Empty catch-all routes not working as expected

[richard-fine]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have a route with a catch-all set up like this:

app.MapGet("/filesystem/{**path}", async (string path) => { ... });

When I make a request to a URL like /filesystem/blah, it works, and path == "blah".

If I make a request to /filesystem/, I am expecting path == string.Empty, as per the documentation which states "Catch-all parameters can also match the empty string."

However, if I make a request to that URI, instead it throws an exception:

% curl http://localhost:5023/filesystem/
Microsoft.AspNetCore.Http.BadHttpRequestException: Required parameter "string path" was not provided from route.
   at Microsoft.AspNetCore.Http.RequestDelegateFactory.Log.RequiredParameterNotProvided(HttpContext httpContext, String parameterTypeName, String parameterName, String source, Boolean shouldThrow)
   at lambda_method2(Closure, Object, HttpContext)
   at Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

Expected Behavior

An empty catch-all string should be supported as per the documentation, and my path parameter should have a value of string.Empty.

Steps To Reproduce

Create a minimal-API ASP.NET Core web service app using .NET 8, and add a route to it like this:

app.MapGet("/test/{**slug}", (string slug) => Results.Ok($"Slug was {slug}"));

Launch the service and then try calling the endpoint on http://localhost:<port>/test/ - you should see the exception get thrown.

Exceptions (if any)

Microsoft.AspNetCore.Http.BadHttpRequestException: Required parameter "string slug" was not provided from route.
at Microsoft.AspNetCore.Http.RequestDelegateFactory.Log.RequiredParameterNotProvided(HttpContext httpContext, String parameterTypeName, String parameterName, String source, Boolean shouldThrow)
at lambda_method2(Closure, Object, HttpContext)
at Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

.NET Version

8.0.401

Anything else?

CSProj includes package references:

<PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="8.0.8"/>
<PackageReference Include="Swashbuckle.AspNetCore" Version="6.4.0"/>

.NET SDK:
Version: 8.0.401
Commit: 811edcc344
Workload version: 8.0.400-manifests.b6724b7a
MSBuild version: 17.11.4+37eb419ad

Runtime Environment:
OS Name: Mac OS X
OS Version: 14.6
OS Platform: Darwin
RID: osx-arm64
Base Path: /usr/local/share/dotnet/sdk/8.0.401/

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
There are no installed workloads to display.

Host:
Version: 8.0.8
Architecture: arm64
Commit: 08338fcaa5

.NET SDKs installed:
6.0.410 [/usr/local/share/dotnet/sdk]
7.0.203 [/usr/local/share/dotnet/sdk]
8.0.204 [/usr/local/share/dotnet/sdk]
8.0.401 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.18 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.4 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.8 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.18 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.16 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.8 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
x64 [/usr/local/share/dotnet/x64]
registered at [/etc/dotnet/install_location_x64]

Environment variables:
Not set

global.json file:
Not found

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