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

       This functionality affects all supported protocols

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);
         }
       }

NOTES

       This option is only supported on Linux and macOS 10.11 or later.

AVAILABILITY

       Added in curl 7.49.0

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)