Returning binary file from controller in ASP NET Web API

Question

I m working on a web service using ASP NET MVC s new WebAPI that will serve up binary files  mostly  cab and  exe files   The following controller method seems to work  meaning that it returns a file  but it s setting the content type to application json   public HttpResponseMessage lt Stream gt  Post string version  string environment  string filetype        var path     C  Temp test exe       var stream   new FileStream path  FileMode Open       return new HttpResponseMessage lt Stream gt  stream  new MediaTypeHeaderValue  application octet-stream         Is there a better way to do this

User · Answer

The overload that you re using sets the enumeration of serialization formatters   You need to specify the content type explicitly like   httpResponseMessage Content Headers ContentType   new MediaTypeHeaderValue  application octet-stream

User · Answer

For those using  NET Core  You can make use of the IActionResult interface in an API controller method  like so         HttpGet  quot GetReportData  year  quot        public async Task lt IActionResult gt  GetReportData int year                   Render Excel document in memory and return as Byte           Byte   file   await this  reportDao RenderReportAsExcel year            return File file   quot application vnd openxmlformats quot    quot fileName xlsx quot           This example is simplified  but should get the point across  In  NET Core this process is so much simpler than in previous versions of  NET - i e  no setting response type  content  headers  etc  Also  of course the MIME type for the file and the extension will depend on individual needs  Reference  SO Post Answer by  NKosi

User · Answer

Try using a simple HttpResponseMessage with its Content property set to a StreamContent      using System IO     using System Net Http     using System Net Http Headers   public HttpResponseMessage Post string version  string environment      string filetype        var path     C  Temp test exe       HttpResponseMessage result   new HttpResponseMessage HttpStatusCode OK       var stream   new FileStream path  FileMode Open  FileAccess Read       result Content   new StreamContent stream       result Content Headers ContentType            new MediaTypeHeaderValue  application octet-stream        return result      A few things to note about the stream used    You must not call stream Dispose    since Web API still needs to be able to access it when it processes the controller method s result to send data back to the client  Therefore  do not use a using  var stream        block  Web API will dispose the stream for you  Make sure that the stream has its current position set to 0  i e  the beginning of the stream s data   In the above example  this is a given since you ve only just opened the file  However  in other scenarios  such as when you first write some binary data to a MemoryStream   make sure to stream Seek 0  SeekOrigin Begin   or set stream Position   0  With file streams  explicitly specifying FileAccess Read permission can help prevent access rights issues on web servers  IIS application pool accounts are often given only read   list   execute access rights to the wwwroot

User · Answer

While the suggested solution works fine  there is another way to return a byte array from the controller  with response stream properly formatted     In the request  set header  Accept  application octet-stream   Server-side  add a media type formatter to support this mime type    Unfortunately  WebApi does not include any formatter for  application octet-stream   There is an implementation here on GitHub  BinaryMediaTypeFormatter  there are minor adaptations to make it work for webapi 2  method signatures changed    You can add this formatter into your global config    HttpConfiguration config         config Formatters Add new BinaryMediaTypeFormatter false      WebApi should now use BinaryMediaTypeFormatter if the request specifies the correct Accept header   I prefer this solution because an action controller returning byte   is more comfortable to test  Though  the other solution allows you more control if you want to return another content-type than  application octet-stream   for example  image gif

User · Answer

You could try  httpResponseMessage Content Headers Add  Content-Type    application octet-stream

User · Answer

You can try the following code snippet httpResponseMessage Content Headers Add  quot Content-Type quot    quot application octet-stream quot     Hope it will work for you

User · Answer

For Web API 2  you can implement IHttpActionResult  Here s mine   using System  using System IO  using System Net  using System Net Http  using System Net Http Headers  using System Threading  using System Threading Tasks  using System Web  using System Web Http   class FileResult   IHttpActionResult       private readonly string  filePath      private readonly string  contentType       public FileResult string filePath  string contentType   null                if  filePath    null  throw new ArgumentNullException  filePath              filePath   filePath           contentType   contentType             public Task lt HttpResponseMessage gt  ExecuteAsync CancellationToken cancellationToken                var response   new HttpResponseMessage HttpStatusCode OK                        Content   new StreamContent File OpenRead  filePath                       var contentType    contentType    MimeMapping GetMimeMapping Path GetExtension  filePath            response Content Headers ContentType   new MediaTypeHeaderValue contentType            return Task FromResult response             Then something like this in your controller    Route  Images   imagePath     public IHttpActionResult GetImage string imagePath        var serverPath   Path Combine  rootPath  imagePath       var fileInfo   new FileInfo serverPath        return  fileInfo Exists            IHttpActionResult  NotFound             new FileResult fileInfo FullName       And here s one way you can tell IIS to ignore requests with an extension so that the request will make it to the controller    lt  -- web config -- gt   lt system webServer gt     lt modules runAllManagedModulesForAllRequests  true   gt

User · Answer

For anyone having the problem of the API being called more than once while downloading a fairly large file using the method in the accepted answer  please set response buffering to true      System Web HttpContext Current Response Buffer   true   This makes sure that the entire binary content is buffered on the server side before it is sent to the client  Otherwise you will see multiple request being sent to the controller and if you do not handle it properly  the file will become corrupt

[asp.net] Returning binary file from controller in ASP.NET Web API

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