module ActionDispatch::Http::FilterParameters

def env_filter # :doc:
  user_key = fetch_header("action_dispatch.parameter_filter") {
    return NULL_ENV_FILTER
  }
  parameter_filter_for(Array(user_key) + ENV_MATCH)
end

def filtered_env
  @filtered_env ||= env_filter.filter(@env)
end

def filtered_parameters
  @filtered_parameters ||= parameter_filter.filter(parameters)
rescue ActionDispatch::Http::Parameters::ParseError
  @filtered_parameters = {}
end

def filtered_path
  @filtered_path ||= query_string.empty? ? path : "#{path}?#{filtered_query_string}"
end

def filtered_query_string # :doc:
  parts = query_string.split(/([&;])/)
  filtered_parts = parts.map do |part|
    if part.include?("=")
      key, value = part.split("=", 2)
      parameter_filter.filter(key => value).first.join("=")
    else
      part
    end
  end
  filtered_parts.join("")
end

def initialize
  super
  @filtered_parameters = nil
  @filtered_env        = nil
  @filtered_path       = nil
  @parameter_filter    = nil
end

def parameter_filter
  @parameter_filter ||= if has_header?("action_dispatch.parameter_filter")
    parameter_filter_for get_header("action_dispatch.parameter_filter")
  else
    NULL_PARAM_FILTER
  end
end

def parameter_filter_for(filters) # :doc:
  ActiveSupport::ParameterFilter.new(filters)
end