curl_multi_socket_action(3)

1curl_multi_socket_action(3)     libcurl Manual     curl_multi_socket_action(3)
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NAME

6       curl_multi_socket_action - reads/writes available data given an action
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SYNOPSIS

9       #include <curl/curl.h>
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11       CURLMcode curl_multi_socket_action(CURLM *multi_handle,
12                                          curl_socket_t sockfd,
13                                          int ev_bitmask,
14                                          int *running_handles);
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DESCRIPTION

17       When  the  application  has  detected  action  on  a  socket handled by
18       libcurl, it should call curl_multi_socket_action(3) with the sockfd ar‐
19       gument  set  to the socket with the action. When the events on a socket
20       are known, they can be passed as an events bitmask ev_bitmask by  first
21       setting  ev_bitmask to 0, and then adding using bitwise OR (|) any com‐
22       bination of events to be chosen from CURL_CSELECT_IN,  CURL_CSELECT_OUT
23       or  CURL_CSELECT_ERR.  When  the events on a socket are unknown, pass 0
24       instead, and libcurl will test the descriptor internally.  It  is  also
25       permissible  to pass CURL_SOCKET_TIMEOUT to the sockfd parameter in or‐
26       der to initiate the whole process or when a timeout occurs.
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28       At return, running_handles points to the number of running easy handles
29       within  the  multi handle. When this number reaches zero, all transfers
30       are complete/done. When you call curl_multi_socket_action(3) on a  spe‐
31       cific  socket and the counter decreases by one, it DOES NOT necessarily
32       mean that this exact socket/transfer is the  one  that  completed.  Use
33       curl_multi_info_read(3) to figure out which easy handle that completed.
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35       The  curl_multi_socket_action(3) function informs the application about
36       updates in the socket (file descriptor) status by doing none,  one,  or
37       multiple  calls  to  the  socket  callback  function set with the CURL‐
38       MOPT_SOCKETFUNCTION(3) option to curl_multi_setopt(3). They update  the
39       status with changes since the previous time the callback was called.
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41       Get  the  timeout  time by setting the CURLMOPT_TIMERFUNCTION(3) option
42       with curl_multi_setopt(3). Your application will then get  called  with
43       information on how long to wait for socket actions at most before doing
44       the timeout action: call the curl_multi_socket_action(3) function  with
45       the  sockfd  argument  set to CURL_SOCKET_TIMEOUT. You can also use the
46       curl_multi_timeout(3) function to poll the value at any given time, but
47       for an event-based system using the callback is far better than relying
48       on polling the timeout value.
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50       When this function returns error, the state of all transfers are uncer‐
51       tain  and  they cannot be continued. curl_multi_socket_action(3) should
52       not be called again on the same multi handle after an  error  has  been
53       returned, unless first removing all the handles and adding new ones.
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TYPICAL USAGE

56       1. Create a multi handle
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58       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)
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60       3.  Set  the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to
61       know what timeout value to use when waiting for socket activities.
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63       4. Add easy handles with curl_multi_add_handle()
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65       5. Provide some means to manage the sockets libcurl is  using,  so  you
66       can  check them for activity. This can be done through your application
67       code, or by way of an external library such as libevent or glib.
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69       6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...)   to
70       kickstart everything. To get one or more callbacks called.
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72       7. Wait for activity on any of libcurl's sockets, use the timeout value
73       your callback has been told.
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75       8, When activity is detected, call curl_multi_socket_action()  for  the
76       socket(s)  that  got action. If no activity is detected and the timeout
77       expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.
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EXAMPLE

80       /* the event-library gets told when there activity on the socket 'fd',
81          which we translate to a call to curl_multi_socket_action() */
82       int running;
83       rc = curl_multi_socket_action(multi_handle, fd, EVENT,
84                                     &running);
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AVAILABILITY

87       This function was added in libcurl 7.15.4, and is deemed  stable  since
88       7.16.0.
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RETURN VALUE

91       CURLMcode  type,  general  libcurl  multi  interface  error  code.  See
92       libcurl-errors(3)
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