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 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

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

SEE ALSO

CURLOPT_SSL_FALSESTART(3)