Explaining how this Minecraft world forgot its seed

On July 20th, 2024, speedrunner Couriway was working on his quest to complete Minecraft 100,000 times when his 3,606th world forgot its seed, resetting back to 0. Today we dive into the code to investigate how this happened and why it will never happen again. Footage from https://youtu.be/k9FMq8-IOy4?t=4015 Corrections/Comments: - skybt on the Discord pointed out another reason this was able to happen: Minecraft tries to use a BufferedOutputStream to reduce how many times it writes to a file, but it mistakenly applies it *after* the GZIP compressor and not *before*. If this order was swapped, the entire file would be written in one big chunk, which would likely further reduce the chance of corruption like this happening! - If the later 512-byte blocks went missing they could technically work for the "seed 0" part of the exploit, the player just wouldn't be (fully) reset like what happened to Couriway. OST: https://i.qixils.dev/couriway_seed_0_ost.txt Feel free to react :) I stream Minecraft challenges on https://twitch.tv/lexikiq Get updates on progress and post meows on https://discord.gg/ZbMFW2Jpwd I post thumbnails early on https://twitter.com/lexikiq