curl_multi_socket_action(3)     libcurl Manual     curl_multi_socket_action(3)

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 com-
       bination 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  spe-
       cific  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  CURL-
       MOPT_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  ser-
       vice 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.  Prob-
       lems 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

libcurl 7.54.0                   June 07, 2016     curl_multi_socket_action(3)