---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_OPENSOCKETDATA
Section: 3
Source: libcurl
See-also:
  - CURLOPT_CLOSESOCKETFUNCTION (3)
  - CURLOPT_OPENSOCKETFUNCTION (3)
  - CURLOPT_SOCKOPTFUNCTION (3)
Protocol:
  - All
---

# NAME

CURLOPT_OPENSOCKETDATA - pointer passed to open socket callback

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETDATA, void *pointer);
~~~

# DESCRIPTION

Pass a *pointer* that is untouched by libcurl and passed as the first
argument in the open socket callback set with
CURLOPT_OPENSOCKETFUNCTION(3).

# DEFAULT

The default value of this parameter is NULL.

# EXAMPLE

~~~c
/* make libcurl use the already established socket 'sockfd' */

static curl_socket_t opensocket(void *clientp,
                                curlsocktype purpose,
                                struct curl_sockaddr *address)
{
  curl_socket_t sockfd;
  sockfd = *(curl_socket_t *)clientp;
  /* the actual externally set socket is passed in via the OPENSOCKETDATA
     option */
  return sockfd;
}

static int sockopt_callback(void *clientp, curl_socket_t curlfd,
                            curlsocktype purpose)
{
  /* This return code was added in libcurl 7.21.5 */
  return CURL_SOCKOPT_ALREADY_CONNECTED;
}

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    extern int sockfd; /* the already connected one */

    /* libcurl thinks that you connect to the host
     * and port that you specify in the URL option. */
    curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999");
    /* call this function to get a socket */
    curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket);
    curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd);

    /* call this function to set options for the socket */
    curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

    res = curl_easy_perform(curl);

    curl_easy_cleanup(curl);
  }
}
~~~

# AVAILABILITY

Added in 7.17.1

# RETURN VALUE

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