api/src/main/java/com/velocitypowered/api/proxy/config/ProxyConfig.java

@@ -148,4 +148,59 @@ public interface ProxyConfig {
    * @return read timeout (in milliseconds)
    */
   int getReadTimeout();
+
+  /**
+   * Get the rate limit for how fast a player can execute commands.
+   *
+   * @return the command rate limit (in milliseconds)
+   */
+  int getCommandRatelimit();
+
+  /**
+   * Get whether we should forward commands to the backend if the player is rate limited.
+   *
+   * @return whether to forward commands if rate limited
+   */
+  boolean isForwardCommandsIfRateLimited();
+
+  /**
+   * Get the kick limit for commands that are rate limited.
+   * If this limit is 0 or less, the player will be not be kicked.
+   *
+   * @return the rate limited command rate limit
+   */
+  int getKickAfterRateLimitedCommands();
+
+  /**
+   * Get whether the proxy should kick players who are command rate limited.
+   *
+   * @return whether to kick players who are rate limited
+   */
+  default boolean isKickOnCommandRateLimit() {
+    return getKickAfterRateLimitedCommands() > 0;
+  }
+
+  /**
+   * Get the rate limit for how fast a player can tab complete.
+   *
+   * @return the tab complete rate limit (in milliseconds)
+   */
+  int getTabCompleteRatelimit();
+
+  /**
+   * Get the kick limit for tab completes that are rate limited.
+   * If this limit is 0 or less, the player will be not be kicked.
+   *
+   * @return the rate limited command rate limit
+   */
+  int getKickAfterRateLimitedTabCompletes();
+
+  /**
+   * Get whether the proxy should kick players who are tab complete rate limited.
+   *
+   * @return whether to kick players who are rate limited
+   */
+  default boolean isKickOnTabCompleteRateLimit() {
+    return getKickAfterRateLimitedTabCompletes() > 0;
+  }
 }

api/src/main/java/com/velocitypowered/api/proxy/messages/MinecraftChannelIdentifier.java

@@ -11,7 +11,6 @@ import static com.google.common.base.Preconditions.checkArgument;
 
 import com.google.common.base.Strings;
 import java.util.Objects;
-import java.util.regex.Pattern;
 import net.kyori.adventure.key.Key;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -21,8 +20,6 @@ import org.checkerframework.checker.nullness.qual.Nullable;
  */
 public final class MinecraftChannelIdentifier implements ChannelIdentifier {
 
-  private static final Pattern VALID_IDENTIFIER_REGEX = Pattern.compile("[a-z0-9/\\-_]*");
-
   private final String namespace;
   private final String name;
 
@@ -39,7 +36,7 @@ public final class MinecraftChannelIdentifier implements ChannelIdentifier {
    * @return a new channel identifier
    */
   public static MinecraftChannelIdentifier forDefaultNamespace(String name) {
-    return new MinecraftChannelIdentifier("minecraft", name);
+    return new MinecraftChannelIdentifier(Key.MINECRAFT_NAMESPACE, name);
   }
 
   /**
@@ -52,14 +49,10 @@ public final class MinecraftChannelIdentifier implements ChannelIdentifier {
   public static MinecraftChannelIdentifier create(String namespace, String name) {
     checkArgument(!Strings.isNullOrEmpty(namespace), "namespace is null or empty");
     checkArgument(name != null, "namespace is null or empty");
-    checkArgument(VALID_IDENTIFIER_REGEX.matcher(namespace).matches(),
+    checkArgument(Key.parseableNamespace(namespace),
-        "namespace is not valid, must match: %s got %s",
+        "namespace is not valid, must match: [a-z0-9_.-] got %s", namespace);
-        VALID_IDENTIFIER_REGEX.toString(),
+    checkArgument(Key.parseableValue(name),
-        namespace);
+        "name is not valid, must match: [a-z0-9/._-] got %s", name);
-    checkArgument(VALID_IDENTIFIER_REGEX.matcher(name).matches(),
-        "name is not valid, must match: %s got %s",
-        VALID_IDENTIFIER_REGEX.toString(),
-        name);
     return new MinecraftChannelIdentifier(namespace, name);
   }
 
@@ -72,10 +65,9 @@ public final class MinecraftChannelIdentifier implements ChannelIdentifier {
   public static MinecraftChannelIdentifier from(String identifier) {
     int colonPos = identifier.indexOf(':');
     if (colonPos == -1) {
-      throw new IllegalArgumentException("Identifier does not contain a colon.");
+      return create(Key.MINECRAFT_NAMESPACE, identifier);
-    }
+    } else if (colonPos == 0) {
-    if (colonPos + 1 == identifier.length()) {
+      return create(Key.MINECRAFT_NAMESPACE, identifier.substring(1));
-      throw new IllegalArgumentException("Identifier is empty.");
     }
     String namespace = identifier.substring(0, colonPos);
     String name = identifier.substring(colonPos + 1);

api/src/main/java/com/velocitypowered/api/proxy/server/ServerPing.java

@@ -517,6 +517,10 @@ public final class ServerPing {
    */
   public static final class SamplePlayer {
 
