fastapi example: fix response_class

[joris-r]

See issue #30

I've checked the correct response type for SSE: it's "Content-Type: text/event-stream". Thus StreamingResponse

[gazpachoking]

Should it just be DatastarResponse? What does that do to the swagger?

[joris-r]

With response_class=StreamingResponse,
swagger only says there is no parameters and code 200 as Successful Response.
There is no media type documented at all (but previously it incorrectly indicated an application/json, so it's better that way).

So in this way, it's consistent.

With response_class=DatastarResponse,
swagger crash with Fetch error : Internal Server Error /openapi.json
The exception stack trace says:

...
        external_docs=self.openapi_external_docs,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/joris/.cache/uv/environments-v2/app-df56c0d93ab9210a/lib/python3.13/site-packages/fastapi/openapi/utils.py", line 520, in get_openapi
    result = get_openapi_path(
        route=route,
    ...<3 lines>...
        separate_input_output_schemas=separate_input_output_schemas,
    )
  File "/home/joris/.cache/uv/environments-v2/app-df56c0d93ab9210a/lib/python3.13/site-packages/fastapi/openapi/utils.py", line 352, in get_openapi_path
    operation.setdefault("responses", {}).setdefault(status_code, {})[
                                                     ^^^^^^^^^^^
UnboundLocalError: cannot access local variable 'status_code' where it is not associated with a value

[gazpachoking]

Okay thanks for testing. Let's put it how you have for now. I'm curious if we could fix DatastarResponse to be usable as a response_class (for both swagger and automatically transforming the returns) and what that would look like. For the swagger purposes I still don't think it's that important, because a d* app would tend to be a non-api app.

[gazpachoking]

Thanks!