"Date" header not changing between requests

[arjwilliams]

I am testing out some cache-control headers in my web app, but the auto-generated "Date" header seems to only be changing when a new connection is established, rather than with each new request, which is preventing the browser from caching new responses, as it sees the response as being older than it actually is.

I would expect that the "Date" header to change between requests, even when using an existing connection.

I am testing on Python 3.10.5, with Uvicorn 0.18.2.

Possible test case, which is currently failing for me:

import asyncio

from email.utils import parsedate_to_datetime
from contextlib import asynccontextmanager

import httpx

from uvicorn import Config, Server

async def test_default_date_header_different():
    config = Config(app=app, loop="asyncio", limit_max_requests=2)
    async with run_server(config):
        async with httpx.AsyncClient() as client:
            response1 = await client.get("http://127.0.0.1:8000")
            await asyncio.sleep(2)
            response2 = await client.get("http://127.0.0.1:8000")

            response1_date = parsedate_to_datetime(response1.headers["date"])
            response2_date = parsedate_to_datetime(response2.headers["date"])
            assert(response2_date > response1_date)

async def app(scope, receive, send):
    assert scope["type"] == "http"
    await send({"type": "http.response.start", "status": 200, "headers": []})
    await send({"type": "http.response.body", "body": b"", "more_body": False})

@asynccontextmanager
async def run_server(config: Config):
    server = Server(config=config)
    cancel_handle = asyncio.ensure_future(server.serve())
    await asyncio.sleep(0.1)
    try:
        yield server
    finally:
        await server.shutdown()
        cancel_handle.cancel()

asyncio.run(test_date_header_different())

[iudeen]

I checked the behavior with hypercorn (Daphne, doesn't support date header)

Server Code

from hypercorn import Config
from hypercorn.asyncio import serve

config = Config()
config.max_app_queue_size=2

asyncio.run(serve(app, config))

The date header is changing on each request.

>response1_date = parsedate_to_datetime(response1.headers["date"])
>response2_date = parsedate_to_datetime(response2.headers["date"])
>print(response2_date, response1_date)

2022-08-30 18:29:09+00:00 2022-08-30 18:29:07+00:00

[iudeen]

On checking Hypercorn's implementation, we see that date is being assigned on formation of response header.

While on Unicorn, its assigned using server state, which I suppose is initiated on new connection. (Not sure)

[iudeen]

If we agree this is an issue to be fixed, here is a way to fix.

We take reference from Hypercorn and set default headers on every response. If we do this, we might not need the on_tick function to update default header on every second.

[Kludex]

This was solved already. I don't remember when, but on 0.20.0 it's already working.