CURLOPT_HSTSREADDATA(3)

💅 CURLOPT_HSTSREADDATA(3) — the pointer you hand to your HSTS read callback

Okay bestie, welcome to another libcurl manual page, this one lives in the Library Functions Manual and it's all about CURLOPT_HSTSREADDATA — the little data pointer that gets passed to your HSTS read callback. 🎀

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✨ NAME ✨

CURLOPT_HSTSREADDATA — pointer passed to the HSTS read callback. that's it, that's the whole vibe.

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🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSREADDATA, void *pointer);

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🦋 DESCRIPTION 🦋

So picture this: it's a data pointer that you pass along to the HSTS read function. If you're using the CURLOPT_HSTSREADFUNCTION(3) option, this is literally the pointer you get as input in the 3rd argument to that callback. no middleman, no extra steps, it just shows up there. 💖

⚠️ okay important thing, don't skip this: setting this option does not enable HSTS. like, at all. you need CURLOPT_HSTS_CTRL(3) for that, fr fr. this option is just the lil package you hand over, not the switch that turns stuff on. 🙈

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🧚 DEFAULT 🧚

NULL

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🌈 PROTOCOLS 🌈

This functionality affects http only. that's the whole list, she's exclusive like that. 👑

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🍓 EXAMPLE 🍓

struct MyData {
  void *custom;
};

int main(void)
{
  CURL *curl = curl_easy_init();
  struct MyData this;
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");

    /* pass pointer that gets passed in to the
       CURLOPT_HSTSREADFUNCTION callback */
    curl_easy_setopt(curl, CURLOPT_HSTSREADDATA, &this);

    curl_easy_perform(curl);
  }
}

see how &this just gets yeeted into the callback later? iconic behavior honestly. ✨

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⭐ AVAILABILITY ⭐

Added in curl 7.74.0 — so if your curl is older than that, she doesn't know this option yet, sorry bestie. 😭

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💜 RETURN VALUE 💜

This returns CURLE_OK. that's it. no drama, no surprises, just a clean little success. 🫶

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🔥 SEE ALSO 🔥

• CURLOPT_HSTS(3)
• CURLOPT_HSTSREADFUNCTION(3)
• CURLOPT_HSTSWRITEDATA(3)
• CURLOPT_HSTSWRITEFUNCTION(3)

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okay that's the whole page, go forth and pass your pointers responsibly 💅✨

mwah 💋 — this gem was brought to you by the fine folks of libcurl, dated 2026-10-12, and yes she's official, in the Library Functions Manual, CURLOPT_HSTSREADDATA(3) and all. slay. 🎀