generate.go

package sntp

import "time"

func int2bytes(i int64) []byte {
	b := make([]byte, 4)
	h1 := i >> 24
	h2 := (i >> 16) - (h1 << 8)
	h3 := (i >> 8) - (h1 << 16) - (h2 << 8)
	h4 := byte(i)
	b[0] = byte(h1)
	b[1] = byte(h2)
	b[2] = byte(h3)
	b[3] = byte(h4)
	return b
}

func generate(request []byte) []byte {
	second := time.Now().Unix() + FROM_1900_TO_1970
	fraction := int64(time.Now().Nanosecond()) + FROM_1900_TO_1970
	response := make([]byte, 48)
	response[0] = (request[0] & 0x38) + 4
	response[1] = 1
	response[2] = request[2]
	response[3] = 0xEC
	response[12] = 0x4E
	response[13] = 0x49
	response[14] = 0x43
	response[15] = 0x54
	copy(response[16:20], int2bytes(second)[0:])
	copy(response[24:32], request[40:48])
	copy(response[32:36], int2bytes(second)[0:])
	copy(response[36:40], int2bytes(fraction)[0:])
	copy(response[40:48], response[32:40])
	return response
}