CURLOPT_CLOSESOCKETFUNCTION - callback to socket close replacement

Added in curl 7.21.7

Use the standard socket close function.

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.

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); }

CURLOPT_CLOSESOCKETFUNCTION - callback to socket close replacement

This functionality affects all supported protocols

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).

CURLOPT_CLOSESOCKETDATA(3), CURLOPT_OPENSOCKETFUNCTION(3) libcurl 2025-06-16 CURLOPT_CLOSESOCKETFUNCTION(3)

#include <curl/curl.h> int closesocket_callback(void *clientp, curl_socket_t item); CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CLOSESOCKETFUNCTION, closesocket_callback);