Parsing encoded data?

[Alan Wake]

I have some torrent file with list of announce urls, f.e. this is the part of it:

announce-listll68:http://iptorrents.com:2790/b6d18a815ab4421a86de672d6833369d/announceel67:http://iptorrents.me:2710/b6d18a815ab4421a86de672d6833369d/announceel67:http://iptorrents.ru:6969/b6d18a815ab4421a86de672d6833369d/announceee

So here is one array with key «announce-list» which contains three elements (bencoded data, http://en.wikipedia.org/wiki/Bencode). So I am using BDecoder.java class from Aeltis to decode it. While parsing I am getting the next values of Map:

{created by=[B@141d683, announce=[B@16a55fa, encoding=[B@32c41a, announce-list=[[[B@e89b94], [[B@13e205f], [[B@1bf73fa]], comment=[B@5740bb, creation date=1310060702, info={pieces=[B@5ac072, name=[B@109a4c, length=34209795, piece length=65536, private=1}}

So announce list filled with some hashes. So how can I convert it to normal string (such as «http://iptorrents.com:2790/b6d18a815ab4421a86de672d6833369d/announce»)? Or it's some algorithm issue in BDecoder.java?

This is the method of upper class to decode data: http://pastebin.com/HimqF0ye

[Rob Spoor]

Welcome to the Ranch!

All these parts that start with [B are byte arrays. When you print a byte[], its toString() method will print the type name ([B) followed by an @ and the hexadecimal hash code. This is how you get to something like [B@141d683.
created by=[B@141d683 => byte[]
announce=[B@16a55fa => byte[]
encoding=[B@32c41a => byte[]
announce-list=[[[B@e89b94], [[B@13e205f], [[B@1bf73fa]] => see below
comment=[B@5740bb => byte[]
creation date=1310060702 => int or long, probably long
info={pieces=[B@5ac072, name=[B@109a4c, length=34209795, piece length=65536, private=1} => see below

First of all, the announce list. You see not one but three starting [ characters. If used without closing ] character that means another array dimension. For example, [[B@e89b94 would be a byte[][] and [[[B@e89b94 a byte[][][]. However, there are closing ] characters. That means that it's not another array dimension, but a List, Set or other Collection; these are usually printed as [] with the elements inside separated by a comma and space. Matching the brackets you get this structure (using Collection since List and Set both extend Collection):
- Collection
-- Collection with one byte[]
-- Collection with one byte[]
-- Collection with one byte[]

Now, info. The {} with inside key=value pair usually indicates a Map. In this case it has the following entries:
- pieces => byte[]
- name => byte[]
- length => Integer or Long
- piece length => Integer or Long
- private => Byte, Short, Integer or Long

Afterwards, I'm guessing that you can turn each byte[] into a String, by using the right String constructor and providing the right encoding. Which one that is I can't tell you, but I'd probably start with UTF-8.

[Alan Wake]

Rob Spoor wrote:Welcome to the Ranch!

All these parts that start with [B are byte arrays. When you print a byte[], its toString() method will print the type name ([B) followed by an @ and the hexadecimal hash code. This is how you get to something like [B@141d683.
created by=[B@141d683 => byte[]
announce=[B@16a55fa => byte[]
encoding=[B@32c41a => byte[]
announce-list=[[[B@e89b94], [[B@13e205f], [[B@1bf73fa]] => see below
comment=[B@5740bb => byte[]
creation date=1310060702 => int or long, probably long
info={pieces=[B@5ac072, name=[B@109a4c, length=34209795, piece length=65536, private=1} => see below

First of all, the announce list. You see not one but three starting [ characters. If used without closing ] character that means another array dimension. For example, [[B@e89b94 would be a byte[][] and [[[B@e89b94 a byte[][][]. However, there are closing ] characters. That means that it's not another array dimension, but a List, Set or other Collection; these are usually printed as [] with the elements inside separated by a comma and space. Matching the brackets you get this structure (using Collection since List and Set both extend Collection):
- Collection
-- Collection with one byte[]
-- Collection with one byte[]
-- Collection with one byte[]

Now, info. The {} with inside key=value pair usually indicates a Map. In this case it has the following entries:
- pieces => byte[]
- name => byte[]
- length => Integer or Long
- piece length => Integer or Long
- private => Byte, Short, Integer or Long

Afterwards, I'm guessing that you can turn each byte[] into a String, by using the right String constructor and providing the right encoding. Which one that is I can't tell you, but I'd probably start with UTF-8.

