UPDATE: I went ahead and created an issue on NSwag after looking through its code. You can see it here: https://github.com/RicoSuter/NSwag/issues/3824

I have a functioning api endpoint that accepts "text/plain" as the body. The user of this endpoint is a third-party that controls the content type so I can't change that. I'm using NSwag to generate a c# client based on a swagger.json.

My main problem is that the generated client's function for calling this endpoint still serializes the string body, which causes the endpoint to fail to parse. I'm not 100% certain if this is a bug in my swagger.json or if it's something unintentional, because the json is also generated. This is why I'm not posting this on the NSwag github issues currently.

Here's what the swagger.json looks like:

{
  "openapi": "3.0.1",
  "info": {
    "title": "PlainTextParser",
    "version": "1.0"
  },
  "paths": {
    "/api/v1/text": {
      "post": {
        "tags": [
          "TextEvent"
        ],
        "summary": "Parses a plain text body",
        "operationId": "PostTextEvent",
        "requestBody": {
          "description": "Accepts a plain text body",
          "content": {
            "text/plain": {
              "schema": {
                "type": "string",
                "nullable": true
              }
            }
          }
        },
        "responses": {
          "202": {
            "description": "Success"
          }
        }
      }
    }
  },
  "components": { }
}

When I run nswag on it, I get this inside of the generated client:

public virtual async System.Threading.Tasks.Task PostTextEventAsync(string body, System.Threading.CancellationToken cancellationToken)
{
  //...

  var content_ = new System.Net.Http.StringContent(Newtonsoft.Json.JsonConvert.SerializeObject(body, _settings.Value));
  content_.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("text/plain");

  //...
}

The SerializeObject method call is what is causing the issue. When I removed it everything worked fine. You can even see on the second line there that it understands the content type, which is why I'm confused why it's trying to serialize it.

So is there something I'm missing in the swagger.json or is there a bug in NSwag?

I do realize I can work around this by making my API endpoint reformat the string to its intended state, but that feels like a hack.