Getting no seeders and leechers for scrape from udp tracker

Question

I am trying to implement the scrape method for an UDP tracker but I keep getting 0 seeders/leechers as response. I am still getting a 2 as the action so no error is reported. I have hardcoded a hash here just to show that it has no effect on the result I am getting.

    final ByteArrayOutputStream byteStream =new ByteArrayOutputStream();
    final DataOutputStream dataStream =new DataOutputStream(byteStream);
    dataStream.writeInt(connectResponse.get("connectionId0"));
    dataStream.writeInt(connectResponse.get("connectionId1"));
    dataStream.writeInt(2);
    dataStream.write(connectResponse.get("transactionId"));
    bencodeWriter.write(byteOut.toString());
    dataStream.writeChars("1D19CC96C1A4965D184E4B215942DBC0A09FF8F2");
    dataStream.close();
    final byte[] scrapeBytes= byteStream.toByteArray();

I tried different trackers but get the same response. What might be the problem?

Edit: Added the hex dump of all the requests and responses:

Connect Request:

Connect Response:

Scrape Request:

Scrape Response:

What exactly are you sending and receiving on the wire? Could you possibly use Wireshark and post a HEX+ASCII dump. — Encombe, Jul 09 '17 at 15:02
I am sending a DatagramPacket the bytes above. I am not sure what you mean by HEX+ASCII dumps. Should I capture the transmissions as normal? — Jesper, Jul 09 '17 at 15:13
Good, but I need to see the full conversation. I.E. Connect request, Connect response, Scrape request and Scrape response — Encombe, Jul 09 '17 at 15:33

Encombe · Accepted Answer · 2017-07-09T16:19:25.700

2

In the Scrape request;
the transaction_id=0x36 is sent as a single byte instead of 4 bytes=0x00000036
and the info_hash is sent as a 80 bytes string that is hex-encoded were every character is prepended by a zero-byte 0x00 instead of as a raw 20 bytes string.
I.E. 0x0031004400310039... instead of 0x1D19...

The Scrape response has no peers, as there is no torrents with the info_hashes sent in the request.

edited Jul 09 '17 at 16:19

answered Jul 09 '17 at 16:12

Encombe

2,003
1
17
26

I had missed dataStream.write instead of dataStream.writeInt for the transaction_id so that fixes that. Do you have any suggestion on how to get the hash into the right format? – Jesper Jul 09 '17 at 16:37
https://stackoverflow.com/questions/13990941/how-to-convert-hex-string-to-java-string or https://stackoverflow.com/questions/32806404/convert-hexadecimal-to-string ?! I don't Java. – Encombe Jul 09 '17 at 16:48
Thanks for the answers! Got it to work with the apache commons hex when having the string but still wondering how to do it with a an info hashmap. Maybe I'll start another question if I don't figure it out... – Jesper Jul 09 '17 at 16:56
Hehe, tack! :-) – Jesper Jul 09 '17 at 17:01

Getting no seeders and leechers for scrape from udp tracker

1 Answers1