One More Week: Fixing a 7-Year-Old Bug

This was my last few days with the System Engineering team, and the first few with the Privacy and Security team. I barely finished the Node 16 update before switching, and was already a bit tired before being overwhelmed by new faces and a ton of documentation.

Our rat terrier Link, attacking his brother under the couch, August 2021

I spent last week working in two neglected libraries, taskcluster/docker-exec-websocket-client and taskcluster/docker-exec-websocket-server, getting them in CI, updating to Node v16, and eventually finding a setting to fix an issue. It felt good to find that bug before my weekend!

The code review of PR 35 and the follow-up (in PR 36 and 37) took a lot of the day, then releasing the 3.0.0 versions of each library. It was late Monday before I bumped the libraries in the original Taskcluster PR 5095. When the updated code ran in CI, I was devastated – the test was still broken. Well, broken in a different way. Previously, it timed out, and now it completed, but now it said the input (a random megabyte of data) didn’t match the output (that data piped through cat in the container). I now had one day left to fix it.

I spent a bit of time Tuesday trying to run it locally, but that had been a dead-end a few weeks ago as well. I tried just the library updates with the existing Node v14 version, and the test failed in exactly the same way! I narrowed the CI jobs to just this test, and added some debugging, and then noticed that the test code was:

assert(data.compare(buf), 'buffer mismatch');

The string .compare() function is in a lot of languages (I first encountered it as strcmp in C), and is often used when sorting. It returns -1 if the first item “sorts” earlier, 1 if the second item sorts earlier, and 0 if they are equal. With the library updates, the strings were now equal, .compare() was returning 0, and the assert was failing on a falsy value. Reading the code, the author of this test wanted to use .equals(), returning true if equal or false if not. I’ve made a similar mistake, and seen others as well. I appreciate that Python 3 dropped the cmp operator and __cmp__ magic method, and eliminated a lot of developer confusion.

Digging in a little, this change was made 7 years ago, around Node 0.10.x or 0.12.x, and close to when .compare() and .equals() were added. Before that, a manual byte-by-byte method was used to compare the buffers, which was probably correct. So, this code has been broken for 7 years, and it took Node v16 to break it in a new way and get some attention.

Luckily, this just took a day to figure out, and we were able to merge Node v16 on my last day. I then transitioned to the Privacy and Security team, to work on Firefox Relay. It is a very different project than the ones I’ve been working on for the last three years, but I think tests and testability will continue to be a focus on the new team. I’ll write more about the new team next week.

I’m a bit tired to make my own recommendations, so here’s some stuff my 11-year-old has been into:

  • Root Beer Milk – I saw this at the store and got it on a whim, and the kid likes it and asked for more. It seemed like a bizarre combo at first, but it is basically a blended root beer float.
  • Roblox – He and his friends continue to play this weekly. It feels a bit like the Flash game scene of a decade or two ago, where game developers can experiment with game types and incentives, or copy ideas from other games, TV shows, or movies. There’s a lot of 3D games, but I’ve seenhim play a game that looks a lot like Populous 2, and another like a Civilization clone. It’s making me interested in RBLX.
  • Minecraft – v1.18 includes the second part of the Caves and Cliffs update. The bedrock layer dropped from Y=0 to Y=-64, adding huge caves where it is easier to stumble on diamonds, or get attacked from a distance. There’s also more mountain biomes and structural variety. He’s bought a realm, and is tweaking server settings again.

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