Inspired by https://pythonspeed.com/articles/json-memory-streaming/

main.py

import io
from typing import Any

import anyio
import ijson
from anyio.streams.buffered import BufferedByteReceiveStream
from anyio.streams.memory import MemoryObjectReceiveStream
from fastapi import FastAPI, Request, UploadFile

app = FastAPI()


@app.post("/file")
async def from_file(file: UploadFile) -> Any:
    async for item in ijson.items(file, "quiz.item"):
        print(item)


@app.post("/json")
async def from_json(request: Request) -> Any:
    file = anyio.wrap_file(io.BytesIO())
    async for chunk in request.stream():
        await file.write(chunk)
    await file.seek(0)

    async for item in ijson.items(file, "quiz.item"):
        print(item)


BufferedByteReceiveStream.read = BufferedByteReceiveStream.receive


async def process_json(receive_stream: MemoryObjectReceiveStream) -> None:
    buffered = BufferedByteReceiveStream(receive_stream)
    async for item in ijson.items(buffered, "quiz.item"):
        print(item)


@app.post("/json-stream")
async def from_json_stream(request: Request) -> Any:
    send_stream, receive_stream = anyio.create_memory_object_stream()

    async with anyio.create_task_group() as tg:
        tg.start_soon(process_json, receive_stream)
        async with send_stream:
            async for chunk in request.stream():
                await send_stream.send(chunk)

requirements.txt

uvicorn==0.18.2
fastapi==0.79.0
ijson==3.1.4

test.json

{
  "quiz": [
    {
      "q1": {
        "question": "Which one is correct team name in NBA?",
        "options": [
          "New York Bulls",
          "Los Angeles Kings",
          "Golden State Warriros",
          "Huston Rocket"
        ],
        "answer": "Huston Rocket"
      }
    },
    {
      "q1": {
        "question": "5 + 7 = ?",
        "options": ["10", "11", "12", "13"],
        "answer": "12"
      },
      "q2": {
        "question": "12 - 8 = ?",
        "options": ["1", "2", "3", "4"],
        "answer": "4"
      }
    }
  ]
}

Using HTTPie http -f POST :8000 [email protected].