[Bug]: JSON on string input gets set to null.

[LBalsa]

[Bug]: JSON on string input gets set to null.

[martincostello]

Hey there - I've just looked into this, and this appears to be a change in the behaviour of swagger-ui between v4.15.5 which was included with Swashbuckle.AspNetCore v6.5.0, and v5.17.10 which is included with Swashbuckle.AspNetCore v6.6.2.

Looking at the generated OpenAPI schema between the two versions, there is only one difference:

{
  "openapi": "3.0.1",
  "info": {
    "title": "JsonOnStringInputNotWorking",
    "version": "1.0"
  },
  "paths": {
    "/notworking": {
      "post": {
        "tags": [
          ""
        ],
        "requestBody": {
          "content": {
            "multipart/form-data": {
              "schema": {
                "type": "object",
                "properties": {
                  "Data": {
                    "type": "string"
                  },
                  "Template": {
                    "type": "string",
                    "format": "binary"
                  }
                }
              },
              "encoding": {
                "Data": {
                  "style": "form"
                },
                "Template": {
                  "style": "form"
                }
              }
            }
          }
        },
        "responses": {
          "200": {
-           "description": "Success"
+           "description": "OK"
          }
        }
      }
    }
  },
  "components": { }
}

However, there is a difference in the cURL commands generated and the request made by swagger-ui for this endpoint:

curl -X 'POST' \
  'https://localhost:7146/notworking' \
  -H 'accept: */*' \
  -H 'Content-Type: multipart/form-data' \
- -F 'Data={ "im": "json" }' \
+ -F 'im=json' \
  -F 'Template='

v4.15.5

v5.17.10

Either this was an issue in swagger-ui that you happened to depend on and they fixed it (which then breaks how you intended it to work), or it's an issue in swagger-ui v5 that needs to be fixed on their side.

If it's the latter, we'll automatically consume the fix during our regular dependabot updates, and can publish a new version of Swashbuckle.AspNetCore containing the fix when it appears.