How to correctly determine the upload file format for ASP

Asp. NET in judging the file format, if by intercepting extension to judge, through ContentType (MIME) judgment is not too safe, because both ways users can forge.

Here's how to get the file type by byte to make judgments

if  (request.files.count > 0) {//test only upload the first image here File[0]    httppostedfile  file0 = request.files[0];          //Conversion to Byte , read the image MIME type     stream stream;    //int contentlength =  file0. contentlength; //file Length     byte[] filebyte = new byte[2];// ContentLength, here we only read the file length of the first two bits used to judge the good, so faster, the rest is not used.     stream = file0. Inputstream;    stream. Read (filebyte, 0, 2);//contentlength, or take the top two     stream. Close ();          string fileflag =  "";     if  (filebyte != null && filebyte.length > 0)// Whether the picture data is empty     {        fileflag = filebyte [0]. ToString ()  + filebyte[1]. ToString ();                       }    string[] fileTypeStr = {  " 255216 ", " 7173 ", " 6677 ", " 13780 " };//corresponding picture format jpg,gif,bmp,png    if   (Filetypestr.contains (fileflag))     {         file0. SaveAs (Server.MapPath ("~/"  + FILE0. FileName));    }    else    {         response.write ("Picture format is incorrect:"  + fileflag);     }}

Byte data corresponding to common file types

7076 flv video file; 6787 swf video file; 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,doc X

Reference: ASP. NET to determine the upload file format http://www.studyofnet.com/news/996.html

How to correctly determine the upload file format for ASP