Lws supports enabling TCP_FASTOPEN oper-vhost for listen sockets.

Enabling per vhost serving

Set the info.fo_listen_queue to nonzero at vhost creation. Different platforms interpret this number differently, zero always disables it but on Linux, the number is interpreted as a SYN queue length.

On FreeBSD, OSX and Windows, the number is basically a bool, with the extra restriction OSX and Windows only allows 0 or 1.

Enabling Linux for serving with TCP_FASTOPEN

To configure the kernel for listening socket TCP_FASTOPEN, you need

# sysctl -w net.ipv4.tcp_fastopen=3

Enabling BSD for serving with TCP_FASTOPEN

At least on FreeBSD, you need to set the net.inet.tcp.fastopen.enabled sysctl to 1

Enabling Windows for serving with TCP_FASTOPEN

> netsh int tcp set global fastopenfallback=disabled

> netsh int tcp show global