Method on_transport_open

cpp/src/handler.cpp:50–50

void messaging_handler::on_transport_close(transport &) {}
void messaging_handler::on_transport_error(transport &t) { on_error(t.error()); }
void messaging_handler::on_transport_open(transport &) {}

void messaging_handler::on_connection_close(connection &) {}
void messaging_handler::on_connection_error(connection &c) { on_error(c.error()); }