SMTP: SSL_connect fails but no errors

Question

I'm having trouble with the openssl library. I'm calling the following function after sending EHLO and STARTTLS:

SSL_CTX *ctx = NULL;
SSL *ssl = NULL;

    void CreateTLSSession(int sockfd)
    {
        printf("///////////////creating TLS Session/////////////////////\n");
        SSL_library_init();
        SSL_load_error_strings();
        OpenSSL_add_all_algorithms();
        ctx = SSL_CTX_new(SSLv23_client_method());
        if (ctx == NULL)
        {
            printf("failed to initialize context\n");
            return;
        }
        SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv2);
        ssl = SSL_new(ctx);
        if (!SSL_set_fd(ssl, sockfd))
        {
            printf("failed to bind to socket fd\n");
            return;
        }
        if (SSL_connect(ssl) < 1)
        {
            ERR_print_errors_fp(stdout);
            fflush(stdout);
            printf("SSL_connect failed\n");
            return;
        }
    }

However, SSL_connect fails but does not print any errors!

Here's the output of my code: (including the replies of the server)

220 mx.google.com ESMTP x3sm39000551eep.17 - gsmtp 




//////////////////////////EHLO////////////////////////// 
250-mx.google.com at your service, [80.149.109.201] 
250-SIZE 35882577 
250-8BITMIME 
250-STARTTLS 
250-ENHANCEDSTATUSCODES 
250 CHUNKING 




//////////////////////////STARTTLS////////////////////////// 
220 2.0.0 Ready to start TLS 




///////////////creating TLS Session///////////////////// 
SSL_connect failed 

so ERR_print_errors_fp(stdout) is not doing anything!

Any idea why this is happening?

BTW, I'm trying to connect to smtp.gmail.com:587

Answer 1

I managed to finally solve the problem. the underlying socket was non-blocking, so SSL_connect does not connect instantly. Using select solved the issue

Answer 2

I don't see a load of private key file or certificate file. use SSL_CTX_use_certificate_file and SSL_CTX_use_PrivateKey_file.