短鏈生成

 1  /// <summary>
 2  /// 短鏈生成
 3  /// </summary>
 4  public class ShortUrlBuilder
 5         {
 6             private static readonly string[] Chars = 
 7             { "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" ,
 8 
 9             "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" , "q" , "r" , "s" , "t" ,
10 
11             "u" , "v" , "w" , "x" , "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" ,
12 
13             "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" , "E" , "F" , "G" , "H" ,
14 
15             "I" , "J" , "K" , "L" , "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" ,
16 
17             "U" , "V" , "W" , "X" , "Y" , "Z"
18             };
19 
20             /// <summary>
21             /// 生成指定URL的摘要
22             /// </summary>
23             /// <param name="url">URL</param>
24             /// <returns>短鏈列表，任取一個存儲就行。</returns>
25             public static List<string> Build(string url)
26             {
27                 var shortUrls = new List<string>();
28                 if (url == null)
29                 {
30                     return shortUrls;
31                 }
32                 var hash = GetMd5(url);
33                 //將32個字元的md5碼分成4段處理，每段8個字元
34                 for (int i = 0; i < 4; i++)
35                 {
36 
37                     int offset = i * 8;
38 
39                     string sub = hash.Substring(offset,   8);
40 
41                     long sub16 = long.Parse(sub, NumberStyles.HexNumber); //將sub當作一個16進位的數，轉成long
42 
43                     // & 0X3FFFFFFF，去掉最前面的2位，只留下30位
44                     sub16 &= 0X3FFFFFFF;
45 
46                     StringBuilder sb = new StringBuilder();
47                     //將剩下的30位分6段處理，每段5位
48                     for (int j = 0; j < 6; j++)
49                     {
50                         //得到一個 <= 61的數字
51                         long t = sub16 & 0x0000003D;
52                         sb.Append(Chars[(int)t]);
53 
54                         sub16 >>= 5;  //將sub16右移5位
55                     }
56 
57                     shortUrls.Add(sb.ToString());
58                 }
59                 return shortUrls;
60             }
61 
62             /// <summary>
63             /// MD5加密
64             /// </summary>
65             /// <param name="myString">原始字元串</param>
66             /// <param name="salt">鹽</param>
67             /// <returns></returns>
68             private static string GetMd5(string myString, string salt = "")
69             {
70                 if (myString != null)
71                 {
72                     var array = myString.ToCharArray();
73                     Array.Reverse(array);
74                     myString = $"{new string(array)}+{{{salt}}}";
75 
76 #if DEBUG
77                     Debugger.Log(1, "2", $"自定義消息：{myString}\r\n");
78 #endif
79                     MD5 md5 = MD5.Create();
80                     byte[] bs = Encoding.UTF8.GetBytes(myString);
81                     byte[] hs = md5.ComputeHash(bs);
82                     StringBuilder sb = new StringBuilder();
83                     foreach (byte b in hs)
84                     {
85                         // 以十六進位格式格式化  
86                         sb.Append(b.ToString("x2"));
87                     }
88                     return sb.ToString();
89 
90                 }
91                 return null;
92             }
93         }