API Usage¶

Most usage of Hypercorn is expected to be via the command line, as explained in the Usage documentation. Alternatively it is possible to use Hypercorn programmatically via the serve function available for either the asyncio or trio Workers (note the asyncio serve can be used with uvloop). In Python 3.7, or better, this can be done as follows, first you need to create a Hypercorn Config instance,

from hypercorn.config import Config

config = Config()
config.bind = ["localhost:8080"]  # As an example configuration setting

Then assuming you have an ASGI framework instance called app, using asyncio,

import asyncio
from hypercorn.asyncio import serve

asyncio.run(serve(app, config))

The same for Trio,

import trio
from hypercorn.trio import serve

trio.run(serve, app, config)

The same for uvloop,

import asyncio

import uvloop
from hypercorn.asyncio import serve

uvloop.install()
asyncio.run(serve(app, config))

Features caveat¶

The API usage assumes that you wish to control how the event loop is configured and where the event loop runs. Therefore the configuration options to change the worker class and number of workers have no affect when using serve.

Graceful shutdown¶

To shutdown the app the serve function takes an additional shutdown_trigger argument that will be awaited by Hypercorn. If the shutdown_trigger returns it will trigger a graceful shutdown. An example use of this functionality is to shutdown on receipt of a TERM signal,

import asyncio
import signal

shutdown_event = asyncio.Event()

def _signal_handler(*_: Any) -> None:
        shutdown_event.set()

loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGTERM, _signal_handler)
loop.run_until_complete(
    serve(app, config, shutdown_trigger=shutdown_event.wait)
)

No signal handling¶

If you don’t want any signal handling you can set the shutdown_trigger to return an awaitable that doesn’t complete, for example returning an empty Future,

loop.run_until_complete(
    serve(app, config, shutdown_trigger=lambda: asyncio.Future())
)

SSL Error reporting¶

SSLErrors can be raised during the SSL handshake with the connecting client. These errors are handled by the event loop and reported via the loop’s exception handler. Using Hypercorn via the command line will mean that these errors are ignored. To ignore (or otherwise handle) these errors when using the API configure the event loop exception handler,

def _exception_handler(loop, context):
    exception = context.get("exception")
    if isinstance(exception, ssl.SSLError):
        pass  # Handshake failure
    else:
        loop.default_exception_handler(context)

loop.set_exception_handler(_exception_handler)

How to guides

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