+    public static final SamplePlayer ANONYMOUS = new SamplePlayer(
+        "Anonymous Player",
+        new UUID(0L, 0L)
+    );
     private final String name;
     private final UUID id;
 

api/src/test/java/com/velocitypowered/api/proxy/messages/MinecraftChannelIdentifierTest.java

@@ -47,17 +47,25 @@ class MinecraftChannelIdentifierTest {
     create("velocity", "test/test2");
   }
 
+  @Test
+  void fromIdentifierDefaultNamespace() {
+    assertEquals("minecraft", from("test").getNamespace());
+    assertEquals("minecraft", from(":test").getNamespace());
+  }
+
+  @Test
+  void fromIdentifierAllowsEmptyName() {
+    from("minecraft:");
+    from(":");
+    from("");
+  }
+
   @Test
   void fromIdentifierThrowsOnBadValues() {
     assertAll(
-        () -> assertThrows(IllegalArgumentException.class, () -> from("")),
-        () -> assertThrows(IllegalArgumentException.class, () -> from(":")),
-        () -> assertThrows(IllegalArgumentException.class, () -> from(":a")),
-        () -> assertThrows(IllegalArgumentException.class, () -> from("a:")),
         () -> assertThrows(IllegalArgumentException.class, () -> from("hello:$$$$$$")),
+        () -> assertThrows(IllegalArgumentException.class, () -> from("he/llo:wor/ld")),
         () -> assertThrows(IllegalArgumentException.class, () -> from("hello::"))
     );
   }
-
+}
-
-}

gradle/libs.versions.toml

@@ -3,7 +3,7 @@ configurate3 = "3.7.3"
 configurate4 = "4.1.2"
 flare = "2.0.1"
 log4j = "2.24.1"
-netty = "4.1.119.Final"
+netty = "4.2.0.Final"
 
 [plugins]
 indra-publishing = "net.kyori.indra.publishing:2.0.6"
@@ -53,8 +53,8 @@ netty-codec-haproxy = { module = "io.netty:netty-codec-haproxy", version.ref = "
 netty-codec-http = { module = "io.netty:netty-codec-http", version.ref = "netty" }
 netty-handler = { module = "io.netty:netty-handler", version.ref = "netty" }
 netty-transport-native-epoll = { module = "io.netty:netty-transport-native-epoll", version.ref = "netty" }
-netty-transport-native-iouring = { module = "io.netty.incubator:netty-incubator-transport-native-io_uring", version = "0.0.25.Final" }
 netty-transport-native-kqueue = { module = "io.netty:netty-transport-native-kqueue", version.ref = "netty" }
+netty-transport-native-iouring = { module = "io.netty:netty-transport-native-io_uring", version.ref = "netty" }
 nightconfig = "com.electronwill.night-config:toml:3.6.7"
 slf4j = "org.slf4j:slf4j-api:2.0.12"
 snakeyaml = "org.yaml:snakeyaml:1.33"

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -75,6 +75,7 @@ import io.netty.channel.ChannelInitializer;
 import io.netty.channel.EventLoopGroup;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.http.HttpClient;
 import java.nio.file.Files;
@@ -162,7 +163,9 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
   private final Map<UUID, ConnectedPlayer> connectionsByUuid = new ConcurrentHashMap<>();
   private final Map<String, ConnectedPlayer> connectionsByName = new ConcurrentHashMap<>();
   private final VelocityConsole console;
-  private @MonotonicNonNull Ratelimiter ipAttemptLimiter;
+  private @MonotonicNonNull Ratelimiter<InetAddress> ipAttemptLimiter;
+  private @MonotonicNonNull Ratelimiter<UUID> commandRateLimiter;
+  private @MonotonicNonNull Ratelimiter<UUID> tabCompleteRateLimiter;
   private final VelocityEventManager eventManager;
   private final VelocityScheduler scheduler;
   private final VelocityChannelRegistrar channelRegistrar = new VelocityChannelRegistrar();
@@ -295,6 +298,8 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     }
 
     ipAttemptLimiter = Ratelimiters.createWithMilliseconds(configuration.getLoginRatelimit());
+    commandRateLimiter = Ratelimiters.createWithMilliseconds(configuration.getCommandRatelimit());
+    tabCompleteRateLimiter = Ratelimiters.createWithMilliseconds(configuration.getTabCompleteRatelimit());
     loadPlugins();
 
