[Bug/Question] Response from the server is never received in case of using middleware.

Describe the bug Response from the server is never received in case of using middleware.

To Reproduce Steps to reproduce the behavior:

$ cat main.py

# !/usr/bin/env python
# -*- coding: utf-8 -*-
"""Entry point of the application."""


import logging

from fastapi import Depends, FastAPI, HTTPException
from pydantic import BaseModel
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.responses import Response

logger = logging.getLogger(__name__)


class AuthMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        response = Response("Faled to authenticate", status_code=401)
        try:
            json = await request.json()
            request.state.is_authenticated = True
            logger.info(f"request.body: {json} ")
            response = await call_next(request)
        finally:
            request.state.is_authenticated = False
        return response


app = FastAPI(title="Nice Server",
              description="This is a very fancy project, with auto docs for the API and everything",
              version="0.1.0",
              docs_url="/docs", redoc_url=None)

app.add_middleware(AuthMiddleware)


class SomeTimestamp(BaseModel):
    ts: int


async def is_authenticated(request: Request):
    return request.state.is_authenticated


@app.post("/latest", response_model=SomeTimestamp, summary="Returning the latest ")
async def latest(*, some_timestamp: SomeTimestamp, is_authenticated: bool = Depends(is_authenticated)):
    logger.info(f"Let's see if this is authenticated: {is_authenticated}")
    if not is_authenticated:
        raise HTTPException(status_code=401, detail="Failed to verify the incoming token")

    logger.info(f"Received for prediction {some_timestamp.ts}")
    return some_timestamp.ts

Now run the server:

uvicorn main_server:app --reload

Now query this using curl:

curl --header "Content-Type: application/json" \
  --request POST \
  --data '{"ts":"123123"}' \
  http://127.0.0.1:8000/latest

Expected behavior The server is stuck before sending response.

Screenshots If applicable, add screenshots to help explain your problem.

Environment:

• OS: [ Linux]
• FastAPI Version [e.g. 0.18.0], get it with:

import fastapi
print(fastapi.__version__)

0.18.0

• Python version, get it with:

python --version
3.7

Additional context Add any other context about the problem here.

[gwdekker]

See also https://github.com/encode/starlette/issues/493

[yihuang]

I think this is a starlette problem(https://github.com/encode/starlette/issues/495).