feat: Implement basic in-memory store and change handling.

libs/client-sdk/src/CMakeLists.txt

@@ -17,10 +17,8 @@ add_library(${LIBNAME}
         data_sources/data_source_status_manager.cpp
         event_processor/event_processor.cpp
         event_processor/null_event_processor.cpp
-        boost_signal_connection.cpp
         client_impl.cpp
         client.cpp
-        boost_signal_connection.hpp
         client_impl.hpp
         data_sources/data_source.hpp
         data_sources/data_source_event_handler.hpp

libs/client-sdk/src/data_sources/data_source_status_manager.cpp

@@ -4,8 +4,8 @@
 #include <utility>
 
 #include <launchdarkly/connection.hpp>
+#include <launchdarkly/signals/boost_signal_connection.hpp>
 
-#include "../boost_signal_connection.hpp"
 #include "data_source_status_manager.hpp"
 
 namespace launchdarkly::client_side::data_sources {
@@ -104,15 +104,16 @@ DataSourceStatus DataSourceStatusManager::Status() const {
 std::unique_ptr<IConnection> DataSourceStatusManager::OnDataSourceStatusChange(
     std::function<void(data_sources::DataSourceStatus)> handler) {
     std::lock_guard lock{status_mutex_};
-    return std::make_unique< ::launchdarkly::client_side::SignalConnection>(
+    return std::make_unique<
+        ::launchdarkly::internal::signals::SignalConnection>(
         data_source_status_signal_.connect(handler));
 }
 
 std::unique_ptr<IConnection>
 DataSourceStatusManager::OnDataSourceStatusChangeEx(
     std::function<bool(data_sources::DataSourceStatus)> handler) {
     std::lock_guard lock{status_mutex_};
-    return std::make_unique< ::launchdarkly::client_side::SignalConnection>(
+    return std::make_unique<launchdarkly::internal::signals::SignalConnection>(
         data_source_status_signal_.connect_extended(
             [handler](boost::signals2::connection const& conn,
                       data_sources::DataSourceStatus status) {

libs/client-sdk/src/flag_manager/flag_updater.cpp

@@ -1,6 +1,7 @@
 #include <utility>
 
-#include "../boost_signal_connection.hpp"
+#include <launchdarkly/signals/boost_signal_connection.hpp>
+
 #include "flag_updater.hpp"
 
 namespace launchdarkly::client_side::flag_manager {
@@ -74,7 +75,7 @@ void FlagUpdater::DispatchEvent(FlagValueChangeEvent event) {
     auto handler = signals_.find(event.FlagName());
     if (handler != signals_.end()) {
         if (handler->second.empty()) {
-            // Empty, remove it from the map so it doesn't count toward
+            // Empty, remove it from the map, so it doesn't count toward
             // future calculations.
             signals_.erase(event.FlagName());
         } else {
@@ -123,7 +124,7 @@ std::unique_ptr<IConnection> FlagUpdater::OnFlagChange(
     std::string const& key,
     std::function<void(std::shared_ptr<FlagValueChangeEvent>)> handler) {
     std::lock_guard lock{signal_mutex_};
-    return std::make_unique< ::launchdarkly::client_side::SignalConnection>(
+    return std::make_unique< launchdarkly::internal::signals::SignalConnection>(
         signals_[key].connect(handler));
 }
 

libs/client-sdk/src/boost_signal_connection.hpp → libs/internal/include/launchdarkly/signals/boost_signal_connection.hpp

@@ -4,7 +4,7 @@
 
 #include <launchdarkly/connection.hpp>
 
-namespace launchdarkly::client_side {
+namespace launchdarkly::internal::signals {
 
 class SignalConnection : public IConnection {
    public:

libs/internal/src/CMakeLists.txt

@@ -5,6 +5,7 @@ file(GLOB HEADER_LIST CONFIGURE_DEPENDS
         "${LaunchDarklyInternalSdk_SOURCE_DIR}/include/launchdarkly/network/*.hpp"
         "${LaunchDarklyInternalSdk_SOURCE_DIR}/include/launchdarkly/serialization/*.hpp"
         "${LaunchDarklyInternalSdk_SOURCE_DIR}/include/launchdarkly/serialization/events/*.hpp"
+        "${LaunchDarklyInternalSdk_SOURCE_DIR}/include/launchdarkly/signals/*.hpp"
         )
 
