Function ssl_new

examples/server/httplib.h:7611–7639

template <typename U, typename V>
inline SSL *ssl_new(socket_t sock, SSL_CTX *ctx, std::mutex &ctx_mutex,
                    U SSL_connect_or_accept, V setup) {
  SSL *ssl = nullptr;
  {
    std::lock_guard<std::mutex> guard(ctx_mutex);
    ssl = SSL_new(ctx);
  }

  if (ssl) {
    set_nonblocking(sock, true);
    auto bio = BIO_new_socket(static_cast<int>(sock), BIO_NOCLOSE);
    BIO_set_nbio(bio, 1);
    SSL_set_bio(ssl, bio, bio);

    if (!setup(ssl) || SSL_connect_or_accept(ssl) != 1) {
      SSL_shutdown(ssl);
      {
        std::lock_guard<std::mutex> guard(ctx_mutex);
        SSL_free(ssl);
      }
      set_nonblocking(sock, false);
      return nullptr;
    }
    BIO_set_nbio(bio, 0);
    set_nonblocking(sock, false);
  }

  return ssl;
}

inline void ssl_delete(std::mutex &ctx_mutex, SSL *ssl,
                       bool shutdown_gracefully) {