feat: Support flag change notifications. (#41)

Author: kinyoklion

apps/hello-cpp/main.cpp

@@ -58,6 +58,11 @@ int main() {
         LD_LOG(logger, LogLevel::kInfo) << "Got status: " << status;
     });
 
+    client.FlagNotifier().OnFlagChange(
+        "my-boolean-flag", [&logger](auto event) {
+            LD_LOG(logger, LogLevel::kInfo) << "Got flag change: " << *event;
+        });
+
     client.WaitForReadySync(std::chrono::seconds(30));
 
     auto value = client.BoolVariationDetail("my-boolean-flag", false);

libs/client-sdk/include/launchdarkly/client_side/api.hpp

@@ -18,6 +18,7 @@
 #include "launchdarkly/client_side/event_processor.hpp"
 #include "launchdarkly/client_side/flag_manager/detail/flag_manager.hpp"
 #include "launchdarkly/client_side/flag_manager/detail/flag_updater.hpp"
+#include "launchdarkly/client_side/flag_manager/detail/flag_notifier.hpp"
 #include "logger.hpp"
 #include "value.hpp"
 
@@ -74,6 +75,8 @@ class Client {
 
     data_sources::IDataSourceStatusProvider& DataSourceStatus();
 
+    flag_manager::detail::IFlagNotifier& FlagNotifier();
+
     void WaitForReadySync(std::chrono::seconds timeout);
 
     ~Client();

libs/client-sdk/include/launchdarkly/client_side/flag_manager/detail/flag_change_event.hpp

@@ -59,4 +59,6 @@ class FlagValueChangeEvent {
     std::string flag_name_;
 };
 
+std::ostream& operator<<(std::ostream& out, FlagValueChangeEvent const& event);
+
 }  // namespace launchdarkly::client_side::flag_manager::detail

libs/client-sdk/include/launchdarkly/client_side/flag_manager/detail/flag_notifier.hpp

@@ -1,8 +1,8 @@
 #pragma once
 
+#include "launchdarkly/client_side/connection.hpp"
 #include "launchdarkly/client_side/flag_manager/detail/flag_change_event.hpp"
 #include "value.hpp"
-#include "launchdarkly/client_side/connection.hpp"
 
 namespace launchdarkly::client_side::flag_manager::detail {
 

libs/client-sdk/src/api.cpp

@@ -253,6 +253,10 @@ data_sources::IDataSourceStatusProvider& Client::DataSourceStatus() {
     return status_manager_;
 }
 
+flag_manager::detail::IFlagNotifier& Client::FlagNotifier() {
+    return flag_updater_;
+}
+
 void Client::WaitForReadySync(std::chrono::seconds timeout) {
     std::unique_lock lock(init_mutex_);
     init_waiter_.wait_for(lock, timeout, [this] { return initialized_; });

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

@@ -31,4 +31,15 @@ FlagValueChangeEvent::FlagValueChangeEvent(std::string name, Value old_value)
       old_value_(std::move(old_value)),
       deleted_(true) {}
 
+std::ostream& operator<<(std::ostream& out, FlagValueChangeEvent const& event) {
+    if (event.Deleted()) {
+        out << "Event(name: " << event.FlagName() << " deleted)";
+    } else {
+        out << "Event(name: " << event.FlagName()
+            << ", old value: " << event.OldValue()
+            << ", new value: " << event.NewValue() << ")";
+    }
+    return out;
+}
+
 }  // namespace launchdarkly::client_side::flag_manager::detail