Bump version to 5.1.10 for release

and publishing it, but we don't talk about that

.github/workflows/ci.yml

@@ -22,9 +22,16 @@ jobs:
           distribution: 'temurin'
           java-version: '21'
 
-      # TODO convert to a Gradle plugin later for portability
-      - name: Install Spigot dependency
-        run: ./scripts/install_spigot.sh 1.21.4
+      # We can't use 'maven' prebuilt cache setup because it requires that the project have a pom file.
+      # BuildTools installs to Maven local if available, so it's easier to just rely on that.
+      - name: Cache Spigot dependency
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.m2/repository/org/spigotmc/
+          key: ${{ runner.os }}-buildtools-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-buildtools-
 
       - uses: gradle/actions/setup-gradle@v4
 

.github/workflows/draft_release.yml

@@ -24,17 +24,11 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:
-          name: ${{ env.VERSIONED_NAME }}
-          # May actually want to manually specify Paper versions all the time; they won't all
-          # need to be specified in code thanks to Mojang-mapped server internals.
-          # A bit annoying, but not terribly so.
-          # Instead, fetch min and max (which will also be Spigot version) and manually list intermediate versions?
+          name: OpenInv ${{ env.VERSIONED_NAME }}
           body: |-
             ## Supported server versions
-            ### Paper
-            TODO COMMA-SEPARATED VERSIONS
-            ### Spigot
-            TODO VERSION
+            **Paper:** TODO VERSION, 1.21.4, 1.21.3, 1.21.1
+            **Spigot:** TODO VERSION
             
             TODO HELLO HUMAN, PRESS THE GENERATE CHANGELOG BUTTON PLEASE.
           draft: true

README.MD

@@ -45,10 +45,7 @@ The OpenInv API is available via [JitPack](https://jitpack.io/).
 Note that since JitPack only builds the API now, the "full" OpenInv jar on JitPack is actually the openinvapi artifact. This is a change from previous dependency declaration that I hope to revert.
 
 ### Compilation
-To compile, the relevant Spigot jar must be installed in the local repository.
-As OpenInv is compiled against Mojang's mappings, you must run BuildTools with the `--remapped` argument:  
-`java -jar BuildTools.jar --remapped --rev $serverVersion`  
-`$serverVersion` is the version of the server, i.e. `1.21.4`
-
-Once Spigot is installed, execute the gradle wrapper:  
+Execute the gradle wrapper:  
 `./gradlew build`
+
+If you encounter issues with building the Spigot module, try running BuildTools manually.

api/build.gradle.kts

@@ -8,6 +8,7 @@ publishing {
     create<MavenPublication>("jitpack") {
       groupId = "com.github.Jikoo.OpenInv"
       artifactId = "openinvapi"
+      from(components["java"])
     }
   }
 }

buildSrc/build.gradle.kts

@@ -4,4 +4,10 @@ plugins {
 
 repositories {
   gradlePluginPortal()
+  mavenCentral()
+}
+
+dependencies {
+  val libs = project.extensions.getByType(VersionCatalogsExtension::class.java).named("libs")
+  implementation(libs.findLibrary("specialsource").orElseThrow())
 }

buildSrc/settings.gradle.kts

@@ -0,0 +1,7 @@
+dependencyResolutionManagement {
+  versionCatalogs {
+    create("libs") {
+      from(files("../gradle/libs.versions.toml"))
+    }
+  }
+}

buildSrc/src/main/kotlin/ReobfTask.kt

@@ -1,60 +0,0 @@
-import org.gradle.api.file.RegularFile
-import org.gradle.api.provider.Property
-import org.gradle.api.tasks.Input
-import org.gradle.api.tasks.InputFile
-import org.gradle.api.tasks.TaskAction
-import org.gradle.api.tasks.bundling.Jar
-import java.io.File
-import java.nio.file.Path
-import java.nio.file.Paths
-
-abstract class ReobfTask: Jar() {
-
-  @get:Input
-  open val spigotVersion: Property<String> = objectFactory.property(String::class.java)
-
-  @get:InputFile
-  open val inputFile: Property<RegularFile> = objectFactory.fileProperty()
-
-  @get:Input
-  open val intermediaryClassifier: Property<String> = objectFactory.property(String::class.java).convention("mojang-mapped")
-
-  init {
-    archiveClassifier.convention("reobf")
-  }
-
-  @TaskAction
-  override fun copy() {
-    val spigotVer = spigotVersion.get()
-    val inFile = inputFile.get().asFile
-    val obfPath = inFile.resolveSibling(inFile.name.replace(".jar", "-${intermediaryClassifier.get()}.jar"))
-
-    // https://www.spigotmc.org/threads/510208/#post-4184317
-    val specialsource = project.configurations.named("spigotRemap").get().incoming.artifacts.artifacts
-      .first { it.id.componentIdentifier.toString() == "net.md-5:SpecialSource:1.11.4" }.file.path
-    val repo = Paths.get(project.repositories.mavenLocal().url)
-    val spigotDir = repo.resolve("org/spigotmc/spigot/$spigotVer/")
-    val mappingDir = repo.resolve("org/spigotmc/minecraft-server/$spigotVer/")
-
-    // Remap original Mojang-mapped jar to obfuscated intermediary
-    val mojangServer = spigotDir.resolve("spigot-$spigotVer-remapped-mojang.jar")
-    val mojangMappings = mappingDir.resolve("minecraft-server-$spigotVer-maps-mojang.txt")
-    remapPartial(specialsource, mojangServer, mojangMappings, inFile, obfPath, true)
-
-    // Remap obfuscated intermediary jar to Spigot and replace original
-    val obfServer = spigotDir.resolve("spigot-$spigotVer-remapped-obf.jar")
-    val spigotMappings = mappingDir.resolve("minecraft-server-$spigotVer-maps-spigot.csrg")
-    remapPartial(specialsource, obfServer, spigotMappings, obfPath, archiveFile.get().asFile, false)
-  }
-
-  private fun remapPartial(specialSource: String, serverJar: Path, mapping: Path, input: File, output: File, reverse: Boolean) {
-    project.providers.exec {
-      commandLine("java", "-cp", "$specialSource${File.pathSeparator}$serverJar",
-        "net.md_5.specialsource.SpecialSource", "--live",
-        "-i", input.path, "-o", output.path,
-        "-m", "$mapping",
-        if (reverse) "--reverse" else "")
-    }.result.get()
-  }
-
-}

buildSrc/src/main/kotlin/com/github/jikoo/openinv/BuildToolsValueSource.kt

@@ -0,0 +1,98 @@
+package com.github.jikoo.openinv
+
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.provider.Property
+import org.gradle.api.provider.ValueSource
+import org.gradle.api.provider.ValueSourceParameters
+import org.gradle.process.ExecOperations
+import java.io.File
+import java.net.URI
+import java.nio.file.Files
+import javax.inject.Inject
+
+abstract class BuildToolsValueSource: ValueSource<File, BuildToolsValueSource.Parameters> {
+
+  @get:Inject
+  abstract val exec: ExecOperations
+
+  interface Parameters: ValueSourceParameters {
+    val mavenLocal: Property<File>
+    val workingDir: DirectoryProperty
+
+    val spigotVersion: Property<String>
+    val spigotRevision: Property<String>
+
+    val ignoreCached: Property<Boolean>
+
+    val javaHome: DirectoryProperty
+    val javaExecutable: Property<String>
+  }
+
+  override fun obtain(): File {
+    val version = parameters.spigotVersion.get()
+    val revision = parameters.spigotRevision.get()
+    val installLocation = getInstallLocation(version)
+    // If Spigot is already installed, don't reinstall.
+    if (!parameters.ignoreCached.get() && installLocation.exists()) {
+      println("Skipping Spigot installation, $version is present")
+      return installLocation
+    }
+
+    val buildTools = installBuildTools(parameters.workingDir.get().asFile)
+
+    println("Installing Spigot $version (rev $revision)")
+
+    exec.javaexec {
+      environment["JAVA_HOME"] = parameters.javaHome.get()
+      executable = parameters.javaExecutable.get()
+      workingDir = buildTools.parentFile
+      classpath(buildTools)
+      args = listOf("--nogui", "--rev", revision, "--remapped")
+    }.rethrowFailure()
+
+    // Mark work for delete.
+    cleanUp(buildTools.parentFile)
+
+    if (!installLocation.exists()) {
+      throw IllegalStateException(
+        "Failed to install Spigot $version from $revision. Does the revision point to a different version?")
+    }
+    return installLocation
+  }
+
+  private fun getInstallLocation(version: String): File {
+    return parameters.mavenLocal.get().resolve("org/spigotmc/spigot/$version/spigot-$version-remapped-mojang.jar")
+  }
+
+  private fun installBuildTools(workingDir: File): File {
+    val buildTools = workingDir.resolve("BuildTools.jar")
+    if (buildTools.exists()) {
+      return buildTools
+    }
+
+    workingDir.mkdirs()
+
+    val buildToolsUrl = "https://hub.spigotmc.org/jenkins/job/BuildTools/lastSuccessfulBuild/artifact/target/BuildTools.jar"
+    println("Downloading $buildToolsUrl")
+    val stream = URI.create(buildToolsUrl).toURL().openStream()
+    Files.copy(stream, buildTools.toPath())
+    stream.close()
+
+    return buildTools
+  }
+
+  private fun cleanUp(dir: File) {
+    dir.deleteOnExit()
+    if (!dir.isDirectory) {
+      return
+    }
+
+    dir.listFiles()?.forEach {
+      if (it.isDirectory) {
+        cleanUp(it)
+      } else {
+        it.deleteOnExit()
+      }
+    }
+  }
+}

buildSrc/src/main/kotlin/com/github/jikoo/openinv/SpigotDependencyExtension.kt

@@ -0,0 +1,21 @@
+package com.github.jikoo.openinv
+
+import org.gradle.api.model.ObjectFactory
+import org.gradle.jvm.toolchain.JavaToolchainSpec
+
+abstract class SpigotDependencyExtension (
+  objects: ObjectFactory
+) {
+
+  val version = objects.property(String::class.java)
+  val revision = objects.property(String::class.java)
+    .convention(version.map {
+      it.replace("-R\\d+\\.\\d+-SNAPSHOT".toRegex(), "")
+    })
+  val configuration = objects.property(String::class.java)
+  val classifier = objects.property(String::class.java).convention("remapped-mojang")
+  val ext = objects.property(String::class.java)
+  val java = objects.property(JavaToolchainSpec::class.java)
+  val ignoreCached = objects.property(Boolean::class.java).convention(false)
+
+}

buildSrc/src/main/kotlin/com/github/jikoo/openinv/SpigotReobf.kt

@@ -0,0 +1,56 @@
+package com.github.jikoo.openinv
+
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.attributes.Bundling
+import org.gradle.api.attributes.Category
+import org.gradle.api.attributes.LibraryElements
+import org.gradle.api.attributes.Usage
+import org.gradle.jvm.tasks.Jar
+import org.gradle.kotlin.dsl.named
+import org.gradle.kotlin.dsl.register
+import java.nio.file.Paths
+
+class SpigotReobf: Plugin<Project> {
+
+  companion object {
+    const val ARTIFACT_CONFIG = "reobf"
+  }
+
+  override fun apply(target: Project) {
+    // Re-use extension from Spigot dependency declaration if available to reduce configuration requirements.
+    val spigotExt = target.dependencies.extensions.findByType(SpigotDependencyExtension::class.java)
+      ?: target.dependencies.extensions.create(
+        "spigot",
+        SpigotDependencyExtension::class.java,
+        target.objects
+      )
+
+    val mvnLocal = target.repositories.mavenLocal()
+
+    val reobfTask = target.tasks.register<SpigotReobfTask>("reobfTask") {
+      dependsOn(target.tasks.named("shadowJar"))
+      // ShadowJar extends Jar, so this should be a safe way to get the result without having
+      // to jump through hoops and shift around shadow declarations in the rest of the project.
+      inputFile.convention(target.tasks.named<Jar>("shadowJar").get().archiveFile)
+      spigotVersion.convention(spigotExt.version)
+      getMavenLocal().set(Paths.get(mvnLocal.url).toFile())
+    }
+
+    // Set up configuration for producing reobf jar.
+    target.configurations.consumable(ARTIFACT_CONFIG) {
+      attributes {
+        attribute(Category.CATEGORY_ATTRIBUTE, target.objects.named(Category.LIBRARY))
+        attribute(Usage.USAGE_ATTRIBUTE, target.objects.named(Usage.JAVA_RUNTIME))
+        attribute(Bundling.BUNDLING_ATTRIBUTE, target.objects.named(Bundling.EXTERNAL))
+        attribute(LibraryElements.LIBRARY_ELEMENTS_ATTRIBUTE, target.objects.named(LibraryElements.JAR))
+      }
+    }
+
+    // Add artifact from reobf task.
+    target.artifacts {
+      add(ARTIFACT_CONFIG, reobfTask)
+    }
+  }
+
+}

buildSrc/src/main/kotlin/com/github/jikoo/openinv/SpigotReobfTask.kt

@@ -0,0 +1,85 @@
+package com.github.jikoo.openinv
+
+import net.md_5.specialsource.Jar
+import net.md_5.specialsource.JarMapping
+import net.md_5.specialsource.JarRemapper
+import net.md_5.specialsource.RemapperProcessor
+import net.md_5.specialsource.provider.JarProvider
+import net.md_5.specialsource.provider.JointProvider
+import org.gradle.api.file.RegularFileProperty
+import org.gradle.api.provider.Property
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.InputFile
+import org.gradle.api.tasks.Internal
+import org.gradle.api.tasks.TaskAction
+import java.io.File
+
+abstract class SpigotReobfTask: org.gradle.api.tasks.bundling.Jar() {
+
+  @get:Input
+  val spigotVersion: Property<String> = objectFactory.property(String::class.java)
+
+  @get:InputFile
+  val inputFile: RegularFileProperty = objectFactory.fileProperty()
+
+  @get:Input
+  val intermediaryClassifier: Property<String> = objectFactory.property(String::class.java).convention("mojang-mapped")
+
+  private val mavenLocal: Property<File> = objectFactory.property(File::class.java)
+
+  init {
+    archiveClassifier.convention(SpigotReobf.ARTIFACT_CONFIG)
+  }
+
+  @TaskAction
+  override fun copy() {
+    val spigotVer = spigotVersion.get()
+    val inFile = inputFile.get().asFile
+    val obfPath = inFile.resolveSibling(inFile.name.replace(".jar", "-${intermediaryClassifier.get()}.jar"))
+
+    // https://www.spigotmc.org/threads/510208/#post-4184317
+    val repo = mavenLocal.get()
+    val spigotDir = repo.resolve("org/spigotmc/spigot/$spigotVer/")
+    val mappingDir = repo.resolve("org/spigotmc/minecraft-server/$spigotVer/")
+
+    // Remap original Mojang-mapped jar to obfuscated intermediary
+    val mojangServer = spigotDir.resolve("spigot-$spigotVer-remapped-mojang.jar")
+    val mojangMappings = mappingDir.resolve("minecraft-server-$spigotVer-maps-mojang.txt")
+    remapPartial(mojangServer, mojangMappings, inFile, obfPath, true)
+
+    // Remap obfuscated intermediary jar to Spigot and replace original
+    val obfServer = spigotDir.resolve("spigot-$spigotVer-remapped-obf.jar")
+    val spigotMappings = mappingDir.resolve("minecraft-server-$spigotVer-maps-spigot.csrg")
+    remapPartial(obfServer, spigotMappings, obfPath, archiveFile.get().asFile, false)
+  }
+
+  private fun remapPartial(server: File, mapping: File, input: File, output: File, reverse: Boolean) {
+    val jarMapping = JarMapping()
+    jarMapping.loadMappings(mapping.path, reverse, false, null, null)
+
+    val inheritance = JointProvider()
+    jarMapping.setFallbackInheritanceProvider(inheritance)
+
+    // Equivalent of --live with server jar on classpath.
+    val serverJar = Jar.init(server)
+    inheritance.add(JarProvider(serverJar))
+
+    val inputJar = Jar.init(input)
+    inheritance.add(JarProvider(inputJar))
+
+    // Remap reflective access.
+    val preprocessor = RemapperProcessor(null, jarMapping, null)
+
+    val remapper = JarRemapper(preprocessor, jarMapping, null)
+    remapper.remapJar(inputJar, output, emptySet())
+
+    serverJar.close()
+    inputJar.close()
+  }
+
+  @Internal
+  internal fun getMavenLocal(): Property<File> {
+    return mavenLocal
+  }
+
+}

buildSrc/src/main/kotlin/com/github/jikoo/openinv/SpigotSetup.kt

@@ -0,0 +1,59 @@
+package com.github.jikoo.openinv
+
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.plugins.JavaPluginExtension
+import org.gradle.jvm.toolchain.JavaToolchainService
+import org.gradle.kotlin.dsl.create
+import java.nio.file.Paths
+import javax.inject.Inject
+
+abstract class SpigotSetup: Plugin<Project> {
+
+  @get:Inject
+  abstract val javaToolchainService: JavaToolchainService
+
+  override fun apply(target: Project) {
+    target.plugins.apply("java")
+
+    // Set up extension for configuring Spigot dependency.
+    val spigotExt = target.dependencies.extensions.findByType(SpigotDependencyExtension::class.java)
+      ?: target.dependencies.extensions.create(
+        "spigot",
+        SpigotDependencyExtension::class.java,
+        target.objects
+      )
+
+    val mvnLocal = target.repositories.mavenLocal()
+
+    target.afterEvaluate {
+      // Get Java requirements, defaulting to version used for compilation.
+      spigotExt.java.convention(target.extensions.getByType(JavaPluginExtension::class.java).toolchain)
+      val launcher = javaToolchainService.launcherFor(spigotExt.java.get()).get()
+
+      // Install Spigot with BuildTools.
+      target.providers.of(BuildToolsValueSource::class.java) {
+        parameters {
+          mavenLocal.set(Paths.get(mvnLocal.url).toFile())
+          workingDir.set(target.layout.buildDirectory.dir("tmp/buildtools"))
+          spigotVersion.set(spigotExt.version)
+          spigotRevision.set(spigotExt.revision)
+          ignoreCached.set(spigotExt.ignoreCached)
+          javaHome.set(launcher.metadata.installationPath)
+          javaExecutable.set(launcher.executablePath.asFile.path)
+        }
+      }.get()
+
+      // Add Spigot dependency.
+      val dependency = target.dependencies.create(
+        "org.spigotmc",
+        "spigot",
+        spigotExt.version.get(),
+        spigotExt.configuration.orNull,
+        spigotExt.classifier.orNull,
+        spigotExt.ext.orNull)
+      target.dependencies.add("compileOnly", dependency)
+    }
+  }
+
+}

gradle.properties

@@ -1,6 +1,6 @@
 # Project meta
 group=com.lishid.openinv
-version=5.1.9
+version=5.1.10
 description=A Bukkit plugin for opening normally-inaccessible inventories.
 
