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CURLOPT_TCP_FASTOPEN(3)	   Library Functions Manual    CURLOPT_TCP_FASTOPEN(3)

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  en-
       abled.  TCP Fast	Open is	also known to be problematic on	or across cer-
       tain networks.

DEFAULT
       0

PROTOCOLS
       This functionality affects tcp only

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
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK	(0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLOPT_SSL_FALSESTART(3)

libcurl				  2025-06-03	       CURLOPT_TCP_FASTOPEN(3)

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