Honor [Consumes] / IAcceptsMetadata on form endpoints

[rmasciarella]

Summary

HttpChain.fillRequestType only honors [Consumes] / IAcceptsMetadata when the endpoint has a body request type and is not a form endpoint (HasRequestType && !IsFormData). Form endpoints fall through and apiDescription.SupportedRequestFormats stays empty.

ASP.NET Core 10's OpenApiDocumentService.GetFormRequestBody then defaults to application/x-www-form-urlencoded:

if (supportedRequestFormats.Count == 0)
{
    supportedRequestFormats = [new ApiRequestFormat { MediaType = "application/x-www-form-urlencoded" }];
}

This silently drops [Consumes("multipart/form-data")] on file-upload endpoints, so generated clients (Orval, NSwag, Kiota) emit URLSearchParams bodies instead of FormData — file uploads break at runtime.

Fix

Extend CreateApiDescription so that for endpoints with form-source parameters and no formats already populated, IAcceptsMetadata flows into SupportedRequestFormats:

if (apiDescription.SupportedRequestFormats.Count == 0 &&
    apiDescription.ParameterDescriptions.Any(p =>
        p.Source == BindingSource.Form || p.Source == BindingSource.FormFile))
{
    foreach (var metadata in Endpoint!.Metadata.OfType<IAcceptsMetadata>())
    {
        foreach (var contentType in metadata.ContentTypes)
        {
            apiDescription.SupportedRequestFormats.Add(new ApiRequestFormat
            {
                MediaType = contentType
            });
        }
    }
}

Semantics

• No [Consumes] → no change. Wolverine still emits zero formats; MS OpenAPI still defaults to application/x-www-form-urlencoded.
• [Consumes("multipart/form-data")] → multipart is added to SupportedRequestFormats; MS OpenAPI no longer adds the urlencoded default (its count == 0 guard); spec correctly emits multipart.
• Non-form body endpoints → unaffected (the form-parameter guard short-circuits).

Regression test

New test endpoint:

[WolverinePost("/form/multipart-consumes")]
[Consumes("multipart/form-data")]
public static string MultipartConsumes([FromForm] string value) => value ?? "";

New test:

[Fact]
public void form_endpoints_honor_consumes_metadata_for_supported_request_formats()
{
    var chain = HttpChains.ChainFor("POST", "/form/multipart-consumes");
    var apiDescription = chain!.CreateApiDescription("POST");

    apiDescription.SupportedRequestFormats
        .Select(f => f.MediaType)
        .ShouldContain("multipart/form-data");
}

Fails on main:

but was actually
Failed!  - Failed: 1, Passed: 0

Passes after the fix:

Passed!  - Failed: 0, Passed: 1

Test plan

• New test fails on main
• New test passes after fix
• Form + OpenAPI / Swashbuckle filtered run: 64 passed, 0 failed, 8 pre-existing skips

Related

Independent of #2587 (which fixes a separate ParameterDescriptor null-deref in the same file). Either can land first.

[Copilot]

Pull request overview

Fixes OpenAPI request-format discovery for Wolverine form endpoints so that [Consumes] / IAcceptsMetadata is reflected in ApiDescription.SupportedRequestFormats, preventing ASP.NET Core OpenAPI from silently defaulting form endpoints to application/x-www-form-urlencoded and breaking generated multipart clients.

Changes:

• Seed SupportedRequestFormats from IAcceptsMetadata for form endpoints when no formats are already present.
• Add a regression endpoint that declares [Consumes("multipart/form-data")] on a form-bound parameter.
• Add a regression test asserting multipart is present in SupportedRequestFormats for the new endpoint.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/Http/WolverineWebApi/Forms/FormEndpoints.cs	Adds a form endpoint decorated with [Consumes("multipart/form-data")] to reproduce the issue.
src/Http/Wolverine.Http/HttpChain.ApiDescription.cs	Extends CreateApiDescription to flow IAcceptsMetadata into SupportedRequestFormats for form endpoints.
src/Http/Wolverine.Http.Tests/using_form_parameters.cs	Adds a regression test ensuring form endpoints honor consumes metadata in SupportedRequestFormats.

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[jeremydmiller]

@rmasciarella Thank you for taking this on. OpenAPI is about my least favorite part of working on Wolverine.

[jeremydmiller]

Approving — the form-endpoint OpenAPI fix is correct and the regression test demonstrates the bug clearly. Will follow up with the Copilot review's dedup recommendation in a separate PR.

[rmasciarella]

@jeremydmiller no worries it just came up for me while vibe coding, i did run it through a few different models from different angles to make sure before i put it up, glad that it was helpful.