curl_multi_socket_action.md (4592B)
1 --- 2 c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3 SPDX-License-Identifier: curl 4 Title: curl_multi_socket_action 5 Section: 3 6 Source: libcurl 7 See-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 Protocol: 14 - All 15 Added-in: 7.15.4 16 --- 17 18 # NAME 19 20 curl_multi_socket_action - read/write available data given an action 21 22 # SYNOPSIS 23 24 ~~~c 25 #include <curl/curl.h> 26 27 CURLMcode curl_multi_socket_action(CURLM *multi_handle, 28 curl_socket_t sockfd, 29 int ev_bitmask, 30 int *running_handles); 31 ~~~ 32 33 # DESCRIPTION 34 35 When the application has detected action on a socket handled by libcurl, it 36 should call curl_multi_socket_action(3) with the **sockfd** argument 37 set to the socket with the action. When the events on a socket are known, they 38 can be passed as an events bitmask **ev_bitmask** by first setting 39 **ev_bitmask** to 0, and then adding using bitwise OR (|) any combination of 40 events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or 41 CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and 42 libcurl tests the descriptor internally. It is also permissible to pass 43 CURL_SOCKET_TIMEOUT to the **sockfd** parameter in order to initiate the 44 whole process or when a timeout occurs. 45 46 At return, **running_handles** points to the number of running easy handles 47 within the multi handle. When this number reaches zero, all transfers are 48 complete/done. When you call curl_multi_socket_action(3) on a specific 49 socket and the counter decreases by one, it DOES NOT necessarily mean that 50 this exact socket/transfer is the one that completed. Use 51 curl_multi_info_read(3) to figure out which easy handle that completed. 52 53 The curl_multi_socket_action(3) function informs the application about 54 updates in the socket (file descriptor) status by doing none, one, or multiple 55 calls to the socket callback function set with the 56 CURLMOPT_SOCKETFUNCTION(3) option to curl_multi_setopt(3). They 57 update the status with changes since the previous time the callback was 58 called. 59 60 Get the timeout time by setting the CURLMOPT_TIMERFUNCTION(3) option 61 with curl_multi_setopt(3). Your application then gets called with 62 information on how long to wait for socket actions at most before doing the 63 timeout action: call the curl_multi_socket_action(3) function with the 64 **sockfd** argument set to CURL_SOCKET_TIMEOUT. You can also use the 65 curl_multi_timeout(3) function to poll the value at any given time, but 66 for an event-based system using the callback is far better than relying on 67 polling the timeout value. 68 69 When this function returns error, the state of all transfers are uncertain and 70 they cannot be continued. curl_multi_socket_action(3) should not be 71 called again on the same multi handle after an error has been returned, unless 72 first removing all the handles and adding new ones. 73 74 # TYPICAL USAGE 75 76 1. Create a multi handle 77 78 2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3) 79 80 3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to 81 know what timeout value to use when waiting for socket activities. 82 83 4. Add easy handles with curl_multi_add_handle() 84 85 5. Provide some means to manage the sockets libcurl is using, so you can check 86 them for activity. This can be done through your application code, or by way 87 of an external library such as libevent or glib. 88 89 6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) 90 to kickstart everything. To get one or more callbacks called. 91 92 7. Wait for activity on any of libcurl's sockets, use the timeout value your 93 callback has been told. 94 95 8, When activity is detected, call curl_multi_socket_action() for the 96 socket(s) that got action. If no activity is detected and the timeout expires, 97 call curl_multi_socket_action(3) with *CURL_SOCKET_TIMEOUT*. 98 99 # %PROTOCOLS% 100 101 # EXAMPLE 102 103 ~~~c 104 int main(void) 105 { 106 /* the event-library gets told when there activity on the socket 'fd', 107 which we translate to a call to curl_multi_socket_action() */ 108 int running = 0; 109 int fd = 3; /* the descriptor that had action */ 110 int bitmask = 2; /* what activity that happened */ 111 112 CURLM *multi = curl_multi_init(); 113 114 CURLMcode mc = curl_multi_socket_action(multi, fd, bitmask, &running); 115 if(mc) 116 printf("error: %s\n", curl_multi_strerror(mc)); 117 } 118 ~~~ 119 120 # %AVAILABILITY% 121 122 # RETURN VALUE 123 124 This function returns a CURLMcode indicating success or error. 125 126 CURLM_OK (0) means everything was OK, non-zero means an error occurred, see 127 libcurl-errors(3).