From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Warrior <50800980+Warriorrrr@users.noreply.github.com>
Date: Tue, 25 Oct 2022 21:15:37 +0200
Subject: [PATCH] Add /paper dumplisteners command

Co-authored-by: TwoLeggedCat <80929284+TwoLeggedCat@users.noreply.github.com>

diff --git a/src/main/java/io/papermc/paper/command/PaperCommand.java b/src/main/java/io/papermc/paper/command/PaperCommand.java
index 724592234e2a178a518f6ab7d09c3180780371a7..92154550b41b2e1d03deb1271b71bb3baa735e0a 100644
--- a/src/main/java/io/papermc/paper/command/PaperCommand.java
+++ b/src/main/java/io/papermc/paper/command/PaperCommand.java
@@ -2,6 +2,7 @@ package io.papermc.paper.command;
 
 import io.papermc.paper.command.subcommands.ChunkDebugCommand;
 import io.papermc.paper.command.subcommands.DumpItemCommand;
+import io.papermc.paper.command.subcommands.DumpListenersCommand;
 import io.papermc.paper.command.subcommands.EntityCommand;
 import io.papermc.paper.command.subcommands.FixLightCommand;
 import io.papermc.paper.command.subcommands.HeapDumpCommand;
@@ -50,6 +51,7 @@ public final class PaperCommand extends Command {
         commands.put(Set.of("syncloadinfo"), new SyncLoadInfoCommand());
         commands.put(Set.of("dumpitem"), new DumpItemCommand());
         commands.put(Set.of("mobcaps", "playermobcaps"), new MobcapsCommand());
+        commands.put(Set.of("dumplisteners"), new DumpListenersCommand());
 
         return commands.entrySet().stream()
             .flatMap(entry -> entry.getKey().stream().map(s -> Map.entry(s, entry.getValue())))
diff --git a/src/main/java/io/papermc/paper/command/subcommands/DumpListenersCommand.java b/src/main/java/io/papermc/paper/command/subcommands/DumpListenersCommand.java
new file mode 100644
index 0000000000000000000000000000000000000000..dab8d6fb489f8b3acc7c8fdaa1b5b6b83fa0eeb4
--- /dev/null
+++ b/src/main/java/io/papermc/paper/command/subcommands/DumpListenersCommand.java
@@ -0,0 +1,120 @@
+package io.papermc.paper.command.subcommands;
+
+import com.destroystokyo.paper.util.SneakyThrow;
+import io.papermc.paper.command.PaperSubcommand;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Field;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.Set;
+import java.util.stream.Stream;
+import net.minecraft.server.MinecraftServer;
+import org.bukkit.Bukkit;
+import org.bukkit.command.CommandSender;
+import org.bukkit.event.HandlerList;
+import org.bukkit.plugin.Plugin;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+import static net.kyori.adventure.text.Component.space;
+import static net.kyori.adventure.text.Component.text;
+import static net.kyori.adventure.text.format.NamedTextColor.GRAY;
+import static net.kyori.adventure.text.format.NamedTextColor.GREEN;
+import static net.kyori.adventure.text.format.NamedTextColor.RED;
+
+@DefaultQualifier(NonNull.class)
+public final class DumpListenersCommand implements PaperSubcommand {
+    private static final MethodHandle EVENT_TYPES_HANDLE;
+
+    static {
+        try {
+            final Field eventTypesField = HandlerList.class.getDeclaredField("EVENT_TYPES");
+            eventTypesField.setAccessible(true);
+            EVENT_TYPES_HANDLE = MethodHandles.lookup().unreflectGetter(eventTypesField);
+        } catch (final ReflectiveOperationException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    public boolean execute(final CommandSender sender, final String subCommand, final String[] args) {
+        this.doDumpListeners(sender, args);
+        return true;
+    }
+
+    private void doDumpListeners(final CommandSender sender, final String[] args) {
+        if (args.length == 0) {
+            sender.sendMessage(text("Usage: /paper dumplisteners [className]", RED));
+            return;
+        }
+
+        try {
+            final HandlerList handlers = (HandlerList) findClass(args[0]).getMethod("getHandlerList").invoke(null);
+
+            if (handlers.getRegisteredListeners().length == 0) {
+                sender.sendMessage(text(args[0] + " does not have any registered listeners."));
+                return;
+            }
+
+            sender.sendMessage(text("Listeners for " + args[0] + ":"));
+
+            Stream.of(handlers.getRegisteredListeners())
+                .map(listener -> text(listener.getPlugin().getName(), GREEN)
+                    .append(space())
+                    .append(text("(" + listener.getListener().getClass().getName() + ")", GRAY)
+                        .hoverEvent(text("Priority: " + listener.getPriority().name() + " (" + listener.getPriority().getSlot() + ")", GRAY))))
+                .forEach(sender::sendMessage);
+
+            sender.sendMessage(text("Total listeners: " + handlers.getRegisteredListeners().length));
+
+        } catch (final ClassNotFoundException e) {
+            sender.sendMessage(text("Unable to find a class named '" + args[0] + "'. Make sure to use the fully qualified name.", RED));
+        } catch (final NoSuchMethodException e) {
+            sender.sendMessage(text("Class '" + args[0] + "' does not have a valid getHandlerList method.", RED));
+        } catch (final ReflectiveOperationException e) {
+            sender.sendMessage(text("Something went wrong, see the console for more details.", RED));
+            MinecraftServer.LOGGER.warn("Error occurred while dumping listeners for class " + args[0], e);
+        }
+    }
+
+    @Override
+    public List<String> tabComplete(final CommandSender sender, final String subCommand, final String[] args) {
+        return switch (args.length) {
+            case 0 -> List.copyOf(getEventClasses());
+            case 1 -> getEventClasses().stream()
+                .filter(clazz -> clazz.toLowerCase(Locale.ROOT).contains(args[0].toLowerCase(Locale.ROOT)))
+                .toList();
+            default -> Collections.emptyList();
+        };
+    }
+
+    @SuppressWarnings("unchecked")
+    private static Set<String> getEventClasses() {
+        try {
+            return (Set<String>) EVENT_TYPES_HANDLE.invokeExact();
+        } catch (final Throwable e) {
+            SneakyThrow.sneaky(e);
+            return Collections.emptySet(); // Unreachable
+        }
+    }
+
+    private static Class<?> findClass(final String className) throws ClassNotFoundException {
+        try {
+            return Class.forName(className);
+        } catch (final ClassNotFoundException ignore) {
+            for (final Plugin plugin : Bukkit.getServer().getPluginManager().getPlugins()) {
+                if (!plugin.isEnabled()) {
+                    continue;
+                }
+
+                try {
+                    return Class.forName(className, false, plugin.getClass().getClassLoader());
+                } catch (final ClassNotFoundException ignore0) {
+                }
+            }
+        }
+        throw new ClassNotFoundException(className);
+    }
+}