NAME

       CURLOPT_TCP_FASTOPEN - TCP Fast Open

SYNOPSIS

       #include <curl/curl.h>

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

DESCRIPTION

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

       TCP Fast Open (RFC 7413) is a mechanism that allows data to be carried in the SYN and SYN-
       ACK packets and consumed by the receiving end during  the  initial  connection  handshake,
       saving up to one full round-trip time (RTT).

       Beware:  the  TLS session cache does not work when TCP Fast Open is enabled. TCP Fast Open
       is also known to be problematic on or across certain networks.

DEFAULT

       0

PROTOCOLS

       All

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_TCP_FASTOPEN, 1L);
           curl_easy_perform(curl);
         }
       }

AVAILABILITY

       Added in 7.49.0. This option is currently only supported  on  Linux  and  macOS  10.11  or
       later.

RETURN VALUE

       Returns  CURLE_OK  if  fast  open  is supported by the operating system, otherwise returns
       CURLE_NOT_BUILT_IN.

SEE ALSO

       CURLOPT_SSL_FALSESTART(3),