     // Go ahead and fire the proxy initialization event. We block since plugins should have a chance
@@ -654,10 +659,18 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
     return cm.createHttpClient();
   }
 
-  public Ratelimiter getIpAttemptLimiter() {
+  public @MonotonicNonNull Ratelimiter<InetAddress> getIpAttemptLimiter() {
     return ipAttemptLimiter;
   }
 
+  public @MonotonicNonNull Ratelimiter<UUID> getCommandRateLimiter() {
+    return commandRateLimiter;
+  }
+
+  public @MonotonicNonNull Ratelimiter<UUID> getTabCompleteRateLimiter() {
+    return tabCompleteRateLimiter;
+  }
+
   /**
    * Checks if the {@code connection} can be registered with the proxy.
    *

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -78,6 +78,8 @@ public class VelocityConfiguration implements ProxyConfig {
   private boolean onlineModeKickExistingPlayers = false;
   @Expose
   private PingPassthroughMode pingPassthrough = PingPassthroughMode.DISABLED;
+  @Expose
+  private boolean samplePlayersInPing = false;
   private final Servers servers;
   private final ForcedHosts forcedHosts;
   @Expose
@@ -105,8 +107,9 @@ public class VelocityConfiguration implements ProxyConfig {
       boolean preventClientProxyConnections, boolean announceForge,
       PlayerInfoForwarding playerInfoForwardingMode, byte[] forwardingSecret,
       boolean onlineModeKickExistingPlayers, PingPassthroughMode pingPassthrough,
-      boolean enablePlayerAddressLogging, Servers servers, ForcedHosts forcedHosts,
+      boolean samplePlayersInPing, boolean enablePlayerAddressLogging, Servers servers,
-      Advanced advanced, Query query, Metrics metrics, boolean forceKeyAuthentication) {
+      ForcedHosts forcedHosts, Advanced advanced, Query query, Metrics metrics,
+      boolean forceKeyAuthentication) {
     this.bind = bind;
     this.motd = motd;
     this.showMaxPlayers = showMaxPlayers;
@@ -117,6 +120,7 @@ public class VelocityConfiguration implements ProxyConfig {
     this.forwardingSecret = forwardingSecret;
     this.onlineModeKickExistingPlayers = onlineModeKickExistingPlayers;
     this.pingPassthrough = pingPassthrough;
+    this.samplePlayersInPing = samplePlayersInPing;
     this.enablePlayerAddressLogging = enablePlayerAddressLogging;
     this.servers = servers;
     this.forcedHosts = forcedHosts;
@@ -230,6 +234,11 @@ public class VelocityConfiguration implements ProxyConfig {
       valid = false;
     }
 
+    if (advanced.commandRateLimit < 0) {
+      logger.error("Invalid command rate limit {}", advanced.commandRateLimit);
+      valid = false;
+    }
+
     loadFavicon();
 
     return valid;
@@ -351,6 +360,31 @@ public class VelocityConfiguration implements ProxyConfig {
     return advanced.getReadTimeout();
   }
 
+  @Override
+  public int getCommandRatelimit() {
+    return advanced.getCommandRateLimit();
+  }
+
+  @Override
+  public int getTabCompleteRatelimit() {
+    return advanced.getTabCompleteRateLimit();
+  }
+
+  @Override
+  public int getKickAfterRateLimitedTabCompletes() {
+    return advanced.getKickAfterRateLimitedTabCompletes();
+  }
+
+  @Override
+  public boolean isForwardCommandsIfRateLimited() {
+    return advanced.isForwardCommandsIfRateLimited();
+  }
+
+  @Override
+  public int getKickAfterRateLimitedCommands() {
+    return advanced.getKickAfterRateLimitedCommands();
+  }
+
   public boolean isProxyProtocol() {
     return advanced.isProxyProtocol();
   }
@@ -371,6 +405,10 @@ public class VelocityConfiguration implements ProxyConfig {
     return pingPassthrough;
   }
 
+  public boolean getSamplePlayersInPing() {
+    return samplePlayersInPing;
+  }
+
   public boolean isPlayerAddressLoggingEnabled() {
     return enablePlayerAddressLogging;
   }
@@ -507,6 +545,8 @@ public class VelocityConfiguration implements ProxyConfig {
       final PingPassthroughMode pingPassthroughMode = config.getEnumOrElse("ping-passthrough",
               PingPassthroughMode.DISABLED);
 
