1--- 2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3SPDX-License-Identifier: curl 4Title: curl_multi_assign 5Section: 3 6Source: libcurl 7See-also: 8 - curl_multi_setopt (3) 9 - curl_multi_socket_action (3) 10Protocol: 11 - All 12--- 13 14# NAME 15 16curl_multi_assign - set data to associate with an internal socket 17 18# SYNOPSIS 19 20~~~c 21#include <curl/curl.h> 22 23CURLMcode curl_multi_assign(CURLM *multi_handle, curl_socket_t sockfd, 24 void *sockptr); 25~~~ 26 27# DESCRIPTION 28 29This function creates an association in the multi handle between the given 30socket and a private pointer of the application. This is designed for 31curl_multi_socket_action(3) uses. 32 33When set, the *sockptr* pointer is passed to all future socket callbacks 34for the specific *sockfd* socket. 35 36If the given *sockfd* is not already in use by libcurl, this function 37returns an error. 38 39libcurl only keeps one single pointer associated with a socket, so calling 40this function several times for the same socket makes the last set pointer get 41used. 42 43The idea here being that this association (socket to private pointer) is 44something that just about every application that uses this API needs and then 45libcurl can just as well do it since it already has the necessary 46functionality. 47 48It is acceptable to call this function from your multi callback functions. 49 50# EXAMPLE 51 52~~~c 53int main(void) 54{ 55 CURLM *multi = curl_multi_init(); 56 void *ourstructp; /* pointer to our data */ 57 curl_socket_t fd; /* file descriptor to associate our data with */ 58 59 /* make our struct pointer associated with socket fd */ 60 CURLMcode mc = curl_multi_assign(multi, fd, ourstructp); 61 if(mc) 62 printf("error: %s\n", curl_multi_strerror(mc)); 63} 64~~~ 65 66# AVAILABILITY 67 68Added in 7.15.5 69 70# RETURN VALUE 71 72The standard CURLMcode for multi interface error codes. 73 74# TYPICAL USAGE 75 76In a typical application you allocate a struct or at least use some kind of 77semi-dynamic data for each socket that we must wait for action on when using 78the curl_multi_socket_action(3) approach. 79 80When our socket-callback gets called by libcurl and we get to know about yet 81another socket to wait for, we can use curl_multi_assign(3) to point out 82the particular data so that when we get updates about this same socket again, 83we do not have to find the struct associated with this socket by ourselves. 84
