Allow JSON payload for GET calls

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• [ x] I already checked if it is not related to FastAPI but to Swagger UI.
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Example

Here’s a self-contained minimal, reproducible, example with my use case:

from fastapi import FastAPI

app = FastAPI()


class Sample(BaseModel):
    countryId: int

@router.get("/foo/bar",
            response_model=Sample)
def get_sample(sample: Sample):
    return {"Hello": "World"}

### Description

* Open the browser and call the GET endpoint `/foo/bar`.
* Pass in JSON body with `{"countryId": 1}`.
* TypeError: Failed to execute 'fetch' on 'Window': Request with GET/HEAD method cannot have body.

### The solution you would like

It doesn't throw the TypeError and allows GET calls to pass in JSON payloads

### Environment

* OS: [e.g. Linux / Windows / macOS]: macOS
* FastAPI Version [e.g. 0.3.0]: 0.60.1


* Python version:

3.7.7

### Additional context

![Screen Shot 2020-09-02 at 2 00 10 PM](https://user-images.githubusercontent.com/5025518/92019556-ca7cbf00-ed24-11ea-84d6-52dbc18a8aec.png)

[ycd]

@stevesuh the code piece works when you send a request with cURL

curl -X GET "http://127.0.0.1:8000/foo/bar" -d "{\"countryID\":1}"

So basically FastAPI allows request body with GET operations, however, Swagger UI doesn’t support it.

They are also very strict about not supporting it.

See: https://github.com/swagger-api/swagger-ui/issues/2136

If you want you can open another issue in Swagger UI’s repository but FastAPI can not do anything about this topic since your issue is completely about the Swagger UI.

[ycd]

@ArcLightSlavik thanks, just read that publication ,actually you were right, in practice it’s fine but in theory it’s not a good idea i think… 🤕