This .NET 7 minimal API always returns 200

Question

I'm quite new to the concept of a minimal API, but the documentation seems quite clear. You only have to use Results or TypedResults to return the response code you want.

So I made a very basic try:

app.MapPost("/api/test", async context =>
{
    var form = await context.Request.ReadFormAsync();
    var file = form.Files["File"];
    Results.NoContent();
});

But even with that, it always returns a 200 status code. I also checked a lot of other material from .NET 6 and 7 (I target .NET 7) with method delegates that have a return type of Task<IResult> as specified here in the documentation, but I got the same result (200). Note that I also tried returning NotFound, but I still got the same.

app.MapPost("/api/test", TestReturn);

static async Task<IResult> TestReturn(HttpContext context)
{
    var form = await context.Request.ReadFormAsync();
    var file = form.Files["File"];
    return TypedResults.NoContent();
}

Why can't I get anything else than a 200?

Answer 1

There are two issues here:

1. You forgot to use return:

   app.MapPost("/api/test", async context =>
   {
       var form = await context.Request.ReadFormAsync();
       var file = form.Files["File"];
       return Results.NoContent();
   });
   

2. There is a known issue with async handlers accepting HttpContext only, you can workaround by adding extra parameter (for example CancellationToken):

   app.MapPost("/api/test", async (HttpContext context, CancellationToken ct) =>
   {
       var form = await context.Request.ReadFormAsync();
       var file = form.Files["File"];
       return Results.NoContent();
   });
   

Also note that in ASP.NET Core 7 binding form files is supported out of the box:

app.MapPost("/api/test", async (IFormFileCollection files) =>
{
    var file = files["File"];
    return Results.NoContent();
});

See also:

• Why does 'foo' return an empty body?
• POST request return empty response
• Minimal APIs async handlers with single HttpContext parameter are not working

Answer 2

You need to actually return the result using return. If you don't by default 200 Ok will be returned.

The following Program.cs will work and return 204 No Content on .NET 7. I've tested it using Postman. Make sure to get the URL, port as well as HTTP method right (e.g. GET http://localhost:5097/test).

FYI: the project was created using dotnet new webapi -o WebApiDemo and then just the Program.cs was changed to what is shown below:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
var app = builder.Build();

app.MapGet("/test", () =>
{
    return TypedResults.NoContent();
});
app.MapControllers();
app.Run();

Answer 3

In your code, the issue is with the usage of Results.NoContent() and TypedResults.NoContent(). These methods don't actually return the desired HTTP status code; instead, they create a result object that represents a "No Content" response, but they need to be returned from the endpoint to have any effect. In your code, you are calling these methods but not returning their result from the endpoint.

To fix the issue and return the appropriate status code from your minimal API endpoint, you need to return the result from the endpoint itself. Here's how you can modify your code to achieve that:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapPost("/api/test", async context =>
{
    var form = await context.Request.ReadFormAsync();
    var file = form.Files["File"];
    // Returning a NoContentResult from the endpoint
    await context.Results.NoContent();
});

app.Run();

By calling await context.Results.NoContent();, you are returning a NoContentResult from the endpoint, which will result in a 204 No Content response when the endpoint is accessed.

Alternatively, if you prefer to use a method delegate, you can do it like this:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapPost("/api/test", TestReturn);

static async Task TestReturn(HttpContext context)
{
    var form = await context.Request.ReadFormAsync();
    var file = form.Files["File"];
    // Returning a NoContentResult from the method delegate
    await context.Results.NoContent();
}

app.Run();

In both cases, the NoContentResult returned from the endpoint or the method delegate will correctly produce a 204 No Content response when the endpoint is called.