org.klomp.snark.bencode

Class BDecoder

java.lang.Object

org.klomp.snark.bencode.BDecoder

public class BDecoder
extends Object

Decodes a bencoded stream to BEValues.

A bencoded byte stream can represent byte arrays, numbers, lists and maps (dictionaries).

It currently contains a hack to indicate a name of a dictionary of which a SHA-1 digest hash should be calculated (the hash over the original bencoded bytes).

Constructor Summary

Constructors

Constructor and Description
BDecoder(InputStream in) Initializes a new BDecoder.

Method Summary

Modifier and Type	Method and Description
BEValue	bdecode() Gets the next indicator and returns either null when the stream has ended or bdecodes the rest of the stream and returns the appropriate BEValue encoded object.
static BEValue	bdecode(InputStream in) Creates a new BDecoder and immediatly decodes the first value it sees.
BEValue	bdecodeBytes() Returns the next bencoded value on the stream and makes sure it is a byte array.
BEValue	bdecodeList() Returns the next bencoded value on the stream and makes sure it is a list.
BEValue	bdecodeMap() Returns the next bencoded value on the stream and makes sure it is a map (dictionary).
BEValue	bdecodeNumber() Returns the next bencoded value on the stream and makes sure it is a number.
byte[]	get_special_map_digest() Ugly hack.
int	getNextIndicator() Returns what the next bencoded object will be on the stream or -1 when the end of stream has been reached.
static void	main(String[] args) Prints out the decoded data from a torrent file.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BDecoder

public BDecoder(InputStream in)

Initializes a new BDecoder. Nothing is read from the given InputStream yet.

Parameters:

in - the InputStream to decode from

Method Detail

bdecode

public BEValue bdecode()
                throws IOException

Gets the next indicator and returns either null when the stream has ended or bdecodes the rest of the stream and returns the appropriate BEValue encoded object.

Returns:

the next BEValue on the stream, or null if the stream has ended

Throws:

IOException - if an I/O error occurs or the stream is not bencoded

bdecode

public static BEValue bdecode(InputStream in)
                       throws IOException

Creates a new BDecoder and immediatly decodes the first value it sees.

Returns:

The first BEValue on the stream or null when the stream has ended.

Throws:

InvalidBEncodingException - when the stream doesn't start with a bencoded value or the stream isn't a bencoded stream at all.

IOException - when somthing bad happens with the stream to read from.

bdecodeBytes

public BEValue bdecodeBytes()
                     throws IOException

Returns the next bencoded value on the stream and makes sure it is a byte array. If it is not a bencoded byte array it will throw InvalidBEncodingException.

Returns:

the next BEValue as a byte array

Throws:

IOException - if an I/O error occurs

InvalidBEncodingException - if the next value is not a byte array

bdecodeList

public BEValue bdecodeList()
                    throws IOException

Returns the next bencoded value on the stream and makes sure it is a list. If it is not a list it will throw InvalidBEncodingException.

Returns:

the next BEValue as a List

Throws:

IOException - if an I/O error occurs

InvalidBEncodingException - if the next value is not a list

bdecodeMap

public BEValue bdecodeMap()
                   throws IOException

Returns the next bencoded value on the stream and makes sure it is a map (dictionary). If it is not a map it will throw InvalidBEncodingException.

Returns:

the next BEValue as a Map

Throws:

IOException - if an I/O error occurs

InvalidBEncodingException - if the next value is not a map

bdecodeNumber

public BEValue bdecodeNumber()
                      throws IOException

Returns the next bencoded value on the stream and makes sure it is a number. If it is not a number it will throw InvalidBEncodingException.

Returns:

the next BEValue as a Number

Throws:

IOException - if an I/O error occurs

InvalidBEncodingException - if the next value is not a number

get_special_map_digest

public byte[] get_special_map_digest()

Ugly hack. Return the SHA hash over bytes that make up the special map.

Returns:

the SHA-1 digest of the special map bytes, or null if there was no special map

getNextIndicator

public int getNextIndicator()
                     throws IOException

Returns what the next bencoded object will be on the stream or -1 when the end of stream has been reached. Can return something unexpected (not '0' .. '9', 'i', 'l' or 'd') when the stream isn't bencoded.

This might or might not read one extra byte from the stream.

Throws:

IOException

main

public static void main(String[] args)

Prints out the decoded data from a torrent file.

Parameters:

args - command line arguments (expects one argument: the torrent file path)