Improve UUID generator

https://github.com/XTLS/Xray-core/issues/158

common/uuid/uuid.go

@@ -50,6 +50,8 @@ func (u *UUID) Equals(another *UUID) bool {
 func New() UUID {
 	var uuid UUID
 	common.Must2(rand.Read(uuid.Bytes()))
+	uuid[6] = (uuid[6] & 0x0f) | (4 << 4)
+	uuid[8] = (uuid[8]&(0xff>>2) | (0x02 << 6))
 	return uuid
 }
 

main/commands/all/uuid.go

@@ -8,15 +8,33 @@ import (
 )
 
 var cmdUUID = &base.Command{
-	UsageLine: "{{.Exec}} uuid",
-	Short:     "Generate new UUIDs",
+	UsageLine: `{{.Exec}} uuid [-i "example"]`,
+	Short:     `Generate UUIDv4 or UUIDv5`,
 	Long: `
-Generate new UUIDs.
-	`,
-	Run: executeUUID,
+Generate UUIDv4 or UUIDv5.
+
+UUIDv4 (random): {{.Exec}} uuid
+
+UUIDv5 (from input): {{.Exec}} uuid -i "example"
+`,
 }
 
-func executeUUID(cmd *base.Command, args []string) {
-	u := uuid.New()
-	fmt.Println(u.String())
+func init() {
+	cmdUUID.Run = executeUUID // break init loop
+}
+
+var input = cmdUUID.Flag.String("i", "", "")
+
+func executeUUID(cmd *base.Command, args []string) {
+	var output string
+	if l := len(*input); l == 0 {
+		u := uuid.New()
+		output = u.String()
+	} else if l <= 30 {
+		u, _ := uuid.ParseString(*input)
+		output = u.String()
+	} else {
+		output = "Input must be within 30 bytes."
+	}
+	fmt.Println(output)
 }