Tuesday, 1 December 2020

Getting Docker, Clojure and VSCode all playing nice (well... almost...)

I'm trying to re-motivate myself to do some tech type stuff in my spare time. I have a lot of spare time at the moment. 24h of the day. I still haven't really looked for a job having been made redundant a few months back (coughJunecough), and I've been largely wasting my time sleeping, napping (yes, two distinct things), and playing computer games. On one hand 2020 is a bit of a rubbish year, and a new work environment is likely to be a subpar experience, even if I can find work. On the other hand I can afford to not work for quite a while thanks to my redundancy pay out, but on still another hand (yes, fine, I have three hands for the purposes of this story), I really am not taking advantage of this spare time I have. That's why I had a look at Mingo's CF problem the other day ("looking at an issue Mingo had with ehcache and cachePut and cacheGet"). Just trying to do anything marginally "productive".

I've been wanting to learn a bit of Clojure for a while now. Not for any particular reason, and I'm not looking to shift to doing that over PHP, but just cos it's a completely different language from anything I've used before - which have all been C-ish "curly brace" type things - and my mate Sean has banged on about how good it is. I think at his suggestion I bought Living Clojure by Carin Meier a while back when I had some down time in NZ. I read the first few pages and then realised Auckland has a lot of pubs, so did that instead. This would have been about four(?) years ago. I ain't touched it since.

Here I am, sporadically trying to get to grips with Docker, and this seemed like a good mini-project... get Clojure up and running within a container, set up a project, integrate it with an IDE, and get to the point where I have a running (and passing) test for some sort of "G'day world" function. In the past I would install whatever language I was wanting to mess with natively on my PC, but I decided running it in a container is the way to go.

Note that this is pretty much just a record of what I needed to do to get to the point I could write the code and run the tests. I have very little experience with Docker, and hardly any experience with Clojure. What this means is that this is def a newbie account of what I did, and I really would not take it as instructions of how to do stuff. All I will say is that I needed to do a whole bunch of googling to work shit out, and I will summarise the results of the googling here. This is more an exercise for me to verify what I've done actually works, as having done it once... I'm now getting-rid and starting from scratch.

OK. I am starting with a minimal "empty" repo, living-clojure:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ tree -aF --dirsfirst -L 1 .
├── .git/
├── .gitignore*
└── README.md*

1 directory, 3 files

This just gives me a directory I can mount in the container to expose my code in there.

Now I need the container. Looking at dockerhub/clojure, the options there are just for running the app, not doing development, so ain't much help. I was hoping to be able to copy and paste something like "a container with Clojure and Leiningen in it wot you can as a shell for building yer project, testing it, developing it, and running it". Nothing to copy and paste and run, so I'm gonna have to work out what to do. Remember I'm a complete noob with Docker.

Getting the image down was easy enough:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker pull clojure
Using default tag: latest
latest: Pulling from library/clojure
852e50cd189d: Already exists
ef17c1a94464: Pull complete
477589359411: Pull complete
0a40767d8190: Downloading [==================> ] 71.81MB/197.1MB
434967525bea: Download complete
c89e9081a4db: Download complete
b7cd84bcb910: Download complete
214999e8c5eb: Download complete
0bdd8adb02ca: Download complete

(Just showing it mid-pull there)

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker image ls
php rc-cli 657d0925a963 6 days ago 407MB
clojure latest 846a444b258f 6 days ago 586MB

Just to start with, I just need a container based on the Clojure image, but doing nothing else. I just need to run a shell with it so I can create my Clojure project. I came up with this:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker create --name living-clojure --mount type=bind,source=/mnt/c/src/living-clojure,target=/usr/src/living-clojure --workdir /usr/src/living-clojure --interactive --tty clojure /bin/bash
  • I'm mounting my host's project directory within the container;
  • and setting that to be my working dir in there too;
  • I don't completely get these two, but I wanna be able to type shit into my shell that I'm running, and this seems to make it happen;
  • and it's bash I want to interact with.

And I start this:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker start --interactive living-clojure

Hurrah! This seems promising: I'm in a different shell, and I'm in the working directory I specified when doing the docker create before.

Let's see if I can create a new Clojure project (which I'm lifting from the the Leiningen docs):

root@a1be067ee435:/usr/src/living-clojure# cd ..
root@a1be067ee435:/usr/src# lein new app living-clojure --force
Generating a project called living-clojure based on the 'app' template.

I need to go up a directory level and to use --force because I already have the project directory in place, and lein new assumes one doesn't.

