GNURLOPT_IOCTLFUNCTION(3)

💅 GNURLOPT_IOCTLFUNCTION(3) 💅

okay so bestie, you found a page from the curl_easy_setopt options manual — name tag folded in right at the top 🫶. This one is about a callback for I/O operations, and it is deprecated, so read up but do not get attached, mmkay?

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🎀 NAME 🎀

CURLOPT_IOCTLFUNCTION — callback for I/O operations

🦋 SYNOPSIS 🦋

bestie, here's the exact shape of everything:

#include <gnurl/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, and make sure it matches the prototype shown above. libcurl calls this callback when something special and 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. That rewinding of the read data stream may be necessary when doing an HTTP PUT or POST with a multi-pass authentication method. slay? sure, but also: deprecated, so keep your distance 💀.

The callback MUST return CURLIOE_UNKNOWNCMD if the input cmd is not CURLIOCMD_RESTARTREAD. Like, mandatory. No cap.

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. That's the vibe: deprecated means leave it alone, bestie. 💀

🍓 DEFAULT 🍓

By default, this parameter is set to NULL. Not used. Literally just vibing as NULL.

🌈 PROTOCOLS 🌈

Used with HTTP.

💖 EXAMPLE 💖

Here's the example, with all its little details so you can see the callback and the setup together:

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. Simple as that.

🔥 SEE ALSO 🔥

• CURLOPT_IOCTLDATA(3), CURLOPT_SEEKFUNCTION(3),

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that's the tea 🫶 this page is from libcurl 7.37.0, dated 16 Jun 2014, and it's the GNURLOPT_IOCTLFUNCTION(3) page. bye bestie 💅✨