CURLOPT_MIME_OPTIONS(3)

💅 CURLOPT_MIME_OPTIONS(3) — like, the libcurl manual, bestie edition

okay so real talk: this is a page out of the Library Functions Manual, and it's all about CURLOPT_MIME_OPTIONS — the little bitmask that tells libcurl how to encode your MIME tree / multipart form data. no cap, it's a niche icon but it matters. 🎀

---

✨ NAME ✨

CURLOPT_MIME_OPTIONS — set MIME option flags. that's it. that's the whole name. short, sweet, iconic. 👑

---

🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MIME_OPTIONS, long options);

---

🦋 DESCRIPTION 🦋

so you pass a long, and that long is a bitmask of options. every bit in there is a lil boolean flag that gets used while libcurl is encoding a MIME tree or multipart form data. think of it as a vibe check for each individual bit. ✨

the available bits are:

• CURLMIMEOPT_FORMESCAPE — this one tells libcurl to escape multipart form fields and filenames using the backslash-escaping algorithm instead of percent-encoding. and yes, that's HTTP only, bestie. 💅

backslash-escaping is literally just: put a backslash in front of backslashes and double quotes. that's the whole thing. percent-encoding, meanwhile, maps every occurrence of double quote, carriage return and line feed to %22, %0D and %0A respectively. 🎀

ngl, before version 7.81.0, percent-encoding was never applied. so if you're dealing with ancient history, that's your lore. 😭

so here's the tea: HTTP browsers used to do backslash-escaping back in the day, but over time they transitioned to percent-encoding. this option exists so you can still talk to server-side applications that haven't been converted yet. main character energy for legacy servers, honestly. 🫶

as an example, consider field or filename strangename"kind. when the containing multipart form is sent, this is normally transmitted as strangename%22kind. when this option is set, it is sent as strangename"kind. 🔥

---

🎀 DEFAULT 🎀

0, meaning disabled. it's giving "chill by default", and honestly? we respect it. 💜

---

🌈 PROTOCOLS 🌈

this functionality affects http, imap and smtp — a little trio of slay. ⭐

---

💖 EXAMPLE 💖

here's the whole thing, verbatim, because i would never do you dirty like that:

int main(void)
{
  CURL *curl = curl_easy_init();
  curl_mime *form = NULL;

  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    curl_easy_setopt(curl, CURLOPT_MIME_OPTIONS, CURLMIMEOPT_FORMESCAPE);

    form = curl_mime_init(curl);
    if(form) {
      curl_mimepart *part = curl_mime_addpart(form);

      if(part) {
        curl_mime_filedata(part, "strange\\file\\name");
        curl_mime_name(part, "strange\"field\"name");
        curl_easy_setopt(curl, CURLOPT_MIMEPOST, form);

        /* Perform the request */
        curl_easy_perform(curl);
      }
    }

    curl_easy_cleanup(curl);
    curl_mime_free(form);
  }
}

like, look at those escaped backslashes and quotes — she ate and left no crumbs. 🍓

---

🧚 HISTORY 🧚

okay so the CURLMIMEOPT_FORMESCAPE macro became long type in 8.16.0. prior to this version, a long cast was necessary when passed to curl_easy_setopt(3). so if you're on old curl, cast it. no cap. 💀

---

🎀 AVAILABILITY 🎀

added in curl 7.81.0. she's not vintage, she's just well-established. 💅

---

👑 RETURN VALUE 👑

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK. non-zero means an error occurred — go check libcurl-errors(3) and we'll figure it out together, bestie. 🫶

---

🌟 SEE ALSO 🌟

• CURLOPT_HTTPPOST(3)
• CURLOPT_MIMEPOST(3)

go read those too, iykyk. 🔥

---

and that's the whole page!! 🌸 this was brought to you by libcurl, dated 2026-10-12, page CURLOPT_MIME_OPTIONS(3) — mwah, love u, go escape some filenames responsibly 💖✨🎀