And this all seems to work fine (well… in that it's done "stuff"):

root@a1be067ee435:/usr/src# tree -F -a --dirsfirst -L 1 living-clojure/
├── .git/
├── doc/
├── resources/
├── src/
├── test/
├── .gitignore*
├── .hgignore*
├── README.md*
└── project.clj*

5 directories, 6 files

git status shows something interesting though:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ git status
On branch main
Your branch is up to date with 'origin/main'.

Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git restore <file>..." to discard changes in working directory)
modified: .gitignore
modified: LICENSE
modified: README.md

Untracked files:
(use "git add <file>..." to include in what will be committed)

no changes added to commit (use "git add" and/or "git commit -a")

Note how .gitignore, LICENSE and README.md have all changed. Such is the price of doing that --force I guess. I'm gonna revert the LICENSE and README.md, but leave the .gitignore; I presume the Leiningen bods have a better idea of what git should ignore in the context of a Clojure project than GitHub's boilerplate one does.

Next… what's the code in the default project actually do?

(ns living-clojure.core

(defn -main
"I don't do a whole lot ... yet."
[& args]
(println "Hello, World!"))

That will do for a start. Let's see if it runs:

root@a1be067ee435:/usr/src# cd living-clojure/
root@a1be067ee435:/usr/src/living-clojure# lein run
Hello, World!

Cool! Is it bad I'm so pleased with a computer saying "Hello, World!"? Ha.

I'm being a bit naughty because I'm running the code before I've tested it. But I figure... not my code, so it's OK. Anyway, there is a test, although it does not test the code in the app. Sigh. But anyhow:

root@a1be067ee435:/usr/src/living-clojure# cat test/living_clojure/core_test.clj
(ns living-clojure.core-test
(:require [clojure.test :refer :all]
[living-clojure.core :refer :all]))

(deftest a-test
(testing "FIXME, I fail."
(is (= 0 1))))
root@a1be067ee435:/usr/src/living-clojure# lein test

lein test living-clojure.core-test

lein test :only living-clojure.core-test/a-test

FAIL in (a-test) (core_test.clj:7)
FIXME, I fail.
expected: (= 0 1)
actual: (not (= 0 1))

Ran 1 tests containing 1 assertions.
1 failures, 0 errors.
Tests failed.

I guess this is in-keeping with "start with a failing test". Fair enough then. At least the test runs correctly, which is good.

The last bit of checking the baseline project is… will it compile and run as a jar?

root@a1be067ee435:/usr/src/living-clojure# lein uberjar
Compiling living-clojure.core
Created /usr/src/living-clojure/target/uberjar/living-clojure-0.1.0-SNAPSHOT.jar
Created /usr/src/living-clojure/target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar
root@a1be067ee435:/usr/src/living-clojure# java -jar target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar
Hello, World!


Right. Now I actually need to write some code. I wanna change that main function to read the first argument from the command-line - if present - and say "G'day [value]" (eg: "G'day Zachary"), or if there's no argument, then stick with just "G'day World".

Given that's all very simple, I could just do it with a text editor, but I'll hook an IDE up to this lot too. I googled around and found that VSCode and the Calva Clojure plug-in. I've already set all that up and can't be arsed redoing it for the purposes of this article. One issue I had… and still have… is that Calva is supposed to be able to connect to an external REPL, instead of using its own one. Whilst experimenting trying to get this working, I tweaked my docker create statement to run a headless REPL instead of bash:

docker create --name living-clojure --mount type=bind,source=/mnt/c/src/living-clojure,target=/usr/src/living-clojure --expose 56505 -p 56505:56505 --workdir /usr/src/living-clojure --interactive --tty clojure lein repl :headless :host :port 56505

The new stuff is as follows:

  • I probably don't need the --expose here for what I'm doing, but the -p exposes the container's port 56505 to the host PC (56505 has no significance… it was just one of the ports a previous REPL had used, so I copied that).
  • I start a headless REPL (so basically a REPL as a service, that just listens for REPL connections) that listens on that port 56505
  • I have to use here because when I tried to use, that worked fine from within the container, but was no good on the host machine. It took me a bit of googling to crack that one.

