NAME

       curl_multi_socket_action - reads/writes available data given an action

SYNOPSIS

       #include <curl/curl.h>

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

DESCRIPTION

       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) 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_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.

CALLBACK DETAILS

       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,
                                                     NULL if not
                                                     previously assigned with
                                                     curl_multi_assign(3) */

       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)
                     unregister

       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 CURLMOPT_SOCKETDATA option.

RETURN VALUE

       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 individual transfers even when one of these functions return OK.

TYPICAL USAGE

       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(...,  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.

AVAILABILITY

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

SEE ALSO

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