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CURLOPT_IOCTLFUNCTION(3)   Library Functions Manual   CURLOPT_IOCTLFUNCTION(3)

NAME
       CURLOPT_IOCTLFUNCTION - callback	for I/O	operations

SYNOPSIS
       #include	<curl/curl.h>

       typedef enum {
	 CURLIOE_OK,		/* I/O operation successful */
	 CURLIOE_UNKNOWNCMD,	/* command was unknown to callback */
	 CURLIOE_FAILRESTART,	/* failed to restart the read */
	 CURLIOE_LAST		/* never use */
       } curlioerr;

       typedef enum  {
	 CURLIOCMD_NOP,		/* no operation	*/
	 CURLIOCMD_RESTARTREAD,	/* restart the read stream from	start */
	 CURLIOCMD_LAST		/* never use */
       } curliocmd;

       curlioerr ioctl_callback(CURL *handle, int cmd, void *clientp);

       CURLcode	curl_easy_setopt(CURL *handle, CURLOPT_IOCTLFUNCTION, ioctl_callback);

DESCRIPTION
       Pass a pointer to your callback function, which should match the	proto-
       type shown above.

       This  callback  function	 gets called by	libcurl	when something special
       I/O-related needs to be done that the library cannot do by itself.  For
       now,  rewinding the read	data stream is the only	action it can request.
       The rewinding of	the read data stream may be necessary  when  doing  an
       HTTP PUT	or POST	with a multi-pass authentication method.

       The  callback  MUST  return  CURLIOE_UNKNOWNCMD if the input cmd	is not
       CURLIOCMD_RESTARTREAD.

       The clientp argument to the callback is	set  with  the	CURLOPT_IOCTL-
       DATA(3) option.

       This  option  is	deprecated. Do not use it. Use CURLOPT_SEEKFUNCTION(3)
       instead to provide seeking. If CURLOPT_SEEKFUNCTION(3) is set, this pa-
       rameter is ignored when seeking.

DEFAULT
       NULL

PROTOCOLS
       This functionality affects all supported	protocols

EXAMPLE
       #include	<unistd.h> /* for lseek	*/

       struct data {
	 int fd; /* our	file descriptor	*/
       };

       static curlioerr	ioctl_callback(CURL *handle, int cmd, void *clientp)
       {
	 struct	data *io = (struct data	*)clientp;
	 if(cmd	== CURLIOCMD_RESTARTREAD) {
	   lseek(io->fd, 0, SEEK_SET);
	   return CURLIOE_OK;
	 }
	 return	CURLIOE_UNKNOWNCMD;
       }
       int main(void)
       {
	 struct	data ioctl_data;
	 CURL *curl = curl_easy_init();
	 if(curl) {
	   curl_easy_setopt(curl, CURLOPT_IOCTLFUNCTION, ioctl_callback);
	   curl_easy_setopt(curl, CURLOPT_IOCTLDATA, &ioctl_data);
	 }
       }

DEPRECATED
       Deprecated since	7.18.0.

AVAILABILITY
       Added in	curl 7.12.3

RETURN VALUE
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK	(0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLOPT_IOCTLDATA(3), CURLOPT_SEEKFUNCTION(3)

libcurl				  2025-06-03	      CURLOPT_IOCTLFUNCTION(3)

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