feat: Implement data source configuration.

libs/common/include/config/detail/config.hpp

@@ -1,7 +1,9 @@
 #pragma once
 
+#include "config/detail/data_source_config.hpp"
 #include "config/detail/endpoints_builder.hpp"
 #include "config/detail/events_builder.hpp"
+#include "config/detail/http_properties.hpp"
 
 namespace launchdarkly::config::detail {
 
@@ -17,11 +19,15 @@ struct Config {
     detail::EndpointsBuilder<SDK> service_endpoints_builder;
     std::optional<std::string> application_tag;
     detail::EventsBuilder<SDK> events_builder;
+    DataSourceConfig<SDK> data_source_config;
+    detail::HttpProperties http_properties;
     Config(std::string sdk_key,
            bool offline,
            detail::EndpointsBuilder<SDK> service_endpoints_builder,
            detail::EventsBuilder<SDK> events_builder,
-           std::optional<std::string> application_tag);
+           std::optional<std::string> application_tag,
+           DataSourceConfig<SDK> data_source_config,
+           detail::HttpProperties http_properties);
 };
 
 }  // namespace launchdarkly::config::detail

libs/common/include/config/detail/config_builder.hpp

@@ -4,8 +4,10 @@
 #include <string>
 #include "config/detail/application_info.hpp"
 #include "config/detail/config.hpp"
+#include "config/detail/data_source_builder.hpp"
 #include "config/detail/endpoints_builder.hpp"
 #include "config/detail/events_builder.hpp"
+#include "config/detail/http_properties_builder.hpp"
 #include "logger.hpp"
 
 namespace launchdarkly::config::detail {
@@ -21,6 +23,8 @@ class ConfigBuilder {
     using EndpointsBuilder = detail::EndpointsBuilder<SDK>;
     using EventsBuilder = detail::EventsBuilder<SDK>;
     using ConfigType = detail::Config<SDK>;
+    using DataSourceBuilder = detail::DataSourceBuilder<SDK>;
+    using HttpPropertiesBuilder = detail::HttpPropertiesBuilder<SDK>;
     /**
      * A minimal configuration consists of a LaunchDarkly SDK Key.
      * @param sdk_key SDK Key.
@@ -59,6 +63,22 @@ class ConfigBuilder {
      */
     ConfigBuilder& events(EventsBuilder builder);
 
+    /**
+     * Sets the configuration of the component that receives feature flag data
+     * from LaunchDarkly.
+     * @param builder A DataSourceConfig builder.
+     * @return Reference to this builder.
+     */
+    ConfigBuilder& data_source(detail::DataSourceBuilder<SDK> builder);
+
+    /**
+     * Sets the SDK's networking configuration, using an HttpPropertiesBuilder.
+     * The builder has methods for setting individual HTTP-related properties.
+     * @param builder A HttpPropertiesBuilder builder.
+     * @return Reference to this builder.
+     */
+    ConfigBuilder& http_properties(detail::HttpPropertiesBuilder<SDK> builder);
+
     /**
      * Builds a Configuration, suitable for passing into an instance of Client.
      * @return
@@ -71,6 +91,8 @@ class ConfigBuilder {
     std::optional<EndpointsBuilder> service_endpoints_builder_;
     std::optional<ApplicationInfo> application_info_builder_;
     std::optional<EventsBuilder> events_builder_;
+    std::optional<DataSourceBuilder> data_source_builder_;
+    std::optional<HttpPropertiesBuilder> http_properties_builder_;
 };
 
