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curl_multi_assign(3)                libcurl               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 will be passed to all future socket
       callbacks for the specific sockfd socket.

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

       libcurl only keeps one single pointer associated with a socket, so
       calling this function several times for the same socket will make 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 will
       need and then libcurl can just as well do it since it already has an
       internal hash table lookup for this.

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

EXAMPLE
        /* make our struct pointer associated with socket fd */
        mc = curl_multi_assign(multi_handle, fd, ourstructp);

AVAILABILITY
       Added in 7.15.5

RETURN VALUE
       The standard CURLMcode for multi interface error codes.

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.

SEE ALSO
       curl_multi_setopt(3), curl_multi_socket_action(3)

libcurl 8.1.2                   April 26, 2023            curl_multi_assign(3)