Protobuf formatter: No response with large results

[M-AV]

I have an ASP.NET Core Web Api (.NET 5) using the Protobuf formatter to serialize responses. When my controller returns a large amount of data the client gets a 200 OK response, but no data.

I reproduced it by creating a new empty web api project (running locally with iisexpress). Adding version 3.0.0 of WebApiContrib.Core.Formatter.Protobuf and configuring it in the Startup like this:

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddControllers(opt => 
        {
            opt.FormatterMappings.SetMediaTypeMappingForFormat("protobuf", MediaTypeHeaderValue.Parse("application/x-protobuf"));
        })
        .AddProtobufFormatters();
}

Then I modified the default WeatherForecastController to look like this:

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    public WeatherForecastController(ILogger<WeatherForecastController> logger) { }

    [HttpGet]
    public IActionResult Get([FromQuery] int count)
    {
        var time = DateTime.UtcNow;
        var result = Enumerable.Range(0, count).Select(i => new Dto()
        {
            Prop1 = 1,
            Prop2 = time,
            Prop3 = time,
            Prop4 = 1,
            Prop5 = 1,
            Prop6 = "Some string",
            Prop7 = 1,
            Prop8 = 1,
            Prop9 = 1,
            Prop10 = 1,

        }).ToList();
        return Ok(result);
    }

    [DataContract]
    public class Dto
    {
        [DataMember(Order = 1)]
        public int Prop1 { get; set; }
        [DataMember(Order = 2)]
        public DateTime Prop2 { get; set; }
        [DataMember(Order = 3)]
        public DateTime Prop3 { get; set; }
        [DataMember(Order = 4)]
        public int Prop4 { get; set; }
        [DataMember(Order = 5)]
        public short Prop5 { get; set; }
        [DataMember(Order = 6)]
        public string Prop6 { get; set; }
        [DataMember(Order = 7)]
        public int Prop7 { get; set; }
        [DataMember(Order = 8)]
        public int Prop8 { get; set; }
        [DataMember(Order = 9)]
        public decimal Prop9 { get; set; }
        [DataMember(Order = 10)]
        public int Prop10 { get; set; }

        public Dto() { }
    }
}

I query this endpoint with the code below. It works fine when count is small. If I increase it to 5.000.000 or more it doesn't. It works if I use Json.

var handler = new HttpClientHandler { AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate };

var client = new HttpClient(handler) { BaseAddress = new Uri("http://localhost:18345"), DefaultRequestHeaders = { Accept = { new MediaTypeWithQualityHeaderValue("application/x-protobuf") } }, Timeout = TimeSpan.FromMinutes(10) };
int count = 500000;        
var formattableString = $"weatherforecast?count={count}";

var response = await client.GetAsync(formattableString);
response.EnsureSuccessStatusCode();

var responseStream = await response.Content.ReadAsStreamAsync();
var dtos = Serializer.Deserialize<IEnumerable<Dto>>(responseStream).ToArray();

Using Fiddler, I can see the data is not returned from the API

Am I doing something wrong or is there an issue here? Why am I getting a 200 OK even though I'm not getting a response?

Appreciate any help