1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_SSL_FALSESTART
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_TCP_FASTOPEN (3)
9Protocol:
10  - TLS
11TLS-backend:
12  - Secure Transport
13Added-in: 7.42.0
14---
15
16# NAME
17
18CURLOPT_SSL_FALSESTART - TLS false start
19
20# SYNOPSIS
21
22~~~c
23#include <curl/curl.h>
24
25CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_FALSESTART, long enable);
26~~~
27
28# DESCRIPTION
29
30Pass a long as parameter set to 1L to enable or 0 to disable.
31
32This option determines whether libcurl should use false start during the TLS
33handshake. False start is a mode where a TLS client starts sending application
34data before verifying the server's Finished message, thus saving a round trip
35when performing a full handshake.
36
37# DEFAULT
38
390
40
41# %PROTOCOLS%
42
43# EXAMPLE
44
45~~~c
46int main(void)
47{
48  CURL *curl = curl_easy_init();
49  if(curl) {
50    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
51    curl_easy_setopt(curl, CURLOPT_SSL_FALSESTART, 1L);
52    curl_easy_perform(curl);
53  }
54}
55~~~
56
57# %AVAILABILITY%
58
59# RETURN VALUE
60
61Returns CURLE_OK if false start is supported by the SSL backend, otherwise
62returns CURLE_NOT_BUILT_IN.
63