Running on .NET 5.0 now results in "A valid non-empty content root must be provided"

Describe the bug

Since upgrading to .NET 5.0, I have noticed that when deploying a product as a single file executable to Alpine Linux and running it under a rootless container via podman, I get the following error now. I really hope Kestrel does not require a directory for static content now, I use Kestrel for lightweight services and am quite happy with the 404 for any path not routed.

Unhandled exception. System.ArgumentException: A valid non-empty content root must be provided. (Parameter 'contentRootPath')
   at Microsoft.AspNetCore.Hosting.Internal.HostingEnvironmentExtensions.Initialize(IHostingEnvironment hostingEnvironment, String contentRootPath, WebHostOptions options)
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.BuildCommonServices(AggregateException& hostingStartupErrors)
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
   at NamespaceChanged.Program.RunAsync(Options options)
   at CommandLine.ParserResultExtensions.WithParsedAsync[T](ParserResult`1 result, Func`2 action)
   at NamespaceChanged.Program.Main(String[] args)
   at NamespaceChanged.Program.<Main>(String[] args)

I should mention that I do not use ASP.NET Core beyond using the Kestrel web server. I use my routing library, Routable and handle requests directly. Routable’s source is available here, but basically it does not do anything except add a handler for requests, check if the request path is matches a known route and handle it if it does, if not, it gives back control to Kestrel which until now would merrily issue a 404 (or hand off to the next handler).

The initialization looks like this:

using var server = new WebHostBuilder()
        .UseKestrel(kestrelOptions => kestrelOptions.ListenAnyIP(options.HttpPort))
        .Configure(appBuilder => appBuilder
                .UseRoutable(routable => routable
                        .AddRouting(new DefaultRouting(routable, options, profileManager))
                        .OnError(new KestrelRouting(routable) {
                                _ => _.Do((context, request, response) => {
                                        response.Status = 500;
                                        response.ClearPendingWrites();
                                        Log.Error(typeof(Program), $"A request encountered an unhandled exception.", context.Error);
                                })      
                        })      
                )       
        )       
        .Build();

using var cancellation = new CancellationTokenSource();
Console.CancelKeyPress += (_, e) => { 
        cancellation.Cancel();
        e.Cancel = true; 
};      

await server.RunAsync(cancellation.Token);

Notes

• This does not occur when debugging on Windows using Visual Studio or running on Windows via dotnet run.
• The executable is published as follows: dotnet publish -o publish/ -r linux-musl-x64 -c Release /p:PublishSingleFile=true /p:PublishTrimmed=true /p:IncludeNativeLibrariesForSelfExtract=true /p:IncludeAllContentForSelfExtract=true src/PROJECT_NAME

(edit: cleaned up structure a bit, added note)

[mmaguigan]

@davidfowl, yep, I’m happy. Thanks guys.

[vitek-karas]

My email is in my github profile. I can forward it to @davidfowl if he’s interested internally.