In two previous posts, “Conditionally Output XML Or JSON Using ASP.NET Minimal API” and “Improving ASP.NET Content Negotiation XML Serialization Performance Using A RecyclableMemoryStream”, we looked at how to generate XML output on ASP.NET using Minimal APIs and the Carter Library.

In this post, we will look at how you can still generate XML with the following constraints:

  • You cannot (or don’t want to) use controllers.
  • You cannot (or don’t want to) use Carter, or any other external package.

Let us take our sample type, the Person.

public sealed class Person
{
  public required string FirstName { get; init; }
  public required string Surname { get; init; }
  public required decimal Salary { get; init; }
}

Our sample API will produce a number of Person objects.

Given that we are using a minimal API, all the goodies we get for free when we use controllers are unavailable, such as automatic content negotiation.

We therefore cannot configure serialization into the native pipeline, so we have to do the serialization ourselves.

The code will look like this:

app.MapGet("/Generate", async (HttpContext ctx) =>
{
    var faker = new Faker<Person>().UseSeed(0)
        .RuleFor(person => person.FirstName, faker => faker.Person.FirstName)
        .RuleFor(person => person.Surname, faker => faker.Person.LastName)
        .RuleFor(person => person.Salary, faker => faker.Random.Decimal(10_000, 99_000));

    var serializer = new XmlSerializer(typeof(List<Person>));
    await using var ms = new MemoryStream();
    await using (var writer = XmlWriter.Create(
                     ms,
                     new XmlWriterSettings
                     {
                         Encoding = Encoding.UTF8,
                         Indent = true,
                         Async = true
                     }))
    {
        serializer.Serialize(writer, faker.Generate(5));
    }

    ms.Position = 0;
    await ms.CopyToAsync(ctx.Response.Body);
});

A couple of things to note here:

  1. We are injecting the HttpContext so we can write directly to its response stream.
  2. We are serializing the collection of Person objects into a MemoryStream, rather than directly into the HttpResponse body. This is because the runtime does not like synchronous operations, and in fact throws an exception if a synchronous method tries to manipulate the response body.
  3. Once we have the serialized data in the MemoryStream, we asynchronously write it to the response body.

If we run this code, we should see the following:

XMLSerialize

And thus, we can generate XML with our API.

TLDR

To generate XML using Minimal APIs without external libraries like Carter, you need to serialize yourself.

The code is in my Github.

Happy hacking!