Sinatra using respond_to with url extensions (.json)

Since I work most of the time in Rails, I found that using the Sinatra responds_to provided in Sinatra-Contrib to be a bit confusing. It didn’t match my expectations mostly in terms of setting content type based on url extensions. It worked fine when curling a url with the proper accepts settings curl -i -H "Accept: application/json" but not when using a browser with the .json extension on the end of the url.

I ended up solving this by setting the request.accept array based matching a optionally appended format on the url. It was also hard to use named url parameters along with a optional format parameter across all the urls I wanted to support. I saw one solution that allowed a optional format on a url, but it required modifying the path of each url. I didn’t want to alter each of my uris with complex regex. I eventually got everything working as I would like, with a bit of hacking.

I added a before filter that checks the current request, if it matches the extension json (although this would work for any format), I set the request.accept headers. I then remove the extension from the path_info so that the urls work with the standard Sinatra route helpers. After adding that hack, the Sinatra-Contrib respond_to works as I expected.

Sinatra optional format before filter

require 'sinatra/contrib'

before /.*/ do
  if request.url.match(/.json$/)
    request.accept.unshift('application/json')
    request.path_info = request.path_info.gsub(/.json$/,'')
  end
end

#...

get '/projects', :provides => [:html, :json] do
  @projects = Project.projects
  respond_to do |format|
    format.json { @projects.to_json }
    format.html { erb :index }
  end
end

Is there a better way?

Perhaps I am missing something, it took me a bit to figure out a good solution to this. Normally I find Sinatra matches my expectations very well and follows the principle of least surprise. That is why I decided to share my solution and see if there was just some other more simple way to solve the problem.

Anyways, using this I was able to make the churn-site api pretty nice to browse over a browser. Especially if you have the JSONview chrome extension which I highly recommend.