#!/bin/bash

set -o errexit -o nounset -o pipefail

umask 077

if [[ -e /etc/tcp_fastopen_seed ]]; then
    rand=$(b3sum --keyed -l 16 --no-names </etc/tcp_fastopen_seed <(date -uI))
else
    rand=$(xxd -l 16 -p /dev/random)
fi

new_key=${rand:0:8}-${rand:8:8}-${rand:16:8}-${rand:24:8}
echo new_key: $new_key

old_key="$(sysctl net.ipv4.tcp_fastopen_key | awk '{ print $3 }' | cut -d ',' -f 1)"
echo old_key: $old_key

echo "net.ipv4.tcp_fastopen_key=$new_key,$old_key" >/etc/sysctl.d/50-tcp_fastopen_key.conf
sysctl -p /etc/sysctl.d/50-tcp_fastopen_key.conf