CODEWITHSUNDEEP
clojurecompojureringcompojure-api
Bob Kuhar
Bob Kuhar

Reputation: 11140

How do I make middleware to put a response header only when `:swagger {:deprecated true}`?

We use the compojure-api to get us some nice swagger integration in our ring apps. The :swagger {:deprecated true} meta works like a champ to get the swagger page correct, but I have a requirement that I put a specific header on the response when the route is :swagger {:deprecated true}. I am struggling to figure out how to do this with the middleware pattern that I've been using to do similar response header manipulations.

(ns bob.routes
  (:require [clojure.tools.logging :as log]
            [compojure.api.sweet :refer :all]
            [ring.util.http-response :as status]
            [schema.core :as s]
            [ring.swagger.schema :as rs]))

(s/defschema BobResponse {:message (rs/describe String "Message")})

(defn wrap-bob-response-header [handler]
  (fn [request]
    (let [response (handler request)]
      ;; can I reach into the request or the response to see what
      ;; route served this and if it has the :swagger {:deprecated true}
      ;; meta on it and NOT emit the x-bob header if it does?
      (assoc-in response [:headers "x-bob"] "Robert"))))

(defroutes bob-routes
  (context "" []
    :middleware [wrap-bob-response-header]
    :tags ["bob"]
    :description ["Tease out how to do swagger driven response header"]
    (GET "/notdeprectated" [:as request]
      :swagger {:deprecated false}
      :new-relic-name "GET_notdeprecated"
      :return BobResponse
      (status/ok {:message "All is well"}))
    (GET "/isdeprecated" [:as request]
      :swagger {:deprecated true}
      :new-relic-name "GET_isdeprecated"
      :return BobResponse
      (status/ok {:message "You came to the wrong neighborhood."}))))

How do I modify wrap-bob-response-header to only emit x-bob on routes with :swagger {:deprecated true}?

Upvotes: 0

Views: 943

Answers (1)

Tommi Reiman
Tommi Reiman

Reputation: 268

With Compojure-API, the middleware are invoked in-place, at the path context they are defined at. In your example, the wrap-bob-response-header doesn't yet know where the request is going to go (or will it even match anything). If it knew, you could use the injected route information from the request (see https://github.com/metosin/compojure-api/blob/master/src/compojure/api/api.clj#L71-L73) to determine if the endpoints would have the swagger information set.

What you could do, is mount the header-setting middleware only to the routes that need it.

There is a library called reitit (also by Metosin) which solves this by applying a route-first architecture: the full path lookup is done first and the middleware chain is applied after that. Because of this, all the middleware know the endpoint they are mounted to. Middleware can just query the endpoint data (either at request-time or at compile-time) and act accordingly. They can even decide not to mount to that spesific route.

Reitit is feature-par with compojure-api, just with different syntax, e.g. fully data-driven.

Good examples in the blog: https://www.metosin.fi/blog/reitit-ring/

PS. I'm co-author of both of the libs.

EDIT.

Solution to inject data to the response after a match:

1) create middleware that adds data (or meta-data) to the response

2) add or modify a restructuring handler to mount the middleware from 1 into the endpoint, with the given data (available in the handler)

3) read the data in the response pipeline and act accordingly

(defn wrap-add-response-data [handler data]
  (let [with-data #(assoc % ::data data)]
    (fn
      ([request]
       (with-data (handler request)))
      ([request respond raise]
       (handler #(respond (with-data %)) raise)))))

(defmethod compojure.api.meta/restructure-param :swagger [_ swagger acc]
  (-> acc
      (assoc-in [:info :public :swagger] swagger)
      (update-in [:middleware] into `[[wrap-add-response-data ~swagger]])))

(def app
  (api
    (context "/api" []
      (GET "/:kikka" []
        :swagger {:deprecated? true}
        (ok "jeah")))))

(app {:request-method :get, :uri "/api/kukka"})
; {:status 200, :headers {}, :body "jeah", ::data {:deprecated? true}}

Upvotes: 1

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