CURLOPT_HEADEROPT(3)

💖 NAME 💖

okay so bestie, welcome to the CURLOPT_HEADEROPT(3) page from the Library Functions Manual 💅 this one is literally about sending HTTP headers to both proxy and host, or separately. That's the whole vibe: are your custom headers going to the server, the proxy, or both? 👀

---

✨ SYNOPSIS ✨

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADEROPT, long bitmask);

---

🦋 DESCRIPTION 🦋

You pass a long that is a bitmask of options telling libcurl how to deal with headers. The two options are mutually exclusive, bestie — pick one vibe, not both 🚨

• CURLHEADER_UNIFIED — the headers specified in CURLOPT_HTTPHEADER(3) are used in requests both to servers and proxies. With this option enabled, CURLOPT_PROXYHEADER(3) does not have any effect. It's giving "one header list to rule them all" 👑
• CURLHEADER_SEPARATE — makes CURLOPT_HTTPHEADER(3) headers only get sent to a server and not to a proxy. Proxy headers must be set with CURLOPT_PROXYHEADER(3) to get used. Note that if a non-CONNECT request is sent to a proxy, libcurl sends both server headers and proxy headers. When doing CONNECT, libcurl sends CURLOPT_PROXYHEADER(3) headers only to the proxy and then CURLOPT_HTTPHEADER(3) headers only to the server. Separate lanes, separate drama 🛣️✨

---

🎀 DEFAULT 🎀

The default is CURLHEADER_SEPARATE — changed in 7.42.1, and it used CURLHEADER_UNIFIED before then. So yes, the default had a whole glow-up 😌

---

🌈 PROTOCOLS 🌈

This functionality affects http only. That's it — HTTP-only territory, bestie 🌐

---

🍓 EXAMPLE 🍓

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    struct curl_slist *list;
    list = curl_slist_append(NULL, "Shoesize: 10");
    list = curl_slist_append(list, "Accept:");
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_PROXY, "http://localhost:8080");
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);

    /* HTTPS over a proxy makes a separate CONNECT to the proxy, so tell
       libcurl to not send the custom headers to the proxy. Keep them
       separate. */
    curl_easy_setopt(curl, CURLOPT_HEADEROPT, CURLHEADER_SEPARATE);
    result = curl_easy_perform(curl);
    curl_slist_free_all(list);
    curl_easy_cleanup(curl);
  }
}

---

📜 HISTORY 📜

CURLHEADER_* macros became long types in 8.16.0. Prior to this version a long cast was necessary when passed to curl_easy_setopt(3). Iconic little type evolution moment 🧚

---

⭐ AVAILABILITY ⭐

Added in curl 7.37.0. Vintage but still slaying 💅

---

💜 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, see libcurl-errors(3). Zero is the good vibe check ✅

---

👑 SEE ALSO 👑

• CURLOPT_HTTPHEADER(3)
• CURLOPT_PROXYHEADER(3)

---

love and kisses from libcurl, dated 2026-10-12, on the CURLOPT_HEADEROPT(3) page — bye bestie! 🫶💖