CURLOPT_SSL_FALSESTART(3)

💅 CURLOPT_SSL_FALSESTART(3) — the curl library functions manual, bestie edition

okay so this page lives in the Library Functions Manual and it's literally all about CURLOPT_SSL_FALSESTART, aka "TLS false start". yes it sounds like a sports penalty. no it's not. let's get into it 🏃‍♀️💨

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✨ NAME ✨

CURLOPT_SSL_FALSESTART — TLS false start, bestie. that's the whole name, slay.

🌸 SYNOPSIS 🌸

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_FALSESTART, long enable);

that's it. that's the whole vibe. include the header, call curl_easy_setopt, pass the handle, this option, and a long. easy 🫶

💖 DESCRIPTION 💖

so you pass a long as the parameter, and you set it to 1L to enable it or 0 to disable it. that's it. no complicated struct, no callback, no drama 💅

this option decides whether libcurl should do false start during the TLS handshake. and what even is false start, you ask? ok so it's a mode where the TLS client starts yeeting application data over before it's verified the server's Finished message. the whole point? you save a round trip when you're doing a full handshake. it's giving "skip the small talk, we're besties already" energy ⚡

ngl though, the "i haven't verified you yet" part is the whole reason this thing is spicy — that's the trade-off the mode is literally built on, so just know that's what you're signing up for 🔥

🎀 DEFAULT 🎀

0

off. off off off. it's not doing the thing unless you tell it to do the thing 🙈

🦋 PROTOCOLS 🦋

this functionality affects all TLS based protocols, and the manpage lists them as:

• HTTPS
• FTPS
• IMAPS
• POP3S
• SMTPS
• etc. (yes, etc., they really said "you know the rest" 💀)

and now the plot twist, sit down for this one:

No TLS backend supports this option. 😭

not one. zero. the whole squad said "no thank you". so like… it's cross-protocol in theory but backend-less in practice. iykyk.

🌈 EXAMPLE 🌈

here's the whole program, verbatim, no cap:

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    curl_easy_setopt(curl, CURLOPT_SSL_FALSESTART, 1L);
    curl_easy_perform(curl);
  }
}

init the handle, check it's not NULL (main character energy: always check your handle), set the URL to "https://example.com", flip CURLOPT_SSL_FALSESTART to 1L, and curl_easy_perform(curl). go off 👑

💀 DEPRECATED 💀

Deprecated since 8.15.0.

yup. it's deprecated. it had a good run. this option is now the "old friend you still have in your contacts" of libcurl options 🫶

⭐ AVAILABILITY ⭐

Added in curl 7.42.0 — so it's been around a minute. respect the elders 💜

👑 RETURN VALUE 👑

curl_easy_setopt(3) returns a CURLcode indicating success or error. iconic, consistent, as always.

CURLE_OK (0) means everything was OK ✅ — non-zero means an error occurred ❌, and you should go check libcurl-errors(3) for what that number's whole deal is.

🍓 SEE ALSO 🍓

• CURLOPT_TCP_FASTOPEN(3) — the other fast-open-flavored friend, go say hi 🧚

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and that's the page!! mwah 💋 this was the CURLOPT_SSL_FALSESTART(3) entry from the libcurl manual, dated 2026-10-12. now go forth and set your options responsibly, bestie 💖✨🎀