 # Gradle configuration

gradle/libs.versions.toml

@@ -1,16 +1,18 @@
 [versions]
-spigotapi = "1.21.4-R0.1-SNAPSHOT"
-specialsource = "1.11.4"
+spigotapi = "1.21.5-R0.1-SNAPSHOT"
+specialsource = "1.11.5"
 planarwrappers = "3.3.0"
 annotations = "26.0.2"
-paperweight = "2.0.0-beta.14"
+paperweight = "2.0.0-beta.16"
 shadow = "8.3.6"
+folia-scheduler-wrapper = "v0.0.3"
 
 [libraries]
 spigotapi = { module = "org.spigotmc:spigot-api", version.ref = "spigotapi" }
 specialsource = { module = "net.md-5:SpecialSource", version.ref = "specialsource" }
 planarwrappers = { module = "com.github.jikoo:planarwrappers", version.ref = "planarwrappers" }
 annotations = { module = "org.jetbrains:annotations", version.ref = "annotations" }
+folia-scheduler-wrapper = { module = "com.github.NahuLD.folia-scheduler-wrapper:folia-scheduler-wrapper", version.ref = "folia-scheduler-wrapper" }
 
 [plugins]
 paperweight = { id = "io.papermc.paperweight.userdev", version.ref = "paperweight" }

internal/common/build.gradle.kts

@@ -33,7 +33,7 @@ dependencies {
   implementation(project(":openinvapi"))
   implementation(project(":openinvcommon"))
 
-  paperweight.paperDevBundle("1.21.4-R0.1-SNAPSHOT")
+  paperweight.paperDevBundle("1.21.5-R0.1-SNAPSHOT")
 }
 
 val spigot = tasks.register<ShadowJar>("spigotRelocations") {

internal/common/src/main/java/com/lishid/openinv/internal/common/container/OpenInventory.java

@@ -16,6 +16,7 @@ import com.lishid.openinv.internal.common.container.slot.ContentViewOnly;
 import com.lishid.openinv.internal.common.container.slot.SlotViewOnly;
 import com.lishid.openinv.internal.common.container.slot.placeholder.Placeholders;
 import com.lishid.openinv.internal.common.player.PlayerManager;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
 import net.minecraft.ChatFormatting;
 import net.minecraft.core.NonNullList;
 import net.minecraft.network.chat.Component;
@@ -38,13 +39,15 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
+import java.util.Comparator;
 import java.util.List;
+import java.util.Map;
 
 public class OpenInventory implements Container, InternalOwned<ServerPlayer>, ISpecialPlayerInventory {
 
-  private final List<Content> slots;
+  protected final List<Content> slots;
   private final int size;
-  private ServerPlayer owner;
+  protected ServerPlayer owner;
   private int maxStackSize = 99;
   private CraftInventory bukkitEntity;
   public List<HumanEntity> transaction = new ArrayList<>();
@@ -60,15 +63,14 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
     setupSlots();
   }
 
-  private void setupSlots() {
+  protected void setupSlots() {
     // Top of inventory: Regular contents.
     int nextIndex = addMainInventory();
 
     // If inventory is expected size, we can arrange slots to be pretty.
     Inventory ownerInv = owner.getInventory();
-    if (ownerInv.items.size() == 36
-        && ownerInv.armor.size() == 4
-        && ownerInv.offhand.size() == 1
+    if (ownerInv.getNonEquipmentItems().size() == 36
+        && Inventory.EQUIPMENT_SLOT_MAPPING.size() == 5
         && owner.inventoryMenu.getCraftSlots().getContainerSize() == 4) {
       // Armor slots: Bottom left.
       addArmor(36);
@@ -95,7 +97,7 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
   }
 
   private int addMainInventory() {
-    int listSize = owner.getInventory().items.size();
+    int listSize = owner.getInventory().getNonEquipmentItems().size();
     // Hotbar slots are 0-8. We want those to appear on the bottom of the inventory like a normal player inventory,
     // so everything else needs to move up a row.
     int hotbarDiff = listSize - 9;
@@ -113,7 +115,7 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
       slots.set(localIndex, new ContentList(owner, invIndex, type) {
         @Override
         public void setHolder(@NotNull ServerPlayer holder) {
-          items = holder.getInventory().items;
+          items = holder.getInventory().getNonEquipmentItems();
         }
       });
     }
@@ -121,50 +123,36 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
   }
 
   private int addArmor(int startIndex) {
-    int listSize = owner.getInventory().armor.size();
-
-    for (int i = 0; i < listSize; ++i) {
-      // Armor slots go bottom to top; boots are slot 0, helmet is slot 3.
-      // Since we have to display horizontally due to space restrictions,
-      // making the left side the "top" is more user-friendly.
-      int armorIndex;
-      EquipmentSlot slot;
-      switch (i) {
-        case 3 -> {
-          armorIndex = 0;
-          slot = EquipmentSlot.FEET;
-        }
-        case 2 -> {
-          armorIndex = 1;
-          slot = EquipmentSlot.LEGS;
-        }
-        case 1 -> {
-          armorIndex = 2;
-          slot = EquipmentSlot.CHEST;
-        }
-        case 0 -> {
-          armorIndex = 3;
-          slot = EquipmentSlot.HEAD;
-        }
-        default -> {
-          // In the event that new armor slots are added, they can be placed at the end.
-          armorIndex = i;
-          slot = EquipmentSlot.MAINHAND;
-        }
+    // Armor slots go bottom to top; boots are first and helmet is last.
+    // Since we have to display horizontally due to space restrictions,
+    // making the left side the "top" is more user-friendly.
+    EquipmentSlot[] sorted = Inventory.EQUIPMENT_SLOT_MAPPING.int2ObjectEntrySet()
+        .stream()
+        .sorted(Comparator.comparingInt(Int2ObjectMap.Entry::getIntKey))
+        .map(Map.Entry::getValue)
+        .toArray(EquipmentSlot[]::new);
+    int localIndex = 0;
+    for (int i = sorted.length - 1; i >= 0; --i) {
+      // Skip off-hand, handled separately.
+      if (sorted[i] == EquipmentSlot.OFFHAND) {
+        continue;
       }
 
-      slots.set(startIndex + i, new ContentEquipment(owner, armorIndex, slot));
+      slots.set(startIndex + localIndex, new ContentEquipment(owner, sorted[i]));
+      ++localIndex;
     }
 
-    return startIndex + listSize;
+    return startIndex + localIndex;
   }
 
   private int addOffHand(int startIndex) {
-    int listSize = owner.getInventory().offhand.size();
-    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
-      slots.set(startIndex + localIndex, new ContentOffHand(owner, localIndex));
+    // No off-hand?
+    if (!Inventory.EQUIPMENT_SLOT_MAPPING.containsValue(EquipmentSlot.OFFHAND)) {
+      return startIndex;
     }
-    return startIndex + listSize;
+
+    slots.set(startIndex, new ContentOffHand(owner));
+    return startIndex + 1;
   }
 
   private int addCrafting(int startIndex, boolean pretty) {
@@ -280,22 +268,22 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
   }
 
   @Override
-  public ItemStack getItem(int index) {
+  public @NotNull ItemStack getItem(int index) {
     return slots.get(index).get();
   }
 
   @Override
-  public ItemStack removeItem(int index, int amount) {
+  public @NotNull ItemStack removeItem(int index, int amount) {
     return slots.get(index).removePartial(amount);
   }
 
   @Override
-  public ItemStack removeItemNoUpdate(int index) {
+  public @NotNull ItemStack removeItemNoUpdate(int index) {
     return slots.get(index).remove();
   }
 
   @Override
-  public void setItem(int index, ItemStack itemStack) {
+  public void setItem(int index, @NotNull ItemStack itemStack) {
     slots.get(index).set(itemStack);
   }
 
@@ -327,17 +315,17 @@ public class OpenInventory implements Container, InternalOwned<ServerPlayer>, IS
   }
 
   @Override
-  public void onOpen(CraftHumanEntity viewer) {
+  public void onOpen(@NotNull CraftHumanEntity viewer) {
     transaction.add(viewer);
   }
 
   @Override
-  public void onClose(CraftHumanEntity viewer) {
+  public void onClose(@NotNull CraftHumanEntity viewer) {
     transaction.remove(viewer);
   }
 
   @Override
-  public List<HumanEntity> getViewers() {
+  public @NotNull List<HumanEntity> getViewers() {
     return transaction;
   }
 

internal/common/src/main/java/com/lishid/openinv/internal/common/container/bukkit/OpenDummyPlayerInventory.java

@@ -22,12 +22,12 @@ public class OpenDummyPlayerInventory extends OpenDummyInventory implements Play
   }
 
   @Override
-  public @NotNull ItemStack[] getArmorContents() {
+  public @NotNull ItemStack @NotNull [] getArmorContents() {
     return new ItemStack[4];
   }
 
   @Override
-  public @NotNull ItemStack[] getExtraContents() {
+  public @NotNull ItemStack @NotNull [] getExtraContents() {
     return new ItemStack[4];
   }
 
@@ -57,17 +57,17 @@ public class OpenDummyPlayerInventory extends OpenDummyInventory implements Play
   }
 
   @Override
-  public @Nullable ItemStack getItem(@NotNull EquipmentSlot slot) {
-    return null;
+  public @NotNull ItemStack getItem(@NotNull EquipmentSlot slot) {
+    return new ItemStack(Material.AIR);
   }
 
   @Override
-  public void setArmorContents(@Nullable ItemStack[] items) {
+  public void setArmorContents(ItemStack @NotNull [] items) {
 
   }
 
   @Override
-  public void setExtraContents(@Nullable ItemStack[] items) {
+  public void setExtraContents(ItemStack @NotNull [] items) {
 
   }
 

internal/common/src/main/java/com/lishid/openinv/internal/common/container/bukkit/OpenPlayerInventory.java

@@ -14,6 +14,8 @@ import org.bukkit.inventory.PlayerInventory;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.List;
+
 public class OpenPlayerInventory extends CraftInventory implements PlayerInventory {
 
   public OpenPlayerInventory(@NotNull OpenInventory inventory) {
@@ -26,7 +28,7 @@ public class OpenPlayerInventory extends CraftInventory implements PlayerInvento
   }
 
   @Override
-  public ItemStack[] getContents() {
+  public ItemStack @NotNull [] getContents() {
     return asCraftMirror(getInventory().getOwnerHandle().getInventory().getContents());
   }
 
@@ -46,13 +48,13 @@ public class OpenPlayerInventory extends CraftInventory implements PlayerInvento
   }
 
   @Override
-  public ItemStack[] getStorageContents() {
-    return asCraftMirror(getInventory().getOwnerHandle().getInventory().items);
+  public ItemStack @NotNull [] getStorageContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getNonEquipmentItems());
   }
 
   @Override
   public void setStorageContents(ItemStack[] items) throws IllegalArgumentException {
-    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().items;
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().getNonEquipmentItems();
     int size = list.size();
     Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
     for (int index = 0; index < items.length; ++index) {
@@ -71,103 +73,104 @@ public class OpenPlayerInventory extends CraftInventory implements PlayerInvento
   }
 
   @Override
-  public @NotNull ItemStack[] getArmorContents() {
-    return asCraftMirror(getInventory().getOwnerHandle().getInventory().armor);
+  public @NotNull ItemStack @NotNull [] getArmorContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getArmorContents());
   }
 
   @Override
-  public void setArmorContents(@Nullable ItemStack[] items) {
-    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().armor;
-    int size = list.size();
+  public void setArmorContents(ItemStack @NotNull [] items) {
+    int size = Inventory.EQUIPMENT_SLOTS_SORTED_BY_INDEX.length;
     Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
     for (int index = 0; index < items.length; ++index) {
-      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+      getInventory().getOwnerHandle().getInventory().equipment.set(
+          Inventory.EQUIPMENT_SLOTS_SORTED_BY_INDEX[index],
+          CraftItemStack.asNMSCopy(items[index]));
     }
   }
 
   @Override
-  public @NotNull ItemStack[] getExtraContents() {
-    return asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand);
+  public @NotNull ItemStack @NotNull [] getExtraContents() {
+    return asCraftMirror(List.of(getInventory().getOwnerHandle().getInventory().equipment.get(EquipmentSlot.OFFHAND)));
   }
 
   @Override
-  public void setExtraContents(@Nullable ItemStack[] items) {
-    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().offhand;
-    int size = list.size();
-    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
-    for (int index = 0; index < items.length; ++index) {
-      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+  public void setExtraContents(ItemStack @NotNull [] items) {
+    Preconditions.checkArgument(items.length <= 1, "items.length must be <= 1");
+    for (ItemStack item : items) {
+      getInventory().getOwnerHandle().getInventory().equipment.set(EquipmentSlot.OFFHAND, CraftItemStack.asNMSCopy(item));
     }
   }
 
   @Override
-  public @Nullable ItemStack getHelmet() {
-    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
-        .getArmor(EquipmentSlot.HEAD.getIndex()));
+  public @NotNull ItemStack getHelmet() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().equipment
+        .get(EquipmentSlot.HEAD));
   }
 
   @Override
   public void setHelmet(@Nullable ItemStack helmet) {
-    getInventory().getOwnerHandle().getInventory().armor
-        .set(EquipmentSlot.HEAD.getIndex(), CraftItemStack.asNMSCopy(helmet));
+    getInventory().getOwnerHandle().getInventory().equipment
+        .set(EquipmentSlot.HEAD, CraftItemStack.asNMSCopy(helmet));
   }
 
   @Override
-  public @Nullable ItemStack getChestplate() {
-    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
-        .getArmor(EquipmentSlot.HEAD.getIndex()));
+  public @NotNull ItemStack getChestplate() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().equipment
+        .get(EquipmentSlot.CHEST));
   }
 
   @Override
   public void setChestplate(@Nullable ItemStack chestplate) {
-    getInventory().getOwnerHandle().getInventory().armor
-        .set(EquipmentSlot.CHEST.getIndex(), CraftItemStack.asNMSCopy(chestplate));
+    getInventory().getOwnerHandle().getInventory().equipment
+        .set(EquipmentSlot.CHEST, CraftItemStack.asNMSCopy(chestplate));
   }
 
   @Override
-  public @Nullable ItemStack getLeggings() {
-    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
-        .getArmor(EquipmentSlot.LEGS.getIndex()));
+  public @NotNull ItemStack getLeggings() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().equipment
+        .get(EquipmentSlot.LEGS));
   }
 
   @Override
   public void setLeggings(@Nullable ItemStack leggings) {
-    getInventory().getOwnerHandle().getInventory().armor
-        .set(EquipmentSlot.LEGS.getIndex(), CraftItemStack.asNMSCopy(leggings));
+    getInventory().getOwnerHandle().getInventory().equipment
+        .set(EquipmentSlot.LEGS, CraftItemStack.asNMSCopy(leggings));
   }
 
   @Override
-  public @Nullable ItemStack getBoots() {
-    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
-        .getArmor(EquipmentSlot.FEET.getIndex()));
+  public @NotNull ItemStack getBoots() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().equipment
+        .get(EquipmentSlot.FEET));
   }
 
   @Override
   public void setBoots(@Nullable ItemStack boots) {
-    getInventory().getOwnerHandle().getInventory().armor
-        .set(EquipmentSlot.FEET.getIndex(), CraftItemStack.asNMSCopy(boots));
+    getInventory().getOwnerHandle().getInventory().equipment
+        .set(EquipmentSlot.FEET, CraftItemStack.asNMSCopy(boots));
   }
 
   @Override
   public @NotNull ItemStack getItemInMainHand() {
     Inventory internal = getInventory().getOwnerHandle().getInventory();
-    return CraftItemStack.asCraftMirror(internal.getItem(internal.selected));
+    return CraftItemStack.asCraftMirror(internal.getSelectedItem());
   }
 
   @Override
   public void setItemInMainHand(@Nullable ItemStack item) {
     Inventory internal = getInventory().getOwnerHandle().getInventory();
-    internal.setItem(internal.selected, CraftItemStack.asNMSCopy(item));
+    internal.setSelectedItem(CraftItemStack.asNMSCopy(item));
   }
 
   @Override
   public @NotNull ItemStack getItemInOffHand() {
-    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand.getFirst());
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().equipment
+        .get(EquipmentSlot.OFFHAND));
   }
 
   @Override
   public void setItemInOffHand(@Nullable ItemStack item) {
-    getInventory().getOwnerHandle().getInventory().offhand.set(0, CraftItemStack.asNMSCopy(item));
+    getInventory().getOwnerHandle().getInventory().equipment
+        .set(EquipmentSlot.OFFHAND, CraftItemStack.asNMSCopy(item));
   }
 
   @Deprecated
@@ -185,17 +188,17 @@ public class OpenPlayerInventory extends CraftInventory implements PlayerInvento
   @Override
   public int getHeldItemSlot() {
     Inventory internal = getInventory().getOwnerHandle().getInventory();
-    return internal.items.size() - 9 + internal.selected;
+    return internal.getNonEquipmentItems().size() - 9 + internal.getSelectedSlot();
   }
 
   @Override
   public void setHeldItemSlot(int slot) {
     slot %= 9;
-    getInventory().getOwnerHandle().getInventory().selected = slot;
+    getInventory().getOwnerHandle().getInventory().setSelectedSlot(slot);
   }
 
   @Override
-  public @Nullable ItemStack getItem(@NotNull org.bukkit.inventory.EquipmentSlot slot) {
+  public @NotNull ItemStack getItem(@NotNull org.bukkit.inventory.EquipmentSlot slot) {
     return switch (slot) {
       case HAND -> getItemInMainHand();
       case OFF_HAND -> getItemInOffHand();

internal/common/src/main/java/com/lishid/openinv/internal/common/container/menu/OpenChestMenu.java

