Blog Posts on Shreve Labs

Finding the current Git branch in CodeBuild

Sat, 26 Feb 2022 00:00:00 +0000

I want to use the name of the current git branch in nearly every automated build I run on CodeBuild, usually for tagging docker images. CodeBuild doesn’t make this value available, just the commit hash it fetched.

No problem! There’s a command that’s pretty commonly seen for grabbing the branch name yourself:

git rev-parse --abbrev-ref HEAD

The command rev-parse fetches information about a revision, the parameter HEAD means where we are now, and the option --abbrev-ref asks for a non-ambiguous name for the revision in question. This typically results in the name of the current branch.

Creating a generic set type in Go

Wed, 11 Nov 2020 00:00:00 +0000

tl;dr: map[interface{}]struct{} gives us the properties we want with a low memory overhead. There’s a great implementation of this idea (including thread safety) at dekarep/golang-set.

First things first, if you’re not familiar, a set is a data structure that maintains a unique collection of elements. They work similarly to other collection types like vectors, but with a few special properties: In order to maintain uniqueness, inserting an element that’s already in the set does nothing, and in order to make this check reasonable to do often, the Contains(el) algorithm is as fast as possible. This is typically achieved by arranging the elements in a way that they can be looked up, rather than searching the list from start to finish, which yields a complexity of O(log n) or even O(1) rather than O(n).

Obfuscating your email on the web

Thu, 06 Aug 2020 00:00:00 +0000

I really like having my email address publicly available on my website. Email is a great medium for feedback or discussions about the articles I post here, and making it accessible increases the chance readers will think to reach out with it. The problem is, I don’t like getting email from robots, and that is an inevitable consequence of this publicity.

The solution to this is to not include my email address in the plaintext of the page, but to instead dynamically provide it to the user when they ask for it. Cloudflare has a tool for this called Scrape Shield, which hides sensitive info in the HTML of the page and injects it back in after it’s loaded in the visitor’s browser using javascript. This prevents basic bots from scraping one’s website for contact information. The problem with this solution is that their scheme is easily broken, and it’s widespread use makes breaking it valuable. I’ll show you.

Creating a website theme that respects user preference

Sat, 27 Jun 2020 00:00:00 +0000

A neat website theming option I’ve seen used more frequently lately is the use of the prefers-color-scheme media query. It allows the user’s browser to specify if they want a light or a dark theme, or if they have no-preference. If the user went through the trouble of requesting a theme, you might as well give it to them, right? Here’s what I came up with to do that.

The starting point for this was honestly some really bad Sass written years ago, but for the sake of explanation, let’s say it was some plain CSS with a theme class. Everything gets some default styles, then descendents of a .dark-theme class get some different colors.

The Juice

Wed, 20 Feb 2019 00:00:00 +0000

A former coworker of mine used to talk about “the juice” and “juicing up” our work. What he meant was making sure all our individual interests were aligned along our work.

Having a job means you’re getting paid and that’s at least one interest being fulfilled, but what else could your work be doing for you? Do you enjoy working on what you’re working on? Are you learning from it? Could you be writing open source code which could gain you some degree of prestige? Is it helping you get where you want to be in life?

IEEE-754 Floating Point Numbers

Thu, 04 Oct 2018 00:00:00 +0000

Many programmers are aware of floating point numbers, typically called floats, and their value for storing decimal values. Most of them are also aware of some vague danger in using them which can cause some really bizarre-seeming results.

For example, in Ruby,

0.1 + 0.2 = 0.30000000000000004

This is due to the way we store these decimal values.

Floats use scientific notation in binary format, meaning they use 2 as a base instead of 10. These rounding errors occur because we can’t quite represent the exact correct answer within our limits of efficient time or memory usage.

Calculating current CPU usage on Linux

Thu, 28 Sep 2017 00:00:00 +0000

tl;dr: The code

I use a tool called i3blocks to script my own status bar, which includes a CPU usage indicator. Recently, I noticed something odd about it. The output would change for a while, but eventually stick right around 41%. I had previously just copied this script from Stack Overflow, so I decided it was time to dig in and learn about this in order to fix it.

I was able to relocate the Stack Overflow question I had taken the script from: How to get overall CPU Usage (e.g. 57%) on Linux The answer I had chosen is the highest rated, and relies on /proc/stat.

A Gentle Introduction to Kubernetes

Thu, 17 Aug 2017 00:00:00 +0000

Manually managing servers is a pain. Setting up a server you already know the desired configuration for feels like a huge waste of time. There are tools available to help automate this process, like capistrano, puppet, and chef, but they don’t solve the whole problem, and to me felt quite brittle. There has to be A Better Way™.

That’s where Docker and Kubernetes come in. Docker makes your application environment portable, and Kubernetes allows you to easily reproduce and deploy your application.

Hex Color Scales

Sat, 15 Apr 2017 00:00:00 +0000

I recently created a battery module for my i3blocks bar. For this project, I wanted the icon to have a color representing the fullness of the battery — 100% green for full, 100% red for empty, and gradients in-between. i3blocks renders text using pango so it supports hexadecimal colors codes via an HTML-like markup. The desired process can be outlined as:

Calculate the battery percentage (outside the scope of this article)
Calculate the desired level of red, green, and blue based on that percentage
Combine that rgb color into a hexadecimal color

Calculating the RGB color

In my first attempt, I decided to try grading from 100% to 0% green, and 0% to 100% red as the battery percentage declined. This did result in the desired bright green at full and bright red at empty, but the middle was a less satisfying color.

Fixing xbacklight

Thu, 16 Mar 2017 00:00:00 +0000

I recently decided to upgrade from Ubuntu 16.04 LTS to 16.10. This was unfortunate for a couple reasons: 1. The upgrade broke some dependencies leading to apt no longer working and 2. I made the decision at midnight on a worknight.

I ended up reinstalling 16.04 and trying to restore a backup of my home folder. In this process, I ended up breaking plenty of my configuration. The most frustrating of which was the breaking of xbacklight for backlight control. Before the reinstall, xbacklight worked perfectly. Now, it returned a frustrating error: “No outputs have backlight property”

How to download large files on crappy connections with bash and curl

Thu, 12 Jun 2014 00:00:00 +0000

For some reason, my home internet connection has always been terrible, and seems like it always will be. That doesn’t change the fact that I like the internet, and downloading things from it, like video games I purchased from The Humble Bundle. Until recently, I just dealt with the fact that I’d need to pay a visit to my local library or McDonald’s to use their WiFi. No More!

Most of the time when a download interrupts in any of the major browsers, it cannot be resumed. You can use a download manager like Folx to get interruption-tolerant downloading, but I really like to avoid 3rd party software when possible. It turns out, the best downloading software was already installed in my terminal. The answer is curl!