#include <curl/curl.h>

char g_Data[40 * 1024]; // POST 40KB

int sockopt_callback(void *clientp, curl_socket_t curlfd, curlsocktype purpose)
{
    int sndbufsize = 4 * 1024; // 4KB send buffer
    setsockopt(curlfd, SOL_SOCKET, SO_SNDBUF,
           (const char *)&sndbufsize, sizeof(sndbufsize));

    return CURL_SOCKOPT_OK;
}

int main(int argc, char *argv[])
{
    curl_slist* pHeaderList = NULL;
    CURL* pCurl = curl_easy_init();

    curl_easy_setopt(pCurl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

    curl_easy_setopt(pCurl, CURLOPT_CUSTOMREQUEST, "POST");
    curl_easy_setopt(pCurl, CURLOPT_URL, "http://example.com");

    curl_easy_setopt(pCurl, CURLOPT_POSTFIELDS, g_Data);
    curl_easy_setopt(pCurl, CURLOPT_POSTFIELDSIZE, sizeof (g_Data));

    // Remove "Expect: 100-continue"
    pHeaderList = curl_slist_append(pHeaderList, "Expect:");

    curl_easy_setopt(pCurl, CURLOPT_HTTPHEADER, pHeaderList);

    CURLcode code = curl_easy_perform(pCurl);

    if (code == CURLE_OK)
    {
        double uploadSize = 0.0;
        curl_easy_getinfo(pCurl, CURLINFO_SIZE_UPLOAD, &uploadSize);

        printf("uploadSize = %f\n", uploadSize);

        if (static_cast<size_t>(uploadSize) == sizeof (g_Data))
        {
            printf("!!!!!!!!!! PASS\n");
        }
        else
        {
            printf("!!!!!!!!!! FAIL\n");
        }
    }
    else
    {
        printf("curl_easy_perform() failed. e = %d\n", code);
    }

    curl_slist_free_all(pHeaderList);
    curl_easy_cleanup(pCurl);

    return 0;
}