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, int ev_bitmask,
13                                          int *running_handles);
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DESCRIPTION

16       When  the  application  has  detected  action  on  a  socket handled by
17       libcurl, it should call  curl_multi_socket_action(3)  with  the  sockfd
18       argument set to the socket with the action. When the events on a socket
19       are known, they can be passed as an events bitmask ev_bitmask by  first
20       setting  ev_bitmask to 0, and then adding using bitwise OR (|) any com‐
21       bination of events to be chosen from CURL_CSELECT_IN,  CURL_CSELECT_OUT
22       or  CURL_CSELECT_ERR.  When  the events on a socket are unknown, pass 0
23       instead, and libcurl will test the descriptor internally.
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25       At return, the integer running_handles points to will contain the  num‐
26       ber  of  running easy handles within the multi handle. When this number
27       reaches  zero,  all  transfers  are  complete/done.   When   you   call
28       curl_multi_socket_action(3)  on  a  specific  socket  and  the  counter
29       decreases by  one,  it  DOES  NOT  necessarily  mean  that  this  exact
30       socket/transfer  is the one that completed. Use curl_multi_info_read(3)
31       to figure out which easy handle that completed.
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33       The curl_multi_socket_action(3) functions inform the application  about
34       updates  in  the socket (file descriptor) status by doing none, one, or
35       multiple calls to the socket  callback  function  set  with  the  CURL‐
36       MOPT_SOCKETFUNCTION  option  to  curl_multi_setopt(3).  They update the
37       status with changes since the previous time the callback was called.
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39       Get the timeout time by setting the CURLMOPT_TIMERFUNCTION option  with
40       curl_multi_setopt(3). Your application will then get called with infor‐
41       mation on how long to wait for socket actions at most before doing  the
42       timeout  action: call the curl_multi_socket_action(3) function with the
43       sockfd argument set  to  CURL_SOCKET_TIMEOUT.  You  can  also  use  the
44       curl_multi_timeout(3) function to poll the value at any given time, but
45       for an event-based system using the callback is far better than relying
46       on polling the timeout value.
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CALLBACK DETAILS

49       The socket callback function uses a prototype like this
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51         int curl_socket_callback(CURL *easy,      /* easy handle */
52                                  curl_socket_t s, /* socket */
53                                  int action,      /* see values below */
54                                  void *userp,    /* private callback pointer */
55                                  void *socketp); /* private socket pointer */
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57       The callback MUST return 0.
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59       The  easy argument is a pointer to the easy handle that deals with this
60       particular socket. Note that a single  handle  may  work  with  several
61       sockets simultaneously.
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63       The  s  argument  is  the actual socket value as you use it within your
64       system.
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66       The action argument to the callback has one of five values:
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68              CURL_POLL_NONE (0)
69                     register, not interested in readiness (yet)
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71              CURL_POLL_IN (1)
72                     register, interested in read readiness
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74              CURL_POLL_OUT (2)
75                     register, interested in write readiness
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77              CURL_POLL_INOUT (3)
78                     register, interested in both read and write readiness
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80              CURL_POLL_REMOVE (4)
81                     unregister
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83       The socketp argument is a private pointer you have previously set  with
84       curl_multi_assign(3)  to be associated with the s socket. If no pointer
85       has been set, socketp will be NULL. This argument is of course  a  ser‐
86       vice to applications that want to keep certain data or structs that are
87       strictly associated to the given socket.
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89       The userp argument is a private pointer you have  previously  set  with
90       curl_multi_setopt(3) and the CURLMOPT_SOCKETDATA option.
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RETURN VALUE

93       CURLMcode type, general libcurl multi interface error code.
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95       Before  version  7.20.0:  If you receive CURLM_CALL_MULTI_PERFORM, this
96       basically means that you should call curl_multi_socket_action(3)  again
97       before  you  wait for more actions on libcurl's sockets. You don't have
98       to do it immediately, but the return code means that libcurl  may  have
99       more  data  available  to return or that there may be more data to send
100       off before it is "satisfied".
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102       The return code from this function is for the whole multi stack.  Prob‐
103       lems still might have occurred on individual transfers even when one of
104       these functions return OK.
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TYPICAL USAGE

107       1. Create a multi handle
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109       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
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111       3. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know
112       what timeout value to use when waiting for socket activities.
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114       4. Add easy handles with curl_multi_add_handle()
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116       5.  Provide  some  means to manage the sockets libcurl is using, so you
117       can check them for activity. This can be done through your  application
118       code, or by way of an external library such as libevent or glib.
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120       6.  Call  curl_multi_socket_action(...CURL_SOCKET_TIMEOUT...)  to kick‐
121       start everything. To get one or more callbacks called.
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123       7. Wait for activity on any of libcurl's sockets, use the timeout value
124       your callback has been told
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126       8,  When  activity is detected, call curl_multi_socket_action() for the
127       socket(s) that got action. If no activity is detected and  the  timeout
128       expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT
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AVAILABILITY

131       This  function  was added in libcurl 7.15.4, and is deemed stable since
132       7.16.0.
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