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ASP.NET MVC 5 - Limit Upload File Type Extensions Via Custom Data Annotation/Attribute

Restricting or limiting the file type extensions is a key business requirement. It is not necessary that a business allows all file types to be uploaded via their web application. Sometimes, only image files are accepted by the web application, sometimes only documents, and sometimes the combination of image, documents, and compressed file types are accepted by the web system.

Today, I shall be demonstrating the process of limiting/restricting the desired upload file type extensions by implementing custom data annotation/attribute component on ASP.NET MVC5 platform. This article is not specific to image files only, you can use the provided solution with any type of file format as well.

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

Prerequisites

Following are some prerequisites before you proceed any further in this tutorial.

  1. Knowledge of ASP.NET MVC5.
  2. Knowledge of HTML.
  3. Knowledge of Bootstrap.
  4. Knowledge of C# Programming.

You can download the complete source code for this tutorial or you can follow the step by step discussion below. The sample code is being developed in Microsoft Visual Studio 2015 Enterprise.

Let's begin now.

Step 1

Create a new MVC web project and name it as "ImgExtLimit".

Step 2

You need to add/update the "executionTimeout", "maxRequestLength", and "maxAllowedContentLength" property values if not already added in the "Web.config" file, as shown below.

  1.   .....  
  2.   
  3. <system.web>  
  4.   <authentication mode="None" />  
  5.   <compilation debug="true" targetFramework="4.5.2" />  
  6.   <!-- executionTimeout = 30hrs (the value is in seconds) and maxRequestLength = 1GB (the value is in Bytes) -->  
  7.   <httpRuntime targetFramework="4.5.2" executionTimeout="108000" maxRequestLength="1073741824" />  
  8. </system.web>     
  9. <system.webServer>  
  10.   <!-- maxAllowedContentLength = 1GB (the value is in Bytes) -->      
  11.   <security>  
  12.     <requestFiltering>  
  13.       <requestLimits maxAllowedContentLength="1073741824" />  
  14.     </requestFiltering>  
  15.   </security>          
  16.   
  17.   .....  
  18.   
  19. </system.webServer>  
  20.   
  21.   ..... 

executionTimeout -> Amount of time required to process your request on the web server. The value is provided in seconds.

maxRequestLength -> Maximum size which your request can capture and send to the web server. The value is provided in bytes.

maxAllowedContentLength -> Maximum allowed size of your content (e.g. file, text data etc.) that is sent to the web server. The value is provided in bytes.

Step 3

Open the "Views->Shared->_Layout.cshtml" file and replace the code with the following.

  1. <!DOCTYPE html>  
  2. <html>  
  3. <head>  
  4.     <meta charset="utf-8" />  
  5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">  
  6.     <title>@ViewBag.Title</title>  
  7.     @Styles.Render("~/Content/css")  
  8.     @Scripts.Render("~/bundles/modernizr")  
  9.   
  10.     <!-- Font Awesome -->  
  11.     <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.4.0/css/font-awesome.min.css" />  
  12.   
  13. </head>  
  14. <body>  
  15.     <div class="navbar navbar-inverse navbar-fixed-top">  
  16.         <div class="container">  
  17.             <div class="navbar-header">  
  18.                 <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse">  
  19.                     <span class="icon-bar"></span>  
  20.                     <span class="icon-bar"></span>  
  21.                     <span class="icon-bar"></span>  
  22.                 </button>  
  23.             </div>  
  24.         </div>  
  25.     </div>  
  26.     <div class="container body-content">  
  27.         @RenderBody()  
  28.         <hr />  
  29.         <footer>  
  30.             <center>  
  31.                 <p><strong>Copyright © @DateTime.Now.Year - <a href="http://wwww.asmak9.com/">Asma's Blog</a>.</strong> All rights reserved.</p>  
  32.             </center>  
  33.         </footer>  
  34.     </div>  
  35.   
  36.     @*Scripts*@  
  37.     @Scripts.Render("~/bundles/jquery")  
  38.   
  39.     @Scripts.Render("~/bundles/jqueryval")  
  40.     @Scripts.Render("~/bundles/bootstrap")  
  41.   
  42.     @RenderSection("scripts", required: false)  
  43. </body>  
  44. </html> 

In the above code, I have simply created a basic default layout page and linked the require libraries into it.

