Provided by: libcurl4-doc_7.88.1-8ubuntu1_all bug


       curl_multi_socket_action - reads/writes available data given an action


       #include <curl/curl.h>

       CURLMcode curl_multi_socket_action(CURLM *multi_handle,
                                          curl_socket_t sockfd,
                                          int ev_bitmask,
                                          int *running_handles);


       When  the  application  has detected action on a socket handled by libcurl, it should call
       curl_multi_socket_action(3) with the sockfd argument set to the socket  with  the  action.
       When  the events on a socket are known, they can be passed as an events bitmask ev_bitmask
       by first setting ev_bitmask to 0, and then adding using bitwise OR (|) any combination  of
       events  to  be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or CURL_CSELECT_ERR. When the
       events on a socket are unknown, pass 0 instead,  and  libcurl  will  test  the  descriptor
       internally.  It is also permissible to pass CURL_SOCKET_TIMEOUT to the sockfd parameter in
       order to initiate the whole process or when a timeout occurs.

       At return, running_handles points to the number of running easy handles within  the  multi
       handle.  When  this  number  reaches  zero, all transfers are complete/done. When you call
       curl_multi_socket_action(3) on a specific socket and the counter decreases by one, it DOES
       NOT  necessarily  mean  that  this  exact  socket/transfer  is the one that completed. Use
       curl_multi_info_read(3) to figure out which easy handle that completed.

       The curl_multi_socket_action(3) function informs the  application  about  updates  in  the
       socket  (file  descriptor)  status  by  doing  none,  one, or multiple calls to the socket
       callback function set with the CURLMOPT_SOCKETFUNCTION(3) option to  curl_multi_setopt(3).
       They update the status with changes since the previous time the callback was called.

       Get   the   timeout   time   by   setting   the   CURLMOPT_TIMERFUNCTION(3)   option  with
       curl_multi_setopt(3). Your application will then get called with information on  how  long
       to   wait  for  socket  actions  at  most  before  doing  the  timeout  action:  call  the
       curl_multi_socket_action(3) function with the sockfd argument set to  CURL_SOCKET_TIMEOUT.
       You  can  also use the curl_multi_timeout(3) function to poll the value at any given time,
       but for an event-based system using the callback is far better than relying on polling the
       timeout value.

       When this function returns error, the state of all transfers are uncertain and they cannot
       be continued. curl_multi_socket_action(3) should not be called again  on  the  same  multi
       handle  after an error has been returned, unless first removing all the handles and adding
       new ones.


       1. Create a multi handle

       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)

       3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to  know  what  timeout
       value to use when waiting for socket activities.

       4. Add easy handles with curl_multi_add_handle()

       5.  Provide  some  means to manage the sockets libcurl is using, so you can check them for
       activity. This can be done through your application code, or by way of an external library
       such as libevent or glib.

       6.   Call   curl_multi_socket_action(...,   CURL_SOCKET_TIMEOUT,  0,  ...)   to  kickstart
       everything. To get one or more callbacks called.

       7. Wait for activity on any of libcurl's sockets, use the timeout value your callback  has
       been told.

       8,  When  activity is detected, call curl_multi_socket_action() for the socket(s) that got
       action.   If   no   activity   is    detected    and    the    timeout    expires,    call
       curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.


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


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


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


       curl_multi_cleanup(3),  curl_multi_init(3),  curl_multi_fdset(3), curl_multi_info_read(3),
       the hiperfifo.c example