2 files changed, 30 insertions, 4 deletions
diff --git a/src/main/java/org/traccar/helper/Checksum.java b/src/main/java/org/traccar/helper/Checksum.java
index adfa697c5..d41dc2992 100644
--- a/src/main/java/org/traccar/helper/Checksum.java
+++ b/src/main/java/org/traccar/helper/Checksum.java
@@ -168,6 +168,14 @@ public final class Checksum {
         return checksum;
     }
 
+    public static int modulo256(ByteBuffer buf) {
+        int checksum = 0;
+        while (buf.hasRemaining()) {
+            checksum = (checksum + buf.get()) & 0xFF;
+        }
+        return checksum;
+    }
+
     public static String sum(String msg) {
         byte checksum = 0;
         for (byte b : msg.getBytes(StandardCharsets.US_ASCII)) {
diff --git a/src/main/java/org/traccar/helper/ServletHelper.java b/src/main/java/org/traccar/helper/ServletHelper.java
index e3481e249..b6c587ec3 100644
--- a/src/main/java/org/traccar/helper/ServletHelper.java
+++ b/src/main/java/org/traccar/helper/ServletHelper.java
@@ -1,8 +1,22 @@
+/*
+ * Copyright 2020 Anton Tananaev (anton@traccar.org)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package org.traccar.helper;
 
 import javax.servlet.http.HttpServletRequest;
 
-
 public final class ServletHelper {
 
     private ServletHelper() {
@@ -14,10 +28,14 @@ public final class ServletHelper {
             String remoteAddress = request.getHeader("X-FORWARDED-FOR");
 
             if (remoteAddress != null && !remoteAddress.isEmpty()) {
-                return remoteAddress.substring(0, remoteAddress.indexOf(",")); // removes the additional data
+                int separatorIndex = remoteAddress.indexOf(",");
+                if (separatorIndex > 0) {
+                    return remoteAddress.substring(0, separatorIndex); // remove the additional data
+                } else {
+                    return remoteAddress;
+                }
             } else {
-                remoteAddress = request.getRemoteAddr();
-                return remoteAddress;
+                return request.getRemoteAddr();
             }
         } else {
             return null;