Rack-compatible server issues

[Kevin Williams <kevwil@gmail.com>]

I'm implementing a Rack-compatible server for JRuby. I'm having issues
with complex apps returning bad data. Simple lambda apps run fine, but
when a Rack::Builder -created app is used, weird stuff happens.

http://gist.github.com/249506

If I pass just the lambda, my server runs fine, but if I pass the
whole builder-created app (any combination of middleware), I get one
of the middleware classes returned from the #call(env) method.

I thought once my server makes the top @app.call(env) call, it's all
Rack middleware and the user's app chained together. Shouldn't I get
the result of the user's app back to my server no matter what? What
could I be doing wrong that would cause this odd result?

Kevin