Using MimeMapping in ASP.NET Core

The following code should work:

string contentType;
new FileExtensionContentTypeProvider().TryGetContentType(FileName, out contentType);
return contentType ?? "application/octet-stream";

There is a NuGet package MimeTypes which works with .Net Core projects as an alternative to FileExtensionContentTypeProvider. I'm not aware of any other mime-type resolver package, which works with .Net Core (at least so far).

The usage is simple:

string fileName = "trial.jpg";
string mime = MimeKit.MimeTypes.GetMimeType(fileName);