curl/docs/libcurl/opts/CURLOPT_SSL_FALSESTART.md
Daniel Stenberg 08a3e8e19a
TLS: remove support for Secure Transport and BearSSL
These libraries do not support TLS 1.3 and have been marked for removal
for over a year. We want to help users select a TLS dependency that is
future-proof and reliable, and not supporting TLS 1.3 in 2025 does not
infer confidence. Users who build libcurl are likely to be served better
and get something more future-proof with a TLS library that supports
1.3.

Closes #16677
2025-06-11 07:54:19 +02:00

1.2 KiB

c SPDX-License-Identifier Title Section Source See-also Protocol TLS-backend Added-in
Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. curl CURLOPT_SSL_FALSESTART 3 libcurl
CURLOPT_TCP_FASTOPEN (3)
TLS
none
7.42.0

NAME

CURLOPT_SSL_FALSESTART - TLS false start

SYNOPSIS

#include <curl/curl.h>

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

DESCRIPTION

Pass a long as parameter set to 1L to enable or 0 to disable.

This option determines whether libcurl should use false start during the TLS handshake. False start is a mode where a TLS client starts sending application data before verifying the server's Finished message, thus saving a round trip when performing a full handshake.

DEFAULT

0

%PROTOCOLS%

EXAMPLE

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);
  }
}

%AVAILABILITY%

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).