Convert Minecraft Bedrock local player to network player

This is a workaround for Mojang bug BDS-5121, affecting people attempting to transfer a world from being hosted on a device (e.g. a phone) to a Bedrock Dedicated Server. Previously the only known workaround was to place everything from your inventory in a box before transferring the world to a BDS, but this wasn't very satisfactory: among other things, it didn't account for pets. The code in this repository eliminates the need for that workaround by making the appropriate changes directly in the world database.

The hard bit is figuring out how the original local player should be represented in the database. There may well be a better way to do this, but my approach is to get the player in question to connect to a scratch copy of the world, compare the database from before and after that connection to see how Minecraft and BDS themselves decided to represent them, and then rename everything related to the original local player.

Disclaimers: I am not affiliated with Mojang or Microsoft in any way, nor am I a Minecraft expert: in fact, I don't even play Minecraft myself, just somehow ended up fixing this for my family. Writing this was a last resort after failing to find any other acceptable way to fix the problem at hand. As such, I may very well have got various technical details wrong. You must ensure that you have a backup of the world before using this program and that you know how to restore it. While I've tried to include somewhat reasonable error handling, I only had a single sample world to work with when writing this, so there may be problems I couldn't foresee.

You will need Python >= 3.6.

Usage

1. Grab and build these Python bedrock bindings and (if necessary) leveldb-mcpe. Add the bedrock directory to your PYTHONPATH for the remaining steps.
2. Take a clean copy of the world from the original device. (I used adb backup and Android Backup Extractor, but of course this depends on your original device.)
3. Upload the world to a BDS instance (renaming its directory as usual - at a minimum it needs to not end with the = character to avoid confusing the BDS server.properties parser, but it's probably least confusing to rename it to match levelname.txt), configure server.properties to use it, and start the server.
4. Get the original local player to connect to the world.
5. Stop the server and copy the world back out. Make sure to put it in a different path from the clean copy you took in step 2, because you'll need to compare them.
6. Run ./compare-worlds.py <path to old world> <path to new world>. This should find a single new player and print various UUIDs associated with them.
7. Take another copy of the original world from step 2, and run ./convert-local-player.py <path to copied world> <MSA ID> <self-signed ID> <player server ID>, using the UUIDs printed in step 6.
8. Upload this modified copy to the BDS instance, overwriting the one you uploaded before, and restart the server.
9. The original local player should now be able to connect and see their inventory.

Once this modification has been made, the world will no longer be suitable for use on the original device. (My guess is that the original local player will end up with no inventory, similar to the issue I was trying to solve but in reverse.) It should be possible to reverse the process by renaming the appropriate database row back to ~local-player, but I haven't tested this. PRs welcome if anyone else needs this.