Yep it works with String constructor such as:

String str = new String((byte[])announce_list.get(0))

So the result working code is:

        if(m.containsKey("announce-list"))
        {
            ArrayList tmp = (ArrayList) m.get("announce-list");
            tmp = (ArrayList) tmp.get(0);
            this.torrent.announceURL = new String((byte[]) tmp.get(0));
        }

Where "m" is map of torrent data from torrent file such as announce urls, pieces and so on. This code works for one announce url from announce list because I need just only one.
But I don't understand why in this class the error happens when I change this lines:

                Object tempElement = null;
                while ((tempElement = decodeInputStream(bais, nesting + 1)) != null) {
                    //add the element
                    tempList.add(tempElement);
                }

Where tempElement contains byte array to this:

                Object tempElement = null;
                while ((tempElement = decodeInputStream(bais, nesting + 1)) != null) {
                    //add the element
                    tempList.add(new String((byte[]) tempElement));
                }

Here is hole method:

    private Object
            decodeInputStream(
                    InputStream bais,
                    int nesting)

            throws IOException {
        if (nesting == 0 && !bais.markSupported()) {

            throw new IOException("InputStream must support the mark() method");
        }

        //set a mark
        bais.mark(Integer.MAX_VALUE);

        //read a byte
        int tempByte = bais.read();

        //decide what to do
        switch (tempByte) {
        case 'd':

            //create a new dictionary object
            Map tempMap = new HashMap();

            try {
                //get the key
                byte[] tempByteArray = null;

                while ((tempByteArray = (byte[]) decodeInputStream(bais,
                        nesting + 1)) != null) {

                    //decode some more

                    Object value = decodeInputStream(bais, nesting + 1);

                    //add the value to the map

                    CharBuffer cb = Constants.BYTE_CHARSET.decode(ByteBuffer.
                            wrap(tempByteArray));

                    String key = new String(cb.array(), 0, cb.limit());
                    
                    tempMap.put(key, value);
                }

                bais.mark(Integer.MAX_VALUE);
                tempByte = bais.read();
                bais.reset();
                if (nesting > 0 && tempByte == -1) {

                    throw (new IOException(
                            "BDecoder: invalid input data, 'e' missing from end of dictionary"));
                }
            } catch (Throwable e) {

                if (!recovery_mode) {

                    if (e instanceof IOException) {

                        throw ((IOException) e);
                    }

                    throw (new IOException(e.toString()));
                }
            }

            //return the map
            return tempMap;

        case 'l':

            //create the list
            List tempList = new ArrayList();

            try {
                //create the key
                Object tempElement = null;
                while ((tempElement = decodeInputStream(bais, nesting + 1)) != null) {
                    //add the element
                    tempList.add(tempElement);
                }

                bais.mark(Integer.MAX_VALUE);
                tempByte = bais.read();

                bais.reset();
                if (nesting > 0 && tempByte == -1) {

                    throw (new IOException(
                            "BDecoder: invalid input data, 'e' missing from end of list"));
                }
            } catch (Throwable e) {

                if (!recovery_mode) {

                    if (e instanceof IOException) {

                        throw ((IOException) e);
                    }

                    throw (new IOException(e.toString()));
                }
            }
            
            //return the list
            return tempList;

        case 'e':
        case -1:
            return null;

        case 'i':
            return new Long(getNumberFromStream(bais, 'e'));

        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':

            //move back one
            bais.reset();

            //get the string
            return getByteArrayFromStream(bais);

        default: {

            int rem_len = bais.available();

            if (rem_len > 256) {

                rem_len = 256;
            }

            byte[] rem_data = new byte[rem_len];

            bais.read(rem_data);

            throw (new IOException(
                    "BDecoder: unknown command '" + tempByte + ", remainder = " +
                    new String(rem_data)));
        }
        }
    }

In tempList there just only one string and somewhere it's brokes and don't go to return address. So I can't describe it you should see it ones and you'll understand what I mean. This is brokes just when I changes those three lines.

[Rob Spoor]

What error are you getting? Please post the full stack trace.

[Alan Wake]

Rob Spoor wrote:What error are you getting? Please post the full stack trace.

Hm there are no any exceptions happens but it suspend running at some moment.