```python
import asyncio
from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse

import helpers  # noqa: F401

app = FastAPI()


@app.post("/thumbnail")
async def thumbnail(request: Request):
    data = await request.body()
    result = await asyncio.to_thread(helpers.resize_image, data)
    return JSONResponse({"size": len(result)})
```