I have a server socket connected by many clients using boost::asio::ip::tcp::socket to set up server socket connection and to use boost::asio::ip::tcp::acceptor async_accept for new client connections. The client may come and go, so I need to check if the connection is still valid or not before sending message to clients. How can I check if a client connection is no longer valid? My server does not seem get any indication when a client terminate the connection.