sonyflake fix (#180)

internal/id/sonyflake.go

@@ -1,6 +1,10 @@
 package id
 
 import (
+	"errors"
+	"net"
+	"os"
+
 	"strconv"
 	"time"
 
@@ -22,7 +26,53 @@ func (s *sonyflakeGenerator) Next() (string, error) {
 var (
 	SonyFlakeGenerator = Generator(&sonyflakeGenerator{
 		sonyflake.NewSonyflake(sonyflake.Settings{
+			MachineID: lower16BitPrivateIP,
 			StartTime: time.Date(2019, 4, 29, 0, 0, 0, 0, time.UTC),
 		}),
 	})
 )
+
+// the following is a copy of sonyflake (https://github.com/sony/sonyflake/blob/master/sonyflake.go)
+//with the change of using the "POD-IP" if no private ip is found
+func privateIPv4() (net.IP, error) {
+	as, err := net.InterfaceAddrs()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, a := range as {
+		ipnet, ok := a.(*net.IPNet)
+		if !ok || ipnet.IP.IsLoopback() {
+			continue
+		}
+
+		ip := ipnet.IP.To4()
+		if isPrivateIPv4(ip) {
+			return ip, nil
+		}
+	}
+
+	//change: use "POD_IP"
+	ip := net.ParseIP(os.Getenv("POD_IP"))
+	if ip == nil {
+		return nil, errors.New("no private ip address")
+	}
+	if ipV4 := ip.To4(); ipV4 != nil {
+		return ipV4, nil
+	}
+	return nil, errors.New("no pod ipv4 address")
+}
+
+func isPrivateIPv4(ip net.IP) bool {
+	return ip != nil &&
+		(ip[0] == 10 || ip[0] == 172 && (ip[1] >= 16 && ip[1] < 32) || ip[0] == 192 && ip[1] == 168)
+}
+
+func lower16BitPrivateIP() (uint16, error) {
+	ip, err := privateIPv4()
+	if err != nil {
+		return 0, err
+	}
+
+	return uint16(ip[2])<<8 + uint16(ip[3]), nil
+}