Implement Navis protocol frame decoder

src/org/traccar/protocol/NvsFrameDecoder.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2016 Anton Tananaev (anton.tananaev@gmail.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.traccar.protocol;
+
+import org.jboss.netty.buffer.ChannelBuffer;
+import org.jboss.netty.channel.Channel;
+import org.jboss.netty.channel.ChannelHandlerContext;
+import org.jboss.netty.handler.codec.frame.FrameDecoder;
+
+public class NvsFrameDecoder extends FrameDecoder {
+
+    @Override
+    protected Object decode(
+            ChannelHandlerContext ctx,
+            Channel channel,
+            ChannelBuffer buf) throws Exception {
+
+        if (buf.readableBytes() < 4 + 2) {
+            return null;
+        }
+
+        int length;
+        if (buf.getUnsignedByte(buf.readerIndex()) == 0) {
+            length = buf.getUnsignedShort(buf.readerIndex());
+        } else {
+            length = 4 + buf.getUnsignedShort(buf.readerIndex() + 4) + 2;
+        }
+
+        if (buf.readableBytes() >= length) {
+            return buf.readBytes(length);
+        }
+
+        return null;
+    }
+
+}

src/org/traccar/protocol/NvsProtocol.java

@@ -34,7 +34,7 @@ public void initTrackerServers(List<TrackerServer> serverList) {
         serverList.add(new TrackerServer(new ServerBootstrap(), this.getName()) {
             @Override
             protected void addSpecificHandlers(ChannelPipeline pipeline) {
-                pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(1024, 4, 2, 2, 0));
+                pipeline.addLast("frameDecoder", new NvsFrameDecoder());
                 pipeline.addLast("objectDecoder", new NvsProtocolDecoder(NvsProtocol.this));
             }
         });

src/org/traccar/protocol/NvsProtocolDecoder.java

@@ -46,10 +46,8 @@ protected Object decode(
 
         ChannelBuffer buf = (ChannelBuffer) msg;
 
-        buf.skipBytes(4); // marker
-        int length = buf.readUnsignedShort();
 
-        if (length == 15 + 3) {
+        if (buf.getUnsignedByte(buf.readerIndex()) == 0) {
 
             String imei = buf.toString(buf.readerIndex(), 15, Charset.defaultCharset());
 
@@ -63,6 +61,8 @@ protected Object decode(
 
             List<Position> positions = new LinkedList<>();
 
+            buf.skipBytes(4); // marker
+            buf.readUnsignedShort(); // length
             buf.readLong(); // imei
             buf.readUnsignedByte(); // codec
             int count = buf.readUnsignedByte();

test/org/traccar/protocol/NvsProtocolDecoderTest.java

@@ -11,7 +11,10 @@ public void testDecode() throws Exception {
         NvsProtocolDecoder decoder = new NvsProtocolDecoder(new NvsProtocol());
 
         verifyNothing(decoder, binary(
-                "cccccccc0012313233343536373839303132333435312E310000"));
+                "0012333537303430303630303137383234312e38"));
+
+        verifyNothing(decoder, binary(
+                "0012313233343536373839303132333435312E31"));
 
         verifyPositions(decoder, binary(
                 "CCCCCCCC00FE00007048860DDF79020446a6f1ce010f14f650209cca80006f00d6040004010300030101150316030001460000015d0046a6f1dc0d0f14ffe0209cc580006e00c7050001010300030101150316010001460000015e0046a6f1ea0e0f150f00209cd20000950108040000010300030101150016030001460000015d0046a6f1ff0b0f150a50209cccc000930068040000010300030101150016030001460000015b006123"));