Do `curl -X GET -I www.example.com` with liburl

libcurl_demo.c

#include <stdlib.h>
#include <string.h>

#include "libcurl_demo.h"

struct string {
    char *ptr;
    size_t len;
};

void init_string(struct string *s) {
    s->len = 0;
    s->ptr = malloc(s->len+1);
    if (s->ptr == NULL) {
        fprintf(stderr, "malloc() failed\n");
        exit(EXIT_FAILURE);
    }
    s->ptr[0] = '\0';
}

size_t writefunc(void *ptr, size_t size, size_t nmemb, struct string *s) {
    size_t new_len = s->len + size*nmemb;
    s->ptr = realloc(s->ptr, new_len+1);
    if (s->ptr == NULL) {
        fprintf(stderr, "realloc() failed\n");
        exit(EXIT_FAILURE);
    }
    memcpy(s->ptr+s->len, ptr, size*nmemb);
    s->ptr[new_len] = '\0';
    s->len = new_len;
    
    return size*nmemb;
}

CURLcode getUrlHeader(char *url) {
    CURL *curl;
    CURLcode res = CURLE_OK;
    curl = curl_easy_init();
    if (curl) {
        struct string s;
        init_string(&s);
        
        curl_easy_setopt(curl, CURLOPT_URL,url);
        // Line below will change HTTP Method to "HEAD".
        curl_easy_setopt(curl, CURLOPT_NOBODY, 1L);
        curl_easy_setopt(curl, CURLOPT_HEADER, 1L);
        // Force to set HTTP Method to "GET"
        curl_easy_setopt(curl, CURLOPT_HTTPGET, 1L);
//        curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "GET");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writefunc);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &s);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        printf("%s\n", s.ptr);
        free(s.ptr);
    }
    return res;
}

libcurl_demo.h

#import "curl.h"

CURLcode getUrlHeader(char *url);