Send DHT queries to "router.bittorrent.com" response garbled text

Question

I read the DHT Protocol in bep_0005 page.

But when I send a ping query or a find_node query, the server response a garbled text (both of router.bittorrent.com:6881 or dht.transmissionbt.com:6881)

Here is the Java source code bellow

    public String ping(final String id) {
    System.out.println("Start ping:" + id);
    Bencode bencode = new Bencode();
    byte[] encoded = bencode.encode(new HashMap<Object, Object>() {
        private static final long serialVersionUID = 4225164001818744013L;

        {
            put("t", "tr");
            put("y", "q");
            put("q", "ping");
            put("a", new HashMap<Object, Object>() {
                private static final long serialVersionUID = -6092073963971093460L;

                {
                    put("id", id);
                }
            });
        }
    });
    byte[] result = client.send(new String(encoded, bencode.getCharset()));
    Map<String, Object> dict = bencode.decode(result, Type.DICTIONARY);
    System.out.println("Bdecoded Data:" + dict);
    return "";
}

Send Packets

ping Query = {"t":"aa", "y":"q", "q":"ping", "a":{"id":"abcdefghij0123456789"}}

bencoded = d1:ad2:id20:abcdefghij0123456789e1:q4:ping1:t2:aa1:y1:qe

Acrodding to the bep_0005 protocol the response with be like:

Response = {"t":"aa", "y":"r", "r": {"id":"mnopqrstuvwxyz123456"}}

bencoded = d1:rd2:id20:mnopqrstuvwxyz123456e1:t2:aa1:y1:re

But my response is:

Response = {ip=��P���, r={id=2�NisQ�J�)ͺ����F|�g}, t=tr, y=r}

bencoded = d2:ip6:��P���1:rd2:id20:2�NisQ�J�)ͺ����F|�ge1:t2:tr1:y1:re

Send udp part Java code is:

    public byte[] send(String sendData) {
    DatagramSocket client;
    try {
        client = new DatagramSocket();
        client.setSoTimeout(5000);
        byte[] sendBuffer;
        sendBuffer = sendData.getBytes();
        InetAddress addr = InetAddress.getByName("router.bittorrent.com");
        int port = 6881;
        DatagramPacket sendPacket = new DatagramPacket(sendBuffer, sendBuffer.length, addr, port);
        client.send(sendPacket);
        byte[] receiveBuf = new byte[512];
        DatagramPacket receivePacket = new DatagramPacket(receiveBuf, receiveBuf.length);
        client.receive(receivePacket);
        System.out.println("Client Source Data:" + Arrays.toString(receivePacket.getData()));
        String receiveData = new String(receivePacket.getData(), "UTF-8");
        System.out.println("Client String Data:" + receiveData);
        client.close();
        return receivePacket.getData();
    } catch (SocketException e) {
        e.printStackTrace();
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

read the response in UTF-8 , but the iso-8859-1 is also a garbled text.

who can help me,thanks!

Answer 1

the server response a garbled text

No, the response is bencoded and contains raw binary data.
It CAN NOT be treated as text.

In BEP5, to make the raw binary node_id in the examples printable, it has cleverly been chosen to consist of only alphanumeric characters.
See:
Bittorrent KRPC - Why are node ID's half the size of an info_hash and use every character a-z?

The ip key is a extension explained in: BEP42 - DHT Security extension

The received response is fully valid.

TODO: Working Java code