+      final boolean samplePlayersInPing = config.getOrElse("sample-players-in-ping", false);
+
       final String bind = config.getOrElse("bind", "0.0.0.0:25565");
       final int maxPlayers = config.getIntOrElse("show-max-players", 500);
       final boolean onlineMode = config.getOrElse("online-mode", true);
@@ -537,6 +577,7 @@ public class VelocityConfiguration implements ProxyConfig {
               forwardingSecret,
               kickExisting,
               pingPassthroughMode,
+              samplePlayersInPing,
               enablePlayerAddressLogging,
               new Servers(serversConfig),
               new ForcedHosts(forcedHostsConfig),
@@ -722,6 +763,16 @@ public class VelocityConfiguration implements ProxyConfig {
     private boolean acceptTransfers = false;
     @Expose
     private boolean enableReusePort = false;
+    @Expose
+    private int commandRateLimit = 50;
+    @Expose
+    private boolean forwardCommandsIfRateLimited = true;
+    @Expose
+    private int kickAfterRateLimitedCommands = 5;
+    @Expose
+    private int tabCompleteRateLimit = 50;
+    @Expose
+    private int kickAfterRateLimitedTabCompletes = 10;
 
     private Advanced() {
     }
@@ -748,6 +799,11 @@ public class VelocityConfiguration implements ProxyConfig {
         this.logPlayerConnections = config.getOrElse("log-player-connections", true);
         this.acceptTransfers = config.getOrElse("accepts-transfers", false);
         this.enableReusePort = config.getOrElse("enable-reuse-port", false);
+        this.commandRateLimit = config.getIntOrElse("command-rate-limit", 25);
+        this.forwardCommandsIfRateLimited = config.getOrElse("forward-commands-if-rate-limited", true);
+        this.kickAfterRateLimitedCommands = config.getIntOrElse("kick-after-rate-limited-commands", 0);
+        this.tabCompleteRateLimit = config.getIntOrElse("tab-complete-rate-limit", 10); // very lenient
+        this.kickAfterRateLimitedTabCompletes = config.getIntOrElse("kick-after-rate-limited-tab-completes", 0);
       }
     }
 
@@ -815,6 +871,26 @@ public class VelocityConfiguration implements ProxyConfig {
       return enableReusePort;
     }
 
+    public int getCommandRateLimit() {
+      return commandRateLimit;
+    }
+
+    public boolean isForwardCommandsIfRateLimited() {
+      return forwardCommandsIfRateLimited;
+    }
+
+    public int getKickAfterRateLimitedCommands() {
+      return kickAfterRateLimitedCommands;
+    }
+
+    public int getTabCompleteRateLimit() {
+      return tabCompleteRateLimit;
+    }
+
+    public int getKickAfterRateLimitedTabCompletes() {
+      return kickAfterRateLimitedTabCompletes;
+    }
+
     @Override
     public String toString() {
       return "Advanced{"

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -84,6 +84,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
   private static final Logger logger = LogManager.getLogger(MinecraftConnection.class);
 
   private final Channel channel;
+  public boolean pendingConfigurationSwitch = false;
   private SocketAddress remoteAddress;
   private StateRegistry state;
   private Map<StateRegistry, MinecraftSessionHandler> sessionHandlers;

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BungeeCordMessageResponder.java

@@ -20,6 +20,7 @@ package com.velocitypowered.proxy.connection.backend;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.proxy.Player;
 import com.velocitypowered.api.proxy.ServerConnection;
+import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.api.proxy.messages.LegacyChannelIdentifier;
 import com.velocitypowered.api.proxy.messages.MinecraftChannelIdentifier;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
@@ -316,9 +317,9 @@ public class BungeeCordMessageResponder {
     });
   }
 
-  static String getBungeeCordChannel(ProtocolVersion version) {
+  static ChannelIdentifier getBungeeCordChannel(ProtocolVersion version) {
-    return version.noLessThan(ProtocolVersion.MINECRAFT_1_13) ? MODERN_CHANNEL.getId()
+    return version.noLessThan(ProtocolVersion.MINECRAFT_1_13) ? MODERN_CHANNEL
-        : LEGACY_CHANNEL.getId();
+        : LEGACY_CHANNEL;
   }
 
   // Note: this method will always release the buffer!
@@ -329,8 +330,8 @@ public class BungeeCordMessageResponder {
   // Note: this method will always release the buffer!
   private static void sendServerResponse(ConnectedPlayer player, ByteBuf buf) {
     MinecraftConnection serverConnection = player.ensureAndGetCurrentServer().ensureConnected();
-    String chan = getBungeeCordChannel(serverConnection.getProtocolVersion());
+    ChannelIdentifier chan = getBungeeCordChannel(serverConnection.getProtocolVersion());
-    PluginMessagePacket msg = new PluginMessagePacket(chan, buf);
+    PluginMessagePacket msg = new PluginMessagePacket(chan.getId(), buf);
     serverConnection.write(msg);
   }
 

