Torrent Management: error with protocol UDP

Question

i'm triying to develop a torrent manager in java using jlibitorrent library, but when exec the program I obtain the following error:

Bencoding Exception: unknown protocol: udp at com.torrent.util.TorrentInfo.(TorrentInfo.java:160) at st.ST.main(ST.java:70)

The argument of the program is a torrent downloaded from internet, it also works in transmission.

the code of the function of give me the error message is:

@SuppressWarnings("unchecked")
public TorrentInfo(byte[] torrent_file_bytes) throws BencodingException
{   
    // Make sure the input is valid
    if(torrent_file_bytes == null || torrent_file_bytes.length == 0)
        throw new IllegalArgumentException("Torrent file bytes must be non-null and have at least 1 byte.");

    // Assign the byte array
    this.torrent_file_bytes = torrent_file_bytes;

    // Assign the metainfo map
    this.torrent_file_map = (Map<ByteBuffer,Object>)Bencoder2.decode(torrent_file_bytes);

    // Try to extract the announce URL
    ByteBuffer url_buff = (ByteBuffer)this.torrent_file_map.get(TorrentInfo.KEY_ANNOUNCE);
    if(url_buff == null)
        throw new BencodingException("Could not retrieve anounce URL from torrent metainfo.  Corrupt file?");

    try {
        String url_string = new String(url_buff.array(), "ASCII");
        URL announce_url = new URL(url_string);
        this.announce_url = announce_url;
    }
    catch(UnsupportedEncodingException uee)
    {
        throw new BencodingException(uee.getLocalizedMessage());
    }
    catch(MalformedURLException murle)
    {
        throw new BencodingException(murle.getLocalizedMessage());
    }

    // Try to extract the info dictionary
    ByteBuffer info_bytes = Bencoder2.getInfoBytes(torrent_file_bytes);
    Map<ByteBuffer,Object> info_map = (Map<ByteBuffer,Object>)this.torrent_file_map.get(TorrentInfo.KEY_INFO);

    if(info_map == null)
        throw new BencodingException("Could not extract info dictionary from torrent metainfo dictionary.  Corrupt file?");
    this.info_map = info_map;

    // Try to generate the info hash value
    try {
        MessageDigest digest = MessageDigest.getInstance("SHA-1");
        digest.update(info_bytes.array());
        byte[] info_hash = digest.digest();
        this.info_hash = ByteBuffer.wrap(info_hash);
    }
    catch(NoSuchAlgorithmException nsae)
    {
        throw new BencodingException(nsae.getLocalizedMessage());
    }

    // Extract the piece length from the info dictionary
    Integer piece_length = (Integer)this.info_map.get(TorrentInfo.KEY_PIECE_LENGTH);
    if(piece_length == null)
        throw new BencodingException("Could not extract piece length from info dictionary.  Corrupt file?");
    this.piece_length = piece_length.intValue();

    // Extract the file name from the info dictionary
    ByteBuffer name_bytes = (ByteBuffer)this.info_map.get(TorrentInfo.KEY_NAME);
    if(name_bytes == null)
        throw new BencodingException("Could not retrieve file name from info dictionary.  Corrupt file?");
    try {
        this.file_name = new String(name_bytes.array(),"ASCII");
    }
    catch(UnsupportedEncodingException uee)
    {
        throw new BencodingException(uee.getLocalizedMessage());
    }

    // Extract the file length from the info dictionary
    Integer file_length = (Integer)this.info_map.get(TorrentInfo.KEY_LENGTH);
    if(file_length == null)
        throw new BencodingException("Could not extract file length from info dictionary.  Corrupt file?");
    this.file_length = file_length.intValue();

    // Extract the piece hashes from the info dictionary
    ByteBuffer all_hashes = (ByteBuffer)this.info_map.get(TorrentInfo.KEY_PIECES);
    if(all_hashes == null)
        throw new BencodingException("Could not extract piece hashes from info dictionary.  Corrupt file?");
    byte[] all_hashes_array = all_hashes.array();

    // Verify that the length of the array is a multiple of 20 bytes (160 bits)
    if(all_hashes_array.length % 20 != 0)
        throw new BencodingException("Piece hashes length is not a multiple of 20.  Corrupt file?");
    int num_pieces = all_hashes_array.length / 20;

    // Copy the values of the piece hashes into the local field
    this.piece_hashes = new ByteBuffer[num_pieces];
    for(int i = 0; i < num_pieces; i++)
    {
        byte[] temp_buff = new byte[20];
        System.arraycopy(all_hashes_array,i*20,temp_buff,0,20);
        this.piece_hashes[i] = ByteBuffer.wrap(temp_buff);
    }
}

}

i don't know where is my error after two days reading the code, I apreciate so much all the help. Thanks.

Answer 1

Torrents can contain udp://... announce URLs used for UDP trackers. Granted the scheme name is a bit too generic, but that's how it is.

Java's URL class cannot handle those by default. See this SO question for possible solutions.

One could argue that this is a bug in the library because it doesn't just return a string so torrent decoding doesn't abort simply due to malformed or unknown URIs. Implementations should be liberal (within reason) in what they accept, so in this case they should simply filter out URI schemes they cannot handle.