Just solved an interesting problem when using the latest Thin web server (1.2.5) with Ruby 1.9.1 and Rails Metal.
The code in Rails Metal endpoint:
def call(env)
if env["PATH_INFO"] =~ /^\/tags.txt/
request = Rack::Request.new(env)
params = request.params
query = params[’q']
[200, { "Content-Type" => "text/plain" }, words_from(query).join("\n")]
[...]