Why does 'foo' return an empty body?

Question

For some reason, foo always returns an empty body:

internal static async Task<string> Foo(HttpContext context)
{
    var response = await Task.Run(() => { return "response"; });
    return response;
}

internal static async Task<string> Bar(HttpContext context, string someParam)
{
    var response = await Task.Run(() => { return "response"; });
    return response;
}

Answer 1

I was able to reproduce the behaviour. Moving the handler with the single parameter of HttpContext into a separate method leads to the empty response:

WebApplicationBuilder builder = WebApplication.CreateBuilder();
WebApplication app = builder.Build();
app.Map("/Fails", Fails);
app.Map("/Fails1", Fails1);
app.Map("/Works", async (HttpContext c) =>
{
    var response = await Task.Run(() => { return "response"; });
    return response;
});
app.Map("/WorksToo", Works);
app.Map("/WorksToo1", Works1);
app.Map("/WorksToo2", Works2);
app.Run();

static async Task<string> Fails1(HttpContext context)
{
    var response = await Task.FromResult("response");
    return response;
}

public partial class Program
{
    internal static async Task<string> Fails(HttpContext context) => await Task.FromResult("response");

    internal static async Task<string> Works(HttpContext context, string someParam) => await Task.FromResult("response");

    internal static async Task<string> Works1(HttpContext context, ILogger<Program> _) => await Task.FromResult("response");

    internal static async Task<string> Works2(HttpRequest context) => await Task.FromResult("response");
}

I submitted a new issue on GitHub. For now, you can add a dummy parameter (for example, CancelationToken) to the handler as I do with Works1.

Update 1

The issue was fixed and everything should work as expected in .NET 7.

Update 2

The issue was introduced back by some following changes and actually got worse. Follow the new issue at GitHub.