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -74,6 +74,7 @@ import com.velocitypowered.proxy.protocol.packet.config.FinishedUpdatePacket;
 import com.velocitypowered.proxy.protocol.packet.title.GenericTitlePacket;
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import com.velocitypowered.proxy.util.CharacterUtil;
+import com.velocitypowered.proxy.util.except.QuietRuntimeException;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufUtil;
 import io.netty.buffer.Unpooled;
@@ -113,6 +114,8 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
   private CompletableFuture<Void> configSwitchFuture;
 
+  private int failedTabCompleteAttempts;
+
   /**
    * Constructs a client play session handler.
    *
@@ -160,7 +163,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
   @Override
   public void activated() {
     configSwitchFuture = new CompletableFuture<>();
-    Collection<String> channels =
+    Collection<ChannelIdentifier> channels =
         server.getChannelRegistrar().getChannelsForProtocol(player.getProtocolVersion());
     if (!channels.isEmpty()) {
       PluginMessagePacket register = constructChannelsPacket(player.getProtocolVersion(), channels);
@@ -308,20 +311,17 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
         logger.warn("A plugin message was received while the backend server was not "
             + "ready. Channel: {}. Packet discarded.", packet.getChannel());
       } else if (PluginMessageUtil.isRegister(packet)) {
-        List<String> channels = PluginMessageUtil.getChannels(packet);
+        List<ChannelIdentifier> channels =
-        List<ChannelIdentifier> channelIdentifiers = new ArrayList<>();
+            PluginMessageUtil.getChannels(this.player.getClientsideChannels().size(), packet,
-        for (String channel : channels) {
+                this.player.getProtocolVersion());
-          try {
+        player.getClientsideChannels().addAll(channels);
-            channelIdentifiers.add(MinecraftChannelIdentifier.from(channel));
-          } catch (IllegalArgumentException e) {
-            channelIdentifiers.add(new LegacyChannelIdentifier(channel));
-          }
-        }
         server.getEventManager()
             .fireAndForget(
-                new PlayerChannelRegisterEvent(player, ImmutableList.copyOf(channelIdentifiers)));
+                new PlayerChannelRegisterEvent(player, ImmutableList.copyOf(channels)));
         backendConn.write(packet.retain());
       } else if (PluginMessageUtil.isUnregister(packet)) {
+        player.getClientsideChannels()
+            .removeAll(PluginMessageUtil.getChannels(0, packet, this.player.getProtocolVersion()));
         backendConn.write(packet.retain());
       } else if (PluginMessageUtil.isMcBrand(packet)) {
         String brand = PluginMessageUtil.readBrandMessage(packet.content());
@@ -377,10 +377,14 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(FinishedUpdatePacket packet) {
+    if (!player.getConnection().pendingConfigurationSwitch) {
+      throw new QuietRuntimeException("Not expecting reconfiguration");
+    }
     // Complete client switch
     player.getConnection().setActiveSessionHandler(StateRegistry.CONFIG);
     VelocityServerConnection serverConnection = player.getConnectedServer();
-    server.getEventManager().fireAndForget(new PlayerEnteredConfigurationEvent(player, serverConnection));
+    server.getEventManager()
+        .fireAndForget(new PlayerEnteredConfigurationEvent(player, serverConnection));
     if (serverConnection != null) {
       MinecraftConnection smc = serverConnection.ensureConnected();
       CompletableFuture.runAsync(() -> {
@@ -567,11 +571,15 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
 
     // Tell the server about the proxy's plugin message channels.
     ProtocolVersion serverVersion = serverMc.getProtocolVersion();
-    final Collection<String> channels = server.getChannelRegistrar()
+    final Collection<ChannelIdentifier> channels = server.getChannelRegistrar()
         .getChannelsForProtocol(serverMc.getProtocolVersion());
     if (!channels.isEmpty()) {
       serverMc.delayedWrite(constructChannelsPacket(serverVersion, channels));
     }
+    // Tell the server about this client's plugin message channels.
+    if (!player.getClientsideChannels().isEmpty()) {
+      serverMc.delayedWrite(constructChannelsPacket(serverVersion, player.getClientsideChannels()));
+    }
 
     // If we had plugin messages queued during login/FML handshake, send them now.
     PluginMessagePacket pm;
@@ -653,6 +661,17 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
       return false;
     }
 
