From 818fff6daf87a9e90a225122d04dc8b93694a8c6 Mon Sep 17 00:00:00 2001
From: Anton Tananaev <anton.tananaev@gmail.com>
Date: Tue, 28 Nov 2017 20:01:45 +1300
Subject: Fix eelink checksum and decode result

---
 src/org/traccar/protocol/EelinkProtocolEncoder.java | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

(limited to 'src/org/traccar/protocol/EelinkProtocolEncoder.java')

diff --git a/src/org/traccar/protocol/EelinkProtocolEncoder.java b/src/org/traccar/protocol/EelinkProtocolEncoder.java
index b9be684a3..917f964fe 100644
--- a/src/org/traccar/protocol/EelinkProtocolEncoder.java
+++ b/src/org/traccar/protocol/EelinkProtocolEncoder.java
@@ -22,6 +22,7 @@ import org.traccar.helper.Log;
 import org.traccar.model.Command;
 
 import javax.xml.bind.DatatypeConverter;
+import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
 
 public class EelinkProtocolEncoder extends BaseProtocolEncoder {
@@ -32,6 +33,14 @@ public class EelinkProtocolEncoder extends BaseProtocolEncoder {
         this.connectionless = connectionless;
     }
 
+    public static int checksum(ByteBuffer buf) {
+        int sum = 0;
+        while (buf.hasRemaining()) {
+            sum = (((sum << 1) | (sum >> 15)) + (buf.get() & 0xFF)) & 0xFFFF;
+        }
+        return sum;
+    }
+
     private ChannelBuffer encodeContent(long deviceId, String content) {
 
         ChannelBuffer buf = ChannelBuffers.dynamicBuffer();
@@ -56,7 +65,7 @@ public class EelinkProtocolEncoder extends BaseProtocolEncoder {
             result.writeByte('E');
             result.writeByte('L');
             result.writeShort(2 + 2 + 2 + buf.readableBytes()); // length
-            result.writeShort(0); // checksum
+            result.writeShort(checksum(buf.toByteBuffer()));
         }
 
         result.writeBytes(buf);
-- 
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