curl / libcurl / API / curl_easy_setopt / CURLOPT_SSL_FALSESTART

CURLOPT_SSL_FALSESTART explained

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

Protocols

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

This option works only with the following TLS backends: Secure Transport

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

Added in curl 7.42.0

Return value

Returns CURLE_OK if false start is supported by the SSL backend, otherwise returns CURLE_NOT_BUILT_IN.