Как проверить несколько расширений файла перед загрузкой на веб-страницу

Question

Я пытаюсь загрузить файл на веб-страницу, который позволяет только расширение PDF. Но если я изменил расширение любого файла (например, a.jpeg) на .pdf, который будет похож на a.jpeg.pdf, а затем его можно загрузить на веб-страницу. Поэтому я хочу проверить несколько расширений в одном файле перед загрузкой на веб-страницу.

Ниже приведено мое кодирование.

if (file != null && file.ContentLength > 0) 
       { 
        int MaxContentLength = 1024 * 1024 * 4; 
        string[] AllowedFileExtensions = new string[] { ".pdf" }; 
        if (!AllowedFileExtensions.Contains(file.FileName.Substring(file.FileName.LastIndexOf('.')))) 
        { 
         ModelState.AddModelError("File", "(SERVER)Please select file of type: " + string.Join(", ", AllowedFileExtensions)); 
         return RedirectToAction("AddNewRule", "CreateRule"); 
        } 
        else if (file.ContentLength > MaxContentLength) 
        { 
         ModelState.AddModelError("File", "(SERVER)Your file is too large, maximum allowed size is: " + MaxContentLength + " MB"); 
         return RedirectToAction("AddNewRule","CreateRule"); 
        } 
        var fileName = Path.GetFileName(file.FileName); 
        var filetype = Path.GetExtension(fileName); 
        var mimeType = MimeMapping.GetMimeMapping(filetype); 
        if (mimeType == "application/pdf") 
        { 
         var path = Path.Combine(Server.MapPath("~/Files"), fileName); 
         file.SaveAs(path); 
         rule_add.File_Name = fileName; 
         rule_add.File_Path = path; 
         rule_add.File_Page = addrule.pagenum; 
        } 
        else 
        { 
         ModelState.AddModelError("File", "(SERVER)This file doesn't has valid content "); 
         return RedirectToAction("AddNewRule", "CreateRule"); 
        } 
       } 

Благодарим за помощь.

Answer 1

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.IO; 
namespace CopaRule.Models 
{ 
    public class MimeType 
    {`enter code here` 
     private static readonly byte[] BMP = { 66, 77 }; 
     private static readonly byte[] DOC = { 208, 207, 17, 224, 161, 177, 26, 225 }; 
     private static readonly byte[] EXE_DLL = { 77, 90 }; 
     private static readonly byte[] GIF = { 71, 73, 70, 56 }; 
     private static readonly byte[] ICO = { 0, 0, 1, 0 }; 
     private static readonly byte[] JPG = { 255, 216, 255 }; 
     private static readonly byte[] MP3 = { 255, 251, 48 }; 
     private static readonly byte[] OGG = { 79, 103, 103, 83, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0 }; 
     private static readonly byte[] PDF = { 37, 80, 68, 70, 45, 49, 46 }; 
     private static readonly byte[] PNG = { 137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82 }; 
     private static readonly byte[] RAR = { 82, 97, 114, 33, 26, 7, 0 }; 
     private static readonly byte[] SWF = { 70, 87, 83 }; 
     private static readonly byte[] TIFF = { 73, 73, 42, 0 }; 
     private static readonly byte[] TORRENT = { 100, 56, 58, 97, 110, 110, 111, 117, 110, 99, 101 }; 
     private static readonly byte[] TTF = { 0, 1, 0, 0, 0 }; 
     private static readonly byte[] WAV_AVI = { 82, 73, 70, 70 }; 
     private static readonly byte[] WMV_WMA = { 48, 38, 178, 117, 142, 102, 207, 17, 166, 217, 0, 170, 0, 98, 206, 108 }; 
     private static readonly byte[] ZIP_DOCX = { 80, 75, 3, 4 }; 

     public static string GetMimeType(byte[] file, string fileName) 
     { 

      string mime = "application/octet-stream"; //DEFAULT UNKNOWN MIME TYPE 

      //Ensure that the filename isn't empty or null 
      if (string.IsNullOrWhiteSpace(fileName)) 
      { 
       return mime; 
      } 

      //Get the file extension 
      string extension = Path.GetExtension(fileName) == null 
            ? string.Empty 
            : Path.GetExtension(fileName).ToUpper(); 

      //Get the MIME Type 
      if (file.Take(2).SequenceEqual(BMP)) 
      { 
       mime = "image/bmp"; 
      } 
      else if (file.Take(8).SequenceEqual(DOC)) 
      { 
       mime = "application/msword"; 
      } 
      else if (file.Take(2).SequenceEqual(EXE_DLL)) 
      { 
       mime = "application/x-msdownload"; //both use same mime type 
      } 
      else if (file.Take(4).SequenceEqual(GIF)) 
      { 
       mime = "image/gif"; 
      } 
      else if (file.Take(4).SequenceEqual(ICO)) 
      { 
       mime = "image/x-icon"; 
      } 
      else if (file.Take(3).SequenceEqual(JPG)) 
      { 
       mime = "image/jpeg"; 
      } 
      else if (file.Take(3).SequenceEqual(MP3)) 
      { 
       mime = "audio/mpeg"; 
      } 
      else if (file.Take(14).SequenceEqual(OGG)) 
      { 
       if (extension == ".OGX") 
       { 
        mime = "application/ogg"; 
       } 
       else if (extension == ".OGA") 
       { 
        mime = "audio/ogg"; 
       } 
       else 
       { 
        mime = "video/ogg"; 
       } 
      } 
      else if (file.Take(7).SequenceEqual(PDF)) 
      { 
       mime = "application/pdf"; 
      } 
      else if (file.Take(16).SequenceEqual(PNG)) 
      { 
       mime = "image/png"; 
      } 
      else if (file.Take(7).SequenceEqual(RAR)) 
      { 
       mime = "application/x-rar-compressed"; 
      } 
      else if (file.Take(3).SequenceEqual(SWF)) 
      { 
       mime = "application/x-shockwave-flash"; 
      } 
      else if (file.Take(4).SequenceEqual(TIFF)) 
      { 
       mime = "image/tiff"; 
      } 
      else if (file.Take(11).SequenceEqual(TORRENT)) 
      { 
       mime = "application/x-bittorrent"; 
      } 
      else if (file.Take(5).SequenceEqual(TTF)) 
      { 
       mime = "application/x-font-ttf"; 
      } 
      else if (file.Take(4).SequenceEqual(WAV_AVI)) 
      { 
       mime = extension == ".AVI" ? "video/x-msvideo" : "audio/x-wav"; 
      } 
      else if (file.Take(16).SequenceEqual(WMV_WMA)) 
      { 
       mime = extension == ".WMA" ? "audio/x-ms-wma" : "video/x-ms-wmv"; 
      } 
      else if (file.Take(4).SequenceEqual(ZIP_DOCX)) 
      { 
       mime = extension == ".DOCX" ? "application/vnd.openxmlformats-officedocument.wordprocessingml.document" : "application/x-zip-compressed"; 
      } 

      return mime; 
     } 
    } 
} 

Finally i got the solution. Above code helped me. 

Thank you all for your suggestions.