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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
       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

       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                           2025-02-08           CURLOPT_TCP_FASTOPEN(3)

curl 8.12.0 - Generated Wed Feb 19 09:22:08 CST 2025
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