From 42e88c2bf95962f1274a8bbb6e8fc09af95f627f Mon Sep 17 00:00:00 2001
From: Stefan Clark <stefanclark@gmail.com>
Date: Thu, 28 Jul 2022 22:37:15 +0100
Subject: Added udp() to Checksum helper and Updated Xexun2 procotol

---
 .../traccar/protocol/Xexun2ProtocolDecoder.java    | 11 +++++++---
 .../traccar/protocol/Xexun2ProtocolEncoder.java    | 24 ++--------------------
 2 files changed, 10 insertions(+), 25 deletions(-)

(limited to 'src/main/java/org/traccar/protocol')

diff --git a/src/main/java/org/traccar/protocol/Xexun2ProtocolDecoder.java b/src/main/java/org/traccar/protocol/Xexun2ProtocolDecoder.java
index 8deb2328b..f0158e6ce 100644
--- a/src/main/java/org/traccar/protocol/Xexun2ProtocolDecoder.java
+++ b/src/main/java/org/traccar/protocol/Xexun2ProtocolDecoder.java
@@ -24,6 +24,7 @@ import org.traccar.session.DeviceSession;
 import org.traccar.NetworkMessage;
 import org.traccar.Protocol;
 import org.traccar.helper.BitUtil;
+import org.traccar.helper.Checksum;
 import org.traccar.helper.UnitsConverter;
 import org.traccar.model.CellTower;
 import org.traccar.model.Network;
@@ -97,13 +98,17 @@ public class Xexun2ProtocolDecoder extends BaseProtocolDecoder {
             return null;
         }
 
+        int payloadSize = buf.readUnsignedShort() & 0x03ff;
+        int checksum = buf.readUnsignedShort(); // checksum
+
+        if (checksum != Checksum.udp(buf.nioBuffer(buf.readerIndex(), payloadSize))) {
+            return null;
+        }
+
         if (type != Xexun2ProtocolEncoder.MSG_COMMAND) {
             sendResponse(channel, type, index, imei);
         }
 
-        buf.readUnsignedShort(); // attributes
-        buf.readUnsignedShort(); // checksum
-
         if (type == MSG_POSITION) {
             List<Integer> lengths = new ArrayList<>();
             List<Position> positions = new ArrayList<>();
diff --git a/src/main/java/org/traccar/protocol/Xexun2ProtocolEncoder.java b/src/main/java/org/traccar/protocol/Xexun2ProtocolEncoder.java
index f876853bf..6e1e1d68d 100644
--- a/src/main/java/org/traccar/protocol/Xexun2ProtocolEncoder.java
+++ b/src/main/java/org/traccar/protocol/Xexun2ProtocolEncoder.java
@@ -18,6 +18,7 @@ package org.traccar.protocol;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import org.traccar.BaseProtocolEncoder;
+import org.traccar.helper.Checksum;
 import org.traccar.helper.DataConverter;
 import org.traccar.model.Command;
 import org.traccar.Protocol;
@@ -62,26 +63,6 @@ public class Xexun2ProtocolEncoder extends BaseProtocolEncoder {
         return result;
     }
 
-    private static int udpchecksum(ByteBuf data) {
-        int sum = 0;
-        int len = data.capacity();
-        for (int j = 0; len > 1; len--) {
-            sum += data.readByte() & 0xff;
-            if ((sum & 0x80000000) > 0) {
-                sum = (sum & 0xffff) + (sum >> 16);
-            }
-        }
-        if (len == 1) {
-            sum += data.readByte() & 0xff;
-        }
-        while ((sum >> 16) > 0) {
-            sum = (sum & 0xffff) + sum >> 16;
-        }
-        sum = (sum == 0xffff) ? sum & 0xffff : (~sum) & 0xffff;
-        return sum;
-    }
-
-
     private static ByteBuf encodeContent(String uniqueId, String content) {
         ByteBuf buf = Unpooled.buffer();
 
@@ -92,8 +73,7 @@ public class Xexun2ProtocolEncoder extends BaseProtocolEncoder {
         buf.writeShort(1); // index
         buf.writeBytes(DataConverter.parseHex(uniqueId + "0"));
         buf.writeShort(message.capacity());
-        buf.writeShort(udpchecksum(message));
-        message.resetReaderIndex();
+        buf.writeShort(Checksum.udp(message.nioBuffer()));
         buf.writeBytes(message);
         buf.writeShort(FLAG);
 
-- 
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