1--- 2c: Copyright (C) Daniel Stenberg, <daniel@haxx.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 13Protocol: 14 - All 15--- 16 17# NAME 18 19curl_multi_socket_action - reads/writes available data given an action 20 21# SYNOPSIS 22 23~~~c 24#include <curl/curl.h> 25 26CURLMcode curl_multi_socket_action(CURLM *multi_handle, 27 curl_socket_t sockfd, 28 int ev_bitmask, 29 int *running_handles); 30~~~ 31 32# DESCRIPTION 33 34When the application has detected action on a socket handled by libcurl, it 35should call curl_multi_socket_action(3) with the **sockfd** argument 36set to the socket with the action. When the events on a socket are known, they 37can be passed as an events bitmask **ev_bitmask** by first setting 38**ev_bitmask** to 0, and then adding using bitwise OR (|) any combination of 39events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or 40CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and 41libcurl tests the descriptor internally. It is also permissible to pass 42CURL_SOCKET_TIMEOUT to the **sockfd** parameter in order to initiate the 43whole process or when a timeout occurs. 44 45At return, **running_handles** points to the number of running easy handles 46within the multi handle. When this number reaches zero, all transfers are 47complete/done. When you call curl_multi_socket_action(3) on a specific 48socket and the counter decreases by one, it DOES NOT necessarily mean that 49this exact socket/transfer is the one that completed. Use 50curl_multi_info_read(3) to figure out which easy handle that completed. 51 52The curl_multi_socket_action(3) function informs the application about 53updates in the socket (file descriptor) status by doing none, one, or multiple 54calls to the socket callback function set with the 55CURLMOPT_SOCKETFUNCTION(3) option to curl_multi_setopt(3). They 56update the status with changes since the previous time the callback was 57called. 58 59Get the timeout time by setting the CURLMOPT_TIMERFUNCTION(3) option 60with curl_multi_setopt(3). Your application then gets called with 61information on how long to wait for socket actions at most before doing the 62timeout action: call the curl_multi_socket_action(3) function with the 63**sockfd** argument set to CURL_SOCKET_TIMEOUT. You can also use the 64curl_multi_timeout(3) function to poll the value at any given time, but 65for an event-based system using the callback is far better than relying on 66polling the timeout value. 67 68When this function returns error, the state of all transfers are uncertain and 69they cannot be continued. curl_multi_socket_action(3) should not be 70called again on the same multi handle after an error has been returned, unless 71first removing all the handles and adding new ones. 72 73# TYPICAL USAGE 74 751. Create a multi handle 76 772. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3) 78 793. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to 80know what timeout value to use when waiting for socket activities. 81 824. Add easy handles with curl_multi_add_handle() 83 845. Provide some means to manage the sockets libcurl is using, so you can check 85them for activity. This can be done through your application code, or by way 86of an external library such as libevent or glib. 87 886. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) 89to kickstart everything. To get one or more callbacks called. 90 917. Wait for activity on any of libcurl's sockets, use the timeout value your 92callback has been told. 93 948, When activity is detected, call curl_multi_socket_action() for the 95socket(s) that got action. If no activity is detected and the timeout expires, 96call curl_multi_socket_action(3) with *CURL_SOCKET_TIMEOUT*. 97 98# EXAMPLE 99 100~~~c 101int main(void) 102{ 103 /* the event-library gets told when there activity on the socket 'fd', 104 which we translate to a call to curl_multi_socket_action() */ 105 int running; 106 CURLM *multi; /* the stack we work with */ 107 int fd; /* the descriptor that had action */ 108 int bitmask; /* what activity that happened */ 109 CURLMcode mc = curl_multi_socket_action(multi, fd, bitmask, &running); 110 if(mc) 111 printf("error: %s\n", curl_multi_strerror(mc)); 112} 113~~~ 114 115# AVAILABILITY 116 117This function was added in libcurl 7.15.4, and is deemed stable since 7.16.0. 118 119# RETURN VALUE 120 121CURLMcode type, general libcurl multi interface error code. See 122libcurl-errors(3) 123