class Rack::QueryParser

def parse_query(qs, separator = nil, &unescaper)

(which defaults to '&').
to parse cookies by changing the characters used in the second parameter
Parses a query string by breaking it up at the '&'. You can also use this
Stolen from Mongrel, with some small modifications: 
def parse_query(qs, separator = nil, &unescaper)
  unescaper ||= method(:unescape)
  params = make_params
  (qs || '').split(separator ? (COMMON_SEP[separator] || /[#{separator}] */n) : DEFAULT_SEP).each do |p|
    next if p.empty?
    k, v = p.split('=', 2).map!(&unescaper)
    if cur = params[k]
      if cur.class == Array
        params[k] << v
      else
        params[k] = [cur, v]
      end
    else
      params[k] = v
    end
  end
  return params.to_h
end