+ helpers: parseIPv4()

helpers.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -387,3 +388,18 @@ func _Func() string {
 	f := runtime.FuncForPC(pc[0])
 	return path.Base(f.Name())
 }
+
+// Parse input string and return IPv4 address
+func parseIPv4(s string) net.IP {
+	ip := net.ParseIP(s)
+	if ip == nil {
+		return nil
+	}
+
+	v4InV6Prefix := []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}
+	if !bytes.Equal(ip[0:12], v4InV6Prefix) {
+		return nil
+	}
+
+	return ip.To4()
+}