Since HTTP.open closes the web socket for you when the passed function exits, I’d use a different mechanism for communicating that the socket should be closed rather than closing the socket manually. E.g. pass a channel to the function handling the websocket, put! a message that you want to exit in it and return based on that. The idea is to not pass the socket around and have a bunch of places reading/writing from/to it, but only one instead. That makes your code easier to maintain, since you don’t have to hunt down erronous writes (and safer as well, since you don’t have multiple tasks potentially writing to the socket at the same time…).
You’ll also have to handle the socket closing prematurely, e.g. if the server doesn’t respond anymore and communicate that to Rocket.jl as well.