# 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). 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 or WSGI 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)

## Forcing ASGI or WSGI mode

The `serve` function takes a `mode` argument that can be `"asgi"` or `"wsgi"` to force the app to be considered ASGI or WSGI as required.