Step 4

Create a new "Helper_Code\Common\AllowExtensionsAttribute.cs" file and add the following code.

  1. //-----------------------------------------------------------------------  
  2. // <copyright file="AllowExtensionsAttribute.cs" company="None">  
  3. //     Copyright (c) Allow to distribute this code and utilize this code for personal or commercial purpose.  
  4. // </copyright>  
  5. // <author>Asma Khalid</author>  
  6. //-----------------------------------------------------------------------  
  7.   
  8. namespace ImgExtLimit.Helper_Code.Common  
  9. {  
  10.     using System;  
  11.     using System.Collections.Generic;  
  12.     using System.ComponentModel.DataAnnotations;  
  13.     using System.Linq;  
  14.     using System.Web;  
  15.   
  16.     /// <summary>  
  17.     /// File extensions attribute class  
  18.     /// </summary>  
  19.     [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = true)]  
  20.     public class AllowExtensionsAttribute : ValidationAttribute  
  21.     {  
  22.         #region Public / Protected Properties  
  23.   
  24.         /// <summary>  
  25.         /// Gets or sets extensions property.  
  26.         /// </summary>  
  27.         public string Extensions { get; set; } = "png,jpg,jpeg,gif";  
  28.  
  29.         #endregion  
  30.  
  31.         #region Is valid method  
  32.   
  33.         /// <summary>  
  34.         /// Is valid method.  
  35.         /// </summary>  
  36.         /// <param name="value">Value parameter</param>  
  37.         /// <returns>Returns - true is specify extension matches.</returns>  
  38.         public override bool IsValid(object value)  
  39.         {  
  40.             // Initialization  
  41.             HttpPostedFileBase file = value as HttpPostedFileBase;  
  42.             bool isValid = true;  
  43.   
  44.             // Settings.  
  45.             List<string> allowedExtensions = this.Extensions.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries).ToList();  
  46.   
  47.             // Verification.  
  48.             if (file != null)  
  49.             {  
  50.                 // Initialization.  
  51.                 var fileName = file.FileName;  
  52.   
  53.                 // Settings.  
  54.                 isValid = allowedExtensions.Any(y => fileName.EndsWith(y));  
  55.             }  
  56.   
  57.             // Info  
  58.             return isValid;  
  59.         }  
  60.  
  61.         #endregion  
  62.     }  
  63. } 

In ASP.NET MVC 5, creating customized data annotations/attributes is one of the cool features. The ASP.NET MVC 5 platform already contains a default FileExtensions attribute, but, the issue with this pre-built data annotation/attribute is that it is applicable only on string type view model properties and in my case, I am uploading the files via "HttpPostedFileBase" data type view model property. This means that the pre-built data annotation/attribute does not have any means to know the data type of the file(s) that I am uploading which will have  no effect on the limitation that is considered to be applied on the uploaded file type extensions. Of course, there are many other tricks or workarounds to go through while working with the pre-built FileExtensions attribute, but, I prefer the custom data annotation/attribute mechanism, which is much simpler.

So, in the above code, I have created a new class "AllowExtensionsAttribute" (by following the naming convention of custom attribute class) and inherited the ValidationAttribute class. Then, I have created a public property "Extensions" and set the default value with image file type extensions, which means that my custom attribute will accept only image file type to be uploaded. So, in order to allow the required file type extensions, this property will be updated at the time of my custom attribute utilization accordingly. Finally, I have overridden the "IsValid(....)" method which will receive my uploaded file as "HttpPostedFileBase" data type and from this, I will extract the file type extension of the uploaded file and then validate whether it is according to either default file type extension restriction or according to my provided file type extensions.

Step 5

Now, create a new "Models\ImgViewModel.cs" file and replace the following code in it i.e.

