basic64

 

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace basic64
{
    public class Basic64
    {

  
        private Hashtable hash = new Hashtable();
        private Encoding encoding;
        private char[] dataMapping ={ 
                     'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P', 
                     'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f', 
                     'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v', 
                     'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/',
                     '=' 
                    };

        public Basic64(Encoding encoding)
        {
            InitTable();
            this.encoding = encoding;
        }
        public Basic64()
        {
            InitTable();

            this.encoding = Encoding.GetEncoding("gb2312");
        }
        private void InitTable()
        {
            // A-Z 0-25
            for (int i = 0; i <= 25; i++)
            {
                string letter = "" + Convert.ToChar('A' + i);
                hash.Add(letter, i);
            }
            for (int i = 26; i <= 51; i++)
            {
                string letter = "" + Convert.ToChar('a' + i - 26);
                hash.Add(letter, i);
            }
            for (int i = 52; i <= 61; i++)
            {
                hash.Add("" + (i - 52), i);
            }

            hash.Add("+", 62);
            hash.Add("/", 63);
            hash.Add("=", 64);
        }

        /// <summary>
        /// basic64编码
        /// </summary>
        /// <param name="code"></param>
        /// <returns></returns>
        public string ToBase64(string code)
        {
            byte[] bytes = this.encoding.GetBytes(code);
            int size = (bytes.Length % 3 == 0) ? 3 : (bytes.Length % 3);
            byte[] buffer = new byte[bytes.Length + (3 - size)];
            string ret = "";
            Buffer.BlockCopy(bytes, 0, buffer, 0, bytes.Length);
            byte[] dBuffer = new byte[buffer.Length / 3 * 4];
            int j = 0;
            for (int i = 0; i < buffer.Length / 3; i++)
            {
                int q = i * 3;
                dBuffer[j] = (byte)((buffer[q] >> 2) & 0x3f);
                dBuffer[++j] = (byte)((((buffer[q] << 6) >> 2) & 0x3f) | (((buffer[q + 1] >> 4)) & 0x0f));
                dBuffer[++j] = (byte)(((buffer[q + 1] << 4 >> 2) & 0x3f) | ((buffer[q + 2] >> 6) & 0x03));
                dBuffer[++j] = (byte)((buffer[q + 2] << 2 >> 2) & 0x3f);
                j++;
            }
            for (int i = 0; i < dBuffer.Length - (3 - size); i++)
            {
                ret += dataMapping[(int)dBuffer[i]] + "";
            }
            if ((3 - size) > 0)
            {
                for (int i = 0; i < (3 - size); i++)
                    ret += '=';
            }
            return ret;
        }


        /// <summary>
        /// basic64解码
        /// </summary>
        /// <param name="code"></param>
        /// <returns></returns>
        public string FromBasic64(string code)
        {
            if (code.Length % 4 != 0) throw new Exception("不正确的Basic64编码长度！");
            byte[] buffer = new byte[code.Length / 4 * 3];
            int j = 0;
            int padCount = findPadStr(code);
            for (int i = 0; i < code.Length / 4; i++)
            {
                int q = i * 4;
                int _a = Convert.ToInt32(hash[code[q].ToString()]);
                int _b = Convert.ToInt32(hash[code[q + 1].ToString()]);
                int _c = Convert.ToInt32(hash[code[q + 2].ToString()]);
                int _d = Convert.ToInt32(hash[code[q + 3].ToString()]);

                string a = fill8bits(Convert.ToString(_a, 2)).Substring(2, 6);
                string b = fill8bits(Convert.ToString(_b, 2)).Substring(2, 6);
                string c = fill8bits(Convert.ToString(_c, 2)).Substring(2, 6);
                string d = fill8bits(Convert.ToString(_d, 2)).Substring(2, 6);

                buffer[j] = Convert.ToByte(a + b.Substring(0, 2), 2);
                buffer[++j] = Convert.ToByte(b.Substring(2, 4) + c.Substring(0, 4), 2);
                buffer[++j] = Convert.ToByte((c.Substring(4, 2) + d), 2);
                j++;
            }
            return this.encoding.GetString(buffer, 0, buffer.Length - padCount);
        }
        #region helper
        private string fill8bits(string str)
        {
            int len = str.Length;
            if (len < 8)
            {
                for (int i = 0; i < (8 - len); i++)
                    str = "0" + str;
            }
            return str;
        }
        private int findPadStr(string code)
        {
            int j = 0;
            int len = code.Length;
            for (int i = 0; i < 3; i++)
            {
                if (code.Substring(len - i - 1, 1).Equals("="))
                {
                    j++;
                }
            }
            return j;

        }
        #endregion
    }
}