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curl_multi_assign(3) libcurl Manual curl_multi_assign(3)
curl_multi_assign - set data to associate with an internal socket
CURLMcode curl_multi_assign(CURLM *multi_handle, curl_socket_t sockfd,
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
/* make our struct pointer associated with socket fd */
mc = curl_multi_assign(multi_handle, fd, ourstructp);
Added in 7.15.5
The standard CURLMcode for multi interface error codes.
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.
libcurl 7.86.0 May 17, 2022 curl_multi_assign(3)