I start this one without being interactive:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker start living-clojure

Doing it this way I am exposing a REPL to other sessions, whilst still being able to bash my way along too:

adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker exec --interactive --tty living-clojure lein repl :connect localhost:56505
Connecting to nREPL at localhost:56505
REPL-y 0.4.4, nREPL 0.6.0
Clojure 1.10.1
OpenJDK 64-Bit Server VM
Docs: (doc function-name-here)
(find-doc "part-of-name-here")
Source: (source function-name-here)
Javadoc: (javadoc java-object-or-class-here)
Exit: Control+D or (exit) or (quit)
Results: Stored in vars *1, *2, *3, an exception in *e

living-clojure.core=> (println "G'day world")
G'day world
living-clojure.core=> quit
Bye for now!
adam@DESKTOP-QV1A45U:/mnt/c/src/living-clojure$ docker exec --interactive --tty living-clojure /bin/bash
root@222940f1eafd:/usr/src/living-clojure# ls
CHANGELOG.md LICENSE README.md doc project.clj resources src target test
root@222940f1eafd:/usr/src/living-clojure# exit

I could get VSCode on my desktop PC to see this REPL:

But I could not get it to do stuff like running tests, which it was able to do using the built-in REPL. So that sucked. I googled a bit and I am not the only person with this problem when using external REPLs, so I have just decided to give up on that. I'll cheat and use the built-in REPL.

Oh god. I now need to write some Clojure code (I've now caught up with my previous progress, and am typing this article "live" now… Bear with me for a bit).

Time passes…

More time passes and there is swearing…

OK, got there. I abandoned using VSCode and Calva because Calva seems to have this strange idea that when I go to delete things (like extra or misplaced parentheses), that it knows better and doesn't just do what it's frickin' told. It's probably me not knowing some special trick that people accustomed to using it know, but… for the love of god if I ask a frickin' text editor to do something in the edit window, I expect it to just do it even if I'm asking it to do something less than ideal. I will seek out a different plugin later. Once I dropped back to using Notepad++, things went better. I have done a lot of googling in the last two hours though. Sigh.

Anyhow, here are my tests:

(ns living-clojure.core-test
  (:require [clojure.test :refer :all]
    [living-clojure.core :refer :all]))

(deftest test-greet-default-behaviour
  (testing "it should return G'day world if no name is passed"
    (is (= "G'day World" (greet [])))))

(deftest test-greet-by-single-name
  (testing "it should return G'day [name] if just that name is passed"
  (is (= "G'day Zachary" (greet ["Zachary"])))))

(deftest test-greet-by-multiple-name
  (testing "it should return G'day [name] if more than one names are passed"
  (is (= "G'day Zachary" (greet ["Zachary" "Cameron" "Lynch"])))))

And here is the code:

(ns living-clojure.core

(defn greet
    (str "G'day " (or (first args) "World"))))
(defn -main
  "I greet someone or everyone"
  [& args]
  (println (greet args)))

And here's the output of the tests, running the code, and compiling and running the code:

root@222940f1eafd:/usr/src/living-clojure# lein test

lein test living-clojure.core-test

Ran 3 tests containing 3 assertions.
0 failures, 0 errors.

root@222940f1eafd:/usr/src/living-clojure# lein run
G'day World

root@222940f1eafd:/usr/src/living-clojure# lein run Zachary
G'day Zachary

root@222940f1eafd:/usr/src/living-clojure# lein run Zachary Cameron Lynch
G'day Zachary

root@222940f1eafd:/usr/src/living-clojure# lein uberjar
Compiling living-clojure.core
Created /usr/src/living-clojure/target/uberjar/living-clojure-0.1.0-SNAPSHOT.jar
Created /usr/src/living-clojure/target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar

root@222940f1eafd:/usr/src/living-clojure# java -jar target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar
G'day World

root@222940f1eafd:/usr/src/living-clojure# java -jar target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar Zachary
G'day Zachary

root@222940f1eafd:/usr/src/living-clojure# java -jar target/uberjar/living-clojure-0.1.0-SNAPSHOT-standalone.jar Zachary Cameron Lynch
G'day Zachary


I got a bit snagged on the variadic parameters syntax for a while, largely cos to me that just says "it's a reference", so I need to unlearn that in this context. And then cos I've been staring at the screen too long now, I had a brain-disconnect on only the parameters of main were variadic… by the time they got to greet it was just an array (or a list or whatever Clojure calls it). So due to dumbarsey on my part I variously had the tests passing but the behaviour at runtime slightly off, or the tests failing but the program actually running correctly. What this says is that I probably should have been testing main, not greet. My bad.

OK. It's 22:30 and I've been at this on and off for quite a few hours now. I'm pretty pleased with the exercise as a whole - I learned a lot - but now I want to go shoot things. Parentheses. I want to shoot parentheses. But I guess I will settle for shooting raiders in Fall Out 4.