https-proxy-test.c

#include <stdio.h>
#include <curl/curl.h>

/*
 * $ gcc -Wall -L ./lib/.libs/ -I./include/ -lcurl https-proxy-test.c -o https-proxy-test
 * $ ./https-proxy-test
 */

#define VERBOSE 0

size_t WriteOutput(void *ptr, size_t size, size_t nmemb, void *stream);
size_t WriteHeader(void *ptr, size_t size, size_t nmemb, void *stream);

long realHeaderSize = 0;

int main(int argc, char *argv[])
{
    CURL *curl;
    long headerSize;

#if VERBOSE > 0
    curl_version_info_data *data = curl_version_info(CURLVERSION_NOW);
    printf("libcurl version: %s\n\n", data->version);
#endif

    curl_global_init(CURL_GLOBAL_ALL);
    curl = curl_easy_init();

    curl_easy_setopt(curl, CURLOPT_PROXY, "proxy:8080");

    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, *WriteOutput);
    curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, *WriteHeader);

    curl_easy_setopt(curl, CURLOPT_URL, "https://www.google.com/");
    curl_easy_perform(curl);

    curl_easy_getinfo(curl, CURLINFO_HEADER_SIZE, &headerSize);
    printf("header length is ........: %lu\n", headerSize);
    printf("header length should be..: %lu\n", realHeaderSize);

    return 0;
}

size_t WriteOutput(void *ptr, size_t size, size_t nmemb, void *stream)
{
    return nmemb * size;
}

size_t WriteHeader(void *ptr, size_t size, size_t nmemb, void *stream)
{
    realHeaderSize += size * nmemb;

#if VERBOSE > 1
    printf("%s", (char *)(ptr));
#endif

    return nmemb * size;
}