @param source Streaming source configuration.
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* @return Reference to this.
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*/
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FDv2Builder& Synchronizer(Streaming source);
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/**
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* @brief Appends a polling synchronizer to the synchronizers list. See
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* Synchronizer(Streaming) for ordering semantics.
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* @param source Polling source configuration.
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* @return Reference to this.
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*/
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FDv2Builder& Synchronizer(Polling source);
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using FDv1Streaming =
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launchdarkly::config::shared::builders::StreamingBuilder<
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launchdarkly::config::shared::ServerSDK>;
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using FDv1Polling = launchdarkly::config::shared::builders::PollingBuilder<
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launchdarkly::config::shared::ServerSDK>;
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/**
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* @brief Configures the FDv1 streaming source used as a last-resort
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* fallback when the LaunchDarkly service signals (via the
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* X-LD-FD-Fallback header) that the SDK should switch to FDv1. The
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* fallback reads its endpoint from the top-level ServiceEndpoints; to
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* point the fallback at a custom URL, configure ServiceEndpoints
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* accordingly.
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* @param source FDv1 streaming source configuration.
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* @return Reference to this.
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*/
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FDv2Builder& FDv1Fallback(FDv1Streaming source);
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/**
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* @brief Configures the FDv1 polling source used as a last-resort
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* fallback when the LaunchDarkly service signals (via the
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* X-LD-FD-Fallback header) that the SDK should switch to FDv1. The
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* fallback reads its endpoint from the top-level ServiceEndpoints; to
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* point the fallback at a custom URL, configure ServiceEndpoints
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* accordingly.
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* @param source FDv1 polling source configuration.
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* @return Reference to this.
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*/
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FDv2Builder& FDv1Fallback(FDv1Polling source);
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/**
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* @brief Disables the FDv1 fallback. After this call, an FDv1
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* fallback directive from the service leaves the data source in
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* the interrupted state and schedules an FDv2 retry on the
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* directive's TTL.
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* @return Reference to this.
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*/
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FDv2Builder& DisableFDv1Fallback();
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/**
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* @brief Sets how long the active synchronizer may remain interrupted
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* before the orchestrator falls back to the next-preferred synchronizer.
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* @param timeout Duration the synchronizer must be continuously
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* interrupted for before fallback fires.
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* @return Reference to this.
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*/
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FDv2Builder& FallbackTimeout(std::chrono::milliseconds timeout);
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/**
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* @brief Sets how long a fallback synchronizer must run successfully
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* before the orchestrator attempts to recover to the primary
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* synchronizer.
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* @param timeout Duration the fallback synchronizer must run before a
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* recovery attempt is made.
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* @return Reference to this.
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*/
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FDv2Builder& RecoveryTimeout(std::chrono::milliseconds timeout);
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[[nodiscard]] built::FDv2Config Build() const;
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private:
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FDv2Builder();
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built::FDv2Config config_;
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};
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} // namespace launchdarkly::server_side::config::builders

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

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

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

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#pragma once
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#include <launchdarkly/config/shared/built/data_source_config.hpp>
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#include <launchdarkly/config/shared/sdks.hpp>
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#include <chrono>
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#include <optional>
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#include <string>
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#include <variant>
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#include <vector>
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namespace launchdarkly::server_side::config::built {
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struct FDv2Config {
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struct StreamingConfig {
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std::chrono::milliseconds initial_reconnect_delay;
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std::optional<std::string> base_url_override;
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friend bool operator==(StreamingConfig const& lhs,
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StreamingConfig const& rhs) {
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return lhs.initial_reconnect_delay == rhs.initial_reconnect_delay &&
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lhs.base_url_override == rhs.base_url_override;
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}
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};
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struct PollingConfig {
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std::chrono::seconds poll_interval;
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std::optional<std::string> base_url_override;
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friend bool operator==(PollingConfig const& lhs,
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PollingConfig const& rhs) {
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return lhs.poll_interval == rhs.poll_interval &&
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lhs.base_url_override == rhs.base_url_override;
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}
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};
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using FDv1StreamingConfig =
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launchdarkly::config::shared::built::StreamingConfig<
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launchdarkly::config::shared::ServerSDK>;
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using FDv1PollingConfig =
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launchdarkly::config::shared::built::PollingConfig<
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launchdarkly::config::shared::ServerSDK>;
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std::vector<PollingConfig> initializers;
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std::vector<std::variant<StreamingConfig, PollingConfig>> synchronizers;
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std::optional<std::variant<FDv1StreamingConfig, FDv1PollingConfig>>
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fdv1_fallback;
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std::chrono::milliseconds fallback_timeout;
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std::chrono::milliseconds recovery_timeout;
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};
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} // namespace launchdarkly::server_side::config::built

‎libs/server-sdk/src/CMakeLists.txt‎

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@@ -30,6 +30,7 @@ target_sources(${LIBNAME}
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config/builders/data_system/background_sync_builder.cpp
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config/builders/data_system/bootstrap_builder.cpp
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config/builders/data_system/data_system_builder.cpp
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config/builders/data_system/fdv2_builder.cpp
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config/builders/data_system/lazy_load_builder.cpp
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config/builders/data_system/data_destination_builder.cpp
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config/builders/big_segments_builder.cpp
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data_systems/fdv2/fdv2_data_system.cpp
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data_systems/fdv2/fdv1_adapter_synchronizer.hpp
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data_systems/fdv2/fdv1_adapter_synchronizer.cpp
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data_systems/fdv2/synchronizer_factories.hpp
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data_systems/fdv2/synchronizer_factories.cpp
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data_systems/fdv2/initializer_factories.hpp
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data_systems/fdv2/initializer_factories.cpp
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data_systems/background_sync/sources/streaming/streaming_data_source.hpp
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data_systems/background_sync/sources/streaming/streaming_data_source.cpp
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data_systems/background_sync/sources/streaming/event_handler.hpp

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