nREPL over HTTP(s) with Drawbridge in 2020

  1. Server
  2. Client
    1. Lein
    2. clj

Sometimes the only way to get REPL into your production application is to tunnel it over HTTP. nREPL has a transport and Ring handler for that provided by Drawbridge. Heroku has a nice but too dated guide on using nREPL with Drawbridge. I would like to fill the missing bits here.

Server

Using

[ring/ring-core "1.8.0"]
[ring/ring-jetty-adapter "1.8.0"]
[nrepl/nrepl "0.6.0"]
[nrepl/drawbridge "0.2.1"]

we start Jetty and hook nREPL into it via Drawbridge:

(ns minbedrift-uav.webrepl
  "Start a nREPL server over HTTP"
  (:require
    [drawbridge.core]
    [ring.adapter.jetty :refer [run-jetty]]
    [ring.middleware.keyword-params]
    [ring.middleware.nested-params]
    [ring.middleware.params]
    [ring.middleware.session]))

(def drawbridge-handler
  (-> (drawbridge.core/ring-handler)
      (ring.middleware.keyword-params/wrap-keyword-params)
      (ring.middleware.nested-params/wrap-nested-params)
      (ring.middleware.params/wrap-params)
      (ring.middleware.session/wrap-session)))


      (defn -main []
        (run-jetty
          #(if (= "/repl" (:uri %))
             (drawbridge-handler %)
             {:status "OK" :body "Do something else..."})
         {:port 5555, :join? true}))

In practice you would run it in addition to your main API/.. and thus wanted :join? false so that the process doesn’t block on starting the REPL server.

Refer to the original Heroku Drawbridge guide for details and regarding adding authentication

Client

Lein

The simples way I have found to connect is using Leiningen:

;; project.clj
(defproject whatever "0.1.0-SNAPSHOT"
  :plugins [[nrepl/drawbridge "0.2.1"]])

and lein :connect http://localhost:5555/repl (the http:// is key).

clj

It should be possible to do this with clj:

clj -Sdeps '{:deps {nrepl/drawbridge {:mvn/version "0.2.1"}}}' \
  -m nrepl.cmdline --transport drawbridge.client/ring-client-transport \
  --connect --host localhost --port 5555

but it doesn’t as of v.0.2.1, see nrepl/drawbridge#40.

(If you get instead an exception in bencode.clj then you forgot to specify the drawbridge transport and use the default bencode one.)


Tags: clojure tool


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