CODEWITHSUNDEEP
c++sslopensslnetwork-programming
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Reputation: 9089

How to get OpenSSL BIO_do_connect() failure reason?

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;
}

Upvotes: 1

Views: 4595

Answers (1)

Rost
Rost

Reputation: 9089

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);
    }

Upvotes: 3

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