CURLOPT_CLOSESOCKETFUNCTION(3) Library Functions Manual
NAME
CURLOPT_CLOSESOCKETFUNCTION - callback to socket close replacement
SYNOPSIS
#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
This functionality affects all supported protocols
EXAMPLE
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();
/* call this function to close sockets */
curl_easy_setopt(curl, CURLOPT_CLOSESOCKETFUNCTION, closesocket);
curl_easy_setopt(curl, CURLOPT_CLOSESOCKETDATA, &myown);
curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
AVAILABILITY
Added in curl 7.21.7
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).
SEE ALSO
CURLOPT_CLOSESOCKETDATA(3), CURLOPT_OPENSOCKETFUNCTION(3)
libcurl 2026-03-23 CURLOPT_CLOSESOCKETFUNCTION(3)
curl 8.19.0 - Generated Fri Mar 27 07:22:06 CDT 2026