CURLOPT_SSL_FALSESTART(3) Library Functions Manual CURLOPT_SSL_FALSESTART(3)

CURLOPT_SSL_FALSESTART - TLS false start

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_FALSESTART, long enable);

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.

0

All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

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

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);
  }
}

Added in 7.42.0. This option is currently only supported by the Secure Transport (on iOS 7.0 or later, or OS X 10.9 or later) TLS backend.

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

CURLOPT_TCP_FASTOPEN(3)

2024-05-22 libcurl