---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_CLOSESOCKETFUNCTION
Section: 3
Source: libcurl
See-also:
  - CURLOPT_CLOSESOCKETDATA (3)
  - CURLOPT_OPENSOCKETFUNCTION (3)
Protocol:
  - All
Added-in: 7.21.7
---

# NAME

CURLOPT_CLOSESOCKETFUNCTION - callback to socket close replacement

# SYNOPSIS

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

int closesocket_callback(void *clientp, curl_socket_t item);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CLOSESOCKETFUNCTION,
                          closesocket_callback);
~~~

# DESCRIPTION

Pass a pointer to your callback function, which should match the prototype
shown above.

This callback function gets called by libcurl instead of the *close(3)* or
*closesocket(3)* call when sockets are closed (not for any other file
descriptors). This is pretty much the reverse to the
CURLOPT_OPENSOCKETFUNCTION(3) option. Return 0 to signal success and 1
if there was an error.

The *clientp* pointer is set with
CURLOPT_CLOSESOCKETDATA(3). *item* is the socket libcurl wants to be
closed.

Note that when using multi/share handles, your callback may get invoked even
after the easy handle has been cleaned up. The callback and data is
inherited by a new connection and that connection may live longer
than the transfer itself in the multi/share handle's connection cache.

# DEFAULT

Use the standard socket close function.

# %PROTOCOLS%

# EXAMPLE

~~~c
struct priv {
  void *custom;
};

static int closesocket(void *clientp, curl_socket_t item)
{
  struct priv *my = clientp;
  printf("our ptr: %p\n", my->custom);

  printf("libcurl wants to close %d now\n", (int)item);
  return 0;
}

int main(void)
{
  struct priv myown;
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    /* call this function to close sockets */
    curl_easy_setopt(curl, CURLOPT_CLOSESOCKETFUNCTION, closesocket);
    curl_easy_setopt(curl, CURLOPT_CLOSESOCKETDATA, &myown);

    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
~~~

# %AVAILABILITY%

# RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
libcurl-errors(3).