@@ -8,6 +8,7 @@ import com.lishid.openinv.internal.common.container.slot.SlotPlaceholder;
 import com.lishid.openinv.internal.common.container.slot.SlotViewOnly;
 import it.unimi.dsi.fastutil.ints.IntArrayList;
 import it.unimi.dsi.fastutil.ints.IntList;
+import net.minecraft.network.HashedStack;
 import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.world.Container;
 import net.minecraft.world.entity.player.Player;
@@ -19,6 +20,7 @@ import net.minecraft.world.inventory.ContainerListener;
 import net.minecraft.world.inventory.ContainerSynchronizer;
 import net.minecraft.world.inventory.DataSlot;
 import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.RemoteSlot;
 import net.minecraft.world.inventory.Slot;
 import net.minecraft.world.item.ItemStack;
 import org.bukkit.craftbukkit.inventory.CraftInventoryView;
@@ -47,12 +49,12 @@ public abstract class OpenChestMenu<T extends Container & ISpecialInventory & In
   protected final int topSize;
   private CraftInventoryView<OpenChestMenu<T>, Inventory> bukkitEntity;
   // Syncher fields
-  private @Nullable ContainerSynchronizer synchronizer;
-  private final List<DataSlot> dataSlots = new ArrayList<>();
-  private final IntList remoteDataSlots = new IntArrayList();
-  private final List<ContainerListener> containerListeners = new ArrayList<>();
-  private ItemStack remoteCarried = ItemStack.EMPTY;
-  private boolean suppressRemoteUpdates;
+  protected @Nullable ContainerSynchronizer synchronizer;
+  protected final List<DataSlot> dataSlots = new ArrayList<>();
+  protected final IntList remoteDataSlots = new IntArrayList();
+  protected final List<ContainerListener> containerListeners = new ArrayList<>();
+  private RemoteSlot remoteCarried = RemoteSlot.PLACEHOLDER;
+  protected boolean suppressRemoteUpdates;
 
   protected OpenChestMenu(
       @NotNull MenuType<ChestMenu> type,
@@ -304,7 +306,7 @@ public abstract class OpenChestMenu<T extends Container & ISpecialInventory & In
     slot.index = this.slots.size();
     this.slots.add(slot);
     this.lastSlots.add(ItemStack.EMPTY);
-    this.remoteSlots.add(ItemStack.EMPTY);
+    this.remoteSlots.add(this.synchronizer != null ? this.synchronizer.createSlot() : RemoteSlot.PLACEHOLDER);
     return slot;
   }
 
@@ -333,32 +335,38 @@ public abstract class OpenChestMenu<T extends Container & ISpecialInventory & In
   @Override
   public void setSynchronizer(@NotNull ContainerSynchronizer containerSynchronizer) {
     this.synchronizer = containerSynchronizer;
+    this.remoteCarried = synchronizer.createSlot();
+    this.remoteSlots.replaceAll(slot -> synchronizer.createSlot());
     this.sendAllDataToRemote();
   }
 
   @Override
   public void sendAllDataToRemote() {
+    List<ItemStack> contentsCopy = new ArrayList<>();
     for (int index = 0; index < slots.size(); ++index) {
       Slot slot = slots.get(index);
-      this.remoteSlots.set(index, (slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem()).copy());
+      ItemStack itemStack = slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem();
+      contentsCopy.add(itemStack);
+      this.remoteSlots.get(index).force(itemStack);
     }
 
-    remoteCarried = getCarried().copy();
+    remoteCarried.force(getCarried());
 
     for (int index = 0; index < this.dataSlots.size(); ++index) {
       this.remoteDataSlots.set(index, this.dataSlots.get(index).get());
     }
 
     if (this.synchronizer != null) {
-      this.synchronizer.sendInitialData(this, this.remoteSlots, this.remoteCarried, this.remoteDataSlots.toIntArray());
+      this.synchronizer.sendInitialData(this, contentsCopy, this.getCarried().copy(), this.remoteDataSlots.toIntArray());
     }
   }
 
   @Override
   public void broadcastCarriedItem() {
-    this.remoteCarried = this.getCarried().copy();
+    ItemStack carried = this.getCarried();
+    this.remoteCarried.force(carried);
     if (this.synchronizer != null) {
-      this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+      this.synchronizer.sendCarriedChange(this, carried.copy());
     }
   }
 
@@ -427,12 +435,11 @@ public abstract class OpenChestMenu<T extends Container & ISpecialInventory & In
 
   private void synchronizeSlotToRemote(int i, ItemStack itemStack, Supplier<ItemStack> supplier) {
     if (!this.suppressRemoteUpdates) {
-      ItemStack itemStack1 = this.remoteSlots.get(i);
-      if (!ItemStack.matches(itemStack1, itemStack)) {
-        ItemStack itemstack2 = supplier.get();
-        this.remoteSlots.set(i, itemstack2);
+      RemoteSlot slot = this.remoteSlots.get(i);
+      if (!slot.matches(itemStack)) {
+        slot.force(itemStack);
         if (this.synchronizer != null) {
-          this.synchronizer.sendSlotChange(this, i, itemstack2);
+          this.synchronizer.sendSlotChange(this, i, supplier.get());
         }
       }
     }
@@ -451,17 +458,20 @@ public abstract class OpenChestMenu<T extends Container & ISpecialInventory & In
   }
 
   private void synchronizeCarriedToRemote() {
-    if (!this.suppressRemoteUpdates && !ItemStack.matches(this.getCarried(), this.remoteCarried)) {
-      this.remoteCarried = this.getCarried().copy();
-      if (this.synchronizer != null) {
-        this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+    if (!this.suppressRemoteUpdates) {
+      ItemStack carried = this.getCarried();
+      if (!this.remoteCarried.matches(carried)) {
+        this.remoteCarried.force(carried);
+        if (this.synchronizer != null) {
+          this.synchronizer.sendCarriedChange(this, carried.copy());
+        }
       }
     }
   }
 
   @Override
-  public void setRemoteCarried(ItemStack itemstack) {
-    this.remoteCarried = itemstack.copy();
+  public void setRemoteCarried(@NotNull HashedStack stack) {
+    this.remoteCarried.receive(stack);
   }
 
   @Override

internal/common/src/main/java/com/lishid/openinv/internal/common/container/menu/OpenInventoryMenu.java

@@ -35,7 +35,7 @@ public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
     int size = inventory.getContainerSize();
     // Disallow duplicate access to own main inventory contents.
     if (inventory.getOwnerHandle().equals(viewer)) {
-      size -= viewer.getInventory().items.size();
+      size -= viewer.getInventory().getNonEquipmentItems().size();
       size = ((int) Math.ceil(size / 9.0)) * 9;
     }
 
@@ -44,7 +44,7 @@ public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
 
   @Override
   protected void preSlotSetup() {
-    offset = ownContainer ? viewer.getInventory().items.size() : 0;
+    offset = ownContainer ? viewer.getInventory().getNonEquipmentItems().size() : 0;
   }
 
   @Override
@@ -221,7 +221,7 @@ public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
         // If this is gear, try to move it to the correct slot first.
         case OFFHAND, FEET, LEGS, CHEST, HEAD -> {
           // Locate the correct slot in the contents following the main inventory.
-          for (int extra = container.getOwnerHandle().getInventory().items.size() - offset; extra < topSize; ++extra) {
+          for (int extra = container.getOwnerHandle().getInventory().getNonEquipmentItems().size() - offset; extra < topSize; ++extra) {
             Slot extraSlot = getSlot(extra);
             if (extraSlot instanceof ContentEquipment.SlotEquipment equipSlot
                 && equipSlot.getEquipmentSlot() == equipmentSlot) {
@@ -244,7 +244,7 @@ public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
         }
       } else {
         // If we didn't move to a gear slot, try to move to a main inventory slot.
-        if (!movedGear && !this.moveItemStackTo(itemStack, 0, container.getOwnerHandle().getInventory().items.size(), true)) {
+        if (!movedGear && !this.moveItemStackTo(itemStack, 0, container.getOwnerHandle().getInventory().getNonEquipmentItems().size(), true)) {
           return ItemStack.EMPTY;
         }
       }

internal/common/src/main/java/com/lishid/openinv/internal/common/container/slot/ContentEquipment.java

@@ -3,6 +3,8 @@ package com.lishid.openinv.internal.common.container.slot;
 import com.lishid.openinv.internal.common.container.slot.placeholder.Placeholders;
 import net.minecraft.server.level.ServerPlayer;
 import net.minecraft.world.Container;
+import net.minecraft.world.ContainerHelper;
+import net.minecraft.world.entity.EntityEquipment;
 import net.minecraft.world.entity.EquipmentSlot;
 import net.minecraft.world.inventory.Slot;
 import net.minecraft.world.item.ItemStack;
@@ -12,13 +14,14 @@ import org.jetbrains.annotations.NotNull;
 /**
  * A slot for equipment that displays placeholders if empty.
  */
-public class ContentEquipment extends ContentList {
+public class ContentEquipment implements Content {
 
+  private EntityEquipment equipment;
   private final ItemStack placeholder;
   private final EquipmentSlot equipmentSlot;
 
-  public ContentEquipment(ServerPlayer holder, int index, EquipmentSlot equipmentSlot) {
-    super(holder, index, InventoryType.SlotType.ARMOR);
+  public ContentEquipment(ServerPlayer holder, EquipmentSlot equipmentSlot) {
+    setHolder(holder);
     placeholder = switch (equipmentSlot) {
       case HEAD -> Placeholders.emptyHelmet;
       case CHEST -> Placeholders.emptyChestplate;
@@ -31,7 +34,31 @@ public class ContentEquipment extends ContentList {
 
   @Override
   public void setHolder(@NotNull ServerPlayer holder) {
-    this.items = holder.getInventory().armor;
+    this.equipment = holder.getInventory().equipment;
+  }
+
+  @Override
+  public ItemStack get() {
+    return equipment.get(equipmentSlot);
+  }
+
+  @Override
+  public ItemStack remove() {
+    return equipment.set(equipmentSlot, ItemStack.EMPTY);
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    ItemStack current = get();
+    if (!current.isEmpty() && amount > 0) {
+      return current.split(amount);
+    }
+    return ItemStack.EMPTY;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    equipment.set(equipmentSlot, itemStack);
   }
 
   @Override
@@ -39,6 +66,11 @@ public class ContentEquipment extends ContentList {
     return new SlotEquipment(container, slot, x, y);
   }
 
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.ARMOR;
+  }
+
   public class SlotEquipment extends SlotPlaceholder {
 
     private ServerPlayer viewer;

internal/common/src/main/java/com/lishid/openinv/internal/common/container/slot/ContentOffHand.java

@@ -17,13 +17,13 @@ public class ContentOffHand extends ContentEquipment {
 
   private ServerPlayer holder;
 
-  public ContentOffHand(ServerPlayer holder, int localIndex) {
-    super(holder, localIndex, EquipmentSlot.OFFHAND);
+  public ContentOffHand(ServerPlayer holder) {
+    super(holder, EquipmentSlot.OFFHAND);
   }
 
   @Override
   public void setHolder(@NotNull ServerPlayer holder) {
-    this.items = holder.getInventory().offhand;
+    super.setHolder(holder);
     this.holder = holder;
   }
 

internal/common/src/main/java/com/lishid/openinv/internal/common/container/slot/placeholder/PlaceholderLoader.java

@@ -1,18 +1,40 @@
 package com.lishid.openinv.internal.common.container.slot.placeholder;
 
 import net.minecraft.core.component.DataComponents;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.TagParser;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.component.CustomModelData;
+import net.minecraft.world.item.component.DyedItemColor;
+import net.minecraft.world.item.component.TooltipDisplay;
+import org.jetbrains.annotations.NotNull;
 
+import java.util.LinkedHashSet;
 import java.util.List;
 
 public class PlaceholderLoader extends PlaceholderLoaderBase {
 
   private static final CustomModelData DEFAULT_CUSTOM_MODEL_DATA = new CustomModelData(List.of(), List.of(), List.of("openinv:custom"), List.of());
+  private static final TooltipDisplay HIDE_TOOLTIP = new TooltipDisplay(true, new LinkedHashSet<>());
 
   @Override
-  protected void addModelData(ItemStack itemStack) {
+  protected @NotNull CompoundTag parseTag(@NotNull String itemText) throws Exception {
+    return TagParser.parseCompoundFully(itemText);
+  }
+
+  @Override
+  protected void addModelData(@NotNull ItemStack itemStack) {
     itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
   }
 
+  @Override
+  protected void hideTooltip(@NotNull ItemStack itemStack) {
+    itemStack.set(DataComponents.TOOLTIP_DISPLAY, HIDE_TOOLTIP);
+  }
+
+  @Override
+  protected DyedItemColor getDye(int rgb) {
+    return new DyedItemColor(rgb);
+  }
+
 }

internal/common/src/main/java/com/lishid/openinv/internal/common/container/slot/placeholder/PlaceholderLoaderBase.java

@@ -5,9 +5,7 @@ import net.minecraft.core.RegistryAccess;
 import net.minecraft.core.component.DataComponents;
 import net.minecraft.core.registries.Registries;
 import net.minecraft.nbt.CompoundTag;
-import net.minecraft.nbt.TagParser;
 import net.minecraft.network.chat.Component;
-import net.minecraft.util.Unit;
 import net.minecraft.world.item.DyeColor;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.item.Items;
@@ -63,7 +61,7 @@ public abstract class PlaceholderLoaderBase {
     Placeholders.BLOCKED_GAME_TYPE.put(GameType.SPECTATOR, parse(section, "blocked.spectator", Placeholders.BLOCKED_GAME_TYPE.get(GameType.SPECTATOR)));
   }
 
-  private static @NotNull ItemStack parse(
+  private @NotNull ItemStack parse(
       @Nullable ConfigurationSection section,
       @NotNull String path,
       @NotNull ItemStack defaultStack) throws Exception {
@@ -77,12 +75,18 @@ public abstract class PlaceholderLoaderBase {
       return defaultStack;
     }
 
-    CompoundTag compoundTag = TagParser.parseTag(itemText);
+    CompoundTag compoundTag = parseTag(itemText);
     Optional<ItemStack> parsed = ItemStack.parse(CraftRegistry.getMinecraftRegistry(), compoundTag);
     return parsed.filter(itemStack -> !itemStack.isEmpty()).orElse(defaultStack);
   }
 
-  protected abstract void addModelData(ItemStack itemStack);
+  protected abstract @NotNull CompoundTag parseTag(@NotNull String itemText) throws Exception;
+
+  protected abstract void addModelData(@NotNull ItemStack itemStack);
+
+  protected abstract void hideTooltip(@NotNull ItemStack itemStack);
+
+  protected abstract DyedItemColor getDye(int rgb);
 
   protected @NotNull ItemStack defaultCraftingOutput() {
     // Crafting table: "Crafting"
@@ -106,7 +110,7 @@ public abstract class PlaceholderLoaderBase {
             new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(downRight), DyeColor.WHITE),
             new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(border), DyeColor.GRAY))));
     addModelData(itemStack);
-    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    hideTooltip(itemStack);
     return itemStack;
   }
 
@@ -122,9 +126,9 @@ public abstract class PlaceholderLoaderBase {
   protected @NotNull ItemStack getEmptyArmor(@NotNull ItemLike item) {
     // Inventory-background-grey-ish leather armor with no tooltip
     ItemStack itemStack = new ItemStack(item);
-    DyedItemColor color = new DyedItemColor(0xC8C8C8, false);
+    DyedItemColor color = getDye(0xC8C8C8);
     itemStack.set(DataComponents.DYED_COLOR, color);
-    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    hideTooltip(itemStack);
     addModelData(itemStack);
     return itemStack;
   }
@@ -147,7 +151,7 @@ public abstract class PlaceholderLoaderBase {
             new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(bottomLeft), DyeColor.MAGENTA),
             new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(topRight), DyeColor.BLACK),
             new BannerPatternLayers.Layer(bannerPatterns.wrapAsHolder(bottomRight), DyeColor.BLACK))));
-    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    hideTooltip(itemStack);
     addModelData(itemStack);
     return itemStack;
   }
@@ -155,7 +159,7 @@ public abstract class PlaceholderLoaderBase {
   protected @NotNull ItemStack defaultNotSlot() {
     // White pane with no tooltip
     ItemStack itemStack = new ItemStack(Items.WHITE_STAINED_GLASS_PANE);
-    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+    hideTooltip(itemStack);
     addModelData(itemStack);
     return itemStack;
   }

internal/common/src/main/java/com/lishid/openinv/internal/common/player/OpenPlayer.java

@@ -15,6 +15,7 @@ import org.bukkit.craftbukkit.entity.CraftPlayer;
 import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.Unmodifiable;
 
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -30,7 +31,8 @@ public class OpenPlayer extends CraftPlayer {
    * @see net.minecraft.world.entity.player.Player#addAdditionalSaveData(CompoundTag)
    * @see net.minecraft.world.entity.LivingEntity#addAdditionalSaveData(CompoundTag)
    */
-  private static final Set<String> RESET_TAGS = Set.of(
+  @Unmodifiable
+  protected static final Set<String> RESET_TAGS = Set.of(
       // Entity#saveWithoutId(CompoundTag)
       "CustomName",
       "CustomNameVisible",
@@ -43,6 +45,7 @@ public class OpenPlayer extends CraftPlayer {
       "Passengers",
       // ServerPlayer#addAdditionalSaveData(CompoundTag)
       // Intentional omissions to prevent mount loss: Attach, Entity, and RootVehicle
+      // As of 1.21.5 only ender_pearls tag still needs to be reset. Rest are for backwards compatibility.
       "warden_spawn_tracker",
       "enteredNetherPosition",
       "SpawnX",
@@ -57,18 +60,23 @@ public class OpenPlayer extends CraftPlayer {
       "ShoulderEntityLeft",
       "ShoulderEntityRight",
       "LastDeathLocation",
-      "current_explosion_impact_pos",
+      "current_explosion_impact_pos", // Unnecessary in 1.21.5
       // LivingEntity#addAdditionalSaveData(CompoundTag)
       "active_effects",
       "SleepingX",
       "SleepingY",
       "SleepingZ",
-      "Brain"
+      "Brain",
+      "last_hurt_by_player",
+      "last_hurt_by_player_memory_time",
+      "last_hurt_by_mob",
+      "ticks_since_last_hurt_by_mob",
+      "equipment"
   );
 
   private final PlayerManager manager;
 
-  OpenPlayer(CraftServer server, ServerPlayer entity, PlayerManager manager) {
+  protected OpenPlayer(CraftServer server, ServerPlayer entity, PlayerManager manager) {
     super(server, entity);
     this.manager = manager;
   }
@@ -111,7 +119,7 @@ public class OpenPlayer extends CraftPlayer {
   }
 
