**************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
* are also available at https://curl.se/docs/copyright.html.
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* copies of the Software, and permit persons to whom the Software is
* furnished to do so, under the terms of the COPYING file.
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
**************************************************************************

CURLOPT_IOCTLDATA - pointer passed to I/O callback #include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_IOCTLDATA, void *pointer); Pass the pointer that will be untouched by libcurl and passed as the 3rd argument in the ioctl callback set with CURLOPT_IOCTLFUNCTION(3). By default, the value of this parameter is NULL. Used with HTTP

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);
}

Added in 7.12.3 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not. CURLOPT_IOCTLFUNCTION "(3), " CURLOPT_SEEKFUNCTION "(3), "