Determine if uploaded file is image (any format) on MVC

Question

So I'm using this code for view:

<form action="" method="post" enctype="multipart/form-data">    <label for="file">Filename:</label>   <input type="file" name="file" id="file" />    <input type="submit" /> </form> 

This for model:

[HttpPost] public ActionResult Index(HttpPostedFileBase file) {    if (file.ContentLength > 0) {     var fileName = Path.GetFileName(file.FileName);     var path = Path.Combine(Server.MapPath("~/App_Data/uploads"), fileName);     file.SaveAs(path);   }    return RedirectToAction("Index"); } 

Works great unless the user add a file which isn't an image. How can I assure the file uploaded is an image. Thanks

Answer 1

In case it can helps anyone, Here is a static method for HttpPostedFileBase that checks if a given uploaded file is an image:

public static class HttpPostedFileBaseExtensions {     public const int ImageMinimumBytes = 512;      public static bool IsImage(this HttpPostedFileBase postedFile)     {         //-------------------------------------------         //  Check the image mime types         //-------------------------------------------         if (!string.Equals(postedFile.ContentType, "image/jpg", StringComparison.OrdinalIgnoreCase) &&             !string.Equals(postedFile.ContentType, "image/jpeg", StringComparison.OrdinalIgnoreCase) &&             !string.Equals(postedFile.ContentType, "image/pjpeg", StringComparison.OrdinalIgnoreCase) &&             !string.Equals(postedFile.ContentType, "image/gif", StringComparison.OrdinalIgnoreCase) &&             !string.Equals(postedFile.ContentType, "image/x-png", StringComparison.OrdinalIgnoreCase) &&             !string.Equals(postedFile.ContentType, "image/png", StringComparison.OrdinalIgnoreCase))         {             return false;         }          //-------------------------------------------         //  Check the image extension         //-------------------------------------------         var postedFileExtension = Path.GetExtension(postedFile.FileName);         if (!string.Equals(postedFileExtension , ".jpg", StringComparison.OrdinalIgnoreCase)             && !string.Equals(postedFileExtension , ".png", StringComparison.OrdinalIgnoreCase)             && !string.Equals(postedFileExtension , ".gif", StringComparison.OrdinalIgnoreCase)             && !string.Equals(postedFileExtension , ".jpeg", StringComparison.OrdinalIgnoreCase))         {             return false;         }          //-------------------------------------------         //  Attempt to read the file and check the first bytes         //-------------------------------------------         try         {             if (!postedFile.InputStream.CanRead)             {                 return false;             }             //------------------------------------------             //   Check whether the image size exceeding the limit or not             //------------------------------------------              if (postedFile.ContentLength < ImageMinimumBytes)             {                 return false;             }              byte[] buffer = new byte[ImageMinimumBytes];             postedFile.InputStream.Read(buffer, 0, ImageMinimumBytes);             string content = System.Text.Encoding.UTF8.GetString(buffer);             if (Regex.IsMatch(content, @"<script|<html|<head|<title|<body|<pre|<table|<a\s+href|<img|<plaintext|<cross\-domain\-policy",                 RegexOptions.IgnoreCase | RegexOptions.CultureInvariant | RegexOptions.Multiline))             {                 return false;             }         }         catch (Exception)         {             return false;         }          //-------------------------------------------         //  Try to instantiate new Bitmap, if .NET will throw exception         //  we can assume that it's not a valid image         //-------------------------------------------          try         {             using (var bitmap = new System.Drawing.Bitmap(postedFile.InputStream))             {             }         }         catch (Exception)         {             return false;         }         finally         {              postedFile.InputStream.Position = 0;         }          return true;     } } 

Edit 2/10/2017: According to a suggested edit, added a finally statement to reset the stream, so we can use it later.