   @Contract("null -> new")
-  private @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
+  protected @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
     if (oldData == null) {
       return new CompoundTag();
     }
@@ -120,8 +128,7 @@ public class OpenPlayer extends CraftPlayer {
     oldData = oldData.copy();
 
     // Remove vanilla/server data that is not written every time.
-    oldData.getAllKeys()
-        .removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit"));
+    oldData.keySet().removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit") || key.startsWith("Paper") && key.length() > 5);
 
     return oldData;
   }

internal/common/src/main/java/com/lishid/openinv/internal/common/player/PlayerManager.java

@@ -34,13 +34,14 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.lang.reflect.Field;
+import java.util.Optional;
 import java.util.UUID;
 import java.util.logging.Logger;
 
 public class PlayerManager implements com.lishid.openinv.internal.PlayerManager {
 
   protected final @NotNull Logger logger;
-  private @Nullable Field bukkitEntity;
+  protected @Nullable Field bukkitEntity;
 
   public PlayerManager(@NotNull Logger logger) {
     this.logger = logger;
@@ -154,23 +155,28 @@ public class PlayerManager implements com.lishid.openinv.internal.PlayerManager
     return true;
   }
 
-  private void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
+  protected void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
     // See PlayerList#placeNewPlayer
     World bukkitWorld;
-    if (loadedData.contains("WorldUUIDMost") && loadedData.contains("WorldUUIDLeast")) {
+    Optional<Long> msbs = loadedData.getLong("WorldUUIDMost");
+    Optional<Long> lsbs = loadedData.getLong("WorldUUIDLeast");
+    if (msbs.isPresent() && lsbs.isPresent()) {
       // Modern Bukkit world.
-      bukkitWorld = Bukkit.getServer().getWorld(new UUID(loadedData.getLong("WorldUUIDMost"), loadedData.getLong("WorldUUIDLeast")));
-    } else if (loadedData.contains("world", net.minecraft.nbt.Tag.TAG_STRING)) {
-      // Legacy Bukkit world.
-      bukkitWorld = Bukkit.getServer().getWorld(loadedData.getString("world"));
+      bukkitWorld = Bukkit.getServer().getWorld(new UUID(msbs.get(), lsbs.get()));
     } else {
-      // Vanilla player data.
-      DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
-          .resultOrPartial(logger::warning)
-          .map(player.server::getLevel)
-          // If ServerLevel exists, set, otherwise move to spawn.
-          .ifPresentOrElse(player::setServerLevel, () -> spawnInDefaultWorld(player));
-      return;
+      Optional<String> worldName = loadedData.getString("world");
+      if (worldName.isPresent()) {
+        // Legacy Bukkit world.
+        bukkitWorld = Bukkit.getServer().getWorld(worldName.get());
+      } else {
+        // Vanilla player data.
+        DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
+            .resultOrPartial(logger::warning)
+            .map(player.server::getLevel)
+            // If ServerLevel exists, set, otherwise move to spawn.
+            .ifPresentOrElse(player::setServerLevel, () -> spawnInDefaultWorld(player));
+        return;
+      }
     }
     if (bukkitWorld == null) {
       spawnInDefaultWorld(player);
@@ -179,9 +185,11 @@ public class PlayerManager implements com.lishid.openinv.internal.PlayerManager
     player.setServerLevel(((CraftWorld) bukkitWorld).getHandle());
   }
 
-  private void spawnInDefaultWorld(ServerPlayer player) {
+  protected void spawnInDefaultWorld(ServerPlayer player) {
     ServerLevel level = player.server.getLevel(Level.OVERWORLD);
     if (level != null) {
+      // Adjust player to default spawn (in keeping with Paper handling) when world not found.
+      player.snapTo(player.adjustSpawnLocation(level, level.getSharedSpawnPos()).getBottomCenter(), level.getSharedSpawnAngle(), 0.0F);
       player.spawnIn(level);
     } else {
       logger.warning("Tried to load player with invalid world when no fallback was available!");

internal/paper1_21_1/build.gradle.kts

@@ -21,6 +21,7 @@ dependencies {
   implementation(project(":openinvapi"))
   implementation(project(":openinvcommon"))
   implementation(project(":openinvadaptercommon"))
+  implementation(project(":openinvadapterpaper1_21_4"))
   implementation(project(":openinvadapterpaper1_21_3"))
 
   paperweight.paperDevBundle("1.21.1-R0.1-SNAPSHOT")

internal/paper1_21_1/src/main/java/com/lishid/openinv/internal/paper1_21_1/InternalAccessor.java

@@ -6,10 +6,10 @@ import com.lishid.openinv.internal.ISpecialEnderChest;
 import com.lishid.openinv.internal.ISpecialInventory;
 import com.lishid.openinv.internal.ISpecialPlayerInventory;
 import com.lishid.openinv.internal.common.container.AnySilentContainer;
-import com.lishid.openinv.internal.common.container.OpenEnderChest;
 import com.lishid.openinv.internal.paper1_21_1.container.OpenInventory;
 import com.lishid.openinv.internal.paper1_21_1.container.slot.placeholder.PlaceholderLoader;
 import com.lishid.openinv.internal.paper1_21_1.player.PlayerManager;
+import com.lishid.openinv.internal.paper1_21_4.container.OpenEnderChest;
 import com.lishid.openinv.util.lang.LanguageManager;
 import net.minecraft.world.Container;
 import org.bukkit.configuration.ConfigurationSection;

internal/paper1_21_1/src/main/java/com/lishid/openinv/internal/paper1_21_1/container/OpenInventory.java

@@ -6,7 +6,7 @@ import net.minecraft.server.level.ServerPlayer;
 import org.bukkit.entity.Player;
 import org.jetbrains.annotations.NotNull;
 
-public class OpenInventory extends com.lishid.openinv.internal.common.container.OpenInventory {
+public class OpenInventory extends com.lishid.openinv.internal.paper1_21_4.container.OpenInventory {
 
   public OpenInventory(@NotNull Player bukkitPlayer) {
     super(bukkitPlayer);

internal/paper1_21_1/src/main/java/com/lishid/openinv/internal/paper1_21_1/player/PlayerManager.java

@@ -11,7 +11,8 @@ import org.jetbrains.annotations.NotNull;
 
 import java.util.logging.Logger;
 
-public class PlayerManager extends com.lishid.openinv.internal.common.player.PlayerManager {
+public class PlayerManager extends com.lishid.openinv.internal.paper1_21_4.player.PlayerManager {
+
   public PlayerManager(@NotNull Logger logger) {
     super(logger);
   }

internal/paper1_21_3/build.gradle.kts

@@ -21,6 +21,7 @@ dependencies {
   implementation(project(":openinvapi"))
   implementation(project(":openinvcommon"))
   implementation(project(":openinvadaptercommon"))
+  implementation(project(":openinvadapterpaper1_21_4"))
 
   paperweight.paperDevBundle("1.21.3-R0.1-SNAPSHOT")
 }

internal/paper1_21_3/src/main/java/com/lishid/openinv/internal/paper1_21_3/InternalAccessor.java

@@ -8,7 +8,7 @@ import org.jetbrains.annotations.NotNull;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
-public class InternalAccessor extends com.lishid.openinv.internal.common.InternalAccessor {
+public class InternalAccessor extends com.lishid.openinv.internal.paper1_21_4.InternalAccessor {
 
   public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
     super(logger, lang);

internal/paper1_21_3/src/main/java/com/lishid/openinv/internal/paper1_21_3/container/slot/placeholder/NumericDataPlaceholderLoader.java

@@ -1,31 +1,12 @@
 package com.lishid.openinv.internal.paper1_21_3.container.slot.placeholder;
 
-import com.lishid.openinv.internal.common.container.slot.placeholder.PlaceholderLoaderBase;
-import net.minecraft.core.HolderLookup;
-import net.minecraft.core.Registry;
-import net.minecraft.core.RegistryAccess;
-import net.minecraft.core.component.DataComponents;
-import net.minecraft.core.registries.Registries;
-import net.minecraft.util.Unit;
-import net.minecraft.world.item.DyeColor;
-import net.minecraft.world.item.ItemStack;
-import net.minecraft.world.item.Items;
+import com.lishid.openinv.internal.paper1_21_4.container.slot.placeholder.CustomModelBase;
 import net.minecraft.world.item.component.CustomModelData;
-import net.minecraft.world.level.block.entity.BannerPattern;
-import net.minecraft.world.level.block.entity.BannerPatternLayers;
-import net.minecraft.world.level.block.entity.BannerPatterns;
-import org.bukkit.craftbukkit.CraftRegistry;
-import org.jetbrains.annotations.NotNull;
 
-import java.util.List;
+public class NumericDataPlaceholderLoader extends CustomModelBase {
 
-public class NumericDataPlaceholderLoader extends PlaceholderLoaderBase {
-
-  private static final CustomModelData DEFAULT_CUSTOM_MODEL_DATA = new CustomModelData(9999);
-
-  @Override
-  protected void addModelData(ItemStack itemStack) {
-    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, DEFAULT_CUSTOM_MODEL_DATA);
+  public NumericDataPlaceholderLoader() {
+    super(new CustomModelData(9999));
   }
 
 }

internal/paper1_21_4/build.gradle.kts

@@ -0,0 +1,26 @@
+plugins {
+  `openinv-base`
+  alias(libs.plugins.paperweight)
+}
+
+configurations.all {
+  resolutionStrategy.capabilitiesResolution.withCapability("org.spigotmc:spigot-api") {
+    val paper = candidates.firstOrNull {
+      it.id.let {
+        id -> id is ModuleComponentIdentifier && id.module == "paper-api"
+      }
+    }
+    if (paper != null) {
+      select(paper)
+    }
+    because("module is written for Paper servers")
+  }
+}
+
+dependencies {
+  implementation(project(":openinvapi"))
+  implementation(project(":openinvcommon"))
+  implementation(project(":openinvadaptercommon"))
+
+  paperweight.paperDevBundle("1.21.4-R0.1-SNAPSHOT")
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/InternalAccessor.java

@@ -0,0 +1,80 @@
+package com.lishid.openinv.internal.paper1_21_4;
+
+import com.lishid.openinv.internal.Accessor;
+import com.lishid.openinv.internal.IAnySilentContainer;
+import com.lishid.openinv.internal.ISpecialEnderChest;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.ISpecialPlayerInventory;
+import com.lishid.openinv.internal.common.container.AnySilentContainer;
+import com.lishid.openinv.internal.paper1_21_4.container.OpenEnderChest;
+import com.lishid.openinv.internal.paper1_21_4.container.OpenInventory;
+import com.lishid.openinv.internal.paper1_21_4.container.slot.placeholder.CustomModelPlaceholderLoader;
+import com.lishid.openinv.internal.paper1_21_4.player.PlayerManager;
+import com.lishid.openinv.util.lang.LanguageManager;
+import net.minecraft.world.Container;
+import org.bukkit.configuration.ConfigurationSection;
+import org.bukkit.craftbukkit.inventory.CraftInventory;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.Inventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class InternalAccessor implements Accessor {
+
+  protected final @NotNull Logger logger;
+  private final @NotNull PlayerManager manager;
+  private final @NotNull AnySilentContainer anySilentContainer;
+
+  public InternalAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
+    this.logger = logger;
+    manager = new PlayerManager(logger);
+    anySilentContainer = new AnySilentContainer(logger, lang);
+  }
+
+  @Override
+  public @NotNull PlayerManager getPlayerManager() {
+    return manager;
+  }
+
+  @Override
+  public @NotNull IAnySilentContainer getAnySilentContainer() {
+    return anySilentContainer;
+  }
+
+  @Override
+  public @NotNull ISpecialPlayerInventory createPlayerInventory(@NotNull Player player) {
+    return new OpenInventory(player);
+  }
+
+  @Override
+  public @NotNull ISpecialEnderChest createEnderChest(@NotNull Player player) {
+    return new OpenEnderChest(player);
+  }
+
+  @Override
+  public <T extends ISpecialInventory> @Nullable T get(@NotNull Inventory bukkitInventory, @NotNull Class<T> clazz) {
+    if (!(bukkitInventory instanceof CraftInventory craftInventory)) {
+      return null;
+    }
+    Container container = craftInventory.getInventory();
+    if (clazz.isInstance(container)) {
+      return clazz.cast(container);
+    }
+    return null;
+  }
+
+  @Override
+  public void reload(@NotNull ConfigurationSection config) {
+    ConfigurationSection placeholders = config.getConfigurationSection("placeholders");
+    try {
+      // Reset placeholders to defaults and try to load configuration.
+      new CustomModelPlaceholderLoader().load(placeholders);
+    } catch (Exception e) {
+      logger.log(Level.WARNING, "Caught exception loading placeholder overrides!", e);
+    }
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/OpenEnderChest.java

@@ -0,0 +1,23 @@
+package com.lishid.openinv.internal.paper1_21_4.container;
+
+import com.lishid.openinv.internal.paper1_21_4.container.menu.OpenEnderChestMenu;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenEnderChest extends com.lishid.openinv.internal.common.container.OpenEnderChest{
+
+  public OpenEnderChest(@NotNull Player player) {
+    super(player);
+  }
+
+  public @Nullable AbstractContainerMenu createMenu(net.minecraft.world.entity.player.Player player, int i, boolean viewOnly) {
+    if (player instanceof ServerPlayer serverPlayer) {
+      return new OpenEnderChestMenu(this, serverPlayer, i, viewOnly);
+    }
+    return null;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/OpenInventory.java

@@ -0,0 +1,177 @@
+package com.lishid.openinv.internal.paper1_21_4.container;
+
+import com.lishid.openinv.internal.common.container.slot.ContentCrafting;
+import com.lishid.openinv.internal.common.container.slot.ContentCursor;
+import com.lishid.openinv.internal.common.container.slot.ContentDrop;
+import com.lishid.openinv.internal.common.container.slot.ContentList;
+import com.lishid.openinv.internal.common.container.slot.ContentViewOnly;
+import com.lishid.openinv.internal.common.container.slot.SlotViewOnly;
+import com.lishid.openinv.internal.common.container.slot.placeholder.Placeholders;
+import com.lishid.openinv.internal.paper1_21_4.container.menu.OpenInventoryMenu;
+import com.lishid.openinv.internal.paper1_21_4.container.slot.ContentEquipment;
+import com.lishid.openinv.internal.paper1_21_4.container.slot.ContentOffHand;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Inventory;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenInventory extends com.lishid.openinv.internal.common.container.OpenInventory {
+
+  public OpenInventory(@NotNull org.bukkit.entity.Player bukkitPlayer) {
+    super(bukkitPlayer);
+  }
+
+  @Override
+  protected void setupSlots() {
+    // Top of inventory: Regular contents.
+    int nextIndex = addMainInventory();
+
+    // If inventory is expected size, we can arrange slots to be pretty.
+    Inventory ownerInv = owner.getInventory();
+    if (ownerInv.items.size() == 36
+        && ownerInv.armor.size() == 4
+        && ownerInv.offhand.size() == 1
+        && owner.inventoryMenu.getCraftSlots().getContainerSize() == 4) {
+      // Armor slots: Bottom left.
+      addArmor(36);
+      // Off-hand: Below chestplate.
+      addOffHand(46);
+      // Drop slot: Bottom right.
+      slots.set(53, new ContentDrop(owner));
+      // Cursor slot: Above drop.
+      slots.set(44, new ContentCursor(owner));
+
+      // Crafting is displayed in the bottom right corner.
+      // As we're using the pretty view, this is a 3x2.
+      addCrafting(41, true);
+      return;
+    }
+
+    // Otherwise we'll just add elements linearly.
+    nextIndex = addArmor(nextIndex);
+    nextIndex = addOffHand(nextIndex);
+    nextIndex = addCrafting(nextIndex, false);
+    slots.set(nextIndex, new ContentCursor(owner));
+    // Drop slot last.
+    slots.set(slots.size() - 1, new ContentDrop(owner));
+  }
+
+  private int addMainInventory() {
+    int listSize = owner.getInventory().items.size();
+    // Hotbar slots are 0-8. We want those to appear on the bottom of the inventory like a normal player inventory,
+    // so everything else needs to move up a row.
+    int hotbarDiff = listSize - 9;
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      InventoryType.SlotType type;
+      int invIndex;
+      if (localIndex < hotbarDiff) {
+        invIndex = localIndex + 9;
+        type = InventoryType.SlotType.CONTAINER;
+      } else {
+        type = InventoryType.SlotType.QUICKBAR;
+        invIndex = localIndex - hotbarDiff;
+      }
+
+      slots.set(localIndex, new ContentList(owner, invIndex, type) {
+        @Override
+        public void setHolder(@NotNull ServerPlayer holder) {
+          items = holder.getInventory().items;
+        }
+      });
+    }
+    return listSize;
+  }
+
+  private int addArmor(int startIndex) {
+    int listSize = owner.getInventory().armor.size();
+
+    for (int i = 0; i < listSize; ++i) {
+      // Armor slots go bottom to top; boots are slot 0, helmet is slot 3.
+      // Since we have to display horizontally due to space restrictions,
+      // making the left side the "top" is more user-friendly.
+      int armorIndex;
+      EquipmentSlot slot;
+      switch (i) {
+        case 3 -> {
+          armorIndex = 0;
+          slot = EquipmentSlot.FEET;
+        }
+        case 2 -> {
+          armorIndex = 1;
+          slot = EquipmentSlot.LEGS;
+        }
+        case 1 -> {
+          armorIndex = 2;
+          slot = EquipmentSlot.CHEST;
+        }
+        case 0 -> {
+          armorIndex = 3;
+          slot = EquipmentSlot.HEAD;
+        }
+        default -> {
+          // In the event that new armor slots are added, they can be placed at the end.
+          armorIndex = i;
+          slot = EquipmentSlot.MAINHAND;
+        }
+      }
+
+      slots.set(startIndex + i, new ContentEquipment(owner, armorIndex, slot));
+    }
+
+    return startIndex + listSize;
+  }
+
+  private int addOffHand(int startIndex) {
+    int listSize = owner.getInventory().offhand.size();
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      slots.set(startIndex + localIndex, new ContentOffHand(owner, localIndex));
+    }
+    return startIndex + listSize;
+  }
+
+  private int addCrafting(int startIndex, boolean pretty) {
+    int listSize = owner.inventoryMenu.getCraftSlots().getContents().size();
+    pretty &= listSize == 4;
+
+    for (int localIndex = 0; localIndex < listSize; ++localIndex) {
+      // Pretty display is a 2x2 rather than linear.
+      // If index is in top row, grid is not 2x2, or pretty is disabled, just use current index.
+      // Otherwise, subtract 2 and add 9 to start in the same position on the next row.
+      int modIndex = startIndex + (localIndex < 2 || !pretty ? localIndex : localIndex + 7);
+
+      slots.set(modIndex, new ContentCrafting(owner, localIndex));
+    }
+
+    if (pretty) {
+      slots.set(startIndex + 2, new ContentViewOnly(owner) {
+        @Override
+        public Slot asSlot(Container container, int slot, int x, int y) {
+          return new SlotViewOnly(container, slot, x, y) {
+            @Override
+            public ItemStack getOrDefault() {
+              return Placeholders.craftingOutput;
+            }
+          };
+        }
+      });
+      slots.set(startIndex + 11, getCraftingResult(owner));
+    }
+
+    return startIndex + listSize;
+  }
+
+  public @Nullable AbstractContainerMenu createMenu(Player player, int i, boolean viewOnly) {
+    if (player instanceof ServerPlayer serverPlayer) {
+      return new OpenInventoryMenu(this, serverPlayer, i, viewOnly);
+    }
+    return null;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/bukkit/OpenPlayerInventory.java

