.net 6 web api - bad "Content-Type" property in request body - return 400 status instead of 500

Question

I have an Attachments json array in the request payload, and each attachment has three properties:

Name - string and holds the name of the file to be attached.

ContentType - System.Net.Mime.ContentType and holds the mediatype info of the file and

FileData - string and holds base64encoded string of contents of the file/attachment.

Whenever ContentType is null/empty I see that the control does not even hit the controller, but the API is sending a 500 internal server error, and the error message in the response is not helpful for the client:

Message: This property cannot be set to an empty string. (Parameter 'value')

Is there a way to let the API pass through whatever value is entered for this property(mediaType in ContentType) and I would like to do the validation in the API for this property and throw a 400 with a proper message. Below is the request body that is causing above error:

"Attachments": [
    {
      "Name": "Something.txt",
      "ContentType": {
        "Boundary": null,
        "CharSet": null,
        "MediaType": "", //this is causing the above error and I would like this one to be a bad request not a internal server error.
        "Name": "SampleContentType",
        "Parameters": [
          {
            "Key": "name",
            "Value": "SampleContentType"
          }
        ]
      },
      "FileData": "some base64 encoded string here"
    }
  ]

One solution to this is to use a custom ContentType model which mimics the one being used, do the validation then map it to the original one, but I want to understand why the API is throwing 500, before it even hits the controller.

Answer 1

Use the ConsumesAttribute to let the framework check it.

[Consumes("multipart/form-data")] // example
public async Task<IActionResult> MyAction { ... }

This will return a 415 by default if the Consumes criteria is not met.