Manpages - CURLOPT_TCP_FASTOPEN.3

CURLOPT_TCP_FASTOPEN - TCP Fast Open

#include <curl/curl.h>

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

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

TCP Fast Open (RFC7413) 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).

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  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);
  }

Added in 7.49.0. This option is currently only supported on Linux and OS X El Capitan.

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

*CURLOPT_SSL_FALSESTART*(3),