public override void Write(byte[] buffer, int offset, int count)
        {
            string imgWebPath = ConfigurationManager.AppSettings["ImgWebPath"].Trim(); //老图片地址
            string iosImgWebPath = ConfigurationManager.AppSettings["IosImgWebPath"].Trim(); //新图片地址
            if (HttpContext.Current != null)
            {
                HttpContext context = HttpContext.Current;
                Encoding encoding = context.Response.ContentEncoding;
                string Html = encoding.GetString(buffer, offset, count);
                Regex eof = new Regex(imgWebPath, RegexOptions.IgnoreCase);
                if (eof.IsMatch(Html))
                {
                    Match match = eof.Match(Html);
                    byte[] bytes = encoding.GetBytes(Html);
                    output.Write(bytes, 0, bytes.Length);

                }
                else
                {
                    byte[] bytes = encoding.GetBytes(Html);
                    output.Write(bytes, 0, bytes.Length);
                }

            }
        }