FastAPI: how to read body as any valid json?

Question

I haven't found the docs for that use case. How can I get the request body, ensure it's a valid JSON (any valid JSON, including numbers, string, booleans, and nulls, not only objects and arrays) and get the actual JSON. Using Pydantic forces the JSON to have a specific structure.

Answer 1

You can find nearly everything inside the Request object

You are able to get request body with request.json(), which will give you the parsed JSON as dictionary.

from fastapi import Request, FastAPI

@app.post("/dummypath")
async def get_body(request: Request):
    return await request.json()

If you want access the body as string, you can use request.body()

Answer 2

The accepted answer is valid as well, but FastAPI provides a built-in way to do that - check the Singular values in body section in docs.

A parameter with the default Body gets all the payload that doesn't match passed Pydantic-typed parameters (the whole payload in our case) and converts it to the dict. In case of invalid JSON, a standard validation error would be produced.

from fastapi import Body, FastAPI

app = FastAPI()


@app.post('/test')
async def update_item(
        payload: dict = Body(...)
):
    return payload

UPD: Note on ... (Ellipsis) - it allows marking a value as required. Read more in the Required with Ellipsis docs section

Answer 3

If you are confident that the incoming data is "a valid JSON", you can create a simple type annotation structure to receive the arbitrary JSON data.

from fastapi import FastAPI
from typing import Any, Dict, AnyStr, List, Union

app = FastAPI()

JSONObject = Dict[AnyStr, Any]
JSONArray = List[Any]
JSONStructure = Union[JSONArray, JSONObject]


@app.post("/")
async def root(arbitrary_json: JSONStructure = None):
    return {"received_data": arbitrary_json}

Examples

1. JSON object

curl -X POST "http://0.0.0.0:6022/" -H  "accept: application/json" -H  "Content-Type: application/json" -d "{\"test_key\":\"test_val\"}"

Response:

{
  "received_data": {
    "test_key": "test_val"
  }
}

2. JSON array

curl -X POST "http://0.0.0.0:6022/" -H  "accept: application/json" -H  "Content-Type: application/json" -d "[\"foo\",\"bar\"]"

Response:

{
  "received_data": [
    "foo",
    "bar"
  ]
}

---

If you are not sure about the content type of the incoming data, better to parse the request body.

It can be done as,

from fastapi import FastAPI, Request

app = FastAPI()


@app.post("/")
async def root(request: Request):
    return {"received_request_body": await request.body()}

The advantage of this method is that the body will contain any kind of data, JSON, form-data, multipart-form-data, etc.

Answer 4

from fastapi import Request

async def synonyms__select(request: Request):
    return await request.json()

will return a JSON object.