@@ -0,0 +1,223 @@
+package com.lishid.openinv.internal.paper1_21_4.container.bukkit;
+
+import com.google.common.base.Preconditions;
+import com.lishid.openinv.internal.paper1_21_4.container.OpenInventory;
+import net.minecraft.core.NonNullList;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Inventory;
+import org.bukkit.craftbukkit.inventory.CraftInventory;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.PlayerInventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenPlayerInventory extends CraftInventory implements PlayerInventory {
+
+  public OpenPlayerInventory(@NotNull OpenInventory inventory) {
+    super(inventory);
+  }
+
+  @Override
+  public @NotNull OpenInventory getInventory() {
+    return (OpenInventory) super.getInventory();
+  }
+
+  @Override
+  public ItemStack @NotNull [] getContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getContents());
+  }
+
+  @Override
+  public void setContents(ItemStack[] items) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    int size = internal.getContainerSize();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+
+    for (int index = 0; index < size; ++index) {
+      if (index < items.length) {
+        internal.setItem(index, CraftItemStack.asNMSCopy(items[index]));
+      } else {
+        internal.setItem(index, net.minecraft.world.item.ItemStack.EMPTY);
+      }
+    }
+  }
+
+  @Override
+  public ItemStack @NotNull [] getStorageContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().items);
+  }
+
+  @Override
+  public void setStorageContents(ItemStack[] items) throws IllegalArgumentException {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().items;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull InventoryType getType() {
+    return InventoryType.PLAYER;
+  }
+
+  @Override
+  public @NotNull Player getHolder() {
+    return getInventory().getOwner();
+  }
+
+  @Override
+  public @NotNull ItemStack @NotNull [] getArmorContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().armor);
+  }
+
+  @Override
+  public void setArmorContents(ItemStack @NotNull [] items) {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().armor;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull ItemStack @NotNull [] getExtraContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand);
+  }
+
+  @Override
+  public void setExtraContents(ItemStack @NotNull [] items) {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().offhand;
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull ItemStack getHelmet() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.HEAD.getIndex()));
+  }
+
+  @Override
+  public void setHelmet(@Nullable ItemStack helmet) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.HEAD.getIndex(), CraftItemStack.asNMSCopy(helmet));
+  }
+
+  @Override
+  public @NotNull ItemStack getChestplate() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.CHEST.getIndex()));
+  }
+
+  @Override
+  public void setChestplate(@Nullable ItemStack chestplate) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.CHEST.getIndex(), CraftItemStack.asNMSCopy(chestplate));
+  }
+
+  @Override
+  public @NotNull ItemStack getLeggings() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.LEGS.getIndex()));
+  }
+
+  @Override
+  public void setLeggings(@Nullable ItemStack leggings) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.LEGS.getIndex(), CraftItemStack.asNMSCopy(leggings));
+  }
+
+  @Override
+  public @NotNull ItemStack getBoots() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory()
+        .getArmor(EquipmentSlot.FEET.getIndex()));
+  }
+
+  @Override
+  public void setBoots(@Nullable ItemStack boots) {
+    getInventory().getOwnerHandle().getInventory().armor
+        .set(EquipmentSlot.FEET.getIndex(), CraftItemStack.asNMSCopy(boots));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInMainHand() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return CraftItemStack.asCraftMirror(internal.getItem(internal.selected));
+  }
+
+  @Override
+  public void setItemInMainHand(@Nullable ItemStack item) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    internal.setItem(internal.selected, CraftItemStack.asNMSCopy(item));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInOffHand() {
+    return CraftItemStack.asCraftMirror(getInventory().getOwnerHandle().getInventory().offhand.getFirst());
+  }
+
+  @Override
+  public void setItemInOffHand(@Nullable ItemStack item) {
+    getInventory().getOwnerHandle().getInventory().offhand.set(0, CraftItemStack.asNMSCopy(item));
+  }
+
+  @Deprecated
+  @Override
+  public @NotNull ItemStack getItemInHand() {
+    return getItemInMainHand();
+  }
+
+  @Deprecated
+  @Override
+  public void setItemInHand(@Nullable ItemStack stack) {
+    setItemInMainHand(stack);
+  }
+
+  @Override
+  public int getHeldItemSlot() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return internal.items.size() - 9 + internal.selected;
+  }
+
+  @Override
+  public void setHeldItemSlot(int slot) {
+    slot %= 9;
+    getInventory().getOwnerHandle().getInventory().selected = slot;
+  }
+
+  @Override
+  public @NotNull ItemStack getItem(@NotNull org.bukkit.inventory.EquipmentSlot slot) {
+    return switch (slot) {
+      case HAND -> getItemInMainHand();
+      case OFF_HAND -> getItemInOffHand();
+      case FEET -> getBoots();
+      case LEGS -> getLeggings();
+      case CHEST -> getChestplate();
+      case HEAD -> getHelmet();
+      default -> throw new IllegalArgumentException("Unsupported EquipmentSlot " + slot);
+    };
+  }
+
+  @Override
+  public void setItem(@NotNull org.bukkit.inventory.EquipmentSlot slot, @Nullable ItemStack item) {
+    switch (slot) {
+      case HAND -> setItemInMainHand(item);
+      case OFF_HAND -> setItemInOffHand(item);
+      case FEET -> setBoots(item);
+      case LEGS -> setLeggings(item);
+      case CHEST -> setChestplate(item);
+      case HEAD -> setHelmet(item);
+      default -> throw new IllegalArgumentException("Unsupported EquipmentSlot " + slot);
+    }
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/bukkit/OpenPlayerInventorySelf.java

@@ -0,0 +1,26 @@
+package com.lishid.openinv.internal.paper1_21_4.container.bukkit;
+
+import com.lishid.openinv.internal.paper1_21_4.container.OpenInventory;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenPlayerInventorySelf extends OpenPlayerInventory {
+
+  private final int offset;
+
+  public OpenPlayerInventorySelf(@NotNull OpenInventory inventory, int offset) {
+    super(inventory);
+    this.offset = offset;
+  }
+
+  @Override
+  public ItemStack getItem(int index) {
+    return super.getItem(offset + index);
+  }
+
+  @Override
+  public void setItem(int index, ItemStack item) {
+    super.setItem(offset + index, item);
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/menu/OpenChestMenu.java

@@ -0,0 +1,464 @@
+package com.lishid.openinv.internal.paper1_21_4.container.menu;
+
+import com.google.common.base.Suppliers;
+import com.lishid.openinv.internal.ISpecialInventory;
+import com.lishid.openinv.internal.InternalOwned;
+import com.lishid.openinv.internal.common.container.bukkit.OpenDummyInventory;
+import com.lishid.openinv.internal.common.container.slot.SlotPlaceholder;
+import com.lishid.openinv.internal.common.container.slot.SlotViewOnly;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
+import it.unimi.dsi.fastutil.ints.IntList;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.AbstractContainerMenu;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.ClickType;
+import net.minecraft.world.inventory.ContainerData;
+import net.minecraft.world.inventory.ContainerListener;
+import net.minecraft.world.inventory.ContainerSynchronizer;
+import net.minecraft.world.inventory.DataSlot;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.craftbukkit.inventory.CraftInventoryView;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Supplier;
+
+/**
+ * An extension of {@link AbstractContainerMenu} that supports {@link SlotPlaceholder placeholders}.
+ */
+public abstract class OpenChestMenu<T extends Container & ISpecialInventory & InternalOwned<ServerPlayer>>
+    extends AbstractContainerMenu {
+
+  protected static final int BOTTOM_INVENTORY_SIZE = 36;
+
+  protected final T container;
+  protected final ServerPlayer viewer;
+  protected final boolean viewOnly;
+  protected final boolean ownContainer;
+  protected final int topSize;
+  private CraftInventoryView<OpenChestMenu<T>, Inventory> bukkitEntity;
+  // Syncher fields
+  private @Nullable ContainerSynchronizer synchronizer;
+  private final List<DataSlot> dataSlots = new ArrayList<>();
+  private final IntList remoteDataSlots = new IntArrayList();
+  private final List<ContainerListener> containerListeners = new ArrayList<>();
+  private ItemStack remoteCarried = ItemStack.EMPTY;
+  private boolean suppressRemoteUpdates;
+
+  protected OpenChestMenu(
+      @NotNull MenuType<ChestMenu> type,
+      int containerCounter,
+      @NotNull T container,
+      @NotNull ServerPlayer viewer,
+      boolean viewOnly) {
+    super(type, containerCounter);
+    this.container = container;
+    this.viewer = viewer;
+    this.viewOnly = viewOnly;
+    ownContainer = container.getOwnerHandle().equals(viewer);
+    topSize = getTopSize(viewer);
+
+    preSlotSetup();
+
+    int upperRows = topSize / 9;
+    // View's upper inventory - our container
+    for (int row = 0; row < upperRows; ++row) {
+      for (int col = 0; col < 9; ++col) {
+        // x and y for client purposes, but hey, we're thorough here.
+        // Adapted from net.minecraft.world.inventory.ChestMenu
+        int x = 8 + col * 18;
+        int y = 18 + row * 18;
+        int index = row * 9 + col;
+
+        // Guard against weird inventory sizes.
+        if (index >= container.getContainerSize()) {
+          addSlot(new SlotViewOnly(container, index, x, y));
+          continue;
+        }
+
+        Slot slot = getUpperSlot(index, x, y);
+
+        addSlot(slot);
+      }
+    }
+
+    // View's lower inventory - viewer inventory
+    int playerInvPad = (upperRows - 4) * 18;
+    for (int row = 0; row < 3; ++row) {
+      for (int col = 0; col < 9; ++col) {
+        int x = 8 + col * 18;
+        int y = playerInvPad + row * 18 + 103;
+        addSlot(new Slot(viewer.getInventory(), row * 9 + col + 9, x, y));
+      }
+    }
+    // Hotbar
+    for (int col = 0; col < 9; ++col) {
+      int x = 8 + col * 18;
+      int y = playerInvPad + 161;
+      addSlot(new Slot(viewer.getInventory(), col, x, y));
+    }
+  }
+
+  protected void preSlotSetup() {}
+
+  protected @NotNull Slot getUpperSlot(int index, int x, int y) {
+    Slot slot = new Slot(container, index, x, y);
+    if (viewOnly) {
+      return SlotViewOnly.wrap(slot);
+    }
+    return slot;
+  }
+
+
+  @Override
+  public final @NotNull CraftInventoryView<OpenChestMenu<T>, Inventory> getBukkitView() {
+    if (bukkitEntity == null) {
+      bukkitEntity = createBukkitEntity();
+    }
+
+    return bukkitEntity;
+  }
+
+  protected @NotNull CraftInventoryView<OpenChestMenu<T>, Inventory> createBukkitEntity() {
+    Inventory top;
+    if (viewOnly) {
+      top = new OpenDummyInventory(container, container.getBukkitType());
+    } else {
+      top = container.getBukkitInventory();
+    }
+    return new CraftInventoryView<>(viewer.getBukkitEntity(), top, this) {
+      @Override
+      public @Nullable Inventory getInventory(int rawSlot) {
+        if (viewOnly) {
+          return null;
+        }
+        return super.getInventory(rawSlot);
+      }
+
+      @Override
+      public int convertSlot(int rawSlot) {
+        if (viewOnly) {
+          return InventoryView.OUTSIDE;
+        }
+        return super.convertSlot(rawSlot);
+      }
+
+      @Override
+      public @NotNull InventoryType.SlotType getSlotType(int slot) {
+        if (viewOnly) {
+          return InventoryType.SlotType.OUTSIDE;
+        }
+        return super.getSlotType(slot);
+      }
+    };
+  }
+
+  private int getTopSize(ServerPlayer viewer) {
+    MenuType<?> menuType = getType();
+    if (menuType == MenuType.GENERIC_9x1) {
+      return 9;
+    } else if (menuType == MenuType.GENERIC_9x2) {
+      return 18;
+    } else if (menuType == MenuType.GENERIC_9x3) {
+      return 27;
+    } else if (menuType == MenuType.GENERIC_9x4) {
+      return 36;
+    } else if (menuType == MenuType.GENERIC_9x5) {
+      return 45;
+    } else if (menuType == MenuType.GENERIC_9x6) {
+      return 54;
+    }
+    // This is a bit gross, but allows us a safe fallthrough.
+    return menuType.create(-1, viewer.getInventory()).slots.size() - BOTTOM_INVENTORY_SIZE;
+  }
+
+  /**
+   * Reimplementation of {@link AbstractContainerMenu#moveItemStackTo(ItemStack, int, int, boolean)} that ignores fake
+   * slots and respects {@link Slot#hasItem()}.
+   *
+   * @param itemStack the stack to quick-move
+   * @param rangeLow the start of the range of slots that can be moved to, inclusive
+   * @param rangeHigh the end of the range of slots that can be moved to, exclusive
+   * @param topDown whether to start at the top of the range or bottom
+   * @return whether the stack was modified as a result of being quick-moved
+   */
+  @Override
+  protected boolean moveItemStackTo(ItemStack itemStack, int rangeLow, int rangeHigh, boolean topDown) {
+    boolean modified = false;
+    boolean stackable = itemStack.isStackable();
+    Slot firstEmpty = null;
+
+    for (int index = topDown ? rangeHigh - 1 : rangeLow;
+         !itemStack.isEmpty() && (topDown ? index >= rangeLow : index < rangeHigh);
+         index += topDown ? -1 : 1
+    ) {
+      Slot slot = slots.get(index);
+      // If the slot cannot be added to, check the next slot.
+      if (slot.isFake() || !slot.mayPlace(itemStack)) {
+        continue;
+      }
+
+      if (slot.hasItem()) {
+        // If the item isn't stackable, check the next slot.
+        if (!stackable) {
+          continue;
+        }
+        // Otherwise, add as many as we can from our stack to the slot.
+        modified |= addToExistingStack(itemStack, slot);
+      } else {
+        // If this is the first empty slot, keep track of it for later use.
+        if (firstEmpty == null) {
+          firstEmpty = slot;
+        }
+        // If the item isn't stackable, we've located the slot we're adding it to, so we're done.
+        if (!stackable) {
+          break;
+        }
+      }
+    }
+
+    // If the item hasn't been fully added yet, add as many as we can to the first open slot.
+    if (!itemStack.isEmpty() && firstEmpty != null) {
+      firstEmpty.setByPlayer(itemStack.split(Math.min(itemStack.getCount(), firstEmpty.getMaxStackSize(itemStack))));
+      firstEmpty.setChanged();
+      modified = true;
+    }
+
+    return modified;
+  }
+
+  private static boolean addToExistingStack(ItemStack itemStack, Slot slot) {
+    ItemStack existing = slot.getItem();
+
+    // If the items aren't the same, we can't add our item.
+    if (!ItemStack.isSameItemSameComponents(itemStack, existing)) {
+      return false;
+    }
+
+    int max = slot.getMaxStackSize(existing);
+    int existingCount = existing.getCount();
+
+    // If the stack is already full, we can't add more.
+    if (existingCount >= max) {
+      return false;
+    }
+
+    int total = existingCount + itemStack.getCount();
+
+    // If the existing item can accept the entirety of our item, we're done!
+    if (total <= max) {
+      itemStack.setCount(0);
+      existing.setCount(total);
+      slot.setChanged();
+      return true;
+    }
+
+    // Otherwise, add as many as we can.
+    itemStack.shrink(max - existingCount);
+    existing.setCount(max);
+    slot.setChanged();
+    return true;
+  }
+
+  @Override
+  public void clicked(int i, int j, @NotNull ClickType clickType, @NotNull Player player) {
+    if (viewOnly) {
+      if (clickType == ClickType.QUICK_CRAFT) {
+        sendAllDataToRemote();
+      }
+      return;
+    }
+    super.clicked(i, j, clickType, player);
+  }
+
+  @Override
+  public boolean stillValid(@NotNull Player player) {
+    return true;
+  }
+
+  // Overrides from here on are purely to modify the sync process to send placeholder items.
+  @Override
+  protected @NotNull Slot addSlot(@NotNull Slot slot) {
+    slot.index = this.slots.size();
+    this.slots.add(slot);
+    this.lastSlots.add(ItemStack.EMPTY);
+    this.remoteSlots.add(ItemStack.EMPTY);
+    return slot;
+  }
+
+  @Override
+  protected @NotNull DataSlot addDataSlot(@NotNull DataSlot dataSlot) {
+    this.dataSlots.add(dataSlot);
+    this.remoteDataSlots.add(0);
+    return dataSlot;
+  }
+
+  @Override
+  protected void addDataSlots(ContainerData containerData) {
+    for (int i = 0; i < containerData.getCount(); i++) {
+      this.addDataSlot(DataSlot.forContainer(containerData, i));
+    }
+  }
+
+  @Override
+  public void addSlotListener(@NotNull ContainerListener containerListener) {
+    if (!this.containerListeners.contains(containerListener)) {
+      this.containerListeners.add(containerListener);
+      this.broadcastChanges();
+    }
+  }
+
+  @Override
+  public void setSynchronizer(@NotNull ContainerSynchronizer containerSynchronizer) {
+    this.synchronizer = containerSynchronizer;
+    this.sendAllDataToRemote();
+  }
+
+  @Override
+  public void sendAllDataToRemote() {
+    for (int index = 0; index < slots.size(); ++index) {
+      Slot slot = slots.get(index);
+      this.remoteSlots.set(index, (slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem()).copy());
+    }
+
+    remoteCarried = getCarried().copy();
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      this.remoteDataSlots.set(index, this.dataSlots.get(index).get());
+    }
+
+    if (this.synchronizer != null) {
+      this.synchronizer.sendInitialData(this, this.remoteSlots, this.remoteCarried, this.remoteDataSlots.toIntArray());
+    }
+  }
+
+  @Override
+  public void broadcastCarriedItem() {
+    this.remoteCarried = this.getCarried().copy();
+    if (this.synchronizer != null) {
+      this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+    }
+  }
+
+  @Override
+  public void removeSlotListener(@NotNull ContainerListener containerListener) {
+    this.containerListeners.remove(containerListener);
+  }
+
+  @Override
+  public void broadcastChanges() {
+    for (int index = 0; index < this.slots.size(); ++index) {
+      Slot slot = this.slots.get(index);
+      ItemStack itemstack = slot instanceof SlotPlaceholder placeholder ? placeholder.getOrDefault() : slot.getItem();
+      Supplier<ItemStack> supplier = Suppliers.memoize(itemstack::copy);
+      this.triggerSlotListeners(index, itemstack, supplier);
+      this.synchronizeSlotToRemote(index, itemstack, supplier);
+    }
+
+    this.synchronizeCarriedToRemote();
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      DataSlot dataSlot = this.dataSlots.get(index);
+      int j = dataSlot.get();
+      if (dataSlot.checkAndClearUpdateFlag()) {
+        this.updateDataSlotListeners(index, j);
+      }
+
+      this.synchronizeDataSlotToRemote(index, j);
+    }
+  }
+
+  @Override
+  public void broadcastFullState() {
+    for (int index = 0; index < this.slots.size(); ++index) {
+      ItemStack itemstack = this.slots.get(index).getItem();
+      this.triggerSlotListeners(index, itemstack, itemstack::copy);
+    }
+
+    for (int index = 0; index < this.dataSlots.size(); ++index) {
+      DataSlot containerproperty = this.dataSlots.get(index);
+      if (containerproperty.checkAndClearUpdateFlag()) {
+        this.updateDataSlotListeners(index, containerproperty.get());
+      }
+    }
+
+    this.sendAllDataToRemote();
+  }
+
+  private void updateDataSlotListeners(int i, int j) {
+    for (ContainerListener containerListener : this.containerListeners) {
+      containerListener.dataChanged(this, i, j);
+    }
+  }
+
+  private void triggerSlotListeners(int index, ItemStack itemStack, Supplier<ItemStack> supplier) {
+    ItemStack itemStack1 = this.lastSlots.get(index);
+    if (!ItemStack.matches(itemStack1, itemStack)) {
+      ItemStack itemStack2 = supplier.get();
+      this.lastSlots.set(index, itemStack2);
+
+      for (ContainerListener containerListener : this.containerListeners) {
+        containerListener.slotChanged(this, index, itemStack2);
+      }
+    }
+  }
+
+  private void synchronizeSlotToRemote(int i, ItemStack itemStack, Supplier<ItemStack> supplier) {
+    if (!this.suppressRemoteUpdates) {
+      ItemStack itemStack1 = this.remoteSlots.get(i);
+      if (!ItemStack.matches(itemStack1, itemStack)) {
+        ItemStack itemstack2 = supplier.get();
+        this.remoteSlots.set(i, itemstack2);
+        if (this.synchronizer != null) {
+          this.synchronizer.sendSlotChange(this, i, itemstack2);
+        }
+      }
+    }
+  }
+
+  private void synchronizeDataSlotToRemote(int index, int value) {
+    if (!this.suppressRemoteUpdates) {
+      int existing = this.remoteDataSlots.getInt(index);
+      if (existing != value) {
+        this.remoteDataSlots.set(index, value);
+        if (this.synchronizer != null) {
+          this.synchronizer.sendDataChange(this, index, value);
+        }
+      }
+    }
+  }
+
+  private void synchronizeCarriedToRemote() {
+    if (!this.suppressRemoteUpdates && !ItemStack.matches(this.getCarried(), this.remoteCarried)) {
+      this.remoteCarried = this.getCarried().copy();
+      if (this.synchronizer != null) {
+        this.synchronizer.sendCarriedChange(this, this.remoteCarried);
+      }
+    }
+  }
+
+  @Override
+  public void setRemoteCarried(ItemStack itemstack) {
+    this.remoteCarried = itemstack.copy();
+  }
+
+  @Override
+  public void suppressRemoteUpdates() {
+    this.suppressRemoteUpdates = true;
+  }
+
+  @Override
+  public void resumeRemoteUpdates() {
+    this.suppressRemoteUpdates = false;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/menu/OpenEnderChestMenu.java

