Tribblix: manual page: CURLOPT_TCP

CURLOPT_TCP_FASTOPEN(3) Introduction to Library Functions

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

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).