"Invalid non-ASCII or control character in header: 0x00E7" when redirect to a URL with non-ASCII (e.g: ç)

[TiagoSoczek]

Hi everyone,

When attempting to redirect to a URL containing a non-ASCII character, Kestrel throws the following exception:

System.InvalidOperationException: Invalid non-ASCII or control character in header: 0x00E7
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.FrameHeaders.ThrowInvalidHeaderCharacter(Char ch)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.FrameHeaders.ValidateHeaderCharacters(String headerCharacters)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.FrameHeaders.ValidateHeaderCharacters(StringValues headerValues)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.FrameResponseHeaders.SetValueFast(String key, StringValues value)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.FrameHeaders.Microsoft.AspNetCore.Http.IHeaderDictionary.set_Item(String key, StringValues value)
   at Microsoft.AspNetCore.Http.Internal.DefaultHttpResponse.Redirect(String location, Boolean permanent)
   at Microsoft.AspNetCore.Mvc.Internal.RedirectResultExecutor.Execute(ActionContext context, RedirectResult result)
   at Microsoft.AspNetCore.Mvc.RedirectResult.ExecuteResult(ActionContext context)
   at Microsoft.AspNetCore.Mvc.ActionResult.ExecuteResultAsync(ActionContext context)

Sample code:

    [Route("[controller]")]
    public class HomeController : Controller
    {
        [HttpGet]
        public IActionResult Goto() => Redirect("http://example.com/façade.pdf");
    }

The same Redirect works correctly on ASP.NET MVC 5.2.3.

I'm aware the HTTP don't allow non-ASCII character in the URL, but, this can be considered an bug? If no, what is the best recommendation here? Encode the URL before redirect?

Thanks.

[Tratcher]

Yes, you are expected to properly encode urls, and any other headers for that matter. There are helpers like PathString and UrlHelper for encoding and assembling the components.

[TiagoSoczek]

Thanks @Tratcher. I solved using the Uri class with the AbsoluteUri property

        [HttpGet]
        public IActionResult Goto()
        {
            Uri uri = new Uri("http://some-domain/façade.pdf"); 
            
            return Redirect(uri.AbsoluteUri);
        }

[Tratcher]

Note that won't encode Unicode host names.

[TiagoSoczek]

Ah, good to known, thanks @Tratcher.