 }  // namespace launchdarkly::config::detail

libs/common/include/config/detail/data_source_builder.hpp

@@ -0,0 +1,212 @@
+#pragma once
+
+#include <chrono>
+#include <optional>
+#include <type_traits>
+
+#include "config/detail/data_source_config.hpp"
+#include "config/detail/defaults.hpp"
+#include "config/detail/sdks.hpp"
+
+#include <boost/variant.hpp>
+
+namespace launchdarkly::config::detail {
+
+/**
+ * Used to construct a DataSourceConfiguration for the specified SDK type.
+ * @tparam SDK ClientSDK or ServerSDK.
+ */
+template <typename SDK>
+class DataSourceBuilder;
+
+/**
+ * Builds a configuration for a streaming data source.
+ */
+class StreamingBuilder {
+   public:
+    StreamingBuilder();
+
+    /**
+     * Sets the initial reconnect delay for the streaming connection.
+     *
+     * The streaming service uses a backoff algorithm (with jitter) every time
+     * the connection needs to be reestablished.The delay for the first
+     * reconnection will start near this value, and then increase exponentially
+     * for any subsequent connection failures.
+     *
+     * @param initial_reconnect_delay The initial delay for a reconnection
+     * attempt.
+     * @return Reference to this builder.
+     */
+    StreamingBuilder& initial_reconnect_delay(
+        std::chrono::milliseconds initial_reconnect_delay);
+
+    /**
+     * Build the streaming config. Used internal to the SDK.
+     * @return The built config.
+     */
+    [[nodiscard]] StreamingConfig build() const;
+
+   private:
+    StreamingConfig config_;
+};
+
+/**
+ * Contains methods for configuring the polling data source.
+ */
+class PollingBuilder {
+   public:
+    PollingBuilder();
+
+    /**
+     * Sets the interval at which the SDK will poll for feature flag updates.
+     * @param poll_interval The polling interval.
+     * @return Reference to this builder.
+     */
+    PollingBuilder& poll_interval(std::chrono::seconds poll_interval);
+
+    /**
+     * Build the polling config. Used internal to the SDK.
+     * @return The built config.
+     */
+    [[nodiscard]] PollingConfig build() const;
+
+   private:
+    PollingConfig config_;
+};
+
+/**
+ * The method visitor is only needed inside this file
+ */
+namespace {
+struct MethodVisitor {
+    boost::variant<StreamingConfig, PollingConfig> operator()(
+        StreamingBuilder streaming) {
+        return streaming.build();
+    }
+    boost::variant<StreamingConfig, PollingConfig> operator()(
+        PollingBuilder polling) {
+        return polling.build();
+    }
+};
+}  // namespace
+
+template <>
+class DataSourceBuilder<ClientSDK> {
+   public:
+    using Streaming = StreamingBuilder;
+    using Polling = PollingBuilder;
+
+    DataSourceBuilder();
+
+    /**
+     * Whether LaunchDarkly should provide additional information about how flag
+     * values were calculated.
+     *
+     * The additional information will then be available through the client's
+     * {TODO variation detail} method. Since this increases the size of network
+     * requests, such information is not sent unless you set this option to
+     * true.
+     * @param value True to enable reasons.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& with_reasons(bool value);
+
+    /**
+     * Whether or not to use the REPORT verb to fetch flag settings.
+     *
+     * If this is true, flag settings will be fetched with a REPORT request
+     * including a JSON entity body with the context object.
+     *
+     * Otherwise (by default) a GET request will be issued with the context
+     * passed as a base64 URL-encoded path parameter.
+     *
+     * Do not use unless advised by LaunchDarkly.
+     * @param value True to enable using the REPORT verb.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& use_report(bool value);
+
+    /**
+     * Set the streaming configuration for the builder.
+     *
+     * A data source may either be streaming or polling. Setting a streaming
+     * builder indicates the data source will use streaming. Setting a polling
+     * builder will indicate the use of polling.
+     *
+     * @param stream_builder The streaming builder.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& method(Streaming stream_builder);
+
+    /**
+     * Set the polling configuration for the builder.
+     *
+     * A data source may either be streaming or polling. Setting a stream
+     * builder indicates the data source will use streaming. Setting a polling
+     * builder will indicate the use of polling.
+     *
+     * @param polling_builder The polling builder.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& method(Polling polling_builder);
+
+    /**
+     * Build a data source config. This is used internal to the SDK.
+     *
+     * @return The built config.
+     */
+    [[nodiscard]] DataSourceConfig<ClientSDK> build() const;
+
+   private:
+    boost::variant<Streaming, Polling> method_;
+    bool with_reasons_;
+    bool use_report_;
+};
+
+template <>
+class DataSourceBuilder<ServerSDK> {
+   public:
+    using Streaming = StreamingBuilder;
+    using Polling = PollingBuilder;
+
+    DataSourceBuilder();
+
+    /**
+     * Set the streaming configuration for the builder.
+     *
+     * A data source may either be streaming or polling. Setting a streaming
+     * builder indicates the data source will use streaming. Setting a polling
+     * builder will indicate the use of polling.
+     *
+     * @param stream_builder The streaming builder.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& method(Streaming builder);
+
+    /**
+     * Set the polling configuration for the builder.
+     *
+     * A data source may either be streaming or polling. Setting a stream
+     * builder indicates the data source will use streaming. Setting a polling
+     * builder will indicate the use of polling.
+     *
+     * @param polling_builder The polling builder.
+     * @return Reference to this builder.
+     */
+    DataSourceBuilder& method(Polling builder);
+
+    /**
+     * Build a data source config. This is used internal to the SDK.
+     *
+     * @return The built config.
+     */
+    [[nodiscard]] DataSourceConfig<ServerSDK> build() const;
+
+   private:
+    boost::variant<Streaming, Polling> method_;
+    bool with_reasons_;
+    bool use_report_;
+};
+
+}  // namespace launchdarkly::config::detail