@@ -0,0 +1,59 @@
+package com.lishid.openinv.internal.paper1_21_4.container.menu;
+
+import com.lishid.openinv.internal.common.container.OpenEnderChest;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.jetbrains.annotations.NotNull;
+
+public class OpenEnderChestMenu extends OpenChestMenu<OpenEnderChest> {
+
+  public OpenEnderChestMenu(
+      @NotNull OpenEnderChest enderChest,
+      @NotNull ServerPlayer viewer,
+      int containerId,
+      boolean viewOnly) {
+    super(
+        com.lishid.openinv.internal.common.container.menu.OpenChestMenu.getChestMenuType(enderChest.getContainerSize()),
+        containerId,
+        enderChest,
+        viewer,
+        viewOnly
+    );
+  }
+
+  @Override
+  public @NotNull ItemStack quickMoveStack(@NotNull Player player, int index) {
+    if (viewOnly) {
+      return ItemStack.EMPTY;
+    }
+
+    // See ChestMenu
+    Slot slot = this.slots.get(index);
+
+    if (slot.isFake() || !slot.hasItem()) {
+      return ItemStack.EMPTY;
+    }
+
+    ItemStack itemStack = slot.getItem();
+    ItemStack original = itemStack.copy();
+
+    if (index < topSize) {
+      if (!this.moveItemStackTo(itemStack, topSize, this.slots.size(), true)) {
+        return ItemStack.EMPTY;
+      }
+    } else if (!this.moveItemStackTo(itemStack, 0, topSize, false)) {
+      return ItemStack.EMPTY;
+    }
+
+    if (itemStack.isEmpty()) {
+      slot.setByPlayer(ItemStack.EMPTY);
+    } else {
+      slot.setChanged();
+    }
+
+    return original;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/menu/OpenInventoryMenu.java

@@ -0,0 +1,262 @@
+package com.lishid.openinv.internal.paper1_21_4.container.menu;
+
+import com.google.common.base.Preconditions;
+import com.lishid.openinv.internal.common.container.bukkit.OpenDummyPlayerInventory;
+import com.lishid.openinv.internal.common.container.slot.ContentDrop;
+import com.lishid.openinv.internal.common.container.slot.SlotViewOnly;
+import com.lishid.openinv.internal.paper1_21_4.container.OpenInventory;
+import com.lishid.openinv.internal.paper1_21_4.container.bukkit.OpenPlayerInventorySelf;
+import com.lishid.openinv.internal.paper1_21_4.container.slot.ContentEquipment;
+import com.lishid.openinv.util.Permissions;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.ChestMenu;
+import net.minecraft.world.inventory.MenuType;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.craftbukkit.inventory.CraftInventoryView;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryView;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenInventoryMenu extends OpenChestMenu<OpenInventory> {
+
+  private int offset;
+
+  public OpenInventoryMenu(OpenInventory inventory, ServerPlayer viewer, int i, boolean viewOnly) {
+    super(getMenuType(inventory, viewer), i, inventory, viewer, viewOnly);
+  }
+
+  private static MenuType<ChestMenu> getMenuType(OpenInventory inventory, ServerPlayer viewer) {
+    int size = inventory.getContainerSize();
+    // Disallow duplicate access to own main inventory contents.
+    if (inventory.getOwnerHandle().equals(viewer)) {
+      size -= viewer.getInventory().items.size();
+      size = ((int) Math.ceil(size / 9.0)) * 9;
+    }
+
+    return com.lishid.openinv.internal.common.container.menu.OpenChestMenu.getChestMenuType(size);
+  }
+
+  @Override
+  protected void preSlotSetup() {
+    offset = ownContainer ? viewer.getInventory().items.size() : 0;
+  }
+
+  @Override
+  protected @NotNull Slot getUpperSlot(int index, int x, int y) {
+    index += offset;
+    Slot slot = container.getMenuSlot(index, x, y);
+
+    // If the slot cannot be interacted with there's nothing to configure.
+    if (slot.getClass().equals(SlotViewOnly.class)) {
+      return slot;
+    }
+
+    // Remove drop slot if viewer is not allowed to use it.
+    if (slot instanceof ContentDrop.SlotDrop
+        && (viewOnly || !Permissions.INVENTORY_SLOT_DROP.hasPermission(viewer.getBukkitEntity()))) {
+      return new SlotViewOnly(container, index, x, y);
+    }
+
+    if (slot instanceof ContentEquipment.SlotEquipment equipment) {
+      if (viewOnly) {
+        return SlotViewOnly.wrap(slot);
+      }
+
+      Permissions perm = switch (equipment.getEquipmentSlot()) {
+        case HEAD -> Permissions.INVENTORY_SLOT_HEAD_ANY;
+        case CHEST -> Permissions.INVENTORY_SLOT_CHEST_ANY;
+        case LEGS -> Permissions.INVENTORY_SLOT_LEGS_ANY;
+        case FEET -> Permissions.INVENTORY_SLOT_FEET_ANY;
+        // Off-hand can hold anything, not just equipment.
+        default -> null;
+      };
+
+      // If the viewer doesn't have permission, only allow equipment the viewee can equip in the slot.
+      if (perm != null && !perm.hasPermission(viewer.getBukkitEntity())) {
+        equipment.onlyEquipmentFor(container.getOwnerHandle());
+      }
+
+      // Equipment slots are a core part of the inventory, so they will always be shown.
+      return slot;
+    }
+
+    // When viewing own inventory, only allow access to equipment and drop slots (equipment allowed above).
+    if (ownContainer && !(slot instanceof ContentDrop.SlotDrop)) {
+      return new SlotViewOnly(container, index, x, y);
+    }
+
+    if (viewOnly) {
+      return SlotViewOnly.wrap(slot);
+    }
+
+    return slot;
+  }
+
+  @Override
+  protected @NotNull CraftInventoryView<OpenChestMenu<OpenInventory>, Inventory> createBukkitEntity() {
+    org.bukkit.inventory.Inventory bukkitInventory;
+    if (viewOnly) {
+      bukkitInventory = new OpenDummyPlayerInventory(container);
+    } else if (ownContainer) {
+      bukkitInventory = new OpenPlayerInventorySelf(container, offset);
+    } else {
+      bukkitInventory = container.getBukkitInventory();
+    }
+
+    return new CraftInventoryView<>(viewer.getBukkitEntity(), bukkitInventory, this) {
+      @Override
+      public org.bukkit.inventory.ItemStack getItem(int index) {
+        if (viewOnly || index < 0) {
+          return null;
+        }
+
+        Slot slot = slots.get(index);
+        return CraftItemStack.asCraftMirror(slot.hasItem() ? slot.getItem() : ItemStack.EMPTY);
+      }
+
+      @Override
+      public boolean isInTop(int rawSlot) {
+        return rawSlot < topSize;
+      }
+
+      @Override
+      public @Nullable Inventory getInventory(int rawSlot) {
+        if (viewOnly) {
+          return null;
+        }
+        if (rawSlot == InventoryView.OUTSIDE || rawSlot == -1) {
+          return null;
+        }
+        Preconditions.checkArgument(rawSlot >= 0 && rawSlot < topSize + offset + BOTTOM_INVENTORY_SIZE,
+            "Slot %s outside of inventory", rawSlot);
+        if (rawSlot > topSize) {
+          return getBottomInventory();
+        }
+        Slot slot = slots.get(rawSlot);
+        if (slot.isFake()) {
+          return null;
+        }
+        return getTopInventory();
+      }
+
+      @Override
+      public int convertSlot(int rawSlot) {
+        if (viewOnly) {
+          return InventoryView.OUTSIDE;
+        }
+        if (rawSlot < 0) {
+          return rawSlot;
+        }
+        if (rawSlot < topSize) {
+          Slot slot = slots.get(rawSlot);
+          if (slot.isFake()) {
+            return InventoryView.OUTSIDE;
+          }
+          return rawSlot;
+        }
+
+        int slot = rawSlot - topSize;
+
+        if (slot >= 27) {
+          slot -= 27;
+        } else {
+          slot += 9;
+        }
+
+        return slot;
+      }
+
+      @Override
+      public @NotNull InventoryType.SlotType getSlotType(int slot) {
+        if (viewOnly || slot < 0) {
+          return InventoryType.SlotType.OUTSIDE;
+        }
+        if (slot >= topSize) {
+          slot -= topSize;
+          if (slot >= 27) {
+            return InventoryType.SlotType.QUICKBAR;
+          }
+          return InventoryType.SlotType.CONTAINER;
+        }
+        return OpenInventoryMenu.this.container.getSlotType(offset + slot);
+      }
+
+      @Override
+      public int countSlots() {
+        return topSize + BOTTOM_INVENTORY_SIZE;
+      }
+    };
+  }
+
+  @Override
+  public @NotNull ItemStack quickMoveStack(@NotNull Player player, int index) {
+    if (viewOnly) {
+      return ItemStack.EMPTY;
+    }
+
+    // See ChestMenu and InventoryMenu
+    Slot slot = this.slots.get(index);
+
+    if (!slot.hasItem() || slot.isFake()) {
+      return ItemStack.EMPTY;
+    }
+
+    ItemStack itemStack = slot.getItem();
+    ItemStack originalStack = itemStack.copy();
+
+    if (index < topSize) {
+      // If we're moving top to bottom, do a normal transfer.
+      if (!this.moveItemStackTo(itemStack, topSize, this.slots.size(), true)) {
+        return ItemStack.EMPTY;
+      }
+    } else {
+      EquipmentSlot equipmentSlot = player.getEquipmentSlotForItem(itemStack);
+      boolean movedGear = switch (equipmentSlot) {
+        // If this is gear, try to move it to the correct slot first.
+        case OFFHAND, FEET, LEGS, CHEST, HEAD -> {
+          // Locate the correct slot in the contents following the main inventory.
+          for (int extra = container.getOwnerHandle().getInventory().items.size() - offset; extra < topSize; ++extra) {
+            Slot extraSlot = getSlot(extra);
+            if (extraSlot instanceof ContentEquipment.SlotEquipment equipSlot
+                && equipSlot.getEquipmentSlot() == equipmentSlot) {
+              // If we've found a matching slot, try to move to it.
+              // If this succeeds, even partially, we will not attempt to move to other slots.
+              // Otherwise, armor is already occupied, so we'll fall through to main inventory.
+              yield this.moveItemStackTo(itemStack, extra, extra + 1, false);
+            }
+          }
+          yield false;
+        }
+        // Non-gear gets no special treatment.
+        default -> false;
+      };
+
+      // If main inventory is not available, there's nowhere else to move.
+      if (offset != 0) {
+        if (!movedGear) {
+          return ItemStack.EMPTY;
+        }
+      } else {
+        // If we didn't move to a gear slot, try to move to a main inventory slot.
+        if (!movedGear && !this.moveItemStackTo(itemStack, 0, container.getOwnerHandle().getInventory().items.size(), true)) {
+          return ItemStack.EMPTY;
+        }
+      }
+    }
+
+    if (itemStack.isEmpty()) {
+      slot.setByPlayer(ItemStack.EMPTY);
+    } else {
+      slot.setChanged();
+    }
+
+    return originalStack;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/slot/ContentEquipment.java

@@ -0,0 +1,80 @@
+package com.lishid.openinv.internal.paper1_21_4.container.slot;
+
+import com.lishid.openinv.internal.common.container.slot.ContentList;
+import com.lishid.openinv.internal.common.container.slot.SlotPlaceholder;
+import com.lishid.openinv.internal.common.container.slot.placeholder.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot for equipment that displays placeholders if empty.
+ */
+public class ContentEquipment extends ContentList {
+
+  private final ItemStack placeholder;
+  private final EquipmentSlot equipmentSlot;
+
+  public ContentEquipment(ServerPlayer holder, int index, EquipmentSlot equipmentSlot) {
+    super(holder, index, InventoryType.SlotType.ARMOR);
+    placeholder = switch (equipmentSlot) {
+      case HEAD -> Placeholders.emptyHelmet;
+      case CHEST -> Placeholders.emptyChestplate;
+      case LEGS -> Placeholders.emptyLeggings;
+      case FEET -> Placeholders.emptyBoots;
+      default -> Placeholders.emptyOffHand;
+    };
+    this.equipmentSlot = equipmentSlot;
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.items = holder.getInventory().armor;
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y);
+  }
+
+  public class SlotEquipment extends SlotPlaceholder {
+
+    private ServerPlayer viewer;
+
+    SlotEquipment(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      ItemStack itemStack = getItem();
+      if (!itemStack.isEmpty()) {
+        return itemStack;
+      }
+      return placeholder;
+    }
+
+    public EquipmentSlot getEquipmentSlot() {
+      return equipmentSlot;
+    }
+
+    public void onlyEquipmentFor(ServerPlayer viewer) {
+      this.viewer = viewer;
+    }
+
+    @Override
+    public boolean mayPlace(@NotNull ItemStack itemStack) {
+      if (viewer == null) {
+        return true;
+      }
+
+      return equipmentSlot == EquipmentSlot.OFFHAND || viewer.getEquipmentSlotForItem(itemStack) == equipmentSlot;
+    }
+
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/slot/ContentOffHand.java

@@ -0,0 +1,52 @@
+package com.lishid.openinv.internal.paper1_21_4.container.slot;
+
+import com.lishid.openinv.internal.common.player.OpenPlayer;
+import net.minecraft.network.protocol.game.ClientboundContainerSetSlotPacket;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.InventoryMenu;
+import net.minecraft.world.inventory.Slot;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A slot for equipment that updates held items if necessary.
+ */
+public class ContentOffHand extends ContentEquipment {
+
+  private ServerPlayer holder;
+
+  public ContentOffHand(ServerPlayer holder, int localIndex) {
+    super(holder, localIndex, EquipmentSlot.OFFHAND);
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.items = holder.getInventory().offhand;
+    this.holder = holder;
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.QUICKBAR;
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y) {
+      @Override
+      public void setChanged() {
+        if (OpenPlayer.isConnected(holder.connection) && holder.containerMenu != holder.inventoryMenu) {
+          holder.connection.send(
+              new ClientboundContainerSetSlotPacket(
+                  holder.inventoryMenu.containerId,
+                  holder.inventoryMenu.incrementStateId(),
+                  InventoryMenu.SHIELD_SLOT,
+                  holder.getOffhandItem()));
+        }
+      }
+    };
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/slot/placeholder/CustomModelBase.java

