Web Api 2 custom IHttpActionResult CORS. No 'Access-Control-Allow-Origin' header is present on the requested resource - http-headers

Question

I have a problem with CORS from my WEB API 2 to Angular application.
Everything is working fine till now and all the response headers are receiving the following:
Access-Control-Allow-Origin:*
Cache-Control:no-cache
Content-Length:24
Content-Type:application/json; charset=utf-8
Date:Mon, 13 Nov 2017 08:15:32 GMT
Expires:-1
Pragma:no-cache
Server:Microsoft-IIS/10.0
X-AspNet-Version:4.0.30319
X-Powered-By:ASP.NET
X-SourceFiles:=?UTF-8?B?...
Now I created a custom IHttpActionResult like this:
public class ZipFileActionResult : IHttpActionResult
{
private const long BufferLength = 65536;
public ZipFileActionResult(string file)
{
this.Filepath = file;
}
public string Filepath { get; private set; }
public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
{
HttpResponseMessage result = new HttpResponseMessage();
var zipf = new FilesStream(this.Filepath);
Action<Stream, HttpContent, TransportContext> writeToStream = zipf.WriteToStream;
result.Content = new PushStreamContent(writeToStream, new MediaTypeHeaderValue("application/" + "zip"));
result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
{
FileName = "filename.zip"
};
return Task.FromResult(result);
}
private async void OnStreamConnected(Stream outputStream, HttpContent content, TransportContext context)
{
try
{
var buffer = new byte[BufferLength];
using (var nypdVideo = File.Open(this.Filepath, FileMode.Open, FileAccess.Read, FileShare.Read))
{
var videoLength = (int)nypdVideo.Length;
var videoBytesRead = 1;
while (videoLength > 0 && videoBytesRead > 0)
{
videoBytesRead = nypdVideo.Read(buffer, 0, Math.Min(videoLength, buffer.Length));
await outputStream.WriteAsync(buffer, 0, videoBytesRead);
videoLength -= videoBytesRead;
}
}
}
catch (HttpException ex)
{
return;
}
finally
{
// Close output stream as we are done
outputStream.Close();
}
}
}
and I use this in my DownloadCOntroller like this:
[HttpPost]
[Route("PaperCuts")]
public IHttpActionResult PaperCuts(List<SelectionObject> selections)
{
try
{
string sFileName = <filename> + ".zip";
return new ZipFileActionResult(sFileName);
}
}
catch (Exception ex)
{
throw ex;
}
}
I'm receiving the following error when I call this function correctly:
No 'Access-Control-Allow-Origin' header is present on the requested resource.
And I'm receiving this as response header:
HTTP/1.1 500 Internal Server Error
Cache-Control: private
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
Server: Microsoft-IIS/10.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RDpcUHJvamVjdHNcS25pcHNlbGtyYW50XEtuaXBzZWxrcmFudEFQSVxLbmlwc2Vsa3JhbnRBUElcYXBpXGRvd25sb2FkXFBhcGVyQ3V0cw==?=
X-Powered-By: ASP.NET
Date: Mon, 13 Nov 2017 08:35:33 GMT
I also have this stated in my WebApiConfig.cs (It works for all my other requests except for this one).
var corsAttr = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(corsAttr);
So the problem is that the Access-Control-Allow-Origin header etc are not same as in ALL the other requests. So how is this possible and how can I fix this?
I hope I provided enough information for my question.
Kind regards,
D.

Answer 1

I found the answer and got reminded by #ICantSeeSharp
I added following code in my global exception handler:
public override bool ShouldHandle(ExceptionHandlerContext context)
{
return true;
}