How can I explicitly set content type on compojure response?

Question

I am playing with compojure-api and am blocked at trying to manage Content-Type for my simple webapp. What I want is to emit an HTTP response that is just plain/text, but somehow Compojure-API keeps setting it to "application/json".

    (POST "/echo" []
      :new-relic-name "/v1/echo"
      :summary "info log the input message and echo it back"
      :description nil
      :return String
      :form-params [message :- String]
      (log/infof "/v1/echo message: %s" message)
      (let [resp (-> (resp/response message)
                     (resp/status 200)
                     (resp/header "Content-Type" "text/plain"))]
        (log/infof "response is %s" resp)
        resp))

but curl shows the server responded Content-Type:application/json.

$ curl -X POST -i --header 'Content-Type: application/x-www-form-urlencoded' -d 'message=frickin compojure-api' 'http://localhost:8080/v1/echo'
HTTP/1.1 200 OK
Date: Fri, 13 Jan 2017 02:04:47 GMT
Content-Type: application/json; charset=utf-8
x-http-request-id: 669dee08-0c92-4fb4-867f-67ff08d7b72f
x-http-caller-id: UNKNOWN_CALLER
Content-Length: 23
Server: Jetty(9.2.10.v20150310)

My logging shows that the function requested "plain/text", but somehow the framework trumped it.

2017-01-12 18:04:47,581  INFO [qtp789647098-46]kthxbye.v1.api [669dee08-0c92-4fb4-867f-67ff08d7b72f] - response is {:status 200, :headers {"Content-Type" "text/plain"}, :body "frickin compojure-api"}

How do I gain control over Content-Type in a Compojure-API Ring application?

Answer 1

compojure-api serves response in format requested by HTTP client which is indicated using HTTP Accept header.

With curl you need to add:

-H "Accept: text/plain"

You can also provide a list of acceptable formats and the server will serve the response in the first supported format from that list:

-H "Accept: text/plain, text/html, application/xml, application/json, */*"

Answer 2

I never tried compojure so here goes nothing:

1.) your local val reps has the same name as the aliased namespace - kind of confusing

2.) to get access to the params - it seems - you have to apply ring.middleware.params/wrap-params to your routes

3.) ah yes the Content-Type: since you required :form-params, which didn't get delivered due to missing wrap-params you ended up in some sort of default route - hence not text/plain. Thats what I think happend, at least.

with

lein try compojure ring-server

demo/paste into repl:

(require '[compojure.core :refer :all])
(require '[ring.util.response :as resp])
(require '[ring.server.standalone :as server])
(require '[ring.middleware.params :refer [wrap-params]])

(def x
  (POST "/echo" [message]
      :summary "info log the input message and echo it back"
      :description nil
      :return String
      :form-params [message :- String]
      (let [resp (-> (resp/response (str "message: " message))
                     (resp/status 200)
                     (resp/header "Content-Type" "text/plain"))]
        resp)))

(defroutes app (wrap-params x))

(server/serve app {:port 4042})

test:

curl -X POST -i --header 'Content-Type: application/x-www-form-urlencoded' -d 'message=frickin' 'http://localhost:4042/echo'
HTTP/1.1 200 OK
Date: Fri, 13 Jan 2017 17:32:03 GMT
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 14
Server: Jetty(7.6.13.v20130916)

message: frickin