包含IFormFile属性的复杂类型的FromForm模型绑定列表时，未执行操作方法

Question

I'm now working on a project using AspNetCore 2.2 to build a pure RESTful application. And right now I run into a weird bug when implementing a multipart/form-data upload API.

I tried to use my domain object as model on the POST API. And this is my Controller.

    [ApiController]
    [Route("api/v{v:apiVersion}/[controller]")]
    [ApiVersion("1")]
    public class PhotoController : ControllerBase
    {
        [HttpPost]
        public string Upload([FromForm]TestMultipartModel model)
        {
            return "success";
        }
    }

...and my Model looks like this.

    public class TestMultipartModel
    {
        [Required]
        public int? Num { get; set; }
        public IFormFile File { get; set; }
        public string Str { get; set; }
        public List<TestMultipartSubModel> Details { get; set; }
    }

    public class TestMultipartSubModel
    {
        public string Name { get; set; }
        // public IFormFile File { get; set; }
    }

I use Postman to test my API as below. (I'd love to post a screenshot of Postman but my reputation is too low to do that :(

num: "1"
str: "some string..."
file: "random.png"
details[0].name: "my_name"
details[0].file: "another_random.png"
details[1].name: "second_name"
details[1].file: "second_random.png"

Everything works fine as if the sub-model doesn't contains a IFormFile property.

But if I un-comment that line, after posting API my CPU will start bursting but the program would do nothing but print these log:

Microsoft.AspNetCore.Hosting.Internal.WebHost:Information: Request starting HTTP/1.1 POST http://localhost:44388/api/v1/photo multipart/form-data; boundary=--------------------------565570716756230895912873 30896

Microsoft.AspNetCore.Routing.EndpointMiddleware:Information: Executing endpoint 'MyProject.Controllers.PhotoController.Upload (MyProject)'

Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Route matched with {action = "Upload", controller = "Photo", page = ""}. Executing controller action with signature System.String Upload(MyProject.Controllers.TestMultipartModel) on controller MyProject.Controllers.PhotoController (MyProject).

But it supposed to print this line after these 3 lines, (and of course, run my Upload method).

Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Executing action method MyProject.Controllers.PhotoController.Upload (MyProject) - Validation state: Valid

---

After a few hours of debugging, I still have no idea how to fix this.

If anyone can tell me 1) if this is a bug from Microsoft or 2) how can I fix this bug (like implement my own custom IModelBinder or something else), I would very appreciate!

Answer 1

After Googling with the keyword aspnetcore ModelBinding infinite loop I found my answer in this link .

Seems like Microsoft has fixed this bug in Asp.Net Core 3.0, so what I have to do now is convincing my team to upgrade our project...