feat: Add support for basic offline mode. (#94)

Author: kinyoklion

libs/client-sdk/src/CMakeLists.txt

@@ -34,6 +34,8 @@ add_library(${LIBNAME}
         flag_manager/flag_store.hpp
         flag_manager/flag_updater.hpp
         event_processor.hpp
+        bindings/c/sdk.cpp
+        data_sources/null_data_source.cpp
         flag_manager/context_index.cpp
         serialization/json_all_flags.hpp
         serialization/json_all_flags.cpp

libs/client-sdk/src/client_impl.cpp

@@ -5,6 +5,7 @@
 #include <utility>
 
 #include "client_impl.hpp"
+#include "data_sources/null_data_source.hpp"
 #include "data_sources/polling_data_source.hpp"
 #include "data_sources/streaming_data_source.hpp"
 
@@ -34,6 +35,10 @@ static std::shared_ptr<IDataSource> MakeDataSource(
     IDataSourceUpdateSink& flag_updater,
     data_sources::DataSourceStatusManager& status_manager,
     Logger& logger) {
+    if (config.Offline()) {
+        return std::make_shared<data_sources::NullDataSource>(executor,
+                                                              status_manager);
+    }
     if (config.DataSourceConfig().method.index() == 0) {
         // TODO: use initial reconnect delay.
         return std::make_shared<
@@ -84,7 +89,7 @@ ClientImpl::ClientImpl(Config config, Context context)
       eval_reasons_available_(config.DataSourceConfig().with_reasons) {
     flag_manager_.LoadCache(context_);
 
-    if (config.Events().Enabled()) {
+    if (config.Events().Enabled() && !config.Offline()) {
         event_processor_ = std::make_unique<EventProcessor>(ioc_.get_executor(),
                                                             config, logger_);
     } else {
@@ -103,6 +108,11 @@ ClientImpl::ClientImpl(Config config, Context context)
         }
     });
 
+    if (config.Offline()) {
+        LD_LOG(logger_, LogLevel::kInfo)
+            << "Starting LaunchDarkly client in offline mode";
+    }
+
     // Should listen to status before attempting to start.
     data_source_->Start();
 

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

@@ -0,0 +1,19 @@
+#include "null_data_source.hpp"
+
+#include <boost/asio/post.hpp>
+
+namespace launchdarkly::client_side::data_sources {
+
+void NullDataSource::Start() {
+    status_manager_.SetState(DataSourceStatus::DataSourceState::kSetOffline);
+}
+
+void NullDataSource::ShutdownAsync(std::function<void()> complete) {
+    boost::asio::post(exec_, complete);
+}
+
+NullDataSource::NullDataSource(boost::asio::any_io_executor exec,
+                               DataSourceStatusManager& status_manager)
+    : status_manager_(status_manager), exec_(exec) {}
+
+}  // namespace launchdarkly::client_side::data_sources

libs/client-sdk/src/data_sources/null_data_source.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <boost/asio/any_io_executor.hpp>
+
+#include "data_source.hpp"
+#include "data_source_status_manager.hpp"
+
+namespace launchdarkly::client_side::data_sources {
+
+class NullDataSource : public IDataSource {
+   public:
+    explicit NullDataSource(boost::asio::any_io_executor exec,
+                            DataSourceStatusManager& status_manager);
+    void Start() override;
+    void ShutdownAsync(std::function<void()>) override;
+
+   private:
+    DataSourceStatusManager& status_manager_;
+    boost::asio::any_io_executor exec_;
+};
+
+}  // namespace launchdarkly::client_side::data_sources