Handle GT06 empty string message (fix #1930)

2 files changed, 7 insertions, 3 deletions

diff --git a/src/org/traccar/protocol/Gt06ProtocolDecoder.java b/src/org/traccar/protocol/Gt06ProtocolDecoder.java
index 18524fcfa..6dc382a04 100644
--- a/src/org/traccar/protocol/Gt06ProtocolDecoder.java
+++ b/src/org/traccar/protocol/Gt06ProtocolDecoder.java
@@ -214,9 +214,10 @@ public class Gt06ProtocolDecoder extends BaseProtocolDecoder {
 
                 int commandLength = buf.readUnsignedByte();
 
-                buf.readUnsignedByte(); // server flag (reserved)
-
-                position.set("command", buf.readBytes(commandLength - 1).toString(StandardCharsets.US_ASCII));
+                if (commandLength > 0) {
+                    buf.readUnsignedByte(); // server flag (reserved)
+                    position.set("command", buf.readBytes(commandLength - 1).toString(StandardCharsets.US_ASCII));
+                }
 
                 buf.readUnsignedShort(); // language
 
diff --git a/test/org/traccar/protocol/Gt06ProtocolDecoderTest.java b/test/org/traccar/protocol/Gt06ProtocolDecoderTest.java
index 3bcd2ec3a..46ee223ad 100644
--- a/test/org/traccar/protocol/Gt06ProtocolDecoderTest.java
+++ b/test/org/traccar/protocol/Gt06ProtocolDecoderTest.java
@@ -16,6 +16,9 @@ public class Gt06ProtocolDecoderTest extends ProtocolTest {
         verifyNothing(decoder, binary(
                 "78780D01086471700328358100093F040D0A"));
 
+        verifyNotNull(decoder, binary(
+                "787866150000000000416c726561647920696e20746865207374617465206f66206675656c20737570706c7920746f20726573756d652c74686520636f6d6d616e64206973206e6f742072756e6e696e672100000000000000000000000000000000000001001981e50d0a"));
+
         verifyAttributes(decoder, binary(
                 "78782d152500000000437574206f666620746865206675656c20737570706c793a2053756363657373210002013b898a0d0a"));