Asio C++ Library before 1.13.0 lacks a fallback error code in the case of SSL_ERROR_SYSCALL with no associated error information from the SSL library being used.
https://github.com/chriskohlhoff/asio/compare/asio-1-12-2...asio-1-13-0
https://github.com/chriskohlhoff/asio/commit/93337cba7b013150f5aa6194393e1d94be2853ec