[OpenAPI] Use invariant culture for TextWriter

[martincostello]

Use invariant culture for TextWriter

Use culture-invariant TextWriter implementation for OpenAPI.

Description

Ensure OpenAPI documents are written to a culture-invariant TextWriter implementation.

I couldn't replicate this issue in .NET 10, I'm guessing Microsoft.OpenApi has had some internal refactoring that means that it's no longer using an overload on TextWriter that was hitting this (unless I messed up my test to repro it somehow).

Contributes to #60628.

[Copilot]

Pull Request Overview

This PR updates the OpenAPI implementation to enforce the usage of an invariant culture when writing documents using TextWriter. Key changes include adding a new constructor overload to Utf8BufferTextWriter that accepts an IFormatProvider, updating OpenAPI endpoint routing to explicitly use CultureInfo.InvariantCulture, and adding tests and a sample endpoint ("/getcultureinvariant") to verify the culture invariance behavior.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/SignalR/common/Shared/Utf8BufferTextWriter.cs	Added a new constructor overload to inject an IFormatProvider.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApi3_1/...	Updated snapshots to include a new "/getcultureinvariant" endpoint.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApi3_0/...	Updated snapshots to include a new "/getcultureinvariant" endpoint.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/OpenApiDocumentIntegrationTests.cs	Refactored test data setup using MemberData and updated the verification call.
src/OpenApi/src/Extensions/OpenApiEndpointRouteBuilderExtensions.cs	Modified the instantiation of Utf8BufferTextWriter to use CultureInfo.InvariantCulture.
src/OpenApi/sample/Program.cs	Added middleware to change the current culture for testing invariant behavior.
src/OpenApi/sample/Controllers/TestController.cs	Introduced a new GET endpoint and record type to support culture-invariant document generation.

Comments suppressed due to low confidence (2)

src/OpenApi/sample/Controllers/TestController.cs:35

• [nitpick] The method name 'PostTypedResult' is potentially misleading for a GET endpoint. Consider renaming it to something like 'GetCultureInvariant' to reflect its purpose more clearly.

[HttpGet]

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/OpenApiDocumentIntegrationTests.cs:49

• The change from 'Verifier.Verify(json)' to 'Verify(json)' should be confirmed as intentional, as it alters the API call pattern. If this change is designed to utilize a new verification mechanism, consider adding a brief comment for clarity.

await Verify(json)

[desjoerd]

I think this change should also be applied for GetDocument, but I am not sure.

[martincostello]

GetDocument

Where do you mean exactly?

[desjoerd]

It's not in the filtered solution, but the dotnet tool/executable which extracts the document during build.

[desjoerd]

Found it: https://github.com/dotnet/aspnetcore/blob/faf269645b0338a9f4a7ecc88b46053f80f6f602/src/Tools/GetDocumentInsider/src/Commands/GetDocumentCommandWorker.cs

[martincostello]

Yep you're right.

The code here creates a TextWriter (StreamWriter):

aspnetcore/src/Tools/GetDocumentInsider/src/Commands/GetDocumentCommandWorker.cs

Lines 333 to 353 in faf2696

	using (var writer = new StreamWriter(stream, _utf8EncodingWithoutBOM, bufferSize: 1024, leaveOpen: true))
	{
	var targetMethod = generateWithVersionMethod ?? generateMethod;
	object[] arguments = [documentName, writer];
	if (generateWithVersionMethod != null)
	{
	_reporter.WriteInformation(Resources.VersionedGenerateMethod);
	if (Enum.TryParse<OpenApiSpecVersion>(_context.OpenApiVersion, out var version))
	{
	arguments = [documentName, writer, version];
	}
	else
	{
	if (!string.IsNullOrWhiteSpace(_context.OpenApiVersion))
	{
	_reporter.WriteWarning(Resources.FormatInvalidOpenApiVersion(_context.OpenApiVersion));
	}
	arguments = [documentName, writer, OpenApiSpecVersion.OpenApi3_1];
	}
	}
	using var resultTask = (Task)InvokeMethod(targetMethod, service, arguments);

Then that gets used here:

aspnetcore/src/OpenApi/src/Services/OpenApiDocumentProvider.cs

Lines 58 to 60 in faf2696

	var document = await targetDocumentService.GetOpenApiDocumentAsync(scopedService.ServiceProvider);
	var jsonWriter = new OpenApiJsonWriter(writer);
	await document.SerializeAsync(jsonWriter, openApiSpecVersion);

I'll update that to use the invariant culture too.

[captainsafia]

I couldn't replicate this issue in .NET 10, I'm guessing Microsoft.OpenApi has had some internal refactoring that means that it's no longer using an overload on TextWriter that was hitting this (unless I messed up my test to repro it somehow).

Do you mean that the new tests pass without any of the code changes in this PR?

It might be good to track the change on the Microsoft.OpenApi side that caused this.

[martincostello]

Yeah, they still pass without the fix being present.

My hunch is that they stopped using an overload like Write(double) or similar, which would have gone through a code path that would have used the current culture formatter.

I did try to test the theory by making an equivalent change to the release/9.0 branch, but I had issues running restore.cmd for some reason. I might try that again later this week.