libs/common/include/config/detail/data_source_config.hpp

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <boost/variant.hpp>
+#include <chrono>
+#include <optional>
+#include <type_traits>
+#include "config/detail/sdks.hpp"
+
+namespace launchdarkly::config::detail {
+
+struct StreamingConfig {
+    std::chrono::milliseconds initial_reconnect_delay;
+};
+
+struct PollingConfig {
+    std::chrono::seconds poll_interval;
+};
+
+template <typename SDK>
+struct DataSourceConfig;
+
+template <>
+struct DataSourceConfig<ClientSDK> {
+    boost::variant<StreamingConfig, PollingConfig> method;
+
+    bool with_reasons;
+    bool use_report;
+};
+
+template <>
+struct DataSourceConfig<ServerSDK> {
+    boost::variant<StreamingConfig, PollingConfig> method;
+};
+
+}  // namespace launchdarkly::config::detail

libs/common/include/config/detail/defaults.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "config/detail/data_source_config.hpp"
 #include "config/detail/events.hpp"
 #include "config/detail/http_properties.hpp"
 #include "config/detail/sdks.hpp"
@@ -19,6 +20,15 @@ struct Defaults {
      * @return
      */
     static bool offline() { return false; }
+
+    static StreamingConfig streaming_config() {
+        return {std::chrono::milliseconds{1000}};
+    }
+
+    static PollingConfig polling_config() {
+        // Default to 5 minutes;
+        return {std::chrono::seconds{5 * 60}};
+    }
 };
 
 template <>
@@ -42,6 +52,10 @@ struct Defaults<ClientSDK> {
                 sdk_name() + "/" + sdk_version(),
                 std::map<std::string, std::string>()};
     }
+
+    static DataSourceConfig<ClientSDK> data_source_config() {
+        return {Defaults<AnySDK>::streaming_config(), false, false};
+    }
 };
 
 template <>
@@ -65,6 +79,10 @@ struct Defaults<ServerSDK> {
                 sdk_name() + "/" + sdk_version(),
                 std::map<std::string, std::string>()};
     }
+
+    static DataSourceConfig<ServerSDK> data_source_config() {
+        return {Defaults<AnySDK>::streaming_config()};
+    }
 };
 
 }  // namespace launchdarkly::config::detail

libs/common/include/config/detail/http_properties_builder.hpp

@@ -27,7 +27,7 @@ class HttpPropertiesBuilder {
     HttpPropertiesBuilder& custom_headers(
         std::map<std::string, std::string> base_headers);
 
-    HttpProperties build() const;
+    [[nodiscard]] HttpProperties build() const;
 
    private:
     std::chrono::milliseconds connect_timeout_{};

libs/common/src/CMakeLists.txt

@@ -43,6 +43,7 @@ add_library(${LIBNAME}
         events/conn_pool.cpp
         events/summary_state.cpp
         config/http_properties.cpp
+        config/data_source_builder.cpp
         config/http_properties_builder.cpp)