Returning a file to View Download in ASP NET MVC

Question

I m encountering a problem sending files stored in a database back to the user in ASP NET MVC  What I want is a view listing two links  one to view the file and let the mimetype sent to the browser determine how it should be handled  and the other to force a download   If I choose to view a file called SomeRandomFile bak and the browser doesn t have an associated program to open files of this type  then I have no problem with it defaulting to the download behavior  However  if I choose to view a file called SomeRandomFile pdf or SomeRandomFile jpg I want the file to simply open  But I also want to keep a download link off to the side so that I can force a download prompt regardless of the file type  Does this make sense   I have tried FileStreamResult and it works for most files  its constructor doesn t accept a filename by default  so unknown files are assigned a file name based on the URL  which does not know the extension to give based on content type   If I force the file name by specifying it  I lose the ability for the browser to open the file directly and I get a download prompt  Has anyone else encountered this   These are the examples of what I ve tried so far     Gives me a download prompt  return File document Data  document ContentType  document Name         Opens if it is a known extension type  downloads otherwise  download has bogus name and missing extension  return new FileStreamResult new MemoryStream document Data   document ContentType         Gives me a download prompt  lose the ability to open by default if known type  return new FileStreamResult new MemoryStream document Data   document ContentType   FileDownloadName   document Name     Any suggestions     UPDATE  This questions seems to strike a chord with a lot of people  so I thought I d post an update  The warning on the accepted answer below that was added by Oskar regarding international characters is completely valid  and I ve hit it a few times due to using the ContentDisposition class  I ve since updated my implementation to fix this  While the code below is from my most recent incarnation of this problem in an ASP NET Core  Full Framework  app  it should work with minimal changes in an older MVC application as well since I m using the System Net Http Headers ContentDispositionHeaderValue class   using System Net Http Headers   public IActionResult Download         Document document         Obtain document from database context         attachment  means always prompt the user to download        inline  means let the browser try and handle it     var cd   new ContentDispositionHeaderValue  attachment                 FileNameStar   document FileName            Response Headers Add HeaderNames ContentDisposition  cd ToString          return File document Data  document ContentType         an entity class for the document in my database  public class Document       public string FileName   get  set        public string ContentType   get  set        public byte   Data   get  set          Other properties left out for brevity

User · Accepted Answer

public ActionResult Download         var document           var cd   new System Net Mime ContentDisposition                  for example foo bak         FileName   document FileName               always prompt the user for downloading  set to true if you want             the browser to try to show the file inline         Inline   false              Response AppendHeader  Content-Disposition   cd ToString         return File document Data  document ContentType       NOTE  This example code above fails to properly account for international characters in the filename  See RFC6266 for the relevant standardization  I believe recent versions of ASP Net MVC s File   method and the ContentDispositionHeaderValue class properly accounts for this  - Oskar 2016-02-25

User · Answer

Below code worked for me for getting a pdf file from an API service and response it out to the browser - hope it helps   public async Task lt FileResult gt  PrintPdfStatements string fileName                 var fileContent   await GetFileStreamAsync fileName            var fileContentBytes     MemoryStream fileContent  ToArray             return File fileContentBytes  System Net Mime MediaTypeNames Application Pdf

User · Answer

Darin Dimitrov s answer is correct  Just an addition    Response AppendHeader  Content-Disposition   cd ToString     may cause the browser to fail rendering the file if your response already contains a  Content-Disposition  header  In that case  you may want to use   Response Headers Add  Content-Disposition   cd ToString

User · Answer

Action method needs to return FileResult with either a stream  byte    or virtual path of the file  You will also need to know the content-type of the file being downloaded  Here is a sample  quick dirty  utility method  Sample video link How to download files using asp net core   Route  api  controller     public class DownloadController   Controller        HttpGet      public async Task lt IActionResult gt  Download                 var path     C  Vetrivel winforms png           var memory   new MemoryStream            using  var stream   new FileStream path  FileMode Open                         await stream CopyToAsync memory                     memory Position   0          var ext   Path GetExtension path  ToLowerInvariant            return File memory  GetMimeTypes   ext   Path GetFileName path               private Dictionary lt string  string gt  GetMimeTypes                 return new Dictionary lt string  string gt                           txt    text plain                   pdf    application pdf                   doc    application vnd ms-word                   docx    application vnd ms-word                   png    image png                   jpg    image jpeg

User · Answer

I believe this answer is cleaner   based on https   stackoverflow com a 3007668 550975       public ActionResult GetAttachment long id                FileAttachment attachment          using  var db   new TheContext                          attachment   db FileAttachments FirstOrDefault x   gt  x Id    id                      return File attachment FileData   application force-download   Path GetFileName attachment FileName

User · Answer

FileVirtualPath --  Research Global Office Review pdf  public virtual ActionResult GetFile         return File FileVirtualPath   application force-download   Path GetFileName FileVirtualPath

User · Answer

I had trouble with the accepted answer due to no type hinting on the  document  variable  var document       So I m posting what worked for me as an alternative in case anybody else is having trouble   public ActionResult DownloadFile         string filename    File pdf       string filepath   AppDomain CurrentDomain BaseDirectory     Path To File     filename      byte   filedata   System IO File ReadAllBytes filepath       string contentType   MimeMapping GetMimeMapping filepath        var cd   new System Net Mime ContentDisposition               FileName   filename          Inline   true              Response AppendHeader  Content-Disposition   cd ToString          return File filedata  contentType

User · Answer

To view file  txt for example    return File    TextFileInRootDir txt   MediaTypeNames Text Plain     To download file  txt for example    return File    TextFileInRootDir txt   MediaTypeNames Text Plain   TextFile txt      note  to download file we should pass fileDownloadName argument

User · Answer

If  like me  you ve come to this topic via Razor components as you re learning Blazor  then you ll find you need to think a little more outside of the box to solve this problem   It s a bit of a minefield if  also like me  Blazor is your first forray into the MVC-type world  as the documentation isn t as helpful for such  menial  tasks   So  at the time of writing  you cannot achieve this using vanilla Blazor Razor without embedding an MVC controller to handle the file download part an example of which is as below   using Microsoft AspNetCore Mvc  using Microsoft Net Http Headers    Route  api  controller      ApiController  public class FileHandlingController   ControllerBase        HttpGet      public FileContentResult Download int attachmentId                TaskAttachment taskFile   null           if  attachmentId  gt  0                           taskFile    lt your code to get the file gt                 which assumes it s an object with relevant properties as required below              if  taskFile    null                                var cd   new System Net Http Headers ContentDispositionHeaderValue  attachment                                         FileNameStar   taskFile Filename                                     Response Headers Add HeaderNames ContentDisposition  cd ToString                                      return new FileContentResult taskFile  FileData  taskFile  FileContentType             Next  make sure your application startup  Startup cs  is configured to correctly use MVC and has the following line present  add it if not            services AddMvc         and then finally modify your component to link to the controller  for example  iterative based example using a custom class         lt tbody gt           foreach  var attachment in yourAttachments                     lt tr gt               lt td gt  lt a href  api FileHandling attachmentId  attachment TaskAttachmentId  target   blank  gt  attachment Filename lt  a gt   lt  td gt               lt td gt  attachment CreatedUser lt  td gt               lt td gt  attachment Created  ToString  dd MMM yyyy   lt  td gt               lt td gt  lt ul gt  lt li class  oi oi-circle-x delete-attachment  gt  lt  li gt  lt  ul gt  lt  td gt           lt  tr gt                     lt  tbody gt    Hopefully this helps anyone who struggled  like me   to get an appropriate answer to this seemingly simple question in the realms of Blazor

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