How to return a file FileContentResult in ASP NET WebAPI

Question

In a regular MVC controller  we can output pdf with a FileContentResult   public FileContentResult Test TestViewModel vm        var stream   new MemoryStream              add content to the stream       return File stream GetBuffer     application pdf    test pdf        But how can we change it into an ApiController    HttpPost  public IHttpActionResult Test TestViewModel vm                    return Ok pdfOutput         Here is what I ve tried but it doesn t seem to work     HttpGet  public IHttpActionResult Test         var stream   new MemoryStream                  var content   new StreamContent stream       content Headers ContentType   new MediaTypeHeaderValue  application pdf        content Headers ContentLength   stream GetBuffer   Length      return Ok content                   The returned result displayed in the browser is     Headers     Key   Content-Type   Value    application pdf      Key   Content-Length   Value    152844        And there is a similar post on SO  Returning binary file from controller in ASP NET Web API   It talks about output an existing file  But I could not make it work with a stream   Any suggestions

User · Answer

This question helped me   So  try this   Controller code    HttpGet  public HttpResponseMessage Test         var path   System Web HttpContext Current Server MapPath    Content test docx         HttpResponseMessage result   new HttpResponseMessage HttpStatusCode OK       var stream   new FileStream path  FileMode Open       result Content   new StreamContent stream       result Content Headers ContentDisposition   new ContentDispositionHeaderValue  attachment        result Content Headers ContentDisposition FileName   Path GetFileName path       result Content Headers ContentType   new MediaTypeHeaderValue  application octet-stream        result Content Headers ContentLength   stream Length      return result                View Html markup  with click event and simple url     lt script type  text javascript  gt        document  ready function                  btn   click function                     httproute      - using this to construct proper web api links              window location href     Url Action  GetFile    Data   new   httproute                                lt  script gt     lt button id  btn  gt      Button text  lt  button gt    lt a href    Url Action  GetFile    Data   new   httproute           gt Data lt  a gt

User · Answer

For me it was the difference between   var response   Request CreateResponse HttpStatusCode OK  new StringContent log  System Text Encoding UTF8   application octet-stream      and  var response   Request CreateResponse HttpStatusCode OK   response Content   new StringContent log  System Text Encoding UTF8   application octet-stream      The first one was returning the JSON representation of StringContent    Headers     Key   Content-Type   Value    application octet-stream  charset utf-8       While the second one was returning the file proper   It seems that Request CreateResponse has an overload that takes a string  as the second parameter and this seems to have been what was causing the StringContent object itself to be rendered as a string  instead of the actual content

User · Answer

If you want to return IHttpActionResult you can do it like this    HttpGet  public IHttpActionResult Test         var stream   new MemoryStream         var result   new HttpResponseMessage HttpStatusCode OK                Content   new ByteArrayContent stream GetBuffer               result Content Headers ContentDisposition   new System Net Http Headers ContentDispositionHeaderValue  attachment                 FileName    test pdf             result Content Headers ContentType   new MediaTypeHeaderValue  application octet-stream         var response   ResponseMessage result        return response

User · Answer

Here is an implementation that streams the file s content out without buffering it  buffering in byte     MemoryStream  etc  can be a server problem if it s a big file    public class FileResult   IHttpActionResult       public FileResult string filePath                if  filePath    null              throw new ArgumentNullException nameof filePath             FilePath   filePath             public string FilePath   get         public Task lt HttpResponseMessage gt  ExecuteAsync CancellationToken cancellationToken                var response   new HttpResponseMessage HttpStatusCode OK           response Content   new StreamContent File OpenRead FilePath            var contentType   MimeMapping GetMimeMapping Path GetExtension FilePath            response Content Headers ContentType   new MediaTypeHeaderValue contentType           return Task FromResult response             It can be simply used like this   public class MyController   ApiController       public IHttpActionResult Get                 string filePath   GetSomeValidFilePath            return new FileResult filePath

User · Answer

Instead of returning StreamContent as the Content  I can make it work with ByteArrayContent    HttpGet  public HttpResponseMessage Generate         var stream   new MemoryStream           processing the stream       var result   new HttpResponseMessage HttpStatusCode OK                Content   new ByteArrayContent stream ToArray               result Content Headers ContentDisposition           new System Net Http Headers ContentDispositionHeaderValue  attachment                 FileName    CertificationCard pdf             result Content Headers ContentType           new MediaTypeHeaderValue  application octet-stream         return result

User · Answer

I am not exactly sure which part to blame  but here s why MemoryStream doesn t work for you   As you write to MemoryStream  it increments it s Position property  The constructor of StreamContent takes into account the stream s current Position  So if you write to the stream  then pass it to StreamContent  the response will start from the nothingness at the end of the stream   There s two ways to properly fix this   1  construct content  write to stream   HttpGet  public HttpResponseMessage Test         var stream   new MemoryStream        var response   Request CreateResponse HttpStatusCode OK       response Content   new StreamContent stream                     stream Write                      return response      2  write to stream  reset position  construct content   HttpGet  public HttpResponseMessage Test         var stream   new MemoryStream                      stream Write                      stream Position   0       var response   Request CreateResponse HttpStatusCode OK       response Content   new StreamContent stream       return response      2  looks a little better if you have a fresh Stream  1  is simpler if your stream does not start at 0

[c#] How to return a file (FileContentResult) in ASP.NET WebAPI

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