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 prototype shown above.

       This  callback function gets called by libcurl when something special I/O-related needs to
       be done that the library can't 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 a 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_IOCTLDATA(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 parameter will be ignored when seeking.

DEFAULT

       By default, this parameter is set to NULL. Not used.

PROTOCOLS

       Used with HTTP

EXAMPLE

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

AVAILABILITY

       Added in 7.12.3

RETURN VALUE

       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

SEE ALSO

       CURLOPT_IOCTLDATA(3), CURLOPT_SEEKFUNCTION(3),