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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 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.

       At return, the integer running_handles points to will contain the  num‐
       ber  of	still  running easy handles within the multi handle. When this
       number reaches zero, all transfers are complete/done.  Note  that  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	 CURL‐
       MOPT_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 infor‐
       mation 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

       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


       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.

       CURLMcode type, general libcurl multi interface error code.

       Legacy:	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 immedi‐
       ately, but the return code means that libcurl may have more data avail‐
       able  to return or that there may be more data to send off before it is

       should not be returned and no application needs to care about them.

       NOTE  that the return code is for the whole multi stack. Problems still
       might have occurred on individual 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. Wait for activity on any of libcurl's sockets, use the timeout value
       your callback has been told

       7,  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

       8. Go back to step 6.

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

       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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