[BUG] Body is always parsed as JSON regardless of media_type

Describe the bug

This is to continue the discussion at https://github.com/tiangolo/fastapi/issues/579#issuecomment-589263249. Body accepts an argument media_type, but regardless of the media_type Body is parsed as JSON. This is a problem for other media_types such as plain/text, application/sql, etc. And this is not compliant to OpenAPI content. Body should be able to represent plain text as str too.

Basically I wish I could do this:

request: str = Body(..., media_type='text/plain')

However, this produces 400 parsing error because Body is parsed as JSON anyway.

To Reproduce

1. Create a file with:

from fastapi import FastAPI, Body

app = FastAPI()

@app.post("/")
def read_root(body: str = Body(..., media_type='text/plain')):
    return {"I received:": body}

1. Run the server.

2. Then execute: curl -d 'I want to print this' -H 'Content-Type: plain/text' http://localhost:8000

3. It returns {“detail”:“There was an error parsing the body”}

4. But I expected it to return {"I received": "I want to print this"}.

Expected behavior

My expectation is that the Body should be parsed based on the Content-Type header always.

Screenshots

I think the information is quite comprehensive without screenshots.

Environment

• OS: Ubuntu 18.04
• FastAPI Version: 0.49.0
• Python 3.7.4

Additional context

The associated part is: https://github.com/tiangolo/fastapi/blob/9c3c9b6e78768374868d690bc05918d58481e880/fastapi/routing.py#L114

This does not check Content-Type. My proposal is to fix it as

if body_bytes and request.headers['Content-Type'] == 'application/json':
# if body_bytes and request.headers.get('Content-Type', 'application/json'): # if the content type should be assumed.
    body = await request.json()
else:
    body = body_bytes

I can make a PR for this, but I would like to learn the maintainers’ opinion on this. @tiangolo @dmontagu @phy25, thanks for the great project!

[coryvirok]

Any update on the fix for this? I’d love to be able to get my API docs to include the request body documentation for text/plain POST endpoints. 😃

[AdmiralNemo]

Is there any other way to document the request body in OpenAPI documentation, besides Body(...)?

I have a legacy service that I am porting to FastAPI, and one of the operations accepts a YAML body. I am happy to parse it myself using the raw request, but I do not see any way to express that a) this operation accepts a body, or b) that the body should be application/yaml.

Most of the users of my service use the Swagger UI directly, so not being able to enter the body for the request there would be a huge problem for them.