[CSHARP-NETCORE] ASPNET Core Endpoint taking List<IFormFile> argument causes CSHARP-NETCORE generated client to contain build errors

Att: @jimschubert - Thanks for the preliminary discussion on slack!

Description

I have an ASPNET Core WebApi application which exposes an endpoint that takes List<IFormFile> files as argument:

        [HttpPost]
        public IActionResult PostFiles(List<IFormFile> files)
        {
            foreach(var file in files)
            {
                // do stuff
            }

            return Ok();
        }

Swagger-codegen version

Latest

Swagger declaration file content or url

The generated swagger json looks to be correct:

{
  "openapi": "3.0.1",
  "info": {
    "title": "My API",
    "version": "v1"
  },
  "paths": {
    "/WeatherForecast": {
      "post": {
        "tags": [
          "WeatherForecast"
        ],
        "requestBody": {
          "content": {
            "multipart/form-data": {
              "schema": {
                "type": "object",
                "properties": {
                  "files": {
                    "type": "array",
                    "items": {
                      "type": "string",
                      "format": "binary"
                    },
                    "nullable": true
                  }
                }
              },
              "encoding": {
                "files": {
                  "style": "form"
                }
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "Success"
          }
        }
      }
    }
  },
  "components": { }
}

Command line used for generation

docker run --rm -v c:\TEMP\FormFileBugRepro:/TEMP openapitools/openapi-generator-cli generate -i /TEMP/swagger.json -g csharp-netcore -o /TEMP/Swag

Steps to reproduce

1. Create ASPNET Core WebApi
2. Add Swagger dependencies and setup properly in Startup
3. Create endpoint as specified in description
4. Generate csharp-netcore client using the command specified above
5. Open generated solution and see build errors:

6. Even if you fix the build error by doing so:

7. Its still going to try to add each file to the FileParameter dictionary under the same key, which throws an error. It seems as FileParameter being a dictionary type prevents implementing correct behavior as it's perfectly legal to attach multiple form files with the same name in a HTTP Request.

Start by reproducing the issue with the provided Docker generation command and the csharp-netcore generator. Inspect the generated client’s multipart/form-data handling for the files array and FileParameter dictionary. Done means the generated solution builds and multiple files can be sent under the same form key without an error.