C# 解析torrent文件

基础知识：

torrent文件信息存储格式： 

bencoding是一种以简洁格式指定和组织数据的方法。支持下列类型：字节串、整数、列表和字典。

1 字符串存储格式:  <字符串的长度>:<字符串的内容> 
例如：    4:abcd 表示abcd, 2:ab 表示ab

2 数字的存储格式:  i<整数>e
例如：    i32e 表示整数32, i1024e 表示整数1024

3 列表的存储格式： l<子元素>e  其中：子元素可以是字符串，整数，列表和字典，或者是它们的组合体
例如：    l4:asdf4:qwere    表示 [ "asdf", "qwer" ] 

4 字典的存储格式： d<<key><value><key><value><key><value>...<key><value>>e 
其中：key只能是字符串类型，value则可以是字符串，整数，列表和字典，或者是它们的组合体，key和value必须是成对出现的
例如：    d3:cow3:moo4:spam4:eggse    表示 { "cow" => "moo", "spam" => "eggs" } 
        d4:spaml1:a1:bee            表示 { "spam" => [ "a", "b" ] } 
        d9:publisher3:bob4:spaml1:a1:be5:counti80ee  表示 { "publisher" => "bob", "spam" => [ "a", "b" ], "count" => 80 }

代码：

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using NPOI.OpenXmlFormats.Spreadsheet;
using Newtonsoft.Json;

namespace ConsoleApp
{
    /// <summary>
    /// Summary description for Class1.-change wdq
    /// </summary>
    public class Class1
    {
        static void Main(string[] args)
        {
            if (args.Length != 1)
            {
                Console.WriteLine("请指定torrent文件");
                return;
            }
            string filename = args[0];
            var data = Torrent.DecodeFile(filename);
            //Console.WriteLine(JsonConvert.SerializeObject(data, Newtonsoft.Json.Formatting.Indented));
            ShowData(data);
        }

        private static void ShowData(ItemBase data)
        {
            if (data.ItemType == ItemType.Dictionary)
            {
                foreach (var kv in (data as DictionaryItem).DictionaryData)
                {
                    switch (kv.Value.ItemType)
                    {
                        case ItemType.Dictionary:
                            Console.WriteLine(kv.Key + ":");
                            ShowData(kv.Value);
                            break;
                        case ItemType.List:
                            Console.WriteLine(kv.Key + ":");
                            ShowData(kv.Value);
                            break;
                        case ItemType.String:
                            if (kv.Key == "pieces")
                            {
                                break;
                            }
                            Console.WriteLine(kv.Key + "=" + (kv.Value as StringItem).StringData);
                            break;
                        case ItemType.Number:
                            Console.WriteLine(kv.Key + "=" + (kv.Value as NumberItem).NumberData);
                            break;
                    }
                }
            }
            if (data.ItemType == ItemType.List)
            {
                foreach (var i in (data as ListItem).ListData)
                {
                    switch (i.ItemType)
                    {
                        case ItemType.Dictionary:
                        case ItemType.List:
                            ShowData(i);
                            break;
                        case ItemType.String:
                            Console.WriteLine((i as StringItem).StringData);
                            break;
                        case ItemType.Number:
                            Console.WriteLine((i as NumberItem).NumberData);
                            break;
                    }
                }
            }
        }
    }

    public class Torrent
    {
        public static ItemBase DecodeFile(string filename)
        {
            using (var fs = new FileStream(filename, FileMode.Open))
            {
                using (BinaryReader br = new BinaryReader(fs))
                {
                    return DecodeData(br);
                }
            }
        }

        private static ItemBase DecodeData(BinaryReader br, Stack<bool> st = null)
        {
            var flag = br.PeekChar(); 
            List<byte> ls = new List<byte>();
            byte b = 0;
            switch (flag)
            {
                case 'e':
                    br.ReadByte();
                    return null;
                case 'l'://列表
                    br.ReadByte();
                    var itemLs = new ListItem(); 
                    ItemBase i = null;
                    if (st == null)
                    {
                        st = new Stack<bool>();
                    }
                    st.Push(true);
                    do
                    {
                        i = DecodeData(br, new Stack<bool>());
                        if (i != null)
                        {
                            itemLs.ListData.Add(i);
                        }
                        else
                        {
                            st.Pop();
                        }
                    } while (st.Count != 0 && br.BaseStream.Position != br.BaseStream.Length);

                    return itemLs;                    
                case 'd'://字典
                    br.ReadByte();
                    var itemDic = new DictionaryItem();
                    var key = DecodeData(br);
                    while (key != null && br.BaseStream.Position != br.BaseStream.Length)
                    {
                        var val = DecodeData(br);
                        itemDic.DictionaryData[(key as StringItem).StringData] = val;
                        key = DecodeData(br);
                    }

                    return itemDic; 
                case 'i'://数字
                    br.ReadByte();
                    b = br.ReadByte();
                    while (b != 'e')
                    {
                        ls.Add(b);
                        b = br.ReadByte();
                    }
                    return new NumberItem(long.Parse(Encoding.UTF8.GetString(ls.ToArray()))) { RawBytes = ls.ToArray() };                    
                default://字符串 
                    b = br.ReadByte();
                    while (b != ':')
                    {
                        ls.Add(b);
                        b = br.ReadByte();
                    }
                    var len = int.Parse(Encoding.UTF8.GetString(ls.ToArray()));
                    var bufStr = br.ReadBytes(len);
                    var data = Encoding.UTF8.GetString(bufStr);
                    return new StringItem(data) { RawBytes = bufStr };                    
            } 
        }
    }

    public class ItemBase
    {
        [JsonIgnore]
        public ItemType ItemType { get; set; }
        [JsonIgnore]
        public byte[] RawBytes { get; set; }
    }

    public class StringItem : ItemBase
    {
        public StringItem(string data)
        {
            StringData = data;
            ItemType = ItemType.String;
        }
        public string StringData { get; set; }
    }
    public class NumberItem : ItemBase
    {
        public NumberItem(long num)
        {
            NumberData = num;
            ItemType = ItemType.Number;
        }
        public long NumberData { get; set; }
    }

    public class ListItem : ItemBase
    {
        public ListItem()
        {
            ItemType = ItemType.List;
        }
        public List<ItemBase> ListData { get; set; } = new List<ItemBase>();
    }

    public class DictionaryItem : ItemBase
    {
        public DictionaryItem()
        {
            ItemType = ItemType.Dictionary;
        }
        public Dictionary<string, ItemBase> DictionaryData { get; set; } = new Dictionary<string, ItemBase>();
    }

    public enum ItemType
    {
        String, Number, List, Dictionary
    }
}

Github地址:https://github.com/a14907/AConsoleAppForFun.git

　　效果：