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fastapi_14303

failed NO_PATCH NO_PATCH UNSUBMITTED empty_patch(None) · None tool calls · 0 s · fastapi/fastapi

Task input

🐛 Fix parsing extra `Form` parameter list

## Description

Currently if we declare Form parameters as model with `extra="allow"` and then pass extra parameter with multiple values, only last value of such parameter will be passed to model validator:

```py
from fastapi import FastAPI, Form
from fastapi.testclient import TestClient
from pydantic import BaseModel

app = FastAPI()


class Model(BaseModel):
    param: str

    model_config = {"extra": "allow"}

@app.post("/")
async def model_with_extra(data: Model = Form()):
    return data


def test_pass_extra_list():
    client = TestClient(app)
    resp = client.post(
        "/",
        data={
            "param": "123",
            "param2": ["456", "789"],  # Pass a list of values as extra parameter
        },
    )
    assert resp.status_code == 200
    assert resp.json() == {
        "param": "123",
        "param2": ["456", "789"],
    }
    # AssertionError: assert
    # {'param': '123', 'param2': '789'}
    # ==
    # {'param': '123', 'param2': ['456', '789']}
```

The part of code that adds extra parameters is:

https://github.com/fastapi/fastapi/blob/972a967d5d3fa24d450637c36c6b7ad1f1d8c1b6/fastapi/dependencies/utils.py#L901-L903

The problem is in `received_body.items()` - it returns only last value for each key.
To fix this we need to iterate over all keys in `received_body` and get the values using `received_body.getlist(key)`:

```py
    for key in received_body.keys():
        if key not in values:
            param_values = received_body.getlist(key)
            if len(param_values) == 1:
                values[key] = param_values[0]
            else:
                values[key] = param_values
```

## Alternative implementation

This solution parses single value as string

`extra=string` -> `{"extra": "string"}`

but multiple values as list of strings

`extra=string1&extra=string2` -> `{"extra": ["string1", "string2"]}`

We can consider always parse extra parameters as lists

```py
    for key in received_body.keys():
        if key not in values:
            values[key] = received_body.getlist(key)
```

This way for single value we would also have list with one element:

`extra=string` -> `{"extra": ["string"]}`

It's more consistent, but probably not what people expect for single value.

I think we should go with current implementation (single value -> single string, multiple values -> list of strings)

## Other parameters

Query\Header\Cookie parameters likely have the same issue, I will look at it a bit later and open separate PR to fix this

Tool calls (0)

Test output

.....F
=================================== FAILURES ===================================
____________________________ test_extra_param_list _____________________________

    def test_extra_param_list():
        response = client.post(
            "/form-extra-allow/",
            data={
                "param": "123",
                "extra_params": ["456", "789"],
            },
        )
        assert response.status_code == 200, response.text
>       assert response.json() == {
            "param": "123",
            "extra_params": ["456", "789"],
        }
E       AssertionError: assert {'param': '12...arams': '789'} == {'param': '12...'456', '789']}
E         
E         Omitting 1 identical items, use -vv to show
E         Differing items:
E         {'extra_params': '789'} != {'extra_params': ['456', '789']}
E         Use -v to get more diff

tests/test_forms_single_model.py:177: AssertionError
=============================== warnings summary ===============================
../../../../../../../Users/jp/repos/kaggle-gemini-coding-agent-post-training/.envs/overlays/starlette-0.50.0-py3-none-any/starlette/testclient.py:45
  /Users/jp/repos/kaggle-gemini-coding-agent-post-training/.envs/overlays/starlette-0.50.0-py3-none-any/starlette/testclient.py:45: DeprecationWarning: The anyio.abc.BlockingPortal alias is deprecated, use anyio.from_thread.BlockingPortal instead.
    _PortalFactoryType = Callable[[], AbstractContextManager[anyio.abc.BlockingPortal]]

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
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1 failed, 5 passed, 1 warning in 0.64s