downkyi/DownKyi.Core/BiliApi/BiliUtils/DanmakuSender.cs

using System;

namespace DownKyi.Core.BiliApi.BiliUtils
{
    public static class DanmakuSender
    {
        private const uint CRCPOLYNOMIAL = 0xEDB88320;
        private static readonly uint[] crctable = new uint[256];

        static DanmakuSender()
        {
            CreateTable();
        }

        private static void CreateTable()
        {
            for (int i = 0; i < 256; i++)
            {
                uint crcreg = (uint)i;

                for (int j = 0; j < 8; j++)
                {
                    if ((crcreg & 1) != 0)
                    {
                        crcreg = CRCPOLYNOMIAL ^ (crcreg >> 1);
                    }
                    else
                    {
                        crcreg >>= 1;
                    }
                }
                crctable[i] = crcreg;
            }
        }

        private static uint Crc32(string userId)
        {
            uint crcstart = 0xFFFFFFFF;
            for (int i = 0; i < userId.Length; i++)
            {
                uint index = (uint)(crcstart ^ (int)userId[i]) & 255;
                crcstart = (crcstart >> 8) ^ crctable[index];
            }
            return crcstart;
        }

        private static uint Crc32LastIndex(string userId)
        {
            uint index = 0;
            uint crcstart = 0xFFFFFFFF;
            for (int i = 0; i < userId.Length; i++)
            {
                index = (uint)((crcstart ^ (int)userId[i]) & 255);
                crcstart = (crcstart >> 8) ^ crctable[index];
            }
            return index;
        }

        private static int GetCrcIndex(long t)
        {
            for (int i = 0; i < 256; i++)
            {
                if ((crctable[i] >> 24) == t)
                {
                    return i;
                }
            }
            return -1;
        }

        private static object[] DeepCheck(int i, int[] index)
        {
            object[] resultArray = new object[2];

            string result = "";
            uint tc;// = 0x00;
            var hashcode = Crc32(i.ToString());
            tc = (uint)(hashcode & 0xff ^ index[2]);

            if (!(tc <= 57 && tc >= 48))
            {
                resultArray[0] = 0;
                return resultArray;
            }

            result += (tc - 48).ToString();
            hashcode = crctable[index[2]] ^ (hashcode >> 8);
            tc = (uint)(hashcode & 0xff ^ index[1]);

            if (!(tc <= 57 && tc >= 48))
            {
                resultArray[0] = 0;
                return resultArray;
            }

            result += (tc - 48).ToString();
            hashcode = crctable[index[1]] ^ (hashcode >> 8);
            tc = (uint)(hashcode & 0xff ^ index[0]);

            if (!(tc <= 57 && tc >= 48))
            {
                resultArray[0] = 0;
                return resultArray;
            }

            result += (tc - 48).ToString();
            //hashcode = crctable[index[0]] ^ (hashcode >> 8);

            resultArray[0] = 1;
            resultArray[1] = result;
            return resultArray;
        }

        /// <summary>
        /// 查询弹幕发送者
        /// </summary>
        /// <param name="userId"></param>
        /// <returns></returns>
        public static string FindDanmakuSender(string userId)
        {
            object[] deepCheckData = new object[2];

            int[] index = new int[4];
            uint ht = (uint)Convert.ToInt32($"0x{userId}", 16);
            ht ^= 0xffffffff;

            int i;
            for (i = 3; i > -1; i--)
            {
                index[3 - i] = GetCrcIndex(ht >> (i * 8));
                uint snum = crctable[index[3 - i]];
                ht ^= snum >> ((3 - i) * 8);
            }
            for (i = 0; i < 100000000; i++)
            {
                uint lastindex = Crc32LastIndex(i.ToString());
                if (lastindex == index[3])
                {
                    deepCheckData = DeepCheck(i, index);
                    if ((int)deepCheckData[0] != 0)
                    {
                        break;
                    }
                }
            }
            if (i == 100000000)
            {
                return "-1";
            }
            return $"{i}{deepCheckData[1]}";
        }

    }
}