Startup and Shutdown#
The ASGI lifespan specification includes the ability for awaiting
coroutines before the first byte is received and after the final byte
is sent, through the startup and shutdown lifespan events.
This is particularly useful for creating and destroying connection
pools. Quart supports this via the decorators
before_serving() and
after_serving(), which function like
before_first_request(), and
while_serving() which expects a function that
returns a generator.
The decorated functions are all called within the app context,
allowing current_app and g to be used.
Warning
Use g with caution, as it will reset after startup, i.e. after
all the before_serving functions complete and after the
initial yield in a while serving generator. It can still be used
within this context. If you want to create something used in
routes, try storing it on the app instead.
To use this functionality simply do the following:
@app.before_serving
async def create_db_pool():
app.db_pool = await ...
g.something = something
@app.before_serving
async def use_g():
g.something.do_something()
@app.while_serving
async def lifespan():
... # startup
yield
... # shutdown
@app.route("/")
async def index():
app.db_pool.execute(...)
# g.something is not available here
@app.after_serving
async def create_db_pool():
await app.db_pool.close()
Testing#
Quart’s test client works on a request lifespan and hence does not
call before_serving, or after_serving functions, nor advance
the while_serving generator. Instead Quart’s test app can be used,
for example
@pytest.fixture(name="app", scope="function")
async def _app():
app = create_app() # Initialize app
async with app.test_app() as test_app:
yield test_app
The app fixture can then be used as normal, knowing that the
before_serving, and after_serving functions have been called,
and the while_serving generator has been advanced,
@pytest.mark.asyncio
async def test_index(app):
test_client = app.test_client()
await test_client.get("/")
...