diff --git a/src/main.go b/src/main.go
new file mode 100644
index 0000000..250fddf
--- /dev/null
+++ b/src/main.go
@@ -0,0 +1,53 @@
+package main
+
+import (
+    "fmt"
+    "net"
+    "strconv"
+    "strings"
+)
+
+func isIP(ipAddr string, isRange bool, allowEmpty bool, ipLength int, ipFlag string) bool {
+    var address string
+    if allowEmpty && ipAddr == "" { // empty case
+        return true
+    }
+    if isRange {
+        temp := strings.Split(ipAddr, "/")
+        if len(temp) != 2 { // not {IP_ADDRESS}/{LENGTH} format
+            return false
+        }
+        length, err := strconv.Atoi(temp[1])
+        if err != nil { // range length not a integer
+            return false
+        }
+        if length < 0 || length > ipLength { // length should between 0 ~ ipLength
+            return false
+        }
+        address = temp[0]
+    } else {
+        address = ipAddr
+    }
+    ip := net.ParseIP(address) // try to convert ip
+    return ip != nil && strings.Contains(address, ipFlag)
+}
+
+func isIPv4(ipAddr string, isRange bool, allowEmpty bool) bool {
+    return isIP(ipAddr, isRange, allowEmpty, 32, ".")
+}
+
+func isIPv6(ipAddr string, isRange bool, allowEmpty bool) bool {
+    return isIP(ipAddr, isRange, allowEmpty, 128, ":")
+}
+
+func main() {
+    fmt.Println("XProxy")
+
+    fmt.Println(isIPv4("1.1.1.1", false, false))
+    fmt.Println(isIPv4("1.1.1.1/24", true, false))
+    fmt.Println(isIPv4("", true, true))
+    fmt.Println(isIPv4("::1", true, true))
+    fmt.Println(isIPv6("::1", true, true))
+    fmt.Println(isIPv6("::1/32", true, true))
+    fmt.Println(isIPv6("::1", true, true))
+}