CURLOPT_PROXY_SSLVERSION(3)

💅 CURLOPT_PROXY_SSLVERSION 💅

okay so bestie, this is a page from the Library Functions Manual (yes, that's the manual name, we're being fancy today 🎀) and it's all about CURLOPT_PROXY_SSLVERSION — the option that decides which TLS version your libcurl is gonna try when it links up with an HTTPS proxy. literally the vibe check for your proxy handshake ✨

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🌸 NAME 🌸

CURLOPT_PROXY_SSLVERSION — your preferred HTTPS proxy TLS version, aka which TLS flavor you're serving when you talk to your proxy 💖

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🦋 SYNOPSIS 🦋

#include <curl/curl.h>

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

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✨ DESCRIPTION ✨

So you pass a long as the parameter (yes, a long, we'll get to that drama in HISTORY 👀) and it controls which version of SSL/TLS libcurl should attempt to use when connecting to an HTTPS proxy. that's the whole assignment 💅

Use one of the available defines for this purpose. The available options are:

• CURL_SSLVERSION_DEFAULT — the default action, bestie. this one tries to figure out the remote SSL protocol version on its own 🧚
• CURL_SSLVERSION_TLSv1 — TLSv1.x
• CURL_SSLVERSION_TLSv1_0 — TLSv1.0
• CURL_SSLVERSION_TLSv1_1 — TLSv1.1
• CURL_SSLVERSION_TLSv1_2 — TLSv1.2
• CURL_SSLVERSION_TLSv1_3 — TLSv1.3

The maximum TLS version can be set by using one of the CURL_SSLVERSION_MAX_ macros below. It is also possible to OR one of the CURL_SSLVERSION_ macros with one of the CURL_SSLVERSION_MAX_ macros. The MAX macros are not supported for wolfSSL — no cap, that's just how it is 🐺💀

• CURL_SSLVERSION_MAX_DEFAULT — this flag defines the maximum supported TLS version as TLSv1.2, or the default value from the SSL library. dealer's choice, luv 🎲
• CURL_SSLVERSION_MAX_TLSv1_0 — the flag defines maximum supported TLS version as TLSv1.0.
• CURL_SSLVERSION_MAX_TLSv1_1 — the flag defines maximum supported TLS version as TLSv1.1.
• CURL_SSLVERSION_MAX_TLSv1_2 — the flag defines maximum supported TLS version as TLSv1.2.
• CURL_SSLVERSION_MAX_TLSv1_3 — the flag defines maximum supported TLS version as TLSv1.3.

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🎀 DEFAULT 🎀

CURL_SSLVERSION_DEFAULT

(that's the one, the moment, the default. it's giving "let libcurl figure it out" energy 💅✨)

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🌈 PROTOCOLS 🌈

This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

And the good news? All TLS backends support this option. every single one. universal slay 🫶

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🔥 EXAMPLE 🔥

okay here's the code, and note it does its thing with CURLOPT_URL and CURLOPT_SSLVERSION — copying it exactly because that's the whole point, bestie 😌

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

    /* ask libcurl to use TLS version 1.0 or later */
    curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1);

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

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🦋 HISTORY 🦋

CURL_SSLVERSION_* macros became long types 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 and things are acting weird, that's why — it's giving "era before the glow-up" 😭💅

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⭐ AVAILABILITY ⭐

Added in curl 7.52.0. so if you're ancient, sorry babe 🙈

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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, see libcurl-errors(3). like, zero is the slay number, anything else means go read the errors page 👑🔥

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🌸 SEE ALSO 🌸

• CURLOPT_HTTP_VERSION(3)
• CURLOPT_IPRESOLVE(3)
• CURLOPT_SSLVERSION(3)
• CURLOPT_USE_SSL(3)

go read these next, they're all part of the same friend group 🫶✨

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and that's the whole page, bestie!! brought to you by libcurl, dated 2026-10-12, filed under CURLOPT_PROXY_SSLVERSION(3) — periodt, go configure your proxy TLS in peace 💖🎀🦋