Mounted engines don't get route segment values

[samuelkadolph]

So I've been playing with the 3.1 beta and I really want to package our code as an engine in a gem and also release a multitenant version that lets you mount the engine to /:username. This works fine but it doesn't pass the value of the segment into to controller that the route maps to inside of the engine.

Rails::Application.routes.draw do
  mount Foo::Engine => "/:username"
end

Foo::Engine.routes.draw do
  root :to => "home#home"
end

module Foo
  class HomeController < ApplicationController
    def home
      render :text => params[:username].inspect
    end
  end
end

$ curl http://localhost:3000/username
nil

[samuelkadolph]

I've found the problem and got a solution.
The cause is that Rack::Mount::RouteSet#call is called twice and does not consider that env[@parameters_key] could have been set previously (which it is and correctly contains :username => "blah" the first time).

If you merge in env[@parameters_key] to the new params, everything works as expected.

diff --git a/lib/rack/mount/route_set.rb b/lib/rack/mount/route_set.rb
index bf168be..11959c2 100644
--- a/lib/rack/mount/route_set.rb
+++ b/lib/rack/mount/route_set.rb
@@ -139,6 +139,9 @@ module Rack::Mount
       request = nil
       req = @request_class.new(env)
       recognize(req) do |route, matches, params|
+        # merge existing params
+        params.merge!(env[@parameters_key]) if env[@parameters_key]
+
         # TODO: We only want to unescape params from uri related methods
         params.each { |k, v| params[k] = Utils.unescape_uri(v) if v.is_a?(String) }

@josh, do you want me to open pull request for rack-mount to fix it?

[josh]

Its not a simple as merging. We'd need to maintain a stack of params.

Router A -> Router B -> App 1
         -> Router C -> App 2

Its possible to have a request match A -> B -> 1 then returns X-Cascade: pass forcing A to try to the next route. In that case we'd need to clear away the nested params that were merged in B.

[samuelkadolph]

Right. Do you want some help to implement it? And if so, where would be the best place to implement it? In call or recognize?

[josh]

Please do

You should just have to modify call https://github.com/josh/rack-mount/blob/master/lib/rack/mount/route_set.rb#L149

Open a pull request and I'll walk you through the edge cases.

[samuelkadolph]

Pull request created, closing this issue.

[josevalim]

@samuelkadolph, could you also please add a test to Rails? One of the appropriated places to put this test would be in the file below. You just need to nest to route sets.

https://github.com/rails/rails/blob/master/actionpack/test/dispatch/mount_test.rb

[arunagw]

@josevalim I have added test here for the main problem in engine_test

e72a6f8

if we need then can add here also

[josevalim]

Ah, no need then. Thanks @arunagw!