С++ libcurl проверяет заголовок перед загрузкой тела одним запросом

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

/* Auxiliary function that waits on the socket. */
static int wait_on_socket(curl_socket_t sockfd, int for_recv, long timeout_ms)
{
  struct timeval tv;
  fd_set infd, outfd, errfd;
  int res;

  tv.tv_sec = timeout_ms / 1000;
  tv.tv_usec= (timeout_ms % 1000) * 1000;

  FD_ZERO(&infd);
  FD_ZERO(&outfd);
  FD_ZERO(&errfd);

  FD_SET(sockfd, &errfd); /* always check for error */

  if(for_recv)
  {
    FD_SET(sockfd, &infd);
  }
  else
  {
    FD_SET(sockfd, &outfd);
  }

  /* select() returns the number of signalled sockets or -1 */
  res = select(sockfd + 1, &infd, &outfd, &errfd, &tv);
  return res;
}

int main(void)
{
  CURL *curl;
  CURLcode res;
  /* Minimalistic http request */
  const char *request = "GET / HTTP/1.0\r\nHost: m0g.net\r\n\r\n";
  curl_socket_t sockfd; /* socket */
  long sockextr;
  size_t iolen;
  curl_off_t nread;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "http://m0g.net");
    /* Do not do the transfer - only connect to host */
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    res = curl_easy_perform(curl);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", strerror(res));
      return 1;
    }

    /* Extract the socket from the curl handle - we'll need it for waiting.
     * Note that this API takes a pointer to a 'long' while we use
     * curl_socket_t for sockets otherwise.
     */
    res = curl_easy_getinfo(curl, CURLINFO_LASTSOCKET, &sockextr);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", curl_easy_strerror(res));
      return 1;
    }

    sockfd = sockextr;

    /* wait for the socket to become ready for sending */
    if(!wait_on_socket(sockfd, 0, 60000L))
    {
      printf("Error: timeout.\n");
      return 1;
    }

    puts("Sending request.");
    /* Send the request. Real applications should check the iolen
     * to see if all the request has been sent */
    res = curl_easy_send(curl, request, strlen(request), &iolen);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", curl_easy_strerror(res));
      return 1;
    }
    puts("Reading response.");
    char data[2048];
    int idxread=0;

    /* read the response */
    for(;;)
    {
      char buf[1024];

      wait_on_socket(sockfd, 1, 60000L);
      res = curl_easy_recv(curl, buf, 32, &iolen);

      if(CURLE_OK != res)
        break;

      if (nread+idxread > 2048)
          break;

      strncpy(data+idxread,buf,nread);
      idxread+=nread;

      if (strstr(data,"\r\n\r\n") != NULL) {
        if (strstr(data,"Content-Type: text/html") == NULL) {
            printf("not an html document.");
            return 2;
        }
      }

      nread = (curl_off_t)iolen;

      printf("Received %" CURL_FORMAT_CURL_OFF_T " bytes.\n", nread);
    }
    printf("'''%s'''\n", data);

    /* always cleanup */
    curl_easy_cleanup(curl);
  }
  return 0;
}