How do I deserialize to object with default formatter in net core 5 webapi when supporting multipart/form-data? - asp.net-core

Question

If I make a typical controller and action, with a parameter that comes from the body, the webapi will deserialize the body content into an instance of the class type using the appropriate deserializer, based on the content-type header:
[ApiController]
[Route("[controller]")]
public class TestController : ControllerBase
{
[System.Runtime.Serialization.DataContract]
public class MyObject
{
[System.Runtime.Serialization.DataMember]
public string Text { get; set; }
}
[HttpPost()]
public void Test([FromBody] MyObject value)
{
}
}
If I make a request to it, the request looks like this if using json:
POST https://localhost:44380/Message HTTP/1.1
Host: localhost:44380
Connection: keep-alive
Content-Length: 22
accept: */*
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.114 Safari/537.36
Content-Type: application/json
Referer: https://localhost:44380/swagger/index.html
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
{"Text":"123 abc 123"}
Or this if xml (my web api is set up to support json and xml):
POST https://localhost:44380/Message HTTP/1.1
Host: localhost:44380
Connection: keep-alive
Content-Length: 82
accept: */*
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.114 Safari/537.36
Content-Type: application/*+xml
Referer: https://localhost:44380/swagger/index.html
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
<?xml version="1.0" encoding="UTF-8"?>
<MyObject>
<Text>string</Text>
</MyObject>
If I am changing my webapi to use multipart mime, I can't rely on the automated deserialization of the content body. As I loop through each part, how would I deserialize each sections content based on the content-type header and the configured formatters of the webapi? I could hard code a specific serializer but I'd like to use what's configured.
var boundary = HeaderUtilities.RemoveQuotes(Request.ContentType.Boundary).Value;
MultipartReader reader = new MultipartReader(boundary, HttpContext.Request.Body);
var section = await reader.ReadNextSectionAsync();
while (section != null)
{
ContentDispositionHeaderValue contentDispositionHeaderValue = section.GetContentDispositionHeader();
Stream strData = null;
if (contentDispositionHeaderValue.IsFileDisposition())
{
FileMultipartSection fileSection = section.AsFileSection();
strData = fileSection.FileStream;
fileName = fileSection.FileName;
name = fileSection.Name;
}
else if (contentDispositionHeaderValue.IsFormDisposition())
{
FormMultipartSection formSection = section.AsFormDataSection();
name = formSection.Name;
strData = section.Body;
}
//How to deserialize strData to MyObject using the webap's configured formatters?
section = await reader.ReadNextSectionAsync();
}