ClojureScript On Google Cloud Functions

I wanted to try out Google Cloud Functions, and when I saw that it only supported JavaScript I thought “What a perfect opportunity to try ClojureScript as well. I could have imitated ( and that would have been fine, but I started going through the Modern ClojureScript Tutorials and got taken by boot. (See how easy it is for me to get lost down a rabbit hole?)

Ultimately, I’m only going to end up having two files:

├── build.boot
└── src
    └── cljs
        └── demo
            └── core.cljs

I did this in phases, figuring out one piece at a time. I’ll be walking you through that process, as I think it will make the information easier to digest.

To begin with I just wanted to get a minimal ClojureScript project going. Most of this part is lifted straight from Tutorial 1 of Modern ClojureScript, but even simpler because I don’t need an html file. I’m not going to repeat what’s explained in the tutorial, he does a much better job of describing what’s going on.

;; core.cljs
(ns demo.core)

(defn greet [req res]
  (println "hey")
  (.json res (clj->js (:headers req))))

;; build.boot
 :source-paths #{"src/cljs"}
 :dependencies '[[adzerk/boot-cljs "1.7.228-2"]])

(require '[adzerk.boot-cljs :refer [cljs]])

Now to start making it possible for cloud functions to be able to run this function. There’s a command line tool that we’ll get to later, but for now let’s focus on just being able to paste in some raw javascript. First, for cloud functions to be able to call greet it needs to be added to the export module. Once I figured out what I was looking for, it was pretty easy to pull out of cloud-functions-clojure and add to the end of core.cljs:

(set! (.-exports js/module) #js {:greet greet})

With that in place, I ran boot cljs --optimizations simple target to generate the JavaScript. The nuance here is --optimizations simple, without that, it will use the optimization none which will scatter the code across several files. With the optimization, all the code I need is generated in target/main.js. Then I headed over to Google’s cloud console, and set up a new function. Made the trigger an HTTP trigger, pasted the contents of main.js into the inline editor and set the function to execute to greet.

So I have valid javascript generated, but it’s pretty annoying to be pasting into a text box to deploy a new version. Next up, I used the gcloud cli to deploy automatically. The command I want to use is gcloud beta functions deploy greet --stage-bucket demo_staging --trigger-http, but there are two problems right now with that: it expects the javascript to be in the directory where the command is run and it expects the file to be named index.js. The former I resolved by changing the command to gcloud beta functions deploy greet --local-path target --stage-bucket demo_staging --trigger-http. For the latter I’ll switch the build command to boot cljs --optimizations simple --ids index target.

Now to get this all a bit more operationalized. I’d like to be able to just say boot deploy -f greet, but first I need to understand how to create new tasks. deftask will allows me to build the command, and a less documented function in boot called dosh allows me to execute the gcloud command. I used with-pre-wrap to make it easier to pass the fileset object down the stack, as well as ensure that a deploy happens before any tasks chained with it are called. This is added to the end of build.boot.

(deftask deploy [f function NAME str "Function to deploy"]
  (comp (cljs :optimizations :simple :ids #{"index"})
  (with-pre-wrap fileset
    (dosh "gcloud" "beta" "functions" "deploy" function "--local-path" "target"
          "--stage-bucket" "demo_staging" "--trigger-http")