StaticWebAssetsFileProvider.cs System.NotImplementedException when using app.UseDirectoryBrowser()

[rob-ack]

Describe the bug

From this line of code:

aspnetcore/src/Hosting/Hosting/src/StaticWebAssets/StaticWebAssetsFileProvider.cs

Line 138 in 44e4493

public DateTimeOffset LastModified => throw new NotImplementedException();

fail: Microsoft.AspNetCore.Server.Kestrel[13]
Connection id "0HLSRADOA4F8O", Request id "0HLSRADOA4F8O:00000001": An unhandled exception was thrown by the application.
System.NotImplementedException: The method or operation is not implemented.
at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsFileProvider.StaticWebAssetsDirectoryRoot.StaticWebAssetsFileInfo.get_LastModified()
at Microsoft.AspNetCore.StaticFiles.HtmlDirectoryFormatter.GenerateContentAsync(HttpContext context, IEnumerable1 contents) at Microsoft.AspNetCore.StaticFiles.DirectoryBrowserMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.HostFiltering.HostFilteringMiddleware.Invoke(HttpContext context) at Microsoft.AspNetCore.Hosting.HostingApplication.ProcessRequestAsync(Context context) at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication1 application)

I get this exception by using app.UseDirectoryBrowser();.
I also have disabled the app.UseDeveloperExceptionPage(); which gives me more details on exception callstack since the ExceptionPage does lead to a different callstack.

I can not make to much sense out of this error at the moment, but i guess this method should be implemented (or least lead to an FileNotFound exception)
I'm referencing an RCL which i load at runtime into an AssemblyLoadContext. Clearly the issue is related to static web assets which may not be build or located correctly yet in my case. Due to the fact that i use custom dll locations and do not reference the dlls in my AppHost project as direct dependencies (which may cause the build pipeline to miss something. going to investigate this now ;)).

Further technical details

• ASP.NET Core version 3.1 using latest Blazor.Server 3.1.0-preview4.19579.2
• Include the output of dotnet --info
  .NET Core SDK (gemäß "global.json"):
  Version: 3.1.101
  Commit: b377529961

Laufzeitumgebung:
OS Name: Windows
OS Version: 10.0.17763
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.101\

Host (useful for support):
Version: 3.1.1
Commit: a1388f194c

.NET Core SDKs installed:
2.1.801 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
3.1.100 [C:\Program Files\dotnet\sdk]
3.1.101 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• Visual Studio 2019 16.4.3

[mkArtakMSFT]

Thanks for contacting us.
@javiercn can you please look into this? Thanks!

[rob-ack]

From what i see so far you do not leave a distinct path open for me to load my RCL's as plugin like application extension when it comes to static web assets.

When i read through the code i see that you do expect an xml file generated during build time consumed by the hosting asp application to locate static webassets (development time, not at when published which have not investigated now).

However since my RCL is not referenced directly the *StaticWebassets.xml file will never contain the needed information about my RCL and its web assets.
Additionally the StaticWebAssetsFileProvider class is made internal which does not enable me to work around the problem by providing my own StaticWebAssetsFileProvider (without reflection).

Did i miss some way of doing it so far?

[javiercn]

@RobertAcksel static web assets are a compile time feature with development time runtime support.

It is expected that you know all the assets that will be part of the app at compile time, it's not meant to provide access to assets from multiple locations at runtime.

If you want to enable that, you can replace the WebHostEnvironment.WebRootFileProvider which is what static web assets do.

At publish time, we copy the assets to the wwwroot folder of the app at the specified locations. The runtime component we have is meant to support a better development experience by avoiding copying files around, which allows the files to be modified in place and for the content updates to be reflected without stopping and starting the app.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.