@mccraigmccraig What's the best approach here? Only thing that I see possible is to wrap my initial handler with a middleware that will dereference the Deferred.

derefing is pretty much a no-no for an async program - you will block a thread and possibly cause a deadlock (the only places derefing makes sense are in the repl and maybe in a sync test driving async code). either find a different middleware which is async compatible, or copy the existing middleware and modify it to be async friendly

thank you for the tips! will experiment with that.

@alexyakushev yes, ring.middleware.session/wrap-session is trying to read the Deferred response and fails. Seems there is a project that provides async versions of middlewares -- https://github.com/muhuk/aleph-middleware