Run versioned transformers on player data read and write

src/main/java/com/gtnewhorizons/postea/api/PlayerDataTransformContext.java

@@ -1,8 +1,55 @@
 package com.gtnewhorizons.postea.api;
 
+import java.util.function.Consumer;
+
+import net.minecraft.entity.player.EntityPlayerMP;
+import net.minecraft.nbt.NBTTagCompound;
+
+import com.gtnewhorizons.postea.utility.NbtItemStacks;
 import com.gtnewhorizons.postea.utility.VersionStamps;
 
+/**
+ * A player's saved data as handed to {@link IVersionedTransformer#transformPlayer}: the root tag about to be
+ * loaded into the player, which holds the inventory, ender chest, {@code ForgeData}, and every extended-properties
+ * compound. The player object is constructed but not yet loaded from the tag.
+ */
 public final class PlayerDataTransformContext {
 
     public static final int UNSTAMPED = VersionStamps.UNSTAMPED;
+
+    private final EntityPlayerMP player;
+    private final NBTTagCompound playerTag;
+    private final int storedVersion;
+    private final int currentVersion;
+
+    public PlayerDataTransformContext(EntityPlayerMP player, NBTTagCompound playerTag, int storedVersion,
+        int currentVersion) {
+        this.player = player;
+        this.playerTag = playerTag;
+        this.storedVersion = storedVersion;
+        this.currentVersion = currentVersion;
+    }
+
+    public EntityPlayerMP player() {
+        return player;
+    }
+
+    public NBTTagCompound playerTag() {
+        return playerTag;
+    }
+
+    public int storedVersion() {
+        return storedVersion;
+    }
+
+    public int currentVersion() {
+        return currentVersion;
+    }
+
+    /**
+     * Visits every serialized item stack anywhere in the player's data; see {@link NbtItemStacks#forEach}.
+     */
+    public void forEachItemStackTag(Consumer<NBTTagCompound> visitor) {
+        NbtItemStacks.forEach(playerTag, visitor);
+    }
 }

src/main/java/com/gtnewhorizons/postea/mixins/PosteaLoadingPlugin.java

@@ -45,6 +45,7 @@ public final class PosteaLoadingPlugin implements IEarlyMixinLoader, IFMLLoading
         final List<String> mixins = new ArrayList<>();
         mixins.add("MixinItemStack");
         mixins.add("MixinChunk");
+        mixins.add("MixinEntity");
         mixins.add("MixinAnvilChunkLoader");
         mixins.add("MixinNBTTagList");
         return mixins;

src/main/java/com/gtnewhorizons/postea/mixins/early/MixinEntity.java

@@ -0,0 +1,34 @@
+package com.gtnewhorizons.postea.mixins.early;
+
+import net.minecraft.entity.Entity;
+import net.minecraft.entity.player.EntityPlayerMP;
+import net.minecraft.nbt.NBTTagCompound;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import com.gtnewhorizons.postea.utility.PlayerDataFixerUtility;
+
+@Mixin(Entity.class)
+public abstract class MixinEntity {
+
+    @Unique
+    private NBTTagCompound postea$versionStamps;
+
+    @Inject(method = "readFromNBT", at = @At("HEAD"), require = 1)
+    private void postea$transformPlayerData(NBTTagCompound tag, CallbackInfo ci) {
+        if ((Object) this instanceof EntityPlayerMP player) {
+            postea$versionStamps = PlayerDataFixerUtility.onPlayerRead(player, tag);
+        }
+    }
+
+    @Inject(method = "writeToNBT", at = @At("RETURN"), require = 1)
+    private void postea$stampPlayerData(NBTTagCompound tag, CallbackInfo ci) {
+        if ((Object) this instanceof EntityPlayerMP) {
+            PlayerDataFixerUtility.onPlayerWrite(tag, postea$versionStamps);
+        }
+    }
+}

src/main/java/com/gtnewhorizons/postea/utility/PlayerDataFixerUtility.java

@@ -0,0 +1,55 @@
+package com.gtnewhorizons.postea.utility;
+
+import net.minecraft.entity.player.EntityPlayerMP;
+import net.minecraft.nbt.NBTTagCompound;
+import net.minecraft.util.ReportedException;
+
+import com.gtnewhorizons.postea.Postea;
+import com.gtnewhorizons.postea.api.IVersionedTransformer;
+import com.gtnewhorizons.postea.api.PlayerDataTransformContext;
+import com.gtnewhorizons.postea.api.VersionedReplacementManager;
+
+/**
+ * Runs versioned transformers over a server player's NBT as it is read, and stamps it as it is written. Hooked on
+ * {@code Entity.readFromNBT}/{@code writeToNBT} so both the {@code playerdata/<uuid>.dat} files and the
+ * single-player host's copy inside {@code level.dat} are covered.
+ */
+public final class PlayerDataFixerUtility {
+
+    private PlayerDataFixerUtility() {}
+
+    /**
+     * Transforms {@code tag} in place and returns a copy of the stamps it carried (null when unstamped).
+     */
+    public static NBTTagCompound onPlayerRead(EntityPlayerMP player, NBTTagCompound tag) {
+        NBTTagCompound stamps = VersionStamps.read(tag);
+        for (IVersionedTransformer transformer : VersionedReplacementManager.transformers()) {
+            int current = transformer.currentVersion();
+            int stored = VersionStamps.stored(stamps, transformer.key());
+            if (stored == current) continue;
+            Postea.LOG.debug(
+                "{}: player {} from version {} to {}",
+                transformer.key(),
+                player.getCommandSenderName(),
+                stored,
+                current);
+            try {
+                transformer.transformPlayer(new PlayerDataTransformContext(player, tag, stored, current));
+            } catch (Throwable t) {
+                throw new ReportedException(
+                    ChunkFixerUtility.describe(
+                        t,
+                        transformer,
+                        stored,
+                        current,
+                        "Player",
+                        player.getCommandSenderName() + " (" + player.getUniqueID() + ")"));
+            }
+        }
+        return stamps == null ? null : (NBTTagCompound) stamps.copy();
+    }
+
+    public static void onPlayerWrite(NBTTagCompound tag, NBTTagCompound carried) {
+        VersionStamps.write(tag, carried, VersionedReplacementManager.transformers());
+    }
+}

src/main/resources/mixins.postea.early.json

@@ -8,6 +8,7 @@
   "mixins": [
     "MixinAnvilChunkLoader",
     "MixinChunk",
+    "MixinEntity",
     "MixinItemStack",
     "MixinNBTTagList"
   ],