Fix Bandit.HTTP1.Adapter.inform/3 return value

[wojtekmach]

Per https://hexdocs.pm/plug/Plug.Conn.Adapter.html#c:inform/3, the callback should return:

:ok | {:error, :not_supported}

The way Plug.Conn.inform! is implemented at the moment, https://github.com/elixir-plug/plug/blob/v1.15.2/lib/plug/conn.ex#L1335, it looked like Bandit did not implement inform but it sure does!

[mtrudel]

Looks good! I'm going to add a small note to the bandit telemetry docs now that we're losing tracking of inform responses but otherwise lgtm!

[wojtekmach]

would it help if the adapter allowed you to send {:ok, payload} or whatever makes the most sense? (I believe payload is a name used for arbitrary data, at least in adapter.send_resp/4)

If so that would be a compatible change in Plug and I can help pursuing it.

[mtrudel]

would it help if the adapter allowed you to send {:ok, payload} or whatever makes the most sense?

Ideally, yeah. Returning bare :ok's is a bit of an anti pattern IMO. For example, Plug's chunk api also expects a bare :ok back from the adapter, which in addition to precluding tracking state for e.g. metrics, was also the cause of a recent oddball bug as well. Ideally everything in the adapter behaviour would return the a full tuple that took an updated adapter back, but that's not super realistic.

Happy to hew whichever way the upstream Plug issue wants to go here. Let's keep the discussion going over there.

[wojtekmach]

We need to wait for elixir-plug/plug#1193 in case there's any change in the contract but otherwise I think this is ready. And when there's a new Plug version I'll send a PR that uses the stricter inform!, 18e12ed#diff-6a1dfdf6de8e0ba81a6ae4eef3f45cf79b7d4a55d7130e228463f9f77a0344e3R1339.

[mtrudel]

New plug version is here!

[mtrudel]

Merged this since it's erroring out on a couple of other PRs without this