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