CURLINFO_ACTIVESOCKET - Man Page

#include <curl/curl.h>

CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_ACTIVESOCKET,
                           curl_socket_t *socket);

Pass a pointer to a curl_socket_t to receive the most recently active socket used for the transfer connection by this curl session. If the socket is no longer valid, CURL_SOCKET_BAD is returned. When you are finished working with the socket, you must call curl_easy_cleanup(3) as usual on the easy handle and let libcurl close the socket and cleanup other resources associated with the handle. This option returns the active socket only after the transfer is complete, and is typically used in combination with CURLOPT_CONNECT_ONLY(3), which skips the transfer phase.

CURLINFO_ACTIVESOCKET(3) was added as a replacement for CURLINFO_LASTSOCKET(3) since that one is not working on all platforms.

This functionality affects all supported protocols

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_socket_t sockfd;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* Do not do the transfer - only connect to host */
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    res = curl_easy_perform(curl);
    if(res != CURLE_OK) {
      printf("Error: %s\n", curl_easy_strerror(res));
      curl_easy_cleanup(curl);
      return 1;
    }

    /* Extract the socket from the curl handle */
    res = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);
    if(!res && sockfd != CURL_SOCKET_BAD) {
      /* operate on sockfd */
    }

    curl_easy_cleanup(curl);
  }
}

Added in curl 7.45.0

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLINFO_LASTSOCKET(3), CURLOPT_CONNECT_ONLY(3), curl_easy_getinfo(3), curl_easy_setopt(3)

curl_easy_getinfo(3), curl_easy_recv(3), curl_easy_send(3), CURLINFO_LASTSOCKET(3), CURLOPT_CONNECT_ONLY(3).