[BUG] [Python-fastapi] File input incorrectly generated with FastAPI Form

[reyescabello]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating the specified content in the OpenAPI file, the endpoint that receives a file generates an input of type string in the generated Swagger UI. This happens because the generated FastAPI endpoint uses a Form.

We compared this case with another application using the same file, where the input is correctly generated as a file upload field.

openapi-generator version

v7.9.0

OpenAPI declaration file content or url

https://gist.github.com/reyescabello/6cd965708fd0b03e8eadb9f3c0c0a899#file-query_param_example-yml

Generation Details

Generated with jar:

java -jar openapi-generator-cli.jar generate -i openapi.yml -g python-fastapi -o openapi_server

Steps to reproduce

When generating the specified content in the OpenAPI file, the endpoint that includes the file looks like this:

async def upload_post(
    file: str = Form(None, description=""),
) -> None:
    
    return await BaseExampleApi.subclasses[0]().upload_post(file)

And this is what it looks like in swagger.

The expected code is something like this:

async def upload_post(
    file: UploadFile,
) -> None:
    
    return await BaseExampleApi.subclasses[0]().upload_post(file)

Related issues/PRs

Suggest a fix

[hegerdes]

This can also happen when outputting a file/binary from an api response.

[ampedandwired]

I'm also having a lot of trouble making file uploads work with python-fastapi as it stands. I'm finding when generating an API with something like this:

requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          data:
            type: array
            items:
              type: string
              format: binary

I'm ending up with the data param defined like this in default_api.py:

data: Optional[List[Union[StrictBytes, StrictStr, Tuple[StrictStr, StrictBytes]]]] = Form(None, description=""),

This just doesn't seem to work (data is always None). The following code works though

data: Optional[List[UploadFile]] = File(None, description=""),

[sagarjain13]

Facing the same issue:

name: str = Form(None, description="")
file: str = Form(None, description="The file to be uploaded")

above code auto-generates when using

      requestBody:
        description: Create a new group for a single satellite or a group for different types of satellites
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                name:
                  type: string
                file:
                  type: string
                  format: binary
                  description: "The file to be uploaded"
        required: true

[DGV1995]

Any news about this bug?

[tz-reinberger]

I can confirm the changes from https://github.com/fastapi/fastapi/pull/14953 (FastAPI version 0.129.1 and newer) break the python client generator.
The change from the schema {"type": "string", "format": "binary"} to {"type": "string", "contentMediaType": "application/octet-stream"} broke it.
This workaround reverts the change for better compatibility:

class CompatibleUploadFile(UploadFile):
    @classmethod
    def __get_pydantic_json_schema__(cls, core_schema: Any, handler: Any) -> dict[str, Any]:
        return {"type": "string", "format": "binary"}