For The Win

 

So much of what I want to do with automation is repetition of slight variants. I was reminded of it again last week when I was looking for a way to list the versions of certain dependencies across many versions of a product my team owns.

These dependencies are exposed through the running product's API on an "about" endpoint. They can also be found in our Gradle configuration file, build.gradle, something like this:

thingVersion = System.getenv('THING_VERSION') ?: '4.0'
otherVersion = System.getenv('OTHER_VERSION') ?: '2.3.1'
anotherVersion = System.getenv('ANOTHER_VERSION') ?: "7.6.0"

Conceptually I need to run through released versions of the product, interrogate each for the  dependencies, and aggregate them into some easily-parsable format.

If I was only after a couple of versions of the product I'd just check out the code for those versions, inspect the build.gradle files, and copy-paste the data into a text file. But it's not only a couple of versions and, ideally, I'd like to be able to re-use the same approach in future on versions we haven't released yet.

For that second need, an alternative would be to start recording the dependencies with each build. I considered that, but it means I'd now have two tasks and I think we will only need the dependency combinations occasionally.

So I want some way to automate gathering the information and I can see that this task fits the template at the top:

• something that can be done once (get a dependency version for a given release)
• repeated with slight variations (the dependencies, the release versions)

If there's anything clever about what I did next, it's the thinking about how to do my task once.

I can see that that API could do what I need. I could start a Docker container for every version that I was interested in and fetch data from the about endpoint. But that would be sloooooooooow.

Each of our releases is tagged and I know that it's easy to get Git to give me a list of tags on any repository. So I wondered whether there was a way to check out just the build.gradle file for all of the release versions and grep the data from it. 

A handful of searches, and a couple of false starts, later and I had the first building block:

$ git checkout my_tag build.gradle

That command, run inside a clone of our product's codebase, will update only the build.gradle file to tag my_tag.

Now I could search for the data I needed:

$ grep thingVersion build.gradle
  thingVersion = System.getenv('THING_VERSION') ?: '4.0'

And I could refine the call to get just the version by stripping out everything else:

$ grep thingVersion build.gradle | sed 's/.*\?\://'`
  '4.0'

At that point I had all the pieces:

• a call to get the version of a particular dependency for any release
• a list of dependencies 
• a list of releases

Now the problem was just syntax and this is the script I ended up with:

#!/bin/bash

# get the list of tags
tags=`git tag`

# find and return the build dependency
get_gradle_setting_for() {
    build_parameter=$1
    value=`grep "$build_parameter.*\=" build.gradle | sed 's/.*\?\://'`
    echo $value
}

# loop on tags, get build.gradle, find values
for tag in $tags;
do
    git checkout $tag build.gradle > /dev/null 2>&1

    thing=$(get_gradle_setting_for "thingVersion")
    other=$(get_gradle_setting_for "otherVersion")
    another=$(get_gradle_setting_for "anotherVersion")

    echo $tag, $thing, $other, $another
done

This is not a bash tutorial but I hope you can see that the thing I want to do once is in the function get_gradle_setting_for().

That function is called once for each dependency. That's one set of slight variants.

There's then a loop for another set of variants, the tags for each release.

This is how it looks when run:

$ getbuilds
v1, '4.0', '2.3.1', "7.6.0"
v2, '4.0', '2.5.0', "7.6.0"
v3, '4.2', '2.5.1', "7.6.0"

It takes a few seconds on my laptop to generate permutations for all tags. This is definitely the kind of thing we could do if and when we need it again later.

Now, for sure, the script is not particularly tidy, and has no validation or error handling, and if the build.gradle format changes it might stop working. But for this mission those things don't matter. This is a cheap solution to an occasional problem. The script is re-usable and serves as documentation for solving similar problems in future.

I mention all of this stuff not to brag but to encourage anyone feeling intimidated by automating. I Google how to do even the basics all the time. You can do the same. You already have the key thing you need: a good thinking brain.

P.S. Talking of repetition of slight variants, it makes me smile to think that I have said similar things before.
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