By deprecating faye and celluloid you got rid of the websocket libraries that supported a proxy.

[cyberfox]

I used to be able to connect to Slack's websocket via a proxy, but with the new code it doesn't connect at all.

I, [2021-02-26T16:37:28.739948 #32529]  INFO -- request: POST https://slack.com/api/rtm.start
I, [2021-02-26T16:37:28.740030 #32529]  INFO -- request: Accept: "application/json; charset=utf-8"
User-Agent: "Slack Ruby Client/0.16.0"
Content-Type: "application/x-www-form-urlencoded"
I, [2021-02-26T16:37:43.660278 #32529]  INFO -- response: Status 200
I, [2021-02-26T16:37:43.660412 #32529]  INFO -- response: date: "Sat, 27 Feb 2021 00:37:33 GMT"

It's able to receive the rtm start response, but it can't actually talk to the web socket because async-websocket doesn't support using a proxy to reach a web socket.

Celluloid did, and I was using it. I think faye did. Apparently async-websocket does since...around...0.14.0, roughly a year ago, but this client requires 0.8.0, from about two years ago.

What's preventing an upgrade to a more recent async-websocket?

[dblock]

What's preventing an upgrade to a more recent async-websocket?

I tried a while ago and it didn't just work out of the box. Would love a PR. See #282