discourse/lib/middleware/discourse_public_exceptions.rb

# since all the rescue from clauses are not caught by the application controller for matches
# we need to handle certain exceptions here
module Middleware
  class DiscoursePublicExceptions < ::ActionDispatch::PublicExceptions

    def initialize(path)
      super
    end

    def call(env)
      # this is so so gnarly
      # sometimes we leak out exceptions prior to creating a controller instance
      # this can happen if we have an exception in a route constraint in some cases
      # this code re-dispatches the exception to our application controller so we can
      # properly translate the exception to a page
      exception = env["action_dispatch.exception"]
      response = ActionDispatch::Response.new

      # Special handling for invalid params, in this case we can not re-dispatch
      # the Request object has a "broken" .params which can not be accessed
      exception = nil if Rack::QueryParser::InvalidParameterError === exception

      # We also can not dispatch bad requests as no proper params
      exception = nil if ActionController::BadRequest === exception

      if exception
        begin
          fake_controller = ApplicationController.new
          fake_controller.response = response
          fake_controller.request = ActionDispatch::Request.new(env)

          if ApplicationController.rescue_with_handler(exception, object: fake_controller)
            body = response.body
            if String === body
              body = [body]
            end
            return [response.status, response.headers, body]
          end
        rescue => e
          Discourse.warn_exception(e, message: "Failed to handle exception in exception app middleware")
        end

      end
      super
    end

  end
end