1 files changed, 185 insertions, 0 deletions
diff --git a/getter/time-app.go b/getter/time-app.go
new file mode 100644
index 0000000..cd91751
--- /dev/null
+++ b/getter/time-app.go
@@ -0,0 +1,185 @@
+package getter
+
+import (
+	"encoding/binary"
+	"errors"
+	"log"
+	"net"
+	"time"
+)
+
+const (
+	InfoColor    = "\033[1;34m%s\033[0m"
+	NoticeColor  = "\033[1;36m%s\033[0m"
+	WarningColor = "\033[1;33m%s\033[0m"
+	ErrorColor   = "\033[1;31m%s\033[0m"
+	DebugColor   = "\033[0;36m%s\033[0m"
+)
+const (
+	LI_NO_WARNING      = 0
+	LI_ALARM_CONDITION = 3
+	VN_FIRST           = 1
+	VN_LAST            = 4
+	MODE_CLIENT        = 3
+	FROM_1900_TO_1970  = 2208988800
+)
+
+func Serve(req []byte, addr net.Addr) ([]byte, error) {
+	if validFormat(req) {
+		res := generate(req, addr)
+		return res, nil
+	}
+	return []byte{}, errors.New("invalid format.")
+}
+
+func validFormat(req []byte) bool {
+	var l = req[0] >> 6
+	var v = (req[0] << 2) >> 5
+	var m = (req[0] << 5) >> 5
+	if (l == LI_NO_WARNING) || (l == LI_ALARM_CONDITION) {
+		if (v >= VN_FIRST) && (v <= VN_LAST) {
+			if m == MODE_CLIENT {
+				return true
+			}
+		}
+	}
+	return false
+}
+func unix2ntp(u int64) int64 {
+	return u + FROM_1900_TO_1970
+}
+
+func ntp2unix(n int64) int64 {
+	return n - FROM_1900_TO_1970
+}
+
+func int2bytes(i int64) []byte {
+	var 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 NTPPickup(upntp []string, ClientIP net.Addr) time.Time {
+	for _, addr := range upntp {
+		log.Println("\033[1;34mrequest\033[0m ---> asking for time from", ClientIP)
+		log.Println("\033[1;36maccess\033[0m ----> trying to ntp server:", addr)
+		custom, err := ntpaccessclient(addr)
+		if err == nil {
+			log.Println("\033[1;32msuccess\033[0m ---> time received from:", addr)
+			log.Println("\033[1;32mresponse\033[0m --> answering to the client", ClientIP)
+			return custom
+		}
+		log.Printf("\033[1;31merror\033[0m -----> ntp address: %v (%v)\n", addr, err)
+
+	}
+	log.Println("\033[1;31merror\033[0m -----> can not get anything from ntp servers!")
+	log.Println("\033[1;33mwarining\033[0m --> passing system time to client (might be wrong!)")
+	return time.Now()
+}
+
+var ArgNTP []string
+
+func generate(req []byte, addr net.Addr) []byte {
+	custom := NTPPickup(ArgNTP, addr)
+	var second = unix2ntp(custom.Unix())
+	var fraction = unix2ntp(int64(custom.Nanosecond()))
+	var res = make([]byte, 48)
+	var vn = req[0] & 0x38
+	res[0] = vn + 4
+	res[1] = 1
+	res[2] = req[2]
+	res[3] = 0xEC
+	res[12] = 0x4E
+	res[13] = 0x49
+	res[14] = 0x43
+	res[15] = 0x54
+	copy(res[16:20], int2bytes(second)[0:])
+	copy(res[24:32], req[40:48])
+	copy(res[32:36], int2bytes(second)[0:])
+	copy(res[36:40], int2bytes(fraction)[0:])
+	copy(res[40:48], res[32:40])
+	return res
+}
+
+type mode byte
+
+const (
+	reserved mode = 0 + iota
+	symmetricActive
+	symmetricPassive
+	client
+	server
+	broadcast
+	controlMessage
+	reservedPrivate
+)
+
+type ntpTime struct {
+	Seconds  uint32
+	Fraction uint32
+}
+
+func (t ntpTime) UTC() time.Time {
+	nsec := uint64(t.Seconds)*1e9 + (uint64(t.Fraction) * 1e9 >> 32)
+	return time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC).Add(time.Duration(nsec))
+}
+
+type msg struct {
+	LiVnMode       byte
+	Stratum        byte
+	Poll           byte
+	Precision      byte
+	RootDelay      uint32
+	RootDispersion uint32
+	ReferenceId    uint32
+	ReferenceTime  ntpTime
+	OriginTime     ntpTime
+	ReceiveTime    ntpTime
+	TransmitTime   ntpTime
+}
+
+func (m *msg) SetVersion(v byte) {
+	m.LiVnMode = (m.LiVnMode & 0xc7) | v<<3
+}
+
+func (m *msg) SetMode(md mode) {
+	m.LiVnMode = (m.LiVnMode & 0xf8) | byte(md)
+}
+
+func ntpaccessclient(host string) (time.Time, error) {
+	raddr, err := net.ResolveUDPAddr("udp", host)
+	if err != nil {
+		return time.Now(), err
+	}
+
+	con, err := net.DialUDP("udp", nil, raddr)
+	if err != nil {
+		return time.Now(), err
+	}
+	defer con.Close()
+	con.SetDeadline(time.Now().Add(5 * time.Second))
+
+	m := new(msg)
+	m.SetMode(client)
+	m.SetVersion(4)
+
+	err = binary.Write(con, binary.BigEndian, m)
+	if err != nil {
+		return time.Now(), err
+	}
+
+	err = binary.Read(con, binary.BigEndian, m)
+	if err != nil {
+		return time.Now(), err
+	}
+
+	t := m.ReceiveTime.UTC().Local()
+	return t, nil
+}