public synchronized byte[] getBlock(int offset, int length){
		if(!this.completed)
			return null;
		if(offset + length > this.length)
			return null;
		
		byte[] block = new byte[length];
		
		for(int i = 0; i < length; i++){
			block[i] = this.data[offset + length];
		}
		
		return block;
	}