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curl_multi_socket_action(3)     libcurl Manual     curl_multi_socket_action(3)

       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

       At return, the integer running_handles points to will contain 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) functions inform 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_SOCKETFUNC-
       TION 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 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.

       The socket callback function uses a prototype like this

         int curl_socket_callback(CURL *easy,      /* easy handle */
                                  curl_socket_t s, /* socket */
                                  int action,      /* see values below */
                                  void *userp,    /* private callback pointer */
                                  void *socketp); /* private socket pointer */

       The callback MUST return 0.

       The  easy  argument  is a pointer to the easy handle that deals with this particular socket. Note that a single
       handle may work with several sockets simultaneously.

       The s argument is the actual socket value as you use it within your system.

       The action argument to the callback has one of five values:

              CURL_POLL_NONE (0)
                     register, not interested in readiness (yet)

              CURL_POLL_IN (1)
                     register, interested in read readiness

              CURL_POLL_OUT (2)
                     register, interested in write readiness

              CURL_POLL_INOUT (3)
                     register, interested in both read and write readiness

              CURL_POLL_REMOVE (4)

       The socketp argument is a private pointer you have previously set with curl_multi_assign(3)  to  be  associated
       with  the  s  socket. If no pointer has been set, socketp will be NULL. This argument is of course a service to
       applications that want to keep certain data or structs that are strictly associated to the given socket.

       The userp argument is a private pointer you  have  previously  set  with  curl_multi_setopt(3)  and  the  CURL-
       MOPT_SOCKETDATA option.

       CURLMcode type, general libcurl multi interface error code.

       Before  version  7.20.0:  If  you  receive  CURLM_CALL_MULTI_PERFORM, this basically means that you should call
       curl_multi_socket_action(3) again before you wait for more actions on libcurl's sockets. You don't have  to  do
       it immediately, but the return code means that libcurl may have more data available to return or that there may
       be more data to send off before it is "satisfied".

       The return code from this function is for the whole multi stack.  Problems still might have occurred  on  indi-
       vidual transfers even when one of these functions return OK.

       1. Create a multi handle

       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION

       3.  Set the timeout callback with CURLMOPT_TIMERFUNCTION, 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() 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

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

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

libcurl 7.16.0                    9 Jul 2006       curl_multi_socket_action(3)