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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 net- works. DEFAULT 0 PROTOCOLS This functionality affects tcp only EXAMPLE int main(void) { CURL *curl = curl_easy_init(); if(curl) { CURLcode result; curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); curl_easy_setopt(curl, CURLOPT_TCP_FASTOPEN, 1L); result = curl_easy_perform(curl); curl_easy_cleanup(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 2026-06-11 CURLOPT_TCP_FASTOPEN(3)
NAME | SYNOPSIS | DESCRIPTION | DEFAULT | PROTOCOLS | EXAMPLE | NOTES | AVAILABILITY | RETURN VALUE | SEE ALSO
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