private bool IsAllowedExtension(HttpPostedFile hifile)

        {

            bool ret = false;

            System.IO.FileStream fs = new System.IO.FileStream(hifile.FileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);

            System.IO.BinaryReader r = new System.IO.BinaryReader(fs);

            string fileclass = "";

            byte buffer;

            try

            {

                buffer = r.ReadByte();

                fileclass = buffer.ToString();

                buffer = r.ReadByte();

                fileclass += buffer.ToString();

            }

            catch

            {

                return false;

            }

            r.Close();

            fs.Close();

            /*文件扩展名说明

             *7173        gif

             *255216      jpg

             *13780       png

             *6677        bmp

             *239187      txt,aspx,asp,sql

             *208207      xls.doc.ppt

             *6063        xml

             *6033        htm,html

             *4742        js

             *8075        xlsx,zip,pptx,mmap,zip

             *8297        rar

             *01          accdb,mdb

             *7790        exe,dll

             *5666        psd

             *255254      rdp

             *10056       bt种子

             *64101       bat

             */

            String[] fileType = { "", "", "", "", "", "", "", "", "" };

            for (int i = ; i < fileType.Length; i++)

            {

                if (fileclass == fileType[i])

                {

                    ret = true;

                    break;

                }

            }

            return ret;

        }