The external poll feature has been part of libwebsockets since the beginning, and that's what Mosquitto uses. Relatively recently the developer decided he didn't like that anymore and is going to remove it, but has disabled it for now.
I've asked about it and was told that he didn't want to support it any more and that everybody using the external poll feature should rewrite their code. I'm rewriting to use a different library so I don't have to deal with that kind of breakage again, but in the meantime I don't want my users to suffer - without this change the websockets feature is unusable.