+    if (!server.getTabCompleteRateLimiter().attempt(player.getUniqueId())) {
+      if (server.getConfiguration().isKickOnTabCompleteRateLimit()
+              && failedTabCompleteAttempts++ >= server.getConfiguration().getKickAfterRateLimitedTabCompletes()) {
+        player.disconnect(Component.translatable("velocity.kick.tab-complete-rate-limit"));
+      }
+
+      return true;
+    }
+
+    failedTabCompleteAttempts = 0;
+
     server.getCommandManager().offerBrigadierSuggestions(player, command)
         .thenAcceptAsync(suggestions -> {
           if (suggestions.isEmpty()) {

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -99,6 +99,7 @@ import com.velocitypowered.proxy.tablist.VelocityTabListLegacy;
 import com.velocitypowered.proxy.util.ClosestLocaleMatcher;
 import com.velocitypowered.proxy.util.DurationUtils;
 import com.velocitypowered.proxy.util.TranslatableMapper;
+import com.velocitypowered.proxy.util.collect.CappedSet;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import java.net.InetSocketAddress;
@@ -144,6 +145,7 @@ import org.jetbrains.annotations.NotNull;
 public class ConnectedPlayer implements MinecraftConnectionAssociation, Player, KeyIdentifiable,
     VelocityInboundConnection {
 
+  public static final int MAX_CLIENTSIDE_PLUGIN_CHANNELS = 1024;
   private static final PlainTextComponentSerializer PASS_THRU_TRANSLATE =
       PlainTextComponentSerializer.builder().flattener(TranslatableMapper.FLATTENER).build();
   static final PermissionProvider DEFAULT_PERMISSIONS = s -> PermissionFunction.ALWAYS_UNDEFINED;
@@ -173,6 +175,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
   private final InternalTabList tabList;
   private final VelocityServer server;
   private ClientConnectionPhase connectionPhase;
+  private final Collection<ChannelIdentifier> clientsideChannels;
   private final CompletableFuture<Void> teardownFuture = new CompletableFuture<>();
   private @MonotonicNonNull List<String> serversToTry = null;
   private final ResourcePackHandler resourcePackHandler;
@@ -205,6 +208,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
     this.permissionFunction = PermissionFunction.ALWAYS_UNDEFINED;
     this.connectionPhase = connection.getType().getInitialClientPhase();
     this.onlineMode = onlineMode;
+    this.clientsideChannels = CappedSet.create(MAX_CLIENTSIDE_PLUGIN_CHANNELS);
 
     if (connection.getProtocolVersion().noLessThan(ProtocolVersion.MINECRAFT_1_19_3)) {
       this.tabList = new VelocityTabList(this);
@@ -1314,6 +1318,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
             connection.write(BundleDelimiterPacket.INSTANCE);
           }
           connection.write(StartUpdatePacket.INSTANCE);
+          connection.pendingConfigurationSwitch = true;
           connection.getChannel().pipeline().get(MinecraftEncoder.class).setState(StateRegistry.CONFIG);
           // Make sure we don't send any play packets to the player after update start
           connection.addPlayPacketQueueHandler();
@@ -1342,6 +1347,15 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
     this.connectionPhase = connectionPhase;
   }
 
+  /**
+   * Return all the plugin message channels that registered by client.
+   *
+   * @return the channels
+   */
+  public Collection<ChannelIdentifier> getClientsideChannels() {
+    return clientsideChannels;
+  }
+
   @Override
   public @Nullable IdentifiedKey getIdentifiedKey() {
     return playerKey;

proxy/src/main/java/com/velocitypowered/proxy/connection/util/ServerListPingHandler.java

@@ -30,10 +30,12 @@ import com.velocitypowered.proxy.config.VelocityConfiguration;
 import com.velocitypowered.proxy.server.VelocityRegisteredServer;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
+import java.util.stream.Collectors;
 
 /**
  * Common utilities for handling server list ping results.
@@ -51,11 +53,27 @@ public class ServerListPingHandler {
       version = ProtocolVersion.MAXIMUM_VERSION;
     }
     VelocityConfiguration configuration = server.getConfiguration();
+    List<ServerPing.SamplePlayer> samplePlayers;
+    if (configuration.getSamplePlayersInPing()) {
+      List<ServerPing.SamplePlayer> unshuffledPlayers = server.getAllPlayers().stream()
+              .map(p -> {
+                if (p.getPlayerSettings().isClientListingAllowed()) {
+                  return new ServerPing.SamplePlayer(p.getUsername(), p.getUniqueId());
+                } else {
+                  return ServerPing.SamplePlayer.ANONYMOUS;
+                }
+              })
+              .collect(Collectors.toList());
+      Collections.shuffle(unshuffledPlayers);
+      samplePlayers = unshuffledPlayers.subList(0, Math.min(12, server.getPlayerCount()));
+    } else {
+      samplePlayers = ImmutableList.of();
+    }
     return new ServerPing(
         new ServerPing.Version(version.getProtocol(),
             "Velocity " + ProtocolVersion.SUPPORTED_VERSION_STRING),
         new ServerPing.Players(server.getPlayerCount(), configuration.getShowMaxPlayers(),
-            ImmutableList.of()),
+            samplePlayers),
         configuration.getMotd(),
         configuration.getFavicon().orElse(null),
         configuration.isAnnounceForge() ? ModInfo.DEFAULT : null

proxy/src/main/java/com/velocitypowered/proxy/network/ConnectionManager.java

@@ -104,7 +104,7 @@ public final class ConnectionManager {
         .childOption(ChannelOption.IP_TOS, 0x18)
         .localAddress(address);
 
