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 != )
             {
                 Console.WriteLine("请指定torrent文件");
                 return;
             }
             string filename = args[];
             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 = ;
             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 !=  && 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：