Vfrdtyky

I'm using Ubuntu 18.04/gcc 7.3/OpenSSL 1.1.0g to make C++ app performing TLS/SSL connection with non-blocking BIO API.

When BIO_do_connect() fails connecting, e.g. if using wrong host name or port, there is no errors reported by OpenSSL. ERR_get_error() returns zero and ERR_print_errors_xx() doesn't print anything.

So the question is - how to get actual connection failure reason, e.g. 'Connection refused' or 'Host not resolved' etc?

Used code snippet below:

#include <cstdio>

#include <cstring>

#include <iostream>



#include "openssl/bio.h"

#include "openssl/err.h"

#include "openssl/ssl.h"



int main(int argc, char *argv)

{

    OPENSSL_init_ssl(OPENSSL_INIT_SSL_DEFAULT, nullptr);



    std::cout << OpenSSL_version(OPENSSL_VERSION) << std::endl;



    SSL_CTX* ctx = SSL_CTX_new(TLS_client_method());

    if (!ctx)

    {

        std::cerr << "Error creating SSL context:" << std::endl;

        ERR_print_errors_fp(stderr);

        return 1;

    }



    SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv2);

    SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv3);



    if(!SSL_CTX_load_verify_locations(ctx,

        "/etc/ssl/certs/ca-certificates.crt",

        nullptr))

    {

        std::cerr << "Error loading trust store into SSL context" << std::endl;

        ERR_print_errors_fp(stderr);

        return 1;

    }



    BIO* cbio = BIO_new_ssl_connect(ctx);



    SSL* ssl = nullptr;

    BIO_get_ssl(cbio, &ssl);

    SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);



    BIO_set_conn_hostname(cbio, "not_actually_existing_host.com:https");

    BIO_set_nbio(cbio, 1);



    std::cout << "Start connecting" << std::endl;



    next:

    if (BIO_do_connect(cbio) <= 0)

    {

        if (!BIO_should_retry(cbio))

        {

            std::cerr << "Error attempting to connect:" << std::endl;

            ERR_print_errors_fp(stderr); // <---- PRINTS NOTHING!!!

            BIO_free_all(cbio);

            SSL_CTX_free(ctx);

            return 1;

        }

        else goto next;

    }



    std::cout << "Connected OK" << std::endl;



    BIO_free_all(cbio);

    SSL_CTX_free(ctx);

    return 0;

}

This approach finally works for me:

    const auto sysErrorCode = errno;

    const auto sslErrorCode = ERR_get_error();



    std::string errorDescription;

    if (sslErrorCode != 0) errorDescription = ERR_error_string(sslErrorCode, nullptr);

    if (sysErrorCode != 0)

    {

        if (!errorDescription.empty()) errorDescription += 'n';

        errorDescription += "System error, code=" + std::to_string(sysErrorCode);

        errorDescription += ", ";

        errorDescription += strerror(sysErrorCode);

    }