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Simple stubbing with lein-cooper and lein-oneoff

Work on lein-cooper has been pretty quiet. It's not because it has been abandoned but because it does enough for my needs. As and when it starts getting issues or pull requests coming in I can start adapting it to fit the wider needs of others.

Recently I came across a lovely leiningen plugin called lein-oneoff. oneoff allows you to specify dependencies for a clojure script at the top of a clojure script (a bit like what Grape does in the Groovy world I believe). This means you don't have to spin up all the project infrastructure to run a simple script. So instead of lein new server and editing the core.clj file to mock up a simple "Hello World" sample you could do something like this,

  [[org.clojure/clojure "1.6.0"]
   [ring/ring-jetty-adapter "1.3.0"]
   [ring "1.3.1"]])

(ns server
  (:require [ring.adapter.jetty :refer [run-jetty]]))

(defn handler [request]
  {:status 200
   :headers {"Content-Type" "text/html"}
   :body "Hello World"})

(run-jetty handler { :port 3000 })

If this were saved as server.clj we could use lein-oneoff (declared in the global ~/.lein/profiles.clj) to run it like so,

> lein oneoff server.clj

Notice the defdeps form at the top of the file, this will be used to grab dependencies and set up the appropriate classpath for running the script.

Pretty neat.

I also noticed that this would be a perfect accompaniment for a typical usage of lein-cooper - stubbing out external services. If you're building a system that integrates with other services (either internal or external) you introduce a bit of friction when it comes to developing and testing (at the integration level at least) your system. Either you have to build and run dependent services or rely on external services that may or may not be available. A simple solution is to develop against simple stubs for these services. This is what coop-off (the new power couple portmanteau I've given to the lein-cooper/lein-oneoff combination) can make easier.

Just create a stubs folder in your project, create standalone service stubs (like the example below that also demonstrates the use of oneoffs *command-line-args* for accessing arguments passed with the command),

  [[org.clojure/clojure "1.6.0"]
   [ring/ring-jetty-adapter "1.3.0"]
   [org.clojure/data.json "0.2.5"]
   [ring "1.3.1"]])

(ns server
  (:require [ring.adapter.jetty :refer [run-jetty]]
            [ :as json]))

(defn handler [request]
  { :status 200
    :headers {"Content-Type" "application/json"}
    :body (json/write-str { :success true :data [1 2 3 4] }) })

(def port
  (or (Integer. (first *command-line-args*)) 3000))

(defn start-server
  (run-jetty handler { :port port }))

(start-server port)

And you can integrate the running of this and other stubs alongside using lein-cooper. Just create a Procfile for lein-cooper with commands to run everything,

web: lein ring server
data: lein oneoff stubs/data.clj 3000
auth: lein oneoff stubs/auth.clj 3002

Finally run the whole thing via lein cooper.

The standalone stubs will be executed alongside your own service without the overhead of having to manage separate projects or integrate test code into your own project.

Published in Clojure on August 26, 2014