ApplicationRunner API improvements

Currently, the “usual” way to run an ApplicationSession-derived component is via the ApplicationRunner API. This lumps together several things:

• creates the component (ComponentConfig + instantiating the session)
• possibly sets up TLS options, if wss:// URI
• starts the event-loop (reactor.run() for Twisted or run_until_complete in asyncio).
• starts logging (via txaio.start_logging).
• handles several error-cases

This becomes awkward for certain use-cases, and e.g. spawned a start_reactor=bool kwarg for the Twisted version (which also lumps in logging, because start_logging is only called if it starts the reactor itself).

• users wanting to start their own logging (e.g. https://github.com/crossbario/txaio/issues/75#issuecomment-216651341)
• users wanting to run the event-loop elsewhere (e.g. start_reactor= kwarg)
• users who want to handle errors themselves

I am filing this bug to collect these use-cases as a way to improve the “I wish to run a component” API to ensure they’re covered.

[potens1]

I subscribe to this. IMHO, the ApplicationRunner does too much of magic (well, it’s not magic at all, the code is very short and easy to understand, but you have to check what is going on here when you are discovering autobahn-python), i.e. running the loop and closing the loop. I think this should be done explicitly by the user (or there should be a way to do it manually, if the default is doing all the machinery of the loop) because, when writing software that has already asyncio components, it’s a bit strange not being able to start the loop by yourself, or adding an autobahn component to an already running loop/software, more over, when the connection to the router is lost, the complete program stops (because the loop is stopped), and, if i.e. you want to do asyncio things to clean stuffs (i.e, start an asyncio commit to db, continue running tasks and restart a new session,…) you can’t. I know you can subclass ApplicationRunner to change all those things, by I’m more or less convinced that’s what will happen to the majority of users, rewriting ApplicationRunner in a way or another, so, maybe there is some value to rethink the thing. I also find the documentation should emphase ApplicationRunner is designed for quick tests and development and is likely to be subclassed for more complex setup.

[mayerwin]

It is indeed very annoying not to be able to control logging (I have been struggling to find why logging was duplicate), and the event loop (most asyncio code allows to pass an arbitrary loop to be used).