Fix frame decoding

2 files changed, 6 insertions, 2 deletions

diff --git a/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java b/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
index b5d060ecc..bfefb94a7 100644
--- a/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
+++ b/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
@@ -35,7 +35,7 @@ public class Jt600FrameDecoder extends BaseFrameDecoder {
         char type = (char) buf.getByte(buf.readerIndex());
 
         if (type == '$') {
-            boolean longFormat = buf.getUnsignedByte(buf.readerIndex() + 1) == 0x75;
+            boolean longFormat = Jt600ProtocolDecoder.isLongFormat(buf, buf.readerIndex() + 1);
             int length = buf.getUnsignedShort(buf.readerIndex() + (longFormat ? 8 : 7)) + 10;
             if (length <= buf.readableBytes()) {
                 return buf.readRetainedSlice(length);
diff --git a/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java b/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
index 82abeb42e..f456cd1ef 100644
--- a/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
+++ b/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
@@ -86,13 +86,17 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
 
     }
 
+    static boolean isLongFormat(ByteBuf buf, int flagIndex) {
+        return buf.getUnsignedByte(flagIndex) >> 4 == 0x7;
+    }
+
     private List<Position> decodeBinary(ByteBuf buf, Channel channel, SocketAddress remoteAddress) {
 
         List<Position> positions = new LinkedList<>();
 
         buf.readByte(); // header
 
-        boolean longFormat = buf.getUnsignedByte(buf.readerIndex()) >> 4 == 0x7;
+        boolean longFormat = isLongFormat(buf, buf.readerIndex());
 
         String id = String.valueOf(Long.parseLong(ByteBufUtil.hexDump(buf.readSlice(5))));
         DeviceSession deviceSession = getDeviceSession(channel, remoteAddress, id);