require 'securerandom' require 'active_support/core_ext/string/access' module ActionDispatch # Makes a unique request id available to the action_dispatch.request_id env variable (which is then accessible through # ActionDispatch::Request#uuid) and sends the same id to the client via the X-Request-Id header. # # The unique request id is either based off the X-Request-Id header in the request, which would typically be generated # by a firewall, load balancer, or the web server, or, if this header is not available, a random uuid. If the # header is accepted from the outside world, we sanitize it to a max of 255 chars and alphanumeric and dashes only. # # The unique request id can be used to trace a request end-to-end and would typically end up being part of log files # from multiple pieces of the stack. class RequestId def initialize(app) @app = app end def call(env) env["action_dispatch.request_id"] = external_request_id(env) || internal_request_id @app.call(env).tap { |_status, headers, _body| headers["X-Request-Id"] = env["action_dispatch.request_id"] } end private def external_request_id(env) if request_id = env["HTTP_X_REQUEST_ID"].presence request_id.gsub(/[^\w\-]/, "").first(255) end end def internal_request_id SecureRandom.uuid end end end