I'm looking to build a webapp with a WebSocket component, and a run of the mill rack based frontend. My initial plan was to use Camping for the frontend, running the server on thin, with a rack config.ru looking like this:
require 'rack'
require './parts/web-frontend'
require './parts/websocket'
AppStationary = Rack::File.new("./stationary")
run Rack::Cascade.new(AppWebSockets, AppWebPages, AppStationary)
AppWebSockets is being provided by websocket-rack and works great. In the absence of an Upgrade: WebSocket request it simply 404's and the request runs down the cascade to the camping app, AppWebPages.
It's becoming clear that this camping webapp inevitably requires access to IO, to talk with the CouchDB database using regular http requests. There are plenty of ways to do http requests, including some async libraries compatible with eventmachine. If I subscribe to a callback, rack returns and the page has already responded by the time I'm ready to create a response. I'd like to be able to use em-synchrony to get some concurrency via Ruby 1.9's Fibers - which I've only just gotten my head around - but cannot find any documentation on how to make use of em-synchrony with Thin.
I've encountered a webserver called Goliath which claims to be similar to thin, with em-synchrony support baked in, but it lacks a command line utility to launch and test the server and seems to require I write a different sort of file to a rackup, which is quite distasteful. It also is unclear if it would even support websocket-rack, which only specifies support for Thin currently.
What are some good ways to avoid blocking IO while still making use of familiar rack based tools like camping, and having access to WebSockets?
Here's an example of how to add async support to Camping: https://gist.github.com/1192720 (see 65 for the code you'll have to use in your app). Maybe we should wrap it up in a gem or something…