@@ -0,0 +1,41 @@
+package com.lishid.openinv.internal.paper1_21_4.container.slot.placeholder;
+
+import com.lishid.openinv.internal.common.container.slot.placeholder.PlaceholderLoaderBase;
+import net.minecraft.core.component.DataComponents;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.TagParser;
+import net.minecraft.util.Unit;
+import net.minecraft.world.item.ItemStack;
+import net.minecraft.world.item.component.CustomModelData;
+import net.minecraft.world.item.component.DyedItemColor;
+import org.jetbrains.annotations.NotNull;
+
+public class CustomModelBase extends PlaceholderLoaderBase {
+
+  private final @NotNull CustomModelData defaultCustomModelData;
+
+  public CustomModelBase(@NotNull CustomModelData defaultCustomModelData) {
+    this.defaultCustomModelData = defaultCustomModelData;
+  }
+
+  @Override
+  protected @NotNull CompoundTag parseTag(@NotNull String itemText) throws Exception {
+    return TagParser.parseTag(itemText);
+  }
+
+  @Override
+  protected void addModelData(@NotNull ItemStack itemStack) {
+    itemStack.set(DataComponents.CUSTOM_MODEL_DATA, defaultCustomModelData);
+  }
+
+  @Override
+  protected void hideTooltip(@NotNull ItemStack itemStack) {
+    itemStack.set(DataComponents.HIDE_TOOLTIP, Unit.INSTANCE);
+  }
+
+  @Override
+  protected DyedItemColor getDye(int rgb) {
+    return new DyedItemColor(rgb, false);
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/container/slot/placeholder/CustomModelPlaceholderLoader.java

@@ -0,0 +1,13 @@
+package com.lishid.openinv.internal.paper1_21_4.container.slot.placeholder;
+
+import net.minecraft.world.item.component.CustomModelData;
+
+import java.util.List;
+
+public class CustomModelPlaceholderLoader extends CustomModelBase {
+
+  public CustomModelPlaceholderLoader() {
+    super(new CustomModelData(List.of(), List.of(), List.of("openinv:custom"), List.of()));
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/player/OpenPlayer.java

@@ -0,0 +1,35 @@
+package com.lishid.openinv.internal.paper1_21_4.player;
+
+import com.lishid.openinv.internal.common.player.PlayerManager;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.server.level.ServerPlayer;
+import org.bukkit.craftbukkit.CraftServer;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenPlayer extends com.lishid.openinv.internal.common.player.OpenPlayer {
+
+  protected OpenPlayer(CraftServer server, ServerPlayer entity,
+      PlayerManager manager) {
+    super(server, entity, manager);
+  }
+
+  @Contract("null -> new")
+  @Override
+  protected @NotNull CompoundTag getWritableTag(@Nullable CompoundTag oldData) {
+    if (oldData == null) {
+      return new CompoundTag();
+    }
+
+    // Copy old data. This is a deep clone, so operating on it should be safe.
+    oldData = oldData.copy();
+
+    // Remove vanilla/server data that is not written every time.
+    oldData.getAllKeys()
+        .removeIf(key -> RESET_TAGS.contains(key) || key.startsWith("Bukkit"));
+
+    return oldData;
+  }
+
+}

internal/paper1_21_4/src/main/java/com/lishid/openinv/internal/paper1_21_4/player/PlayerManager.java

@@ -0,0 +1,70 @@
+package com.lishid.openinv.internal.paper1_21_4.player;
+
+import com.mojang.serialization.Dynamic;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtOps;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.DimensionType;
+import org.bukkit.Bukkit;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.CraftWorld;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.UUID;
+import java.util.logging.Logger;
+
+public class PlayerManager extends com.lishid.openinv.internal.common.player.PlayerManager {
+
+  public PlayerManager(@NotNull Logger logger) {
+    super(logger);
+  }
+
+  protected void parseWorld(@NotNull ServerPlayer player, @NotNull CompoundTag loadedData) {
+    // See PlayerList#placeNewPlayer
+    World bukkitWorld;
+    if (loadedData.contains("WorldUUIDMost") && loadedData.contains("WorldUUIDLeast")) {
+      // Modern Bukkit world.
+      bukkitWorld = Bukkit.getServer().getWorld(new UUID(loadedData.getLong("WorldUUIDMost"), loadedData.getLong("WorldUUIDLeast")));
+    } else if (loadedData.contains("world", net.minecraft.nbt.Tag.TAG_STRING)) {
+      // Legacy Bukkit world.
+      bukkitWorld = Bukkit.getServer().getWorld(loadedData.getString("world"));
+    } else {
+      // Vanilla player data.
+      DimensionType.parseLegacy(new Dynamic<>(NbtOps.INSTANCE, loadedData.get("Dimension")))
+          .resultOrPartial(logger::warning)
+          .map(player.server::getLevel)
+          // If ServerLevel exists, set, otherwise move to spawn.
+          .ifPresentOrElse(player::setServerLevel, () -> spawnInDefaultWorld(player));
+      return;
+    }
+    if (bukkitWorld == null) {
+      spawnInDefaultWorld(player);
+      return;
+    }
+    player.setServerLevel(((CraftWorld) bukkitWorld).getHandle());
+  }
+
+  @Override
+  protected void spawnInDefaultWorld(ServerPlayer player) {
+    ServerLevel level = player.server.getLevel(Level.OVERWORLD);
+    if (level != null) {
+      // Adjust player to default spawn (in keeping with Paper handling) when world not found.
+      player.moveTo(player.adjustSpawnLocation(level, level.getSharedSpawnPos()).getBottomCenter(), level.getSharedSpawnAngle(), 0.0F);
+      player.spawnIn(level);
+    } else {
+      logger.warning("Tried to load player with invalid world when no fallback was available!");
+    }
+  }
+
+  protected void injectPlayer(ServerPlayer player) throws IllegalAccessException {
+    if (bukkitEntity == null) {
+      return;
+    }
+
+    bukkitEntity.setAccessible(true);
+    bukkitEntity.set(player, new OpenPlayer(player.server.server, player, this));
+  }
+
+}

internal/spigot/build.gradle.kts

@@ -1,15 +1,18 @@
+import com.github.jikoo.openinv.SpigotDependencyExtension
+import com.github.jikoo.openinv.SpigotReobf
+import com.github.jikoo.openinv.SpigotSetup
+
 plugins {
   `openinv-base`
   alias(libs.plugins.shadow)
 }
 
-repositories {
-  mavenLocal()
-}
+apply<SpigotSetup>()
+apply<SpigotReobf>()
 
-val spigotVer = "1.21.4-R0.1-SNAPSHOT"
-rootProject.extra["spigotVersion"] = spigotVer
-rootProject.extra["craftbukkitPackage"] = "v1_21_R3"
+val spigotVer = "1.21.5-R0.1-SNAPSHOT"
+// Used by common adapter to relocate Craftbukkit classes to a versioned package.
+rootProject.extra["craftbukkitPackage"] = "v1_21_R4"
 
 configurations.all {
   resolutionStrategy.capabilitiesResolution.withCapability("org.spigotmc:spigot-api") {
@@ -25,12 +28,9 @@ configurations.all {
   }
 }
 
-val spigotRemap = configurations.create("spigotRemap")
-
 dependencies {
-  spigotRemap("net.md-5:SpecialSource:1.11.4:shaded")
   compileOnly(libs.spigotapi)
-  compileOnly(create("org.spigotmc", "spigot", spigotVer, classifier = "remapped-mojang"))
+  extensions.getByType(SpigotDependencyExtension::class.java).version = spigotVer
 
   compileOnly(project(":openinvapi"))
   compileOnly(project(":openinvcommon"))
@@ -42,25 +42,3 @@ dependencies {
 tasks.shadowJar {
   relocate("com.lishid.openinv.internal.common", "com.lishid.openinv.internal.reobf")
 }
-
-val reobfTask = tasks.register<ReobfTask>("reobfTask") {
-  notCompatibleWithConfigurationCache("gradle is hard")
-  dependsOn(tasks.shadowJar)
-  inputFile.value(tasks.shadowJar.get().archiveFile.get())
-  spigotVersion.value(spigotVer)
-}
-
-configurations {
-  consumable("reobf") {
-    attributes {
-      attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.LIBRARY))
-      attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage.JAVA_RUNTIME))
-      attribute(Bundling.BUNDLING_ATTRIBUTE, objects.named(Bundling.EXTERNAL))
-      attribute(LibraryElements.LIBRARY_ELEMENTS_ATTRIBUTE, objects.named(LibraryElements.JAR))
-    }
-  }
-}
-
-artifacts {
-  add("reobf", reobfTask)
-}

internal/spigot/src/main/java/com/lishid/openinv/internal/reobf/container/AnySilentContainer.java

@@ -45,10 +45,10 @@ public class AnySilentContainer extends AnySilentContainerBase {
     this.lang = lang;
     try {
       try {
-        this.serverPlayerGameModeGameType = ServerPlayerGameMode.class.getDeclaredField("b");
+        this.serverPlayerGameModeGameType = ServerPlayerGameMode.class.getDeclaredField("gameModeForPlayer");
         this.serverPlayerGameModeGameType.setAccessible(true);
       } catch (NoSuchFieldException e) {
-        logger.warning("The mapping of ServerPlayerGameMode#gameModeForPlayer has changed!");
+        logger.warning("The field ServerPlayerGameMode#gameModeForPlayer is no longer present!");
         logger.warning("Please report this at https://github.com/Jikoo/OpenInv/issues");
         logger.warning("Attempting to fall through using reflection. Please verify that SilentContainer does not fail.");
         // N.B. gameModeForPlayer is (for now) declared before previousGameModeForPlayer so silent shouldn't break.

internal/spigot/src/main/java/com/lishid/openinv/internal/reobf/container/bukkit/OpenPlayerInventory.java

@@ -0,0 +1,188 @@
+package com.lishid.openinv.internal.reobf.container.bukkit;
+
+import com.google.common.base.Preconditions;
+import com.lishid.openinv.internal.reobf.container.OpenInventory;
+import net.minecraft.core.NonNullList;
+import net.minecraft.world.entity.player.Inventory;
+import org.bukkit.craftbukkit.v1_21_R4.inventory.CraftInventory;
+import org.bukkit.craftbukkit.v1_21_R4.inventory.CraftItemStack;
+import org.bukkit.entity.Player;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.PlayerInventory;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class OpenPlayerInventory extends CraftInventory implements PlayerInventory {
+
+  public OpenPlayerInventory(@NotNull OpenInventory inventory) {
+    super(inventory);
+  }
+
+  @Override
+  public @NotNull OpenInventory getInventory() {
+    return (OpenInventory) super.getInventory();
+  }
+
+  @Override
+  public ItemStack @NotNull [] getContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getContents());
+  }
+
+  @Override
+  public void setContents(ItemStack[] items) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    int size = internal.getContainerSize();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+
+    for (int index = 0; index < size; ++index) {
+      if (index < items.length) {
+        internal.setItem(index, CraftItemStack.asNMSCopy(items[index]));
+      } else {
+        internal.setItem(index, net.minecraft.world.item.ItemStack.EMPTY);
+      }
+    }
+  }
+
+  @Override
+  public ItemStack @NotNull [] getStorageContents() {
+    return asCraftMirror(getInventory().getOwnerHandle().getInventory().getNonEquipmentItems());
+  }
+
+  @Override
+  public void setStorageContents(ItemStack[] items) throws IllegalArgumentException {
+    NonNullList<net.minecraft.world.item.ItemStack> list = getInventory().getOwnerHandle().getInventory().getNonEquipmentItems();
+    int size = list.size();
+    Preconditions.checkArgument(items.length <= size, "items.length must be <= %s", size);
+    for (int index = 0; index < items.length; ++index) {
+      list.set(index, CraftItemStack.asNMSCopy(items[index]));
+    }
+  }
+
+  @Override
+  public @NotNull InventoryType getType() {
+    return InventoryType.PLAYER;
+  }
+
+  @Override
+  public @NotNull Player getHolder() {
+    return getInventory().getOwner();
+  }
+
+  @Override
+  public @NotNull ItemStack @NotNull [] getArmorContents() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getArmorContents();
+  }
+
+  @Override
+  public void setArmorContents(ItemStack @NotNull [] items) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setArmorContents(items);
+  }
+
+  @Override
+  public @NotNull ItemStack @NotNull [] getExtraContents() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getExtraContents();
+  }
+
+  @Override
+  public void setExtraContents(ItemStack @NotNull [] items) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setExtraContents(items);
+  }
+
+  @Override
+  public @Nullable ItemStack getHelmet() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getHelmet();
+  }
+
+  @Override
+  public void setHelmet(@Nullable ItemStack helmet) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setHelmet(helmet);
+  }
+
+  @Override
+  public @Nullable ItemStack getChestplate() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getChestplate();
+  }
+
+  @Override
+  public void setChestplate(@Nullable ItemStack chestplate) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setChestplate(chestplate);
+  }
+
+  @Override
+  public @Nullable ItemStack getLeggings() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getLeggings();
+  }
+
+  @Override
+  public void setLeggings(@Nullable ItemStack leggings) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setLeggings(leggings);
+  }
+
+  @Override
+  public @Nullable ItemStack getBoots() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getBoots();
+  }
+
+  @Override
+  public void setBoots(@Nullable ItemStack boots) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setBoots(boots);
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInMainHand() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return CraftItemStack.asCraftMirror(internal.getSelectedItem());
+  }
+
+  @Override
+  public void setItemInMainHand(@Nullable ItemStack item) {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    internal.setSelectedItem(CraftItemStack.asNMSCopy(item));
+  }
+
+  @Override
+  public @NotNull ItemStack getItemInOffHand() {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getItemInOffHand();
+  }
+
+  @Override
+  public void setItemInOffHand(@Nullable ItemStack item) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setItemInOffHand(item);
+  }
+
+  @Deprecated
+  @Override
+  public @NotNull ItemStack getItemInHand() {
+    return getItemInMainHand();
+  }
+
+  @Deprecated
+  @Override
+  public void setItemInHand(@Nullable ItemStack stack) {
+    setItemInMainHand(stack);
+  }
+
+  @Override
+  public int getHeldItemSlot() {
+    Inventory internal = getInventory().getOwnerHandle().getInventory();
+    return internal.getNonEquipmentItems().size() - 9 + internal.getSelectedSlot();
+  }
+
+  @Override
+  public void setHeldItemSlot(int slot) {
+    slot %= 9;
+    getInventory().getOwnerHandle().getInventory().setSelectedSlot(slot);
+  }
+
+  @Override
+  public @Nullable ItemStack getItem(@NotNull org.bukkit.inventory.EquipmentSlot slot) {
+    return getInventory().getOwnerHandle().getBukkitEntity().getInventory().getItem(slot);
+  }
+
+  @Override
+  public void setItem(@NotNull org.bukkit.inventory.EquipmentSlot slot, @Nullable ItemStack item) {
+    getInventory().getOwnerHandle().getBukkitEntity().getInventory().setItem(slot, item);
+  }
+
+}

internal/spigot/src/main/java/com/lishid/openinv/internal/reobf/container/slot/ContentEquipment.java

@@ -0,0 +1,116 @@
+package com.lishid.openinv.internal.reobf.container.slot;
+
+import com.lishid.openinv.internal.reobf.container.slot.placeholder.Placeholders;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.Slot;
+import net.minecraft.world.item.ItemStack;
+import org.bukkit.craftbukkit.v1_21_R4.CraftEquipmentSlot;
+import org.bukkit.craftbukkit.v1_21_R4.inventory.CraftItemStack;
+import org.bukkit.event.inventory.InventoryType;
+import org.bukkit.inventory.PlayerInventory;
+import org.jetbrains.annotations.NotNull;
+
+public class ContentEquipment implements Content {
+
+  private PlayerInventory equipment;
+  private final ItemStack placeholder;
+  private final org.bukkit.inventory.EquipmentSlot equipmentSlot;
+
+  public ContentEquipment(ServerPlayer holder, EquipmentSlot equipmentSlot) {
+    setHolder(holder);
+    placeholder = switch (equipmentSlot) {
+      case HEAD -> Placeholders.emptyHelmet;
+      case CHEST -> Placeholders.emptyChestplate;
+      case LEGS -> Placeholders.emptyLeggings;
+      case FEET -> Placeholders.emptyBoots;
+      default -> Placeholders.emptyOffHand;
+    };
+    this.equipmentSlot = CraftEquipmentSlot.getSlot(equipmentSlot);
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    this.equipment = holder.getBukkitEntity().getInventory();
+  }
+
+  @Override
+  public ItemStack get() {
+    return CraftItemStack.asNMSCopy(equipment.getItem(equipmentSlot));
+  }
+
+  @Override
+  public ItemStack remove() {
+    org.bukkit.inventory.ItemStack old = equipment.getItem(equipmentSlot);
+    equipment.setItem(equipmentSlot, null);
+    return CraftItemStack.asNMSCopy(old);
+  }
+
+  @Override
+  public ItemStack removePartial(int amount) {
+    if (amount <= 0) {
+      return ItemStack.EMPTY;
+    }
+    ItemStack current = get();
+    if (current.isEmpty()) {
+      return ItemStack.EMPTY;
+    }
+    ItemStack split = current.split(amount);
+    set(current);
+    return split;
+  }
+
+  @Override
+  public void set(ItemStack itemStack) {
+    equipment.setItem(equipmentSlot, CraftItemStack.asCraftMirror(itemStack));
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y);
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.ARMOR;
+  }
+
+  public class SlotEquipment extends SlotPlaceholder {
+
+    private ServerPlayer viewer;
+
+    SlotEquipment(Container container, int index, int x, int y) {
+      super(container, index, x, y);
+    }
+
+    @Override
+    public ItemStack getOrDefault() {
+      ItemStack itemStack = getItem();
+      if (!itemStack.isEmpty()) {
+        return itemStack;
+      }
+      return placeholder;
+    }
+
+    public EquipmentSlot getEquipmentSlot() {
+      return CraftEquipmentSlot.getNMS(equipmentSlot);
+    }
+
+    public void onlyEquipmentFor(ServerPlayer viewer) {
+      this.viewer = viewer;
+    }
+
+    @Override
+    public boolean mayPlace(@NotNull ItemStack itemStack) {
+      if (viewer == null) {
+        return true;
+      }
+
+      return equipmentSlot == org.bukkit.inventory.EquipmentSlot.OFF_HAND
+          || viewer.getEquipmentSlotForItem(itemStack) == CraftEquipmentSlot.getNMS(equipmentSlot);
+    }
+
+  }
+
+}

internal/spigot/src/main/java/com/lishid/openinv/internal/reobf/container/slot/ContentOffHand.java

