Parse JSON body from HTTP request (with ring and re-frame-http-fx)

Question

I have a re-frame-based UI and try to communicate with my server using re-frame-http-fx. Sending and responding seems to work. However, I can't figure out how to parse the JSON body into a Clojure map on the server.

Here is my handler.clj as minimal as I could get it:

(ns my.handler
  (:require [compojure.core :refer [GET POST defroutes]]
            [compojure.route :refer [resources]]
            [ring.util.response :refer [resource-response]]
            [ring.middleware.json :refer [wrap-json-response wrap-json-body]]))

(defn json-post [request]
  (let [body (:body request)]
    (prn body)
    body))

(defroutes routes
  (GET       "/"     []      (resource-response "index.html" {:root "public"}))
  (POST      "/post" request json-post)
  (resources "/"))

(def handler (wrap-json-response (wrap-json-body routes {:keywords? true})))

As far as I understand, the wrap-json-body middleware should replace the request body by a parsed version (a map?).

However, the output I get from (prn body) in my json-post handler is something like this: #object[org.httpkit.BytesInputStream 0xda8b162 "BytesInputStream[len=41]"]

If I try something like (prn (:title body)) I get nil (although the original map-turned-json-request contains :title, as well as both the request and response body).

The request and response contain the correct json. The request Content-Type is correctly set to application/json (sent by re-frame-http-fx). The length of the buffer (41) is also the correct body length as per request.

I am running out of things to try. Any ideas?

Can you try slurping the input stream to see what is in it? And can you try without wrapping the JSON response? — Daniel Compton
Slurping the input stream gives me the raw request body that contains the expected json. I did not try to remove the ring middleware, because I stumbled upon the solution (see answer). Thanks and sorry for the trouble. — notan3xit

notan3xit notan3xit · Accepted Answer · 2017-02-09T09:16:17

While investigating the issue further, I found my error that lead to the effect. It concerns the dev-handler from the re-frame template that I conventiently omitted from my minimal example in the question.

I did not realize it was a problem, because the application seems to start fine even if you delete the entire definition of dev-handler from handler.clj, I assume because the server is initialized with handler in server.clj anyway (and the client does not fail fatally).

However, in project.clj of the re-frame template, the following is configured for figwheel:

  :figwheel {:css-dirs ["resources/public/css"]
             :ring-handler my.handler/dev-handler}

This leads to middleware configured for handler not being applied to my requests, thus not unwrapping the json body. Changing either the definition of dev-handler (the the same as handler in the question) or the configuration of figwheel in project.clj (to point to handler instead of dev-handler) solves the problem.

If anybody knows the reasoning of different handlers in project.clj and server.clj, feel free to let me know.

Parse JSON body from HTTP request (with ring and re-frame-http-fx)

1 Answers