github.com/database64128/tfo-go/v2 (go): Package tfo provides TCP Fast Open support for the net dialer and listener.  The dial functions have an additional buffer parameter, which specifies data in SYN. If the buffer is empty, TFO is not used.  This package supports Linux, Windows, macOS, and FreeBSD. On unsupported platforms, ErrPlatformUnsupported is returned.  FreeBSD code is completely untested. Use at your own risk. Feedback is welcome.
Keywords: go|golang|tcp-fastopen