1--- 2c: Copyright (C) Daniel Stenberg, <daniel.se>, et al. 3SPDX-License-Identifier: curl 4Title: curl_multi_socket_action 5Section: 3 6Source: libcurl 7See-also: 8 - curl_multi_cleanup (3) 9 - curl_multi_fdset (3) 10 - curl_multi_info_read (3) 11 - curl_multi_init (3) 12 - the hiperfifo.c example 13--- 14 15# NAME 16 17curl_multi_socket_action - reads/writes available data given an action 18 19# SYNOPSIS 20 21~~~c 22#include <curl/curl.h> 23 24CURLMcode curl_multi_socket_action(CURLM *multi_handle, 25 curl_socket_t sockfd, 26 int ev_bitmask, 27 int *running_handles); 28~~~ 29 30# DESCRIPTION 31 32When the application has detected action on a socket handled by libcurl, it 33should call curl_multi_socket_action(3) with the **sockfd** argument 34set to the socket with the action. When the events on a socket are known, they 35can be passed as an events bitmask **ev_bitmask** by first setting 36**ev_bitmask** to 0, and then adding using bitwise OR (|) any combination of 37events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or 38CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and 39libcurl tests the descriptor internally. It is also permissible to pass 40CURL_SOCKET_TIMEOUT to the **sockfd** parameter in order to initiate the 41whole process or when a timeout occurs. 42 43At return, **running_handles** points to the number of running easy handles 44within the multi handle. When this number reaches zero, all transfers are 45complete/done. When you call curl_multi_socket_action(3) on a specific 46socket and the counter decreases by one, it DOES NOT necessarily mean that 47this exact socket/transfer is the one that completed. Use 48curl_multi_info_read(3) to figure out which easy handle that completed. 49 50The curl_multi_socket_action(3) function informs the application about 51updates in the socket (file descriptor) status by doing none, one, or multiple 52calls to the socket callback function set with the 53CURLMOPT_SOCKETFUNCTION(3) option to curl_multi_setopt(3). They 54update the status with changes since the previous time the callback was 55called. 56 57Get the timeout time by setting the CURLMOPT_TIMERFUNCTION(3) option 58with curl_multi_setopt(3). Your application then gets called with 59information on how long to wait for socket actions at most before doing the 60timeout action: call the curl_multi_socket_action(3) function with the 61**sockfd** argument set to CURL_SOCKET_TIMEOUT. You can also use the 62curl_multi_timeout(3) function to poll the value at any given time, but 63for an event-based system using the callback is far better than relying on 64polling the timeout value. 65 66When this function returns error, the state of all transfers are uncertain and 67they cannot be continued. curl_multi_socket_action(3) should not be 68called again on the same multi handle after an error has been returned, unless 69first removing all the handles and adding new ones. 70 71# TYPICAL USAGE 72 731. Create a multi handle 74 752. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3) 76 773. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to 78know what timeout value to use when waiting for socket activities. 79 804. Add easy handles with curl_multi_add_handle() 81 825. Provide some means to manage the sockets libcurl is using, so you can check 83them for activity. This can be done through your application code, or by way 84of an external library such as libevent or glib. 85 866. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) 87to kickstart everything. To get one or more callbacks called. 88 897. Wait for activity on any of libcurl's sockets, use the timeout value your 90callback has been told. 91 928, When activity is detected, call curl_multi_socket_action() for the 93socket(s) that got action. If no activity is detected and the timeout expires, 94call curl_multi_socket_action(3) with *CURL_SOCKET_TIMEOUT*. 95 96# EXAMPLE 97 98~~~c 99int main(void) 100{ 101 /* the event-library gets told when there activity on the socket 'fd', 102 which we translate to a call to curl_multi_socket_action() */ 103 int running; 104 CURLM *multi; /* the stack we work with */ 105 int fd; /* the descriptor that had action */ 106 int bitmask; /* what activity that happened */ 107 CURLMcode mc = curl_multi_socket_action(multi, fd, bitmask, &running); 108 if(mc) 109 printf("error: %s\n", curl_multi_strerror(mc)); 110} 111~~~ 112 113# AVAILABILITY 114 115This function was added in libcurl 7.15.4, and is deemed stable since 7.16.0. 116 117# RETURN VALUE 118 119CURLMcode type, general libcurl multi interface error code. See 120libcurl-errors(3) 121