Tribblix: manual page: curl_multi

curl_multi_assign(3) Introduction to Library Functions curl_multi_assign(3)

NAME

curl_multi_assign - set data to associate with an internal socket

SYNOPSIS

#include <curl/curl.h>

CURLMcode curl_multi_assign(CURLM *multi_handle, curl_socket_t sockfd,
void *sockptr);

DESCRIPTION

This function creates an association in the multi handle between the
given socket and a private pointer of the application. This is
designed for curl_multi_socket_action(3) uses.

When set, the sockptr pointer is passed to all future socket
callbacks for the specific sockfd socket.

If the given sockfd is not already in use by libcurl, this function
returns an error.

libcurl only keeps one single pointer associated with a socket, so
calling this function several times for the same socket makes the
last set pointer get used.

The idea here being that this association (socket to private pointer)
is something that just about every application that uses this API
needs and then libcurl can just as well do it since it already has
the necessary functionality.

It is acceptable to call this function from your multi callback
functions.

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

int main(void)
{
CURLM *multi = curl_multi_init();
void *ourstructp; /* pointer to our data */
curl_socket_t fd; /* file descriptor to associate our data with */

/* make our struct pointer associated with socket fd */
CURLMcode mc = curl_multi_assign(multi, fd, ourstructp);
if(mc)
printf("error: %s\n", curl_multi_strerror(mc));
}

TYPICAL USAGE

In a typical application you allocate a struct or at least use some
kind of semi-dynamic data for each socket that we must wait for
action on when using the curl_multi_socket_action(3) approach.

When our socket-callback gets called by libcurl and we get to know
about yet another socket to wait for, we can use curl_multi_assign(3)
to point out the particular data so that when we get updates about
this same socket again, we do not have to find the struct associated
with this socket by ourselves.

AVAILABILITY

Added in curl 7.15.5

RETURN VALUE

This function returns a CURLMcode indicating success or error.

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