Summary

If multiple switches is provided in the connection string, 'Couldn't send "endSessions" 'warnings will be logged during exit.

Connection string with a single switch is unaffected.

Environment

mongo-cxx driver v3.10.2

mongo-c-driver v1.28.0

Ubuntu22.04

GCC 11.2.1

Build using vcpkg

 MongoDB server v4.4.25-24

How to Reproduce

#include <mongocxx/instance.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/pool.hpp>
#include <mongocxx/uri.hpp>
#include <mongocxx/logger.hpp>
#include <iostream>
#include <memory>
#include <optional>

class custom_logger final : public mongocxx::logger {
public:
    void operator()(
        mongocxx::log_level level,
        bsoncxx::stdx::string_view domain,
        bsoncxx::stdx::string_view message
    ) noexcept override {
        const char* level_str;
        switch (level)

{             case mongocxx::log_level::k_error:                 level_str = "ERROR";                 break;             case mongocxx::log_level::k_critical:                 level_str = "CRITICAL";                 break;             case mongocxx::log_level::k_warning:                 level_str = "WARNING";                 break;             case mongocxx::log_level::k_message:                 level_str = "MESSAGE";                 break;             case mongocxx::log_level::k_info:                 level_str = "INFO";                 break;             case mongocxx::log_level::k_debug:                 level_str = "DEBUG";                 break;             case mongocxx::log_level::k_trace:                 level_str = "TRACE";                 break;             default:                 level_str = "UNKNOWN";                 break;         }

       
        std::cerr << "MONGO [" << level_str << "@" << domain << "] " << message << std::endl;
    }
};

class MongoTest

{ private:     mongocxx::instance instance_;     std::optional<mongocxx::pool> pool_;     public:     MongoTest(const std::string& uri)         : instance_\{std::make_unique<custom_logger>()}

        , pool_(std::in_place, mongocxx::uri{uri})

{         std::cout << "MongoTest initialized with URI: " << uri << std::endl;     }

   
    void list_databases() {
        try {
            auto client = pool_->acquire();
            auto cursor = client->list_databases();
           
            std::cout << "Databases:" << std::endl;
            for (auto&& doc : cursor)

{                 std::cout << "  - " << doc["name"].get_string().value << std::endl;             }

        } catch (const std::exception& e)

{             std::cerr << "Error listing databases: " << e.what() << std::endl;         }

    }
   
    ~MongoTest()

{         std::cout << "MongoTest destructor called - destroying pool..." << std::endl;         pool_.reset();         std::cout << "Pool destroyed" << std::endl;     }

};

int main(int argc, char* argv[]) {
   
    std::string connection_string = argv[1];
   
   

{         MongoTest test(connection_string);         test.list_databases();     }

   
    return 0;
}

Additional Background

It happens during pool destruction:

...

MongoTest destructor called - destroying pool...
MONGO [WARNING@client] Couldn't send "endSessions": Could not find node xxx
Pool destroyed

...