feat ydb: get read session events in transaction

Relates:(https://nda.ya.ru/t/3Pf5rcwe7YMqT4
commit_hash:c9a8b34012a8e02410f6ca9da79aa2e37b84d836

Author: aiguzhin

ydb/include/userver/ydb/topic.hpp

@@ -47,6 +47,14 @@ class TopicReadSession final {
         size_t max_size_bytes = std::numeric_limits<size_t>::max()
     );
 
+    /// @brief Get read session events
+    ///
+    /// Waits until event occurs
+    /// @param settings ydb native read session settings
+    std::vector<NYdb::NTopic::TReadSessionEvent::TEvent> GetEvents(
+        const NYdb::NTopic::TReadSessionGetEventSettings& settings
+    );
+
     /// @brief Close read session
     ///
     /// Waits for all commit acknowledgments to arrive.

ydb/include/userver/ydb/transaction.hpp

@@ -78,6 +78,12 @@ class Transaction final {
     ) noexcept;
     /// @endcond
 
+    /// Get native transaction
+    /// @warning Use with care! Facilities from
+    /// `<core/include/userver/drivers/subscribable_futures.hpp>` can help with
+    /// non-blocking wait operations.
+    NYdb::TTransactionBase& GetNativeTransaction();
+
 private:
     void MarkError() noexcept;
     auto ErrorGuard();

ydb/src/ydb/topic.cpp

@@ -25,6 +25,13 @@ std::vector<NYdb::NTopic::TReadSessionEvent::TEvent> TopicReadSession::GetEvents
     return read_session_->GetEvents(false, max_events_count, max_size_bytes);
 }
 
+std::vector<NYdb::NTopic::TReadSessionEvent::TEvent> TopicReadSession::GetEvents(
+    const NYdb::NTopic::TReadSessionGetEventSettings& settings
+) {
+    impl::GetFutureValue(read_session_->WaitEvent());
+    return read_session_->GetEvents(settings);
+}
+
 bool TopicReadSession::Close(std::chrono::milliseconds timeout) { return read_session_->Close(timeout); }
 
 std::shared_ptr<NYdb::NTopic::IReadSession> TopicReadSession::GetNativeTopicReadSession() { return read_session_; }

ydb/src/ydb/transaction.cpp

@@ -221,6 +221,10 @@ ExecuteResponse Transaction::Execute(
     return ExecuteResponse(std::move(status));
 }
 
+NYdb::TTransactionBase& Transaction::GetNativeTransaction() {
+    return std::visit([](auto& tx) -> NYdb::TTransactionBase& { return tx; }, ydb_tx_);
+}
+
 }  // namespace ydb
 
 USERVER_NAMESPACE_END