Merge pull request #2387 from vitalidze/jt600c_checksum_replies

For JT600c - added checksum verification and replying for alarms/positions

2 files changed, 45 insertions, 3 deletions

diff --git a/src/org/traccar/helper/Checksum.java b/src/org/traccar/helper/Checksum.java
index 2a4b1191d..dde174545 100644
--- a/src/org/traccar/helper/Checksum.java
+++ b/src/org/traccar/helper/Checksum.java
@@ -194,6 +194,15 @@ public final class Checksum {
         return checksum;
     }
 
+    public static int xor(String string) {
+        byte[] bytes = string.getBytes(StandardCharsets.US_ASCII);
+        byte sum = 0;
+        for (byte b : bytes) {
+            sum ^= b;
+        }
+        return sum;
+    }
+
     public static String nmea(String msg) {
         int checksum = 0;
         for (byte b : msg.getBytes(StandardCharsets.US_ASCII)) {
diff --git a/src/org/traccar/protocol/Jt600ProtocolDecoder.java b/src/org/traccar/protocol/Jt600ProtocolDecoder.java
index fd2448c0d..6d066299a 100644
--- a/src/org/traccar/protocol/Jt600ProtocolDecoder.java
+++ b/src/org/traccar/protocol/Jt600ProtocolDecoder.java
@@ -21,6 +21,7 @@ import org.jboss.netty.channel.Channel;
 import org.traccar.BaseProtocolDecoder;
 import org.traccar.DeviceSession;
 import org.traccar.helper.BcdUtil;
+import org.traccar.helper.Checksum;
 import org.traccar.helper.DateBuilder;
 import org.traccar.helper.Parser;
 import org.traccar.helper.PatternBuilder;
@@ -202,7 +203,7 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
     private static final Pattern PATTERN_U01 = new PatternBuilder()
             .text("(")
             .number("(d+),")                     // id
-            .number("Udd,")                      // type
+            .number("(Udd),")                    // type
             .number("d+,").optional()            // alarm
             .number("(dd)(dd)(dd),")             // date (ddmmyy)
             .number("(dd)(dd)(dd),")             // time
@@ -218,7 +219,8 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
             .number("(d+),")                     // lac
             .number("(d+),")                     // gsm signal
             .number("(d+),")                     // odometer
-            .number("(d+)")                      // index
+            .number("(d+),?")                     // serial number
+            .number("(xx)").optional()           // checksum
             .any()
             .compile();
 
@@ -234,6 +236,8 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
             return null;
         }
 
+        String messageType = parser.next();
+
         Position position = new Position();
         position.setProtocol(getProtocolName());
         position.setDeviceId(deviceSession.getDeviceId());
@@ -259,8 +263,32 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
         position.set(Position.KEY_ODOMETER, parser.nextLong() * 1000);
         position.set(Position.KEY_INDEX, parser.nextInt());
 
-        return position;
+        switch (messageType) {
+            case "U01":
+            case "U02":
+            case "U03":
+                // support protocol with check sum
+                if (parser.hasNext(2)) {
+                    int checkSum = parser.nextInt(16);
+                    int calculatedCheckSum = Checksum.xor(sentence.substring(1, sentence.length() - 3));
+                    if (checkSum == calculatedCheckSum) {
+                        sendResponse(channel, "(S39)");
+                        return position;
+                    } else {
+                        return null;
+                    }
+                // support protocol without check sum
+                } else {
+                    return position;
+                }
+            case "U06":
+                sendResponse(channel, "(S20)");
+                return position;
+            default:
+                return null;
+        }
     }
+
     @Override
     protected Object decode(
             Channel channel, SocketAddress remoteAddress, Object msg) throws Exception {
@@ -282,4 +310,9 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
         return null;
     }
 
+    private void sendResponse(Channel channel, String response) {
+        if (channel != null) {
+            channel.write(ChannelBuffers.copiedBuffer(response, StandardCharsets.US_ASCII));
+        }
+    }
 }