1--- 2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3SPDX-License-Identifier: curl 4Title: CURLOPT_TCP_FASTOPEN 5Section: 3 6Source: libcurl 7See-also: 8 - CURLOPT_SSL_FALSESTART (3) 9Protocol: 10 - All 11--- 12 13# NAME 14 15CURLOPT_TCP_FASTOPEN - TCP Fast Open 16 17# SYNOPSIS 18 19~~~c 20#include <curl/curl.h> 21 22CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TCP_FASTOPEN, long enable); 23~~~ 24 25# DESCRIPTION 26 27Pass a long as parameter set to 1L to enable or 0 to disable. 28 29TCP Fast Open (RFC 7413) is a mechanism that allows data to be carried in the 30SYN and SYN-ACK packets and consumed by the receiving end during the initial 31connection handshake, saving up to one full round-trip time (RTT). 32 33Beware: the TLS session cache does not work when TCP Fast Open is enabled. TCP 34Fast Open is also known to be problematic on or across certain networks. 35 36# DEFAULT 37 380 39 40# EXAMPLE 41 42~~~c 43int main(void) 44{ 45 CURL *curl = curl_easy_init(); 46 if(curl) { 47 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); 48 curl_easy_setopt(curl, CURLOPT_TCP_FASTOPEN, 1L); 49 curl_easy_perform(curl); 50 } 51} 52~~~ 53 54# AVAILABILITY 55 56Added in 7.49.0. This option is currently only supported on Linux and macOS 5710.11 or later. 58 59# RETURN VALUE 60 61Returns CURLE_OK if fast open is supported by the operating system, otherwise 62returns CURLE_NOT_BUILT_IN. 63