-    if (transportType.supportsTcpFastOpenServer() && server.getConfiguration().useTcpFastOpen()) {
+    if (server.getConfiguration().useTcpFastOpen()) {
       bootstrap.option(ChannelOption.TCP_FASTOPEN, 3);
     }
 
@@ -197,7 +197,7 @@ public final class ConnectionManager {
             this.server.getConfiguration().getConnectTimeout())
         .group(group == null ? this.workerGroup : group)
         .resolver(this.resolver.asGroup());
-    if (transportType.supportsTcpFastOpenClient() && server.getConfiguration().useTcpFastOpen()) {
+    if (server.getConfiguration().useTcpFastOpen()) {
       bootstrap.option(ChannelOption.TCP_FASTOPEN_CONNECT, true);
     }
     return bootstrap;

proxy/src/main/java/com/velocitypowered/proxy/network/TransportType.java

@@ -20,27 +20,32 @@ package com.velocitypowered.proxy.network;
 import com.velocitypowered.proxy.util.concurrent.VelocityNettyThreadFactory;
 import io.netty.channel.ChannelFactory;
 import io.netty.channel.EventLoopGroup;
+import io.netty.channel.IoHandlerFactory;
+import io.netty.channel.MultiThreadIoEventLoopGroup;
 import io.netty.channel.epoll.Epoll;
 import io.netty.channel.epoll.EpollDatagramChannel;
-import io.netty.channel.epoll.EpollEventLoopGroup;
+import io.netty.channel.epoll.EpollIoHandler;
 import io.netty.channel.epoll.EpollServerSocketChannel;
 import io.netty.channel.epoll.EpollSocketChannel;
 import io.netty.channel.kqueue.KQueue;
 import io.netty.channel.kqueue.KQueueDatagramChannel;
-import io.netty.channel.kqueue.KQueueEventLoopGroup;
+import io.netty.channel.kqueue.KQueueIoHandler;
 import io.netty.channel.kqueue.KQueueServerSocketChannel;
 import io.netty.channel.kqueue.KQueueSocketChannel;
-import io.netty.channel.nio.NioEventLoopGroup;
+import io.netty.channel.nio.NioIoHandler;
 import io.netty.channel.socket.DatagramChannel;
 import io.netty.channel.socket.ServerSocketChannel;
 import io.netty.channel.socket.SocketChannel;
 import io.netty.channel.socket.nio.NioDatagramChannel;
 import io.netty.channel.socket.nio.NioServerSocketChannel;
 import io.netty.channel.socket.nio.NioSocketChannel;
-import io.netty.incubator.channel.uring.*;
+import io.netty.channel.uring.IoUring;
-
+import io.netty.channel.uring.IoUringDatagramChannel;
+import io.netty.channel.uring.IoUringIoHandler;
+import io.netty.channel.uring.IoUringServerSocketChannel;
+import io.netty.channel.uring.IoUringSocketChannel;
 import java.util.concurrent.ThreadFactory;
-import java.util.function.BiFunction;
+import java.util.function.Supplier;
 
 /**
  * Enumerates the supported transports for Velocity.
@@ -49,50 +54,36 @@ public enum TransportType {
   NIO("NIO", NioServerSocketChannel::new,
       NioSocketChannel::new,
       NioDatagramChannel::new,
-      (name, type) -> new NioEventLoopGroup(0, createThreadFactory(name, type)),
+      NioIoHandler::newFactory),
-      false,
-      false),
   EPOLL("epoll", EpollServerSocketChannel::new,
       EpollSocketChannel::new,
       EpollDatagramChannel::new,
-      (name, type) -> new EpollEventLoopGroup(0, createThreadFactory(name, type)),
+      EpollIoHandler::newFactory),
-      Epoll.isTcpFastOpenServerSideAvailable(),
-      Epoll.isTcpFastOpenClientSideAvailable()),
-  IO_URING("io_uring", IOUringServerSocketChannel::new,
-      IOUringSocketChannel::new,
-      IOUringDatagramChannel::new,
-      (name, type) -> new IOUringEventLoopGroup(0, createThreadFactory(name, type)),
-      IOUring.isTcpFastOpenServerSideAvailable(),
-      IOUring.isTcpFastOpenClientSideAvailable()),
   KQUEUE("kqueue", KQueueServerSocketChannel::new,
       KQueueSocketChannel::new,
       KQueueDatagramChannel::new,
-      (name, type) -> new KQueueEventLoopGroup(0, createThreadFactory(name, type)),
+      KQueueIoHandler::newFactory),
-      KQueue.isTcpFastOpenServerSideAvailable(),
+  IO_URING("io_uring", IoUringServerSocketChannel::new,
-      KQueue.isTcpFastOpenClientSideAvailable());
+      IoUringSocketChannel::new,
+      IoUringDatagramChannel::new,
+      IoUringIoHandler::newFactory);
 