  1. //-----------------------------------------------------------------------  
  2. // <copyright file="ImgViewModel.cs" company="None">  
  3. //     Copyright (c) Allow to distribute this code and utilize this code for personal or commercial purpose.  
  4. // </copyright>  
  5. // <author>Asma Khalid</author>  
  6. //-----------------------------------------------------------------------  
  7.   
  8. namespace ImgExtLimit.Models  
  9. {  
  10.     using System.Collections.Generic;  
  11.     using System.ComponentModel.DataAnnotations;  
  12.     using System.Web;  
  13.     using Helper_Code.Common;  
  14.   
  15.     /// <summary>  
  16.     /// Image view model class.  
  17.     /// </summary>  
  18.     public class ImgViewModel  
  19.     {  
  20.         #region Properties  
  21.   
  22.         /// <summary>  
  23.         /// Gets or sets Image file property.  
  24.         /// </summary>  
  25.         [Required]  
  26.         [Display(Name = "Supported Files .png | .jpg")]  
  27.         [AllowExtensions(Extensions = "png,jpg", ErrorMessage = "Please select only Supported Files .png | .jpg")]  
  28.         public HttpPostedFileBase FileAttach { get; set; }  
  29.   
  30.         /// <summary>  
  31.         /// Gets or sets message property.  
  32.         /// </summary>  
  33.         public string Message { get; set; }  
  34.   
  35.         /// <summary>  
  36.         /// Gets or sets is valid propertty.  
  37.         /// </summary>  
  38.         public bool isValid { get; set; }  
  39.  
  40.         #endregion  
  41.     }  
  42. } 

In the above code, I have created my view model which I will attach with my view. Here, I have created HttpPostedFileBase type file attachment property which will capture uploaded image/file data from the end-user, then I have also applied my custom "AllowExtensions" attribute to the FileAttach property and provide the list of file type extensions separated by a comma (,) that I have allowed my system to accept. Then, I have created two more properties; i.e., Message of data type string and isValid of data type Boolean for processing purpose.

Step 6

Create a new "Controllers\ImgController.cs" file and add the following code to it.

  1. //-----------------------------------------------------------------------  
  2. // <copyright file="ImgController.cs" company="None">  
  3. //     Copyright (c) Allow to distribute this code and utilize this code for personal or commercial purpose.  
  4. // </copyright>  
  5. // <author>Asma Khalid</author>  
  6. //-----------------------------------------------------------------------  
  7.   
  8. namespace ImgExtLimit.Controllers  
  9. {  
  10.     using System;  
  11.     using System.Collections.Generic;  
  12.     using System.Linq;  
  13.     using System.Web;  
  14.     using System.Web.Mvc;  
  15.     using Models;  
  16.   
  17.     /// <summary>  
  18.     /// Image controller class.  
  19.     /// </summary>  
  20.     public class ImgController : Controller  
  21.     {  
  22.         #region Index view method.  
  23.  
  24.         #region Get: /Img/Index method.  
  25.   
  26.         /// <summary>  
  27.         /// Get: /Img/Index method.  
  28.         /// </summary>          
  29.         /// <returns>Return index view</returns>  
  30.         public ActionResult Index()  
  31.         {  
  32.             // Initialization/  
  33.             ImgViewModel model = new ImgViewModel() { FileAttach = null, Message = string.Empty, isValid = false };  
  34.   
  35.             try  
  36.             {  
  37.             }  
  38.             catch (Exception ex)  
  39.             {  
  40.                 // Info  
  41.                 Console.Write(ex);  
  42.             }  
  43.   
  44.             // Info.  
  45.             return this.View(model);  
  46.         }  
  47.  
  48.         #endregion  
  49.  
  50.         #region POST: /Img/Index  
  51.   
  52.         /// <summary>  
  53.         /// POST: /Img/Index  
  54.         /// </summary>  
  55.         /// <param name="model">Model parameter</param>  
  56.         /// <returns>Return - Response information</returns>  
  57.         [HttpPost]  
  58.         [AllowAnonymous]  
  59.         [ValidateAntiForgeryToken]  
  60.         public ActionResult Index(ImgViewModel model)  
  61.         {  
  62.             try  
  63.             {  
  64.                 // Verification  
  65.                 if (ModelState.IsValid)  
  66.                 {  
  67.                     // Settings.  
  68.                     model.Message = "'" + model.FileAttach.FileName + "' file has been successfuly!! uploaded";  
  69.                     model.isValid = true;  
  70.                 }  
  71.                 else  
  72.                 {  
  73.                     // Settings.  
  74.                     model.Message = "'" + model.FileAttach.FileName + "' file is not supported. ";  
  75.                     model.isValid = false;  
  76.                 }  
  77.             }  
  78.             catch (Exception ex)  
  79.             {  
  80.                 // Info  
  81.                 Console.Write(ex);  
  82.             }  
  83.   
  84.             // Info  
  85.             return this.View(model);  
  86.         }  
  87.  
  88.         #endregion  
  89.  
  90.         #endregion  
  91.     }  
  92. } 

In the above code, I have created a GET "Index(...)" method which will initialize the view model with default values and send it to the view page. Finally, I have created a POST "Index(...)" method which will receive an input image file from the end-user, then validate the view model for allowed file type extensions and then send the response message accordingly.

