Exceptions middleware for handling low-level errors for Rails with graphql-ruby app

exceptions_middleware.rb

# NOTE: Add `config.exceptions_app = ExceptionsMiddleware.new` to application.rb

class ExceptionsMiddleware
  def initialize
  end

  def call(env)
    error = env["action_dispatch.exception"]
    request = ActionDispatch::Request.new(env)

    log_request_error(error, request)

    footprint = "#{request.remote_addr}_#{request.forwarded_for}"
    case error
    when ActionController::RoutingError
      Rack::Attack::Fail2Ban.filter("not-found-#{footprint}", maxretry: 10, findtime: 1.minute, bantime: 1.hour) do
        true
      end
    end

    render_error(
      message: error.message,
      code: error.class.to_s.gsub(/:+/, "_").underscore.upcase,
      vars: error.try(:vars)
    )
  end

  private

  def render_error(message:, code:, vars:)
    error = {
      message: message,
      extensions: {
        code: code,
        level: "middleware"
      }
    }
    error[:extensions][:vars] = vars if vars.present?
    response = {
      data: nil,
      errors: [error]
    }
    # rubocop:disable GitlabSecurity/JsonSerialization
    render_format(200, "application/json", response.to_json)
    # rubocop:enable GitlabSecurity/JsonSerialization
  end

  def log_request_error(error, request)
    ServerError.log!(
      error,
      request: request
    )
  end

  def render(status, content_type, body)
    format = "to_#{content_type.to_sym}" if content_type
    render_format(status, content_type, body.public_send(format))
  end

  def render_format(status, content_type, body)
    [
      status,
      {
        "Content-Type" => "#{content_type}; charset=#{ActionDispatch::Response.default_charset}",
        "Content-Length" => body.bytesize.to_s
      },
      [body]
    ]
  end
end