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CURLOPT_IOCTLFUNCTION(3)            libcurl           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
       prototype 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_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. Deprecated since 7.18.0.

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

SEE ALSO
       CURLOPT_IOCTLDATA(3), CURLOPT_SEEKFUNCTION(3),

ibcurl 8.1.2                    April 26, 2023        CURLOPT_IOCTLFUNCTION(3)