/// read from the process' output stream
/// data is stored in the given buffer, at most max_len bytes
/// @return the number of bytes read
std::size_t ReadOut(void *buffer, std::size_t max_len);
/// read from the process' output stream
/// data is stored in the given buffer, at most max_len bytes
/// @return the number of bytes read
std::size_t ReadOut(void *buffer, std::size_t max_len);