@@ -0,0 +1,49 @@
+package com.lishid.openinv.internal.reobf.container.slot;
+
+import com.lishid.openinv.internal.reobf.player.OpenPlayer;
+import net.minecraft.network.protocol.game.ClientboundContainerSetSlotPacket;
+import net.minecraft.server.level.ServerPlayer;
+import net.minecraft.world.Container;
+import net.minecraft.world.entity.EquipmentSlot;
+import net.minecraft.world.inventory.InventoryMenu;
+import net.minecraft.world.inventory.Slot;
+import org.bukkit.event.inventory.InventoryType;
+import org.jetbrains.annotations.NotNull;
+
+public class ContentOffHand extends ContentEquipment {
+
+  private ServerPlayer holder;
+
+  public ContentOffHand(ServerPlayer holder) {
+    super(holder, EquipmentSlot.OFFHAND);
+  }
+
+  @Override
+  public void setHolder(@NotNull ServerPlayer holder) {
+    super.setHolder(holder);
+    this.holder = holder;
+  }
+
+  @Override
+  public InventoryType.SlotType getSlotType() {
+    return InventoryType.SlotType.QUICKBAR;
+  }
+
+  @Override
+  public Slot asSlot(Container container, int slot, int x, int y) {
+    return new SlotEquipment(container, slot, x, y) {
+      @Override
+      public void setChanged() {
+        if (OpenPlayer.isConnected(holder.connection) && holder.containerMenu != holder.inventoryMenu) {
+          holder.connection.send(
+              new ClientboundContainerSetSlotPacket(
+                  holder.inventoryMenu.containerId,
+                  holder.inventoryMenu.incrementStateId(),
+                  InventoryMenu.SHIELD_SLOT,
+                  holder.getOffhandItem()));
+        }
+      }
+    };
+  }
+
+}

internal/spigot/src/main/java/com/lishid/openinv/internal/reobf/player/PlayerManager.java

@@ -19,9 +19,9 @@ import net.minecraft.world.level.Level;
 import org.bukkit.Bukkit;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.Server;
-import org.bukkit.craftbukkit.v1_21_R3.CraftServer;
-import org.bukkit.craftbukkit.v1_21_R3.entity.CraftPlayer;
-import org.bukkit.craftbukkit.v1_21_R3.event.CraftEventFactory;
+import org.bukkit.craftbukkit.v1_21_R4.CraftServer;
+import org.bukkit.craftbukkit.v1_21_R4.entity.CraftPlayer;
+import org.bukkit.craftbukkit.v1_21_R4.event.CraftEventFactory;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.InventoryView;
 import org.jetbrains.annotations.NotNull;

jitpack.yml

@@ -3,4 +3,4 @@ before_install:
   - sdk install java 21-tem
   - sdk use java 21-tem
 install:
-  - ./gradlew :openinvapi:publishJitpackPublicationToMavenLocal
+  - ./gradlew -Djitpack=true :openinvapi:publishJitpackPublicationToMavenLocal

plugin/build.gradle.kts

@@ -1,3 +1,5 @@
+import com.github.jikoo.openinv.SpigotReobf
+
 plugins {
   `openinv-base`
   alias(libs.plugins.shadow)
@@ -11,10 +13,12 @@ dependencies {
   implementation(project(":openinvapi"))
   implementation(project(":openinvcommon"))
   implementation(project(":openinvadaptercommon"))
+  implementation(project(":openinvadapterpaper1_21_4"))
   implementation(project(":openinvadapterpaper1_21_3"))
   implementation(project(":openinvadapterpaper1_21_1"))
-  implementation(project(":openinvadapterspigot", configuration = "reobf"))
+  implementation(project(":openinvadapterspigot", configuration = SpigotReobf.ARTIFACT_CONFIG))
   implementation(libs.planarwrappers)
+  implementation(libs.folia.scheduler.wrapper)
 }
 
 tasks.processResources {
@@ -26,8 +30,11 @@ tasks.jar {
 }
 
 tasks.shadowJar {
+  relocate("me.nahu.scheduler.wrapper", "com.github.jikoo.openinv.lib.nahu.scheduler-wrapper")
+  relocate("com.github.jikoo.planarwrappers", "com.github.jikoo.openinv.lib.planarwrappers")
   minimize {
     exclude(":openinv**")
+    exclude(dependency(libs.folia.scheduler.wrapper.get()))
   }
 }
 

plugin/src/main/java/com/lishid/openinv/OpenInv.java

@@ -38,6 +38,7 @@ import com.lishid.openinv.util.lang.LangMigrator;
 import com.lishid.openinv.util.lang.LanguageManager;
 import com.lishid.openinv.util.setting.PlayerToggle;
 import com.lishid.openinv.util.setting.PlayerToggles;
+import me.nahu.scheduler.wrapper.FoliaWrappedJavaPlugin;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandExecutor;
@@ -59,7 +60,7 @@ import java.util.function.Consumer;
 /**
  * The main class for OpenInv.
  */
-public class OpenInv extends JavaPlugin implements IOpenInv {
+public class OpenInv extends FoliaWrappedJavaPlugin implements IOpenInv {
 
     private InternalAccessor accessor;
     private Config config;

plugin/src/main/java/com/lishid/openinv/command/OpenInvCommand.java

@@ -26,13 +26,13 @@ import com.lishid.openinv.util.TabCompleter;
 import com.lishid.openinv.util.config.Config;
 import com.lishid.openinv.util.lang.LanguageManager;
 import com.lishid.openinv.util.lang.Replacement;
+import me.nahu.scheduler.wrapper.runnable.WrappedRunnable;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandSender;
 import org.bukkit.command.PluginCommand;
 import org.bukkit.command.TabExecutor;
 import org.bukkit.entity.Player;
-import org.bukkit.scheduler.BukkitRunnable;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Collections;
@@ -99,7 +99,7 @@ public class OpenInvCommand implements TabExecutor {
             name = args[0];
         }
 
-        new BukkitRunnable() {
+        new WrappedRunnable() {
             @Override
             public void run() {
                 final OfflinePlayer offlinePlayer = playerLoader.match(name);
@@ -109,7 +109,7 @@ public class OpenInvCommand implements TabExecutor {
                     return;
                 }
 
-                new BukkitRunnable() {
+                new WrappedRunnable() {
                     @Override
                     public void run() {
                         if (!player.isOnline()) {

plugin/src/main/java/com/lishid/openinv/util/InternalAccessor.java

@@ -64,7 +64,7 @@ public class InternalAccessor {
     }
 
     private @Nullable Accessor getAccessor(@NotNull Logger logger, @NotNull LanguageManager lang) {
-        Version maxSupported = Version.of(1, 21, 4);
+        Version maxSupported = Version.of(1, 21, 5);
         Version minSupported = Version.of(1, 21, 1);
 
         // Ensure version is in supported range.
@@ -84,14 +84,18 @@ public class InternalAccessor {
         }
 
         // Paper or a Paper fork, can use Mojang-mapped internals.
-        if (BukkitVersions.MINECRAFT.equals(maxSupported)) { // 1.21.4
+        if (BukkitVersions.MINECRAFT.equals(maxSupported)) { // 1.21.5
             return new com.lishid.openinv.internal.common.InternalAccessor(logger, lang);
-        } else if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 21, 3))) {
+        }
+        if (BukkitVersions.MINECRAFT.equals(Version.of(1, 21, 4))) { // 1.21.4
+            return new com.lishid.openinv.internal.paper1_21_4.InternalAccessor(logger, lang);
+        }
+        if (BukkitVersions.MINECRAFT.lessThan(Version.of(1, 21, 2))) {
             // 1.21.1-1.21.2 placeholder format
             return new com.lishid.openinv.internal.paper1_21_1.InternalAccessor(logger, lang);
         }
 
-        // 1.21.3
+        // 1.21.2, 1.21.3
         return new com.lishid.openinv.internal.paper1_21_3.InternalAccessor(logger, lang);
     }
 

plugin/src/main/java/com/lishid/openinv/util/InventoryManager.java

@@ -3,6 +3,7 @@ package com.lishid.openinv.util;
 import com.github.jikoo.planarwrappers.util.version.BukkitVersions;
 import com.github.jikoo.planarwrappers.util.version.Version;
 import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.OpenInv;
 import com.lishid.openinv.event.OpenEvents;
 import com.lishid.openinv.internal.ISpecialEnderChest;
 import com.lishid.openinv.internal.ISpecialInventory;
@@ -44,11 +45,11 @@ public class InventoryManager implements Listener {
   private final Map<UUID, ISpecialPlayerInventory> inventories = new ConcurrentHashMap<>();
   private final Map<UUID, ISpecialEnderChest> enderChests = new ConcurrentHashMap<>();
   private final Set<UUID> expectedCloses = new HashSet<>();
-  private final @NotNull Plugin plugin;
+  private final @NotNull OpenInv plugin;
   private final @NotNull Config config;
   private final @NotNull InternalAccessor accessor;
 
-  public InventoryManager(@NotNull Plugin plugin, @NotNull Config config, @NotNull InternalAccessor accessor) {
+  public InventoryManager(@NotNull OpenInv plugin, @NotNull Config config, @NotNull InternalAccessor accessor) {
     this.plugin = plugin;
     this.config = config;
     this.accessor = accessor;
@@ -164,7 +165,7 @@ public class InventoryManager implements Listener {
     }
 
     // Schedule task to check in use status later this tick. Closing user is still in viewer list.
-    plugin.getServer().getScheduler().runTask(plugin, () -> {
+    plugin.getScheduler().runTask(() -> {
       if (loaded.isInUse()) {
         return;
       }

plugin/src/main/java/com/lishid/openinv/util/PlayerLoader.java

@@ -3,6 +3,7 @@ package com.lishid.openinv.util;
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
 import com.google.errorprone.annotations.Keep;
+import com.lishid.openinv.OpenInv;
 import com.lishid.openinv.util.config.Config;
 import org.bukkit.Bukkit;
 import org.bukkit.OfflinePlayer;
@@ -18,6 +19,7 @@ import org.jetbrains.annotations.Nullable;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 import java.util.logging.Level;
@@ -28,7 +30,7 @@ import java.util.logging.Logger;
  */
 public class PlayerLoader implements Listener {
 
-  private final @NotNull Plugin plugin;
+  private final @NotNull OpenInv plugin;
   private final @NotNull Config config;
   private final @NotNull InventoryManager inventoryManager;
   private final @NotNull InternalAccessor internalAccessor;
@@ -36,7 +38,7 @@ public class PlayerLoader implements Listener {
   private final @NotNull Cache<String, PlayerProfile> lookupCache;
 
   public PlayerLoader(
-      @NotNull Plugin plugin,
+      @NotNull OpenInv plugin,
       @NotNull Config config,
       @NotNull InventoryManager inventoryManager,
       @NotNull InternalAccessor internalAccessor,
@@ -78,8 +80,8 @@ public class PlayerLoader implements Listener {
       return internalAccessor.getPlayerDataManager().loadPlayer(offline);
     }
 
-    Future<Player> future = Bukkit.getScheduler().callSyncMethod(plugin,
-        () -> internalAccessor.getPlayerDataManager().loadPlayer(offline));
+    CompletableFuture<Player> future = new CompletableFuture<>();
+    plugin.getScheduler().runTask(() -> future.complete(internalAccessor.getPlayerDataManager().loadPlayer(offline)));
 
     try {
       player = future.get();
@@ -195,7 +197,7 @@ public class PlayerLoader implements Listener {
       return;
     }
 
-    plugin.getServer().getScheduler().runTaskLaterAsynchronously(plugin, () -> {
+    plugin.getScheduler().runTaskLaterAsynchronously(() -> {
       Iterator<Map.Entry<String, PlayerProfile>> iterator = lookupCache.asMap().entrySet().iterator();
       while (iterator.hasNext()) {
         Map.Entry<String, PlayerProfile> entry = iterator.next();

plugin/src/main/resources/plugin.yml

@@ -5,6 +5,7 @@ author: lishid
 authors: [Jikoo, ShadowRanger]
 description: Open a player's inventory as a chest and interact with it in real time.
 api-version: "1.13"
+folia-supported: true
 
 permissions:
 

resource-pack/openinv-legibility-pack/pack.mcmeta

@@ -1,13 +1,13 @@
 {
   "pack": {
     "description": "Improve OpenInv's legibility",
-    "pack_format": 46,
-    "supported_formats": [ 34, 46 ]
+    "pack_format": 55,
+    "supported_formats": [ 34, 55 ]
   },
   "overlays": {
     "entries": [
       {
-        "formats": [ 44, 46 ],
+        "formats": [ 44, 55 ],
         "directory": "openinv_44"
       },
       {

scripts/install_spigot.sh

@@ -1,39 +0,0 @@
-#!/bin/bash
-#
-# Copyright (C) 2011-2022 lishid. All rights reserved.
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, version 3.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program. If not, see <http://www.gnu.org/licenses/>.
-#
-
-buildtools_dir=~/buildtools
-buildtools=$buildtools_dir/BuildTools.jar
-
-get_buildtools () {
-  if [[ -d $buildtools_dir && -f $buildtools ]]; then
-    return
-  fi
-
-  mkdir $buildtools_dir
-  wget https://hub.spigotmc.org/jenkins/job/BuildTools/lastSuccessfulBuild/artifact/target/BuildTools.jar -O $buildtools
-}
-
-if [[ ! $1 ]]; then
-  echo "Please specify Spigot version to install."
-  exit 1
-fi
-
-get_buildtools
-
-pushd $buildtools_dir
-java -jar $buildtools -rev $1 --remapped
-popd

scripts/set_curseforge_env.sh

@@ -18,26 +18,41 @@
 # Note that this script is designed for use in GitHub Actions, and is not
 # particularly robust nor configurable. Run from project parent directory.
 
-# Parse Spigot dependency information into major Minecraft versions
-function get_curseforge_minecraft_versions() {
-  # TODO convert to parsing event body
-  readarray -t versions <<< "1.21.4"
+if [[ ! $1 ]]; then
+  echo "No changelog, no Minecraft versions."
+  exit 0
+fi
 
-  for version in "${versions[@]}"; do
-    # Parse Minecraft major version
-    version="${version%[.-]"${version#*.*[.-]}"}"
+# Find line declaring Paper versions.
+raw=$(grep "**Paper:**" <<< "$1")
 
-    # Skip already listed versions
-    if [[ "$minecraft_versions" =~ "$version"($|,) ]]; then
-      continue
-    fi
+# Enable extended glob pattern to match 0 or more whitespace characters.
+shopt -s extglob
+# Trim Paper versions identifier prefix.
+raw=${raw##*([[:space:]])'**'Paper:'**'*([[:space:]])}
+# Replace commas and optional spaces with a newline.
+raw=${raw//,*([[:space:]])/$'\n'}
+# Turn extglob back off.
+shopt -u extglob
 
-    # Append comma if variable is set, then append version
-    minecraft_versions="${minecraft_versions:+${minecraft_versions},}Minecraft ${version}"
-  done
+# Split into an array on newlines.
+readarray -td $'\n' versions <<< "${raw}"
 
-  echo "${minecraft_versions}"
-}
+for version in "${versions[@]}"; do
+  # Parse Minecraft minor version by dropping everything from the second period onward.
+  # CurseForge doesn't usually add patch versions for Bukkit, so we're more likely to
+  # hit a supported identifier this way.
+  version="${version%[.-]"${version#*.*[.-]}"}"
 
-minecraft_versions=$(get_curseforge_minecraft_versions)
-echo "CURSEFORGE_MINECRAFT_VERSIONS=$minecraft_versions" >> "$GITHUB_ENV"
+  # Skip already listed versions
+  if [[ "$minecraft_versions" =~ "$version"($|,) ]]; then
+    continue
+  fi
+
+  # Append comma if variable is set, then append version.
+  # Note that Minecraft versions on CurseForge are declared "Minecraft x.y.z"
+  minecraft_versions="${minecraft_versions:+${minecraft_versions},}Minecraft ${version}"
+done
+
+printf "$minecraft_versions\n"
+#echo "CURSEFORGE_MINECRAFT_VERSIONS=$minecraft_versions" >> "$GITHUB_ENV"

settings.gradle.kts

@@ -3,31 +3,34 @@ rootProject.name = "openinvparent"
 include(":openinvapi")
 project(":openinvapi").projectDir = file("api")
 
-val addons = listOf(
-  "togglepersist"
-)
-for (addon in addons) {
-  include(":addon$addon")
-  val proj = project(":addon$addon")
-  proj.projectDir = file("addon/$addon")
-  proj.name = "openinv$addon"
+if (!java.lang.Boolean.getBoolean("jitpack")) {
+  val addons = listOf(
+    "togglepersist"
+  )
+  for (addon in addons) {
+    include(":addon$addon")
+    val proj = project(":addon$addon")
+    proj.projectDir = file("addon/$addon")
+    proj.name = "openinv$addon"
+  }
+
+  include(":openinvcommon")
+  project(":openinvcommon").projectDir = file("common")
+
+  val internals = listOf(
+    "common",
+    "paper1_21_4",
+    "paper1_21_3",
+    "paper1_21_1",
+    "spigot"
+  )
+  for (internal in internals) {
+    include(":openinvadapter$internal")
+    project(":openinvadapter$internal").projectDir = file("internal/$internal")
+  }
+
+  include(":resource-pack")
+
+  include(":plugin")
+  project(":plugin").name = "openinvplugin"
 }
-
-include(":openinvcommon")
-project(":openinvcommon").projectDir = file("common")
-
-val internals = listOf(
-  "common",
-  "paper1_21_3",
-  "paper1_21_1",
-  "spigot"
-)
-for (internal in internals) {
-  include(":openinvadapter$internal")
-  project(":openinvadapter$internal").projectDir = file("internal/$internal")
-}
-
-include(":resource-pack")
-
-include(":plugin")
-project(":plugin").name = "openinvplugin"