how to resolve SSL Connect Error in curl cpp

Question

I have been working on an application which uses curl for communication to a server. Sometimes I get an "SSL Connect" error.

curl/libcurl version
7.86

operating system
Windows

I tried to increase verbosity on a machine where this issue is occurring, and got an "ssl handshake" error.

static int trace(CURL* handle, curl_infotype type, char* data, size_t size, void* userp)
{
    switch (type)
    {
        case CURLINFO_TEXT:
            CLIENT_LOG_DEBUG("== Info: %s", data);
            break;
        default:
            return 0;
        case CURLINFO_HEADER_OUT:
            CLIENT_LOG_DEBUG("=> Send header: %s", data);
            break;
        case CURLINFO_DATA_OUT:
            CLIENT_LOG_DEBUG("=> Send data: %s", data);
            break;
        case CURLINFO_SSL_DATA_OUT:
            CLIENT_LOG_DEBUG("=> Send SSL data: %s", data);
            break;
        case CURLINFO_HEADER_IN:
            CLIENT_LOG_DEBUG("<= Recv header: %s", data);
            break;
        case CURLINFO_DATA_IN:
            CLIENT_LOG_DEBUG("<= Recv data: %s", data);
            break;
        case CURLINFO_SSL_DATA_IN:
            CLIENT_LOG_DEBUG("<= Recv SSL data: %s", data);
            break;
    }
    return 0;
}

/// at caller method:

CLIENT_LOG_INFO("TRACE_LEVEL_HIGH");
curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, trace);
curl_easy_setopt(curl, CURLOPT_DEBUGDATA, 1L);
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1);

/// Other curl options set while making connection:

curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "PUT");
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, payload.c_str());
curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, payload.size());

#ifndef PLATFORM_UNIX
curl_easy_setopt(curl, CURLOPT_CAINFO, "curl-ca-bundle.crt");
#endif

curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteResponseCallback);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);
curl_easy_setopt(curl, CURLOPT_TIMEOUT, 20L);

curl::SendRequest:314 TRACE_LEVEL_HIGH

trace:45 == Info: Connected to <URL> (<IP>) port 443 (#0)

trace:45 == Info: schannel: disabled automatic use of client certificate

trace:45 == Info: ALPN: offers http/1.1

trace:45 == Info: schannel: failed to receive handshake, SSL/TLS connection failed

trace:45 == Info: Closing connection 0

curl::SendRequest:387 Failed sending curl request with error:SSL connect error

I am only getting CURLINFO_TEXT logs, no header out, data out, etc.

I am stuck here. This doesn't seem to be a certificate-related issue.

CURLOPT_DEBUGDATA expects void* you pass long, this is undefined behavior. CURLOPT_VERBOSE expects long you pass int, this is undefined behavior on non Windows platforms. — 3CEZVQ
– 3CEZVQ, Commented Dec 20, 2022 at 20:34

3CEZVQ · Accepted Answer · 2022-12-20 20:41:43Z

1

This error indicates the TLS handshake key exchange does not finish successfully. Try to experiment with adding one of the lines below:

curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_SSLv3 | CURL_SSLVERSION_MAX_TLSv1_2);
curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_SSLv3 | CURL_SSLVERSION_MAX_TLSv1_1);
curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_SSLv3 | CURL_SSLVERSION_MAX_TLSv1_0);

answered Dec 20, 2022 at 20:41

3CEZVQ

43.3k11 gold badges92 silver badges101 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

how to resolve SSL Connect Error in curl cpp

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related