"Date" header not changing between requests

Discussed in https://github.com/encode/uvicorn/discussions/1610

<div type='discussions-op-text'>

^{Originally posted by arjwilliams August 22, 2022} 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())
```</div>

[Kludex]

This will be available in uvicorn 0.19.0.

[Kludex]

not sure about that, isn’t that the keep-alive of 5s is for, the tests pass fine if for instance we set

    config = Config(app=app, timeout_keep_alive=1.1)
    server = Server(config=config)

Correct. This is not a bug.