Aspnetcore: On linux UseBlazor extension method fails with "The path must be absolute"

[paulvanbladel]

I'm using the FlightFinder sample for reproducing the problem.
https://github.com/aspnet/samples
or my fork: https://github.com/paulvanbladel/samples

steps to reproduce:

1. from the rootfolder of the solution:

dotnet publish FlightFinder.Server/FlightFinder.Server.csproj -c release -o publish

1. from the publish folder inside server project:

dotnet FlightFinder.Server.dll

Unfortunately, this bug makes that blazor can't be used with docker (didn't try with windows images).
```
paul@ubuntu-desktop:~/github/samples/samples/aspnetcore/blazor/FlightFinder/FlightFinder.Server/publish$ dotnet FlightFinder.Server.dll
info: Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
User profile is available. Using '/home/paul/.aspnet/DataProtection-Keys' as key repository; keys will not be encrypted at rest.

Unhandled Exception: System.ArgumentException: The path must be absolute.
Parameter name: root
at Microsoft.Extensions.FileProviders.PhysicalFileProvider..ctor(String root, PhysicalFilesWatcher physicalFilesWatcher)
at Microsoft.AspNetCore.Builder.BlazorAppBuilderExtensions.UseBlazor(IApplicationBuilder applicationBuilder, BlazorOptions options)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure(IApplicationBuilder app)
at Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter.<>c__DisplayClass0_0.b__0(IApplicationBuilder builder)
at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()
at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
at FlightFinder.Server.Program.Main(String[] args) in /home/paul/github/samples/samples/aspnetcore/blazor/FlightFinder/FlightFinder.Server/Program.cs:line 14
Aborted (core dumped)

``

[urvzh]

I have also encountered this issue, it appears to be related to the published files being split between wwwroot and dist under Docker/Linux, whereas when published on my local (Windows) machine, everything goes under dist.

Unfortunately I hadn't had a chance to investigate much further yet, but the following line appears to be the culprit:

https://github.com/aspnet/Blazor/blob/dev/src/Microsoft.AspNetCore.Blazor.Server/BlazorAppBuilderExtensions.cs#L67

FileProvider = new PhysicalFileProvider(config.WebRootPath)

The first line of the .blazor.config file is set to ., resulting in config.WebRootPath being .\wwwroot - Perhaps this could be fixed by resolving the absolute file path prior to passing to the PhysicalFileProvider ctor.

As a temporary workaround, I was able to get Blazor running under Docker by amending my Dockerfile as follows in order to move everything under dist and therefore preventing the second call to UseStaticFiles:

FROM base AS final
WORKDIR /app
COPY --from=publish /app .
RUN mv -n wwwroot/* FlightFinder.Client/dist
RUN rm -rf wwwroot/
ENTRYPOINT ["dotnet", "FlightFinder.Server.dll"]

(Note, this only works when using docker-compose up, and does not work with debugging in Docker through Visual Studio)

[danroth27]

@javiercn Can you take a look at what's happening here and how we might better work with Docker scenarios?

[SteveSandersonMS]

Perhaps this could be fixed by resolving the absolute file path prior to passing to the PhysicalFileProvider ctor.

Yes, we could definitely do that. Thanks for the info!

[kant2002]

I have similar problem in Blazor 0.4.0 where I could not use published output for building docker container.
I generate build using dotnet publish from the blazorhosted template on Windows and try create Docker container using Alpine image.

The error which I receive

Microsoft.AspNetCore.Hosting.Internal.WebHost[6]
      Application startup exception
System.ArgumentException: The directory name '/dist/' does not exist.
Parameter name: path
   at System.IO.FileSystemWatcher..ctor(String path, String filter)
   at System.IO.FileSystemWatcher..ctor(String path)
   at Microsoft.Extensions.FileProviders.PhysicalFileProvider.CreateFileWatcher(String root, ExclusionFilters filters)
   at Microsoft.AspNetCore.Builder.BlazorAppBuilderExtensions.UseBlazor(IApplicationBuilder applicationBuilder, BlazorOptions options)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure(IApplicationBuilder app)
   at Microsoft.AspNetCore.HostFilteringStartupFilter.<>c__DisplayClass0_0.<Configure>b__0(IApplicationBuilder app)
   at Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter.<>c__DisplayClass0_0.<Configure>b__0(IApplicationBuilder builder)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

the problem appears to be that blazor.config when running publish have following content

.
blazorhosted.Client\

but if I change content to

.
blazorhosted.Client/

then docker image start working.

[jskeet]

I've just encountered this as well - and again, changing the trailing backslash to a forward slash seems to fix things.

I think it may be as simple as changing a \ to / in https://github.com/aspnet/Blazor/blob/d4b73de287396a299d8b1f322d8bd4ba5d02aa99/src/Microsoft.AspNetCore.Blazor.Build/targets/Publish.targets#L44

[danroth27]

@SteveSandersonMS I think we should take a look at this one for 0.5.0.

[javiercn]

This is a good candidate for up forcgrabs

[SteveSandersonMS]

The original issue reported here was already fixed in 0.5.0. The issue with the slash style is also now fixed in 9d6cc3d.