Bukkit#getMap(id) no longer works on 1.20.2

[codeHusky]

Expected behavior

Bukkit.getMap(id) should return a MapView for plugin-created maps following a reboot.

Observed/Actual behavior

Bukkit.getMap(id) returns null upon a reboot, breaking plugins that use this API tool. Example:

[...]
[00:35:24 WARN]: [ImageMaps] Map 2848 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2849 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2850 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2851 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2852 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2853 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2854 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2855 referenced but does not exist!
[00:35:24 WARN]: [ImageMaps] Map 2856 referenced but does not exist!
[...]

Steps/models to reproduce

• Install the plugin ImageMaps from SpigotMC https://www.spigotmc.org/resources/imagemaps.81851/
• Place any image
• Restart the server
• The images will no longer be displayed properly, errors printed in console indicate MapView is null.

Plugin and Datapack List

ImageMaps

Paper version

> ver
[00:35:59 INFO]: Checking version, please wait...
[00:35:59 INFO]: This server is running Paper version git-Paper-207 (MC: 1.20.2) (Implementing API version 1.20.2-R0.1-SNAPSHOT) (Git: 38376f4)
You are running the latest version
Previous version: git-Paper-307 (MC: 1.19.2)

Other

This is occurring in a world that's existed for a while primarily with ImageMaps populating the map IDs.

[codeHusky]

Upon some checking it looks like it's failing on this line in net.minecraft.server.level.ServerLevel#getMapData
final MapItemSavedData map = storage.readSavedData(factory.deserializer(), factory.type(), id);

readSavedData here is returning null, presumably because the file doesn't exist. This is because id needs map_ added to the beginning of it, it's attempting to load #.dat which isn't what map files look like.

There's also a logic issue where map isn't reassigned to existing, so when the map is loaded for the first time it's not returned.

Here's my modified code I'm just remapping in a plugin as a POC that this is a fix - someone who can get Paper to compile on their PC can use it to make a proper fix.

public class PaperWorkaround {
    public static MapView getMap(Integer mapId){
        MapView map = null;
        String id = "map_" + mapId;
        try {
            final DimensionDataStorage storage = ((CraftServer) (Bukkit.getServer())).getServer().overworld().getDataStorage();
            net.minecraft.world.level.saveddata.SavedData existing = storage.cache.get(id);
            if (existing == null && !storage.cache.containsKey(id)) {
                final net.minecraft.world.level.saveddata.SavedData.Factory<MapItemSavedData> factory = MapItemSavedData.factory();
                Method method = DimensionDataStorage.class.getDeclaredMethod("a", Function.class, DataFixTypes.class, String.class);
                method.setAccessible(true);
                final MapItemSavedData ourMap = (MapItemSavedData) method.invoke(storage, factory.deserializer(), factory.type(), id);
                if (ourMap != null) {
                    ourMap.id = id;
                }

                storage.cache.put(id, ourMap);
                existing = ourMap;
            }
            map = existing instanceof MapItemSavedData data ? data.mapView : null;
        }catch (Exception e){
            e.printStackTrace();
        }
        return map;
    }
}

[electronicboy]

all calls to that method seem to properly prepend the id already?

[Warriorrrr]

Can you re-test this on build 213 or above?

[codeHusky]

As of build 213 it appears this particular issue has been fixed, the ImageMaps plugin now works without any patches.