package main

import (
	"fmt"
	"golang.org/x/sys/unix"
	"log"
	"math/rand"
	"os"
	"time"
	"unsafe"
)

const BUFSIZE = 512

type rand_pool_info struct {
	entropy_count int
	buf_size      int
	buf           [512]byte
}

var pid int

func init() {
	log.SetFlags(0)
	pid = os.Getpid()
}

func ioctl(fd int, req uint, ptr unsafe.Pointer) error {
	_, _, errno := unix.Syscall(unix.SYS_IOCTL,
		uintptr(fd),
		uintptr(req),
		uintptr(ptr))

	if errno != 0 {
		return fmt.Errorf("ioctl: %w", errno)
	}

	return nil
}

func feed(fd int) error {
	seed := pid * time.Now().Nanosecond()
	rand.Seed(int64(seed))

	output := &rand_pool_info{
		entropy_count: BUFSIZE * 8,
		buf_size:      BUFSIZE,
	}

	rand.Read(output.buf[:])

	err := ioctl(fd, unix.RNDADDENTROPY, unsafe.Pointer(output))
	if err != nil {
		return err
	}

	return nil
}

func main() {
	fd, err := unix.Open("/dev/random", unix.O_RDWR, 0)
	if err != nil {
		log.Fatal(err)
	}
	defer unix.Close(fd)

	for {
		if err := feed(fd); err != nil {
			log.Fatalf("feed failed: %s", err)
		}

		time.Sleep(time.Second)
	}
}