---
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)
  - CURLMOPT_SOCKETFUNCTION (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.

# NOTES ON CONNECTION REUSE

The close socket callback is invoked when libcurl closes a socket it owns.
When using the multi interface, the callback and
CURLOPT_CLOSESOCKETDATA(3) are copied from the *first* easy handle that
creates the socket used for a connection; changing this option on a subsequent
easy handle that reuses the same connection has no effect for that connection.
The callback is stored with the connection because the connection and its
associated socket may outlive the easy handle that created it, so that libcurl
can still invoke it when the socket is closed even after that handle has been
cleaned up.

# 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).
