Altering params in Sinatra before blocks - ruby

Question

I am trying to alter the request params in a before block in Sinatra.
It seems that when using this syntax, it works:
before do
#params['global-before'] = 'yes'
end
But when using this syntax, it does not work:
before '/:id/test' do
#params['route-before'] = 'yes'
end
Here is a full example:
# test.rb
require 'sinatra'
require 'sinatra/reloader'
set :bind, '0.0.0.0'
set :port, 3000
before do
#params['global-before'] = 'yes'
end
before '/:id/test' do
#params['route-before'] = 'yes'
end
get '/' do
params.to_json
end
get '/:id/test' do
params.to_json
end
Then running:
$ ruby test.rb
$ curl localhost:3000
{"global-before":"yes"}
$ curl localhost:3000/123/test
{"global-before":"yes","id":"123"}
I was expecting to see the params['route-before'] populated as well.
I have tried using request.params instead of #params but that did not work at all.
Can anyone shed some light on this?
Update:
Opened an issue in Sinatra's issue tracker

Answer 1

The route filter goes first, and it has route parameters: {"id"=>"123"}, so this happens:
original, #params = #params, #params.merge(params) if params.any?
where original ends up as {} and #params as {"id"=>"123"}. When the global filter runs, there are no route parameters, so original remains unassigned (nil) and #params is the {} that was originally there.
After the filter processes, in the ensure clause, there is this:
#params = original if original
So global filter skips it, because original is nil, because there were no route parameters. The route filter resets the #params to whatever it was before the filter ran, because original is preserved, because there were route parameters.
I can't say whether this is a bug or an intended behaviour, but it's a "how" at least, if not a "why". It may make sense asking the Sinatra team (and reporting back here with the verdict).
tl;dr: #params are reset to pre-filter state if there are parameters in the filter's path pattern.
Note: you can hack around it by making your own instance variable:
before '/:id/test' do
#route_before = 'yes'
end
get '/:id/test' do
"Did we run route before? #{#route_before}"
end