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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 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.

       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  com-
       plete/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 com-
       pleted.

       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 call-
       back function set with the CURLMOPT_SOCKETFUNCTION 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.

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 */

       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, sock-
       etp 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...) 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 7.16.0				    9 Jul 2006		      curl_multi_socket_action(3)
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