1 files changed, 80 insertions, 0 deletions
diff --git a/src/org/traccar/protocol/NavisFrameDecoder.java b/src/org/traccar/protocol/NavisFrameDecoder.java
new file mode 100644
index 000000000..2480629ac
--- /dev/null
+++ b/src/org/traccar/protocol/NavisFrameDecoder.java
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2019 Anton Tananaev (anton@traccar.org)
+ *
+ * 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 io.netty.buffer.ByteBuf;
+import io.netty.channel.Channel;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.handler.codec.TooLongFrameException;
+import org.traccar.BaseFrameDecoder;
+
+public class NavisFrameDecoder extends BaseFrameDecoder {
+
+    private static final int NTCB_HEADER_LENGHT = 16;
+    private static final int NTCB_LENGHT_OFFSET = 12;
+    private static final int MAX_FRAME_LENGHT = 65551;
+
+    private static byte src8Checksum(ByteBuf buf, int length) {
+        byte sum = (byte) 0xFF;
+        for (int i = 0; i < length; i++) {
+            sum ^= buf.getUnsignedByte(i);
+            for (int j = 0; j < 8; j++) {
+                sum = (sum & 0x80) != 0 ? (byte) ((sum << 1) ^ 0x31) : (byte) (sum << 1);
+            }
+        }
+        return sum;
+    }
+
+    @Override
+    protected Object decode(
+            ChannelHandlerContext ctx, Channel channel, ByteBuf buf) throws Exception {
+
+        // Check minimum length
+        if (buf.readableBytes() < 1) {
+            return null;
+        }
+
+        if (buf.getByte(buf.readerIndex()) == 0x7F) {
+            // FLEX keep alive frame
+            return buf.readRetainedSlice(1);
+        } else if (buf.getByte(buf.readerIndex()) == 0x7E /* "~" */) {
+            // FLEX frame
+            if (buf.readableBytes() > MAX_FRAME_LENGHT) {
+                throw new TooLongFrameException();
+            }
+
+            if (src8Checksum(buf, buf.readableBytes() - 1) == buf.getByte(buf.readableBytes() - 1)) {
+                return buf.readRetainedSlice(buf.readableBytes());
+            }
+        } else {
+            // NTCB frame
+            if (buf.readableBytes() < NTCB_HEADER_LENGHT) {
+                return null;
+            }
+
+            int length = buf.getUnsignedShortLE(buf.readerIndex() + NTCB_LENGHT_OFFSET);
+            if (buf.readableBytes() >= NTCB_HEADER_LENGHT + length) {
+                if (buf.readableBytes() > MAX_FRAME_LENGHT) {
+                    throw new TooLongFrameException();
+                }
+                return buf.readRetainedSlice(NTCB_HEADER_LENGHT + length);
+            }
+        }
+
+        return null;
+    }
+
+}