 # Automatic library: static or dynamic based on user config.
@@ -38,7 +39,8 @@ add_library(${LIBNAME} OBJECT
         serialization/json_rule_clause.cpp
         serialization/json_flag.cpp
         encoding/base_64.cpp
-        encoding/sha_256.cpp)
+        encoding/sha_256.cpp
+        signals/boost_signal_connection.cpp)
 
 add_library(launchdarkly::internal ALIAS ${LIBNAME})
 

libs/client-sdk/src/boost_signal_connection.cpp → libs/internal/src/signals/boost_signal_connection.cpp

@@ -1,6 +1,6 @@
-#include "boost_signal_connection.hpp"
+#include <launchdarkly/signals/boost_signal_connection.hpp>
 
-namespace launchdarkly::client_side {
+namespace launchdarkly::internal::signals {
 
 SignalConnection::SignalConnection(boost::signals2::connection connection)
     : connection_(std::move(connection)) {}
@@ -9,4 +9,4 @@ void SignalConnection::Disconnect() {
     connection_.disconnect();
 }
 
-}  // namespace launchdarkly::client_side
+}  // namespace launchdarkly::internal::signals

libs/server-sdk/include/launchdarkly/server_side/change_notifier.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <launchdarkly/connection.hpp>
+
+#include <functional>
+#include <memory>
+#include <set>
+#include <string>
+
+namespace launchdarkly::server_side {
+
+/**
+ * Interface to allow listening for flag changes. Notification events should
+ * be distributed after the store has been updated.
+ */
+class IChangeNotifier {
+   public:
+    using ChangeSet = std::set<std::string>;
+    using ChangeHandler = std::function<void(std::shared_ptr<ChangeSet>)>;
+
+    /**
+     * Listen for changes to flag configuration. The change handler will be called
+     * with a set of affected flag keys. Changes include flags whose dependencies
+     * (either other flags, or segments) changed.
+     *
+     * @param signal The handler for the changes.
+     * @return A connection which can be used to stop listening.
+     */
+    virtual std::unique_ptr<IConnection> OnFlagChange(ChangeHandler handler) = 0;
+
+    virtual ~IChangeNotifier() = default;
+    IChangeNotifier(IChangeNotifier const& item) = delete;
+    IChangeNotifier(IChangeNotifier&& item) = delete;
+    IChangeNotifier& operator=(IChangeNotifier const&) = delete;
+    IChangeNotifier& operator=(IChangeNotifier&&) = delete;
+
+   protected:
+    IChangeNotifier() = default;
+};
+
+}  // namespace launchdarkly::server_side

libs/server-sdk/src/CMakeLists.txt

@@ -6,14 +6,20 @@ file(GLOB HEADER_LIST CONFIGURE_DEPENDS
 # Automatic library: static or dynamic based on user config.
 
 add_library(${LIBNAME}
-        ${HEADER_LIST})
+        ${HEADER_LIST}
+        data_source/data_source_update_sink.hpp
+        data_store/data_store.hpp
+        data_store/data_store_updater.hpp
+        data_store/data_store_updater.cpp
+        data_store/memory_store.cpp
+        data_store/dependency_tracker.hpp data_store/dependency_tracker.cpp)
 
 if (MSVC OR (NOT BUILD_SHARED_LIBS))
     target_link_libraries(${LIBNAME}
             PUBLIC launchdarkly::common
             PRIVATE Boost::headers Boost::json Boost::url launchdarkly::sse launchdarkly::internal foxy)
 else ()
-    # The default static lib builds, for linux, are positition independent.
+    # The default static lib builds, for linux, are position independent.
     # So they do not link into a shared object without issues. So, when
     # building shared objects do not link the static libraries and instead
     # use the "src.hpp" files for required libraries.