Step 7

Now, create a view "Views\Img\Index.cshtml" file and add the following code to it.

  1. @using ImgExtLimit.Models  
  2.   
  3. @model ImgExtLimit.Models.ImgViewModel  
  4.   
  5. @{  
  6.     ViewBag.Title = "ASP.NET MVC5: Limit Upload File Extension";  
  7. }  
  8.   
  9.   
  10. <div class="row">  
  11.     <div class="panel-heading">  
  12.         <div class="col-md-8">  
  13.             <h3>  
  14.                 <i class="fa fa-file-text-o"></i>  
  15.                 <span>ASP.NET MVC5: Limit Upload File Extension</span>  
  16.             </h3>  
  17.         </div>  
  18.     </div>  
  19. </div>  
  20.   
  21. <br />  
  22.   
  23. <div class="row">  
  24.     <div class="col-md-6 col-md-push-2">  
  25.         <section>  
  26.             @using (Html.BeginForm("Index", "Img", FormMethod.Post, new { enctype = "multipart/form-data", @class = "form-horizontal", role = "form" }))  
  27.             {  
  28.                 @Html.AntiForgeryToken()  
  29.   
  30.                 <div class="well bs-component">  
  31.                     <br />  
  32.   
  33.                     <div class="row">  
  34.                         <div class="col-md-12">  
  35.                             <div class="col-md-8 col-md-push-2">  
  36.                                 <div class="input-group">  
  37.                                     <span class="input-group-btn">  
  38.                                         <span class="btn btn-default btn-file">  
  39.                                             Browse…  
  40.                                             @Html.TextBoxFor(m => m.FileAttach, new { type = "file", placeholder = Html.DisplayNameFor(m => m.FileAttach), @class = "form-control" })  
  41.                                         </span>  
  42.                                     </span>  
  43.                                     <input type="text" class="form-control" readonly>  
  44.                                 </div>  
  45.                                 @if (Model.isValid && !string.IsNullOrEmpty(Model.Message))  
  46.                                 {  
  47.                                     <span class="text-success">@Model.Message</span>  
  48.                                 }  
  49.                                 else  
  50.                                 {  
  51.                                     <span class="text-danger">@Model.Message</span>@Html.ValidationMessageFor(m => m.FileAttach, "", new { @class = "text-danger" })  
  52.                                 }  
  53.                             </div>  
  54.                         </div>  
  55.                     </div>  
  56.   
  57.                     <div class="form-group">  
  58.                         <div class="col-md-12">  
  59.                         </div>  
  60.                     </div>  
  61.   
  62.                     <div class="form-group">  
  63.                         <div class="col-md-offset-5 col-md-10">  
  64.                             <input type="submit" class="btn btn-danger" value="Upload" />  
  65.                         </div>  
  66.                     </div>  
  67.                 </div>  
  68.             }  
  69.         </section>  
  70.     </div>  
  71. </div>  
  72.   
  73. @section Scripts  
  74. {  
  75.     @*Scripts*@  
  76.     @Scripts.Render("~/bundles/bootstrap-file")  
  77.   
  78.     @*Styles*@  
  79.     @Styles.Render("~/Content/Bootstrap-file/css")  
  80. } 

In the above code, I have created a simple view for uploading the image file to the server which will validate the allowed file type extensions at the server side.

Step 8

Now, execute the project and you will be able to see the following in action.

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

I have allowed only image files of type ".png" & ".jpg", So, when I try to upload a ".txt" file, I will receive the error message.

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

ASP.NET MVC5 - Limit Upload File Type Extensions via Custom Data Annotation/Attribute

Conclusion

In this article, you learned about uploading of the image file by limiting/restricting the desired upload file type extensions by implementing custom data annotation/attribute component on ASP.NET MVC5 platform. We also learned how to create a custom data annotation/attribute class and then utilize the custom attribute in your view model property of type HttpPostedFileBase.


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