[WIP] Async-ify fetching content-addressed uri contents

[njgheorghita]

What was wrong?

It would be nice to fetch multiple ipfs assets with an async strategy, using all the available ipfs backends.

Still very WIP/experimental - lot's of cleanup / tests to write, but just looking for general feedback on the api / implementing trio

Cute Animal Picture

[pipermerriam]

I think we can do this without re-implementing each endpoint. I recently realized that this allows for both sync and async implementations of an ABC method.

    @abstractmethod
    def fetch_uri_contents(self, uri: URI) -> Union[Union[bytes, URI], Awaitable[Union[bytes, URI]]]:
        """
        Fetch the contents stored at a URI.
        """
        pass

It's a little tricky and I'm not 100% sure about it as a pattern yet but it would allow you to do something like this which sniffs each method and calls them appropriately.

async resolve_all_the_things(backend, uri):
    if asyncio.iscoroutinefunction(backend.fetch_uri_concents):
        return await backend.fetch_uri_contents(uri)
    else:
        return await trio.run_sync_in_worker_thread(backend.fetch_uri_contents, uri)

cc @cburgdorf who might have some opinions about this approach.