libs/server-sdk/src/data_source/data_source_update_sink.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <launchdarkly/data_model/flag.hpp>
+#include <launchdarkly/data_model/item_descriptor.hpp>
+#include <launchdarkly/data_model/sdk_data_set.hpp>
+#include <launchdarkly/data_model/segment.hpp>
+
+namespace launchdarkly::server_side::data_source {
+/**
+ * Interface for handling updates from LaunchDarkly.
+ */
+class IDataSourceUpdateSink {
+   public:
+    using FlagDescriptor = launchdarkly::data_model::ItemDescriptor<
+        launchdarkly::data_model::Flag>;
+    using SegmentDescriptor = launchdarkly::data_model::ItemDescriptor<
+        launchdarkly::data_model::Segment>;
+
+    virtual void Init(launchdarkly::data_model::SDKDataSet data_set) = 0;
+    virtual void Upsert(std::string key, FlagDescriptor flag) = 0;
+    virtual void Upsert(std::string key, SegmentDescriptor segment) = 0;
+
+    IDataSourceUpdateSink(IDataSourceUpdateSink const& item) = delete;
+    IDataSourceUpdateSink(IDataSourceUpdateSink&& item) = delete;
+    IDataSourceUpdateSink& operator=(IDataSourceUpdateSink const&) = delete;
+    IDataSourceUpdateSink& operator=(IDataSourceUpdateSink&&) = delete;
+    virtual ~IDataSourceUpdateSink() = default;
+
+   protected:
+    IDataSourceUpdateSink() = default;
+};
+}  // namespace launchdarkly::server_side::data_source

libs/server-sdk/src/data_store/data_kind.hpp

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <cstddef>
+
+namespace launchdarkly::server_side::data_store {
+    enum class DataKind : std::size_t { kFlag = 0, kSegment = 1, kKindCount = 2 };
+}   // namespace launchdarkly::server_side::data_store

libs/server-sdk/src/data_store/data_store.hpp

@@ -0,0 +1,85 @@
+#pragma once
+
+#include <launchdarkly/data_model/flag.hpp>
+#include <launchdarkly/data_model/item_descriptor.hpp>
+#include <launchdarkly/data_model/segment.hpp>
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+namespace launchdarkly::server_side::data_store {
+
+/**
+ * Interface for readonly access to SDK data.
+ *
+ * The data store is what the client uses to store feature flag data that has
+ * been received from LaunchDarkly.
+ */
+class IDataStore {
+   public:
+    using FlagDescriptor = launchdarkly::data_model::ItemDescriptor<
+        launchdarkly::data_model::Flag>;
+    using SegmentDescriptor = launchdarkly::data_model::ItemDescriptor<
+        launchdarkly::data_model::Segment>;
+
+    /**
+     * Get a flag from the store.
+     *
+     * @param key The key for the flag.
+     * @return Returns a shared_ptr to the FlagDescriptor, or a nullptr if there
+     * is not such flag, or the flag was deleted.
+     */
+    [[nodiscard]] virtual std::shared_ptr<FlagDescriptor> GetFlag(
+        std::string key) const = 0;
+
+    /**
+     * Get a segment from the store.
+     *
+     * @param key The key for the segment.
+     * @return Returns a shared_ptr to the SegmentDescriptor, or a nullptr if
+     * there is no such segment, or the segment was deleted.
+     */
+    [[nodiscard]] virtual std::shared_ptr<SegmentDescriptor> GetSegment(
+        std::string key) const = 0;
+
+    /**
+     * Get all of the flags.
+     *
+     * @return Returns an unordered map of FlagDescriptors.
+     */
+    [[nodiscard]] virtual std::unordered_map<std::string, std::shared_ptr<FlagDescriptor>> AllFlags()
+        const = 0;
+
+    /**
+     * Get all of the segments.
+     *
+     * @return Returns an unordered map of SegmentDescriptors.
+     */
+    [[nodiscard]] virtual std::unordered_map<std::string, std::shared_ptr<SegmentDescriptor>>
+    AllSegments() const = 0;
+
+    /**
+     * Check if the store is initialized.
+     *
+     * @return Returns true if the store is initialized.
+     */
+    [[nodiscard]] virtual bool Initialized() const = 0;
+
+    /**
+     * Get a description of the store.
+     * @return Returns a string containing a description of the store.
+     */
+    [[nodiscard]] virtual std::string const& Description() const = 0;
+
+    IDataStore(IDataStore const& item) = delete;
+    IDataStore(IDataStore&& item) = delete;
+    IDataStore& operator=(IDataStore const&) = delete;
+    IDataStore& operator=(IDataStore&&) = delete;
+    virtual ~IDataStore() = default;
+
+   protected:
+    IDataStore() = default;
+};
+
+}  // namespace launchdarkly::server_side::data_store

