Send messsage from server to GPS device

Question

I have been using TK06A GPS tracker and I 'm developing my own server java file and I have received the initial login message packet as per the TK06A manual and now I need to send back the ack to the device to get the GPS message packet.

I am not getting the GPS message packet which holds the coordinates. I'm adding the code below. I'm sure that till obtaining the IMEI number in the LOC is correct and I'm having problems in the outputstream/sending the ACk. I'm totally struck here. I don't know where am I going wrong.

Kindly help !

public void run() {
DataInputStream inputS = null;
DataOutputStream dos = null;
try {
    inputS = new DataInputStream(socket.getInputStream());
    if (inputS.available() > 0) {
        byte[] bb = getBytesFromInputStream(inputS);
        ChannelBuffer buf = toByteBuffer(bb);
        String imei = readImei(buf);
        System.out.println("IMEI::::: " + imei);
        buf.skipBytes(5); // End

        OutputStream os = socket.getOutputStream();
        dos = new DataOutputStream(os);
        byte[] response = parseHex();

        dos.write(response);
        Thread.sleep(1000);
        dos.flush();

    }

} catch (Exception e) {
    e.printStackTrace();
}

finally {
    try {
        inputS.close();
        if (dos != null)
            dos.close();
        socket.close();
    } catch (IOException e) {

    }
}

}

public byte[] parseHex() {
    String  hexACKlogin = "787805010001D9DC0D0A"; // String in HEX format
    int len = hexACKlogin.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(hexACKlogin.charAt(i), 16) << 4)
                             + Character.digit(hexACKlogin.charAt(i+1), 16));
    }  
     return data;
}

Please tell us what protocol you're implementing. Without that, we won't be able to help you. — Jon Skeet, Dec 28 '14 at 07:45
Basically the way you read from a data socket is also the way you write to this data socket, just with methods write from classes *Writer instead of read and *Reader. — laune, Dec 28 '14 at 07:54
Maybe, this can provide some hints: http://security.stackexchange.com/questions/55365/openssl-heartbeat-heartbleed-bug-whats-the-payload-used-for — user1807337, Dec 28 '14 at 09:11

Gerald Amalraj · Answer 1 · 2014-12-29T22:33:00.683

I'm implementing a logic for a GPS tracking device (TK06A). Client being the GPS tracker and server which I'm using to read the data sent from the tracker.

I'm receiving a 18 bytes data which I found out to be a Login Message packet which doesn't contain the co-ordinates/latitude & longitude.

It is said that I need to send a ACK response to the client[I'm stuck here].

I need to send the byte as a response to the client in my case Gps tracker the byte[] response = {0x78 0x78 0x05 0x01 0x00 0x01 0xD9 0xDC 0x0D 0x0A};

I have used portpeeker to send the ack and it was returning some response of 36 bytes.

PS: I'm using TCP for data transfer

try {
        inputS = new DataInputStream(socket.getInputStream());
        oos = new ObjectOutputStream(socket.getOutputStream());
        if (inputS.available() > 0) {
            System.out.println("Bytes Cap::: "+inputS.available());
            byte[] bb = getBytesFromInputStream(inputS);
            ChannelBuffer buf = toByteBuffer(bb);
            buf.skipBytes(4);
            String imei = readImei(buf);
            System.out.println("IMEI::::: " + imei);
            buf.skipBytes(5); // End

            byte[] response = sendOutputMessage();
            oos.write(response);
            oos.flush();
        }

    } catch (Exception e) {
        e.printStackTrace();
    }finally{
        try {
            inputS.close();
            oos.close();
            socket.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

 public byte[] sendOutputMessage() {
    byte buf[] = new byte[10];
    // Start of the body of setOutput
    // Message type  0x78 0x78 0x05 0x01 0x00 0x01 0xD9 0xDC 0x0D 0x0A
    buf[0] = (byte) 0x78;
    buf[1] = (byte) 0x78;
    buf[2] = (byte) 0x05;
    buf[3] = (byte) 0x01;
    buf[4] = (byte) 0x00;
    buf[5] = (byte) 0x01;
    buf[6] = (byte) 0xD9;
    buf[7] = (byte) 0xDC;
    buf[8] = (byte) 0x0D; // end f1
    buf[9] = (byte) 0x0A;
    return buf;
}

When you send this response, what error do you get? – user1807337 Dec 29 '14 at 21:40 — user1807337, Dec 29 '14 at 21:40

Send messsage from server to GPS device

1 Answers1