   final String name;
   final ChannelFactory<? extends ServerSocketChannel> serverSocketChannelFactory;
   final ChannelFactory<? extends SocketChannel> socketChannelFactory;
   final ChannelFactory<? extends DatagramChannel> datagramChannelFactory;
-  final BiFunction<String, Type, EventLoopGroup> eventLoopGroupFactory;
+  final Supplier<IoHandlerFactory> ioHandlerFactorySupplier;
-  final boolean supportsTcpFastOpenServer;
-  final boolean supportsTcpFastOpenClient;
 
   TransportType(final String name,
       final ChannelFactory<? extends ServerSocketChannel> serverSocketChannelFactory,
       final ChannelFactory<? extends SocketChannel> socketChannelFactory,
       final ChannelFactory<? extends DatagramChannel> datagramChannelFactory,
-      final BiFunction<String, Type, EventLoopGroup> eventLoopGroupFactory,
+      final Supplier<IoHandlerFactory> ioHandlerFactorySupplier) {
-                final boolean supportsTcpFastOpenServer,
-                final boolean supportsTcpFastOpenClient) {
     this.name = name;
     this.serverSocketChannelFactory = serverSocketChannelFactory;
     this.socketChannelFactory = socketChannelFactory;
     this.datagramChannelFactory = datagramChannelFactory;
-    this.eventLoopGroupFactory = eventLoopGroupFactory;
+    this.ioHandlerFactorySupplier = ioHandlerFactorySupplier;
-    this.supportsTcpFastOpenServer = supportsTcpFastOpenServer;
-    this.supportsTcpFastOpenClient = supportsTcpFastOpenClient;
   }
 
   @Override
@@ -100,16 +91,15 @@ public enum TransportType {
     return this.name;
   }
 
+  /**
+   * Creates a new event loop group for the given type.
+   *
+   * @param type the type of event loop group to create
+   * @return the event loop group
+   */
   public EventLoopGroup createEventLoopGroup(final Type type) {
-    return this.eventLoopGroupFactory.apply(this.name, type);
+    return new MultiThreadIoEventLoopGroup(
-  }
+        0, createThreadFactory(this.name, type), this.ioHandlerFactorySupplier.get());
-
-  public boolean supportsTcpFastOpenServer() {
-    return supportsTcpFastOpenServer;
-  }
-
-  public boolean supportsTcpFastOpenClient() {
-    return supportsTcpFastOpenClient;
   }
 
   private static ThreadFactory createThreadFactory(final String name, final Type type) {
@@ -126,7 +116,7 @@ public enum TransportType {
       return NIO;
     }
 
-    if(IOUring.isAvailable()) {
+    if (IoUring.isAvailable() && !Boolean.getBoolean("velocity.disable-iouring-transport")) {
       return IO_URING;
     }
 

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/RateLimitedCommandHandler.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2025 Velocity Contributors
+ *
+ * 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.protocol.packet.chat;
+
+import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.protocol.MinecraftPacket;
+import net.kyori.adventure.text.Component;
+
+public abstract class RateLimitedCommandHandler<T extends MinecraftPacket> implements CommandHandler<T> {
+
+    private final Player player;
+    private final VelocityServer velocityServer;
+
+    private int failedAttempts;
+
+    protected RateLimitedCommandHandler(Player player, VelocityServer velocityServer) {
+        this.player = player;
+        this.velocityServer = velocityServer;
+    }
+
+    @Override
+    public boolean handlePlayerCommand(MinecraftPacket packet) {
+        if (packetClass().isInstance(packet)) {
+            if (!velocityServer.getCommandRateLimiter().attempt(player.getUniqueId())) {
+                if (velocityServer.getConfiguration().isKickOnCommandRateLimit() && failedAttempts++ >= velocityServer.getConfiguration().getKickAfterRateLimitedCommands()) