A few *small* changes and a fix.

.gitignore

@@ -103,6 +103,7 @@ $RECYCLE.BIN/
 
 .gradle
 build/
+remappedSrc
 
 # Ignore Gradle GUI config
 gradle-app.setting

build.gradle

@@ -21,6 +21,10 @@ processResources {
     }
 }
 
+loom {
+    accessWidenerPath = file("src/main/resources/moddetectionpreventer.accesswidener");
+}
+
 def targetJavaVersion = 17
 tasks.withType(JavaCompile).configureEach {
     it.options.encoding = "UTF-8"

gradle.properties

@@ -1,8 +1,8 @@
 org.gradle.jvmargs=-Xmx1G
 
-minecraft_version=1.20.4
-yarn_mappings=1.20.4+build.3
-loader_version=0.15.7
+minecraft_version=1.21.1
+yarn_mappings=1.21.1+build.3
+loader_version=0.16.9
 
-mod_version = 1.2.0
+mod_version = 2.0.1
 archives_base_name = ModDetectionPreventer

src/main/java/me/wolfii/moddetectionpreventer/ModDetectionPreventer.java

@@ -0,0 +1,18 @@
+package me.wolfii.moddetectionpreventer;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public final class ModDetectionPreventer {
+    private ModDetectionPreventer() { throw new UnsupportedOperationException("Consider this class abstract-final"); }
+
+    public static Logger LOGGER = LoggerFactory.getLogger("ModDetectionPreventer");
+
+
+    /// Called when the server tries to abuse the exploit.
+    public static void warnAccess(String action, String kind, String key) {
+        LOGGER.warn("{} incoming request for {} `{}`", action, kind, key);
+    }
+
+}

src/main/java/me/wolfii/moddetectionpreventer/mixin/antidetection/AbstractSignEditScreenMixin.java

@@ -0,0 +1,32 @@
+package me.wolfii.moddetectionpreventer.mixin.antidetection;
+
+import com.llamalad7.mixinextras.injector.wrapoperation.Operation;
+import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
+import me.wolfii.moddetectionpreventer.text.CombinedFilter;
+import net.minecraft.client.gui.screen.ingame.AbstractSignEditScreen;
+import net.minecraft.text.Text;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+
+/// Catches incoming sign screens, filtering out components.
+@Mixin(AbstractSignEditScreen.class)
+class AbstractSignEditScreenMixin {
+
+    @WrapOperation(
+            method = "<init>(Lnet/minecraft/block/entity/SignBlockEntity;ZZLnet/minecraft/text/Text;)V",
+            at     = @At(
+                    value  = "INVOKE",
+                    target = "Ljava/util/stream/Stream;map(Ljava/util/function/Function;)Ljava/util/stream/Stream;"
+            )
+    )
+    private Stream<String> preventSignModDetection(Stream<Text> instance, Function<Text, String> function, Operation<Stream<String>> original) {
+        return original.call(
+                instance.map(CombinedFilter::filterComponents),
+                function
+        );
+    }
+}

src/main/java/me/wolfii/moddetectionpreventer/mixin/antidetection/AnvilEditScreenMixin.java

@@ -0,0 +1,38 @@
+package me.wolfii.moddetectionpreventer.mixin.antidetection;
+
+import com.llamalad7.mixinextras.injector.wrapoperation.Operation;
+import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
+import me.wolfii.moddetectionpreventer.text.CombinedFilter;
+import net.minecraft.client.gui.screen.ingame.AnvilScreen;
+import net.minecraft.text.Text;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+
+
+/// Catches incoming anvil screens, filtering out components.
+@Mixin(AnvilScreen.class)
+class AnvilEditScreenMixin {
+
+    @WrapOperation(
+            method = "onSlotUpdate",
+            at     = @At(
+                    value  = "INVOKE",
+                    target = "Lnet/minecraft/text/Text;getString()Ljava/lang/String;"
+            )
+    )
+    private String preventAnvilItemNameChangeModDetection(Text instance, Operation<String> original) {
+        return original.call(CombinedFilter.filterComponents(instance));
+    }
+
+    @WrapOperation(
+            method = "onRenamed",
+            at     = @At(
+                    value  = "INVOKE",
+                    target = "Lnet/minecraft/text/Text;getString()Ljava/lang/String;"
+            )
+    )
+    private String preventAnvilItemNameCheckModDetection(Text instance, Operation<String> original) {
+        return original.call(CombinedFilter.filterComponents(instance));
+    }
+
+}

src/main/java/me/wolfii/moddetectionpreventer/mixin/antidetection/AnvilScreenHandlerMixin.java

@@ -0,0 +1,27 @@
+package me.wolfii.moddetectionpreventer.mixin.antidetection;
+
+import com.llamalad7.mixinextras.injector.wrapoperation.Operation;
+import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
+import me.wolfii.moddetectionpreventer.text.CombinedFilter;
+import net.minecraft.screen.AnvilScreenHandler;
+import net.minecraft.text.Text;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+
+
+/// Catches incoming anvil screens, filtering out components.
+@Mixin(AnvilScreenHandler.class)
+class AnvilScreenHandlerMixin {
+
+    @WrapOperation(
+            method = "updateResult",
+            at     = @At(
+                    value  = "INVOKE",
+                    target = "Lnet/minecraft/text/Text;getString()Ljava/lang/String;"
+            )
+    )
+    private String preventAnvilModDetection(Text instance, Operation<String> original) {
+        return original.call(CombinedFilter.filterComponents(instance));
+    }
+
+}

src/main/java/me/wolfii/moddetectionpreventer/mixin/datagetter/GameOptionsMixin.java

@@ -0,0 +1,79 @@
+package me.wolfii.moddetectionpreventer.mixin.datagetter;
+
+import com.llamalad7.mixinextras.injector.wrapoperation.Operation;
+import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
+import me.wolfii.moddetectionpreventer.ModDetectionPreventer;
+import me.wolfii.moddetectionpreventer.text.KeybindFilter;
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.client.option.GameOptions;
+import net.minecraft.client.option.KeyBinding;
+import net.minecraft.client.option.StickyKeyBinding;
+import net.minecraft.client.util.InputUtil;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import java.io.File;
+import java.util.function.BooleanSupplier;
+
+
+@Mixin(GameOptions.class)
+class GameOptionsMixin {
+
+    /// When the vanilla keybindings start loading, reset the list of keybindings to pass through.
+    @Inject(
+            method = "<init>",
+            at     = @At(
+                    value  = "INVOKE",
+                    target = "Ljava/lang/Object;<init>()V",
+                    shift  = At.Shift.AFTER
+            )
+    )
+    private void resetAllowedKeys(MinecraftClient client, File optionsFile, CallbackInfo ci) {
+        KeybindFilter.unfilteredKeybindings.clear();
+    }
+
+    /// When the vanilla keybindings are initialised, keep a record of them.
+    @WrapOperation(
+            method = "<init>",
+            at     = @At(
+                    value  = "NEW",
+                    target = "(Ljava/lang/String;Lnet/minecraft/client/util/InputUtil$Type;ILjava/lang/String;)Lnet/minecraft/client/option/KeyBinding;"
+            )
+    )
+    private KeyBinding getAllowedKeys0(String translationKey, InputUtil.Type type, int code, String category, Operation<KeyBinding> original) {
+        KeyBinding keybinding = original.call(translationKey, type, code, category);
+        KeybindFilter.unfilteredKeybindings.put(translationKey, keybinding);
+        return keybinding;
+    }
+
+    /// When the vanilla keybindings are initialised, keep a record of them.
+    @WrapOperation(
+            method = "<init>",
+            at     = @At(
+                    value  = "NEW",
+                    target = "(Ljava/lang/String;ILjava/lang/String;)Lnet/minecraft/client/option/KeyBinding;"
+            )
+    )
+    private KeyBinding getAllowedKeys1(String translationKey, int code, String category, Operation<KeyBinding> original) {
+        KeyBinding keybinding = original.call(translationKey, code, category);
+        KeybindFilter.unfilteredKeybindings.put(translationKey, keybinding);
+        return keybinding;
+    }
+
+    /// When the vanilla keybindings are initialised, keep a record of them.
+    @WrapOperation(
+            method = "<init>",
+            at     = @At(
+                    value  = "NEW",
+                    target = "(Ljava/lang/String;ILjava/lang/String;Ljava/util/function/BooleanSupplier;)Lnet/minecraft/client/option/StickyKeyBinding;"
+            )
+    )
+    private StickyKeyBinding getAllowedKeys2(String translationKey, int code, String category, BooleanSupplier toggleGetter, Operation<StickyKeyBinding> original) {
+        StickyKeyBinding keybinding = original.call(translationKey, code, category, toggleGetter);
+        KeybindFilter.unfilteredKeybindings.put(translationKey, keybinding);
+        return keybinding;
+    }
+
+}