ruby middleware add stack adding middlware - ruby

Question

I am trying to add/append middleware to the stack (in config.ru) on certain requests (where request.path == "/hi")
I was trying to do that with Rack::Builder
But i seem to fail at it.
Rack::Builder.new do
use added_middleware1
use added_middleware2
end.call(#env) if #request.path == "/something"
I am not sure if that makes my problem clear.

Answer 1

The #request variable should only be available when an actual request is happening, but the code you posted is probably getting run at configuration time when the server starts up. There is example code on the front page of the Rack::Builder documentation showing how to do something like you would want:
app = Rack::Builder.new {
use Rack::CommonLogger
use Rack::ShowExceptions
map "/lobster" do
use Rack::Lint
run Rack::Lobster.new
end
}

Answer 2

The stack should look more like this:
use CommonMiddleware
map '/something' do
use SpecialMiddleware
run TheApp.new
end
map '/' do
run TheApp.new
end
Alternatively, you could write a middleware that looks at the request path and runs the other special middleware as needed - sort of like a wrapper for it. The machinery would look something like this:
def initialize app, special_middleware
#app, #special_middleware = app, special_middleware
end
def call env
if route_matches?(env)
#special_middleware.new(#app).call(env) # assumes special_middleware initializer takes no extra parameters
else
#app.call(env)
end
end
def route_matches? env
# examine the rack environment hash, return true or false
end
And the config for using it would look like this:
use RouteMatchingMiddleware, SpecialMiddleware
run TheApp.new