Fix skins of server-only NPCs being unreliable (fixes #486)

src/main/java/com/replaymod/replay/mixin/Mixin_FixNPCSkinCaching.java

@@ -0,0 +1,31 @@
+package com.replaymod.replay.mixin;
+
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.client.network.AbstractClientPlayerEntity;
+import net.minecraft.client.network.PlayerListEntry;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import javax.annotation.Nullable;
+
+@Mixin(AbstractClientPlayerEntity.class)
+public abstract class Mixin_FixNPCSkinCaching {
+    @Shadow @Nullable protected abstract PlayerListEntry getPlayerListEntry();
+
+    @Inject(method = "<init>", at = @At("RETURN"))
+    private void forceCachePlayerListEntry(CallbackInfo ci) {
+        // Server-side NPCs (without a client mod) rely on the player list entry being cached in this class to function
+        // because the remove the entry shortly after spawning the player. However this method is only called when the
+        // player is rendered, and if we are currently jumping around in a replay then it most likely will not be
+        // rendered while the entry is still there. The result is that most NPCs get Steve/Alex skins instead of the
+        // intended ones. To fix that, we make this caching-glitch which servers have come to rely on an actual feature
+        // by just fetching the cache in the constructor which arguably is what MC should have done to begin with,
+        // especially because the spawn packet handling code already requires the entry to be present).
+        if (MinecraftClient.getInstance().getNetworkHandler() != null) { // will be null if this is the client player
+            this.getPlayerListEntry();
+        }
+    }
+}