libs/server-sdk/src/data_store/data_store_updater.cpp

@@ -0,0 +1,75 @@
+#include "data_store_updater.hpp"
+
+#include <launchdarkly/signals/boost_signal_connection.hpp>
+#include <utility>
+
+namespace launchdarkly::server_side::data_store {
+
+std::unique_ptr<IConnection> DataStoreUpdater::OnFlagChange(
+    launchdarkly::server_side::IChangeNotifier::ChangeHandler handler) {
+    std::lock_guard lock{signal_mutex_};
+
+    return std::make_unique<launchdarkly::internal::signals::SignalConnection>(
+        signals_.connect(handler));
+}
+
+void DataStoreUpdater::Init(launchdarkly::data_model::SDKDataSet data_set) {
+    std::optional<DependencySet> change_notifications;
+    if (HasListeners()) {
+        auto updated_items = DependencySet();
+
+        CalculateChanges(DataKind::kFlag, store_->AllFlags(), data_set.flags,
+                         updated_items);
+        CalculateChanges(DataKind::kSegment, store_->AllSegments(),
+                         data_set.segments, updated_items);
+        change_notifications = updated_items;
+    }
+
+    dependency_tracker_.Clear();
+    for (auto const& flag : data_set.flags) {
+        dependency_tracker_.UpdateDependencies(flag.first, flag.second);
+    }
+    for (auto const& segment : data_set.segments) {
+        dependency_tracker_.UpdateDependencies(segment.first, segment.second);
+    }
+    // Data will move into the store, so we want to update dependencies before
+    // it is moved.
+    sink_->Init(data_set);
+    // After updating the sunk let listeners know of changes.
+    if (change_notifications) {
+        NotifyChanges(*change_notifications);
+    }
+}
+
+void DataStoreUpdater::Upsert(std::string key,
+                              launchdarkly::server_side::data_source::
+                                  IDataSourceUpdateSink::FlagDescriptor flag) {
+    UpsertCommon(DataKind::kFlag, key, store_->GetFlag(key), flag);
+}
+
+void DataStoreUpdater::Upsert(
+    std::string key,
+    launchdarkly::server_side::data_source::IDataSourceUpdateSink::
+        SegmentDescriptor segment) {
+    UpsertCommon(DataKind::kSegment, key, store_->GetSegment(key), segment);
+}
+
+bool DataStoreUpdater::HasListeners() const {
+    std::lock_guard lock{signal_mutex_};
+    return !signals_.empty();
+}
+
+void DataStoreUpdater::NotifyChanges(DependencySet changes) {
+    std::lock_guard lock{signal_mutex_};
+    auto flag_changes = changes.SetForKind(DataKind::kFlag);
+    // Only emit an event if there are changes.
+    if (!flag_changes.empty()) {
+        signals_(std::make_shared<ChangeSet>(std::move(flag_changes)));
+    }
+}
+
+DataStoreUpdater::DataStoreUpdater(std::shared_ptr<IDataSourceUpdateSink> sink,
+                                   std::shared_ptr<IDataStore> store)
+    : sink_(std::move(sink)), store_(std::move(store)) {}
+
+}  // namespace launchdarkly::server_side::data_store