CURLOPT_HTTP_VERSION(3)

💅 CURLOPT_HTTP_VERSION — ok bestie, let's pick an HTTP version ✨

So this is a page from the Library Functions Manual, and it's all about CURLOPT_HTTP_VERSION — the libcurl option that tells your handle which HTTP protocol version you wanna speak. Pull up a chair, this one's actually iconic.

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🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);

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✨ DESCRIPTION ✨

Okay so you pass in version — it's a long — and you set it to one of the values listed below. Each one is basically you politely asking libcurl to use that specific HTTP version. 💖

lowkey important caveat: the HTTP version is just a request. libcurl still prioritizes reusing existing connections, so it might end up reusing a connection that's speaking an HTTP version you literally never asked for. It's giving "I hear you but I'm gonna do what I want." 🙈

Here's the whole menu, bestie:

• CURL_HTTP_VERSION_NONE — We genuinely do not care what version the library uses. libcurl uses whatever it thinks fit. Chill vibes only. 🦋
• CURL_HTTP_VERSION_1_0 — Enforce HTTP 1.0 requests. Old school, no notes.
• CURL_HTTP_VERSION_1_1 — Enforce HTTP 1.1 requests. The classic.
• CURL_HTTP_VERSION_2_0 — Attempt HTTP 2 requests. If HTTP 2 can't be negotiated with the server, libcurl falls back to HTTP 1.1. No cap.
  • When libcurl uses HTTP/2 over HTTPS, it does not itself insist on TLS 1.2 or higher — even though that's literally required by the specification. If you want that version requirement, a user can add it with CURLOPT_SSLVERSION(3). 🫶
  • The alias CURL_HTTP_VERSION_2 was added to better reflect the actual protocol name. Cute little nickname, iykyk.
• CURL_HTTP_VERSION_2TLS — Attempt HTTP 2 over TLS (HTTPS) only. libcurl falls back to HTTP 1.1 if HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers, libcurl uses 1.1. 🎀
• CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE — Issue non-TLS HTTP requests using HTTP/2 without the HTTP/1.1 Upgrade. This requires prior knowledge that the server supports HTTP/2 straight away — you gotta know, bestie. HTTPS requests still do HTTP/2 the standard way, with the negotiated protocol version in the TLS handshake.
  • Since 8.10.0, if this option is set for an HTTPS request, then the application layer protocol version (ALPN) offered to the server is only HTTP/2. Prior to that, both HTTP/1.1 and HTTP/2 were offered. Main character energy, honestly. 👑
• CURL_HTTP_VERSION_3 — (Added in 7.66.0) This option makes libcurl attempt to use HTTP/3 to the host given in the URL, with fallback to earlier HTTP versions if needed. So forgiving. 💜
• CURL_HTTP_VERSION_3ONLY — (Added in 7.88.0) Setting this makes libcurl attempt to use HTTP/3 directly to the server given in the URL and does not downgrade to an earlier HTTP version if the server does not support HTTP/3. Periodt. No fallback, no backup plan. 💀

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🎀 DEFAULT 🎀

The defaults have been through some eras, ngl:

• Since curl 8.13.0: CURL_HTTP_VERSION_NONE
• Since curl 7.62.0: CURL_HTTP_VERSION_2TLS
• Before that: CURL_HTTP_VERSION_1_1

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🌈 PROTOCOLS 🌈

This functionality affects http only. That's it. That's the whole vibe check.

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⭐ EXAMPLE ⭐

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
    result = curl_easy_perform(curl);
    if(result == CURLE_HTTP_RETURNED_ERROR) {
      /* an HTTP response error problem */
    }
  }
}

Look at that. Immaculate. 😭

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🧚 HISTORY 🧚

CURL_HTTP_VERSION_* enums became long types in 8.13.0. Prior to this version, a long cast was necessary when passed to curl_easy_setopt(3). So if you're on an older curl and it's complaining… yeah, that's why. 🙈

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🦋 AVAILABILITY 🦋

Added in curl 7.9.1. Ancient. Historian vibes.

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💅 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 peek at libcurl-errors(3) for the deets.

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🫶 SEE ALSO 🫶

• CURLOPT_ALTSVC(3)
• CURLOPT_HTTP09_ALLOWED(3)
• CURLOPT_HTTP200ALIASES(3)
• CURLOPT_SSLVERSION(3)

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okay that's the whole page, bestie — go forth and negotiate your protocols 💖✨

This masterpiece brought to you by libcurl, dated 2026-10-12 — original page title CURLOPT_HTTP_VERSION(3), part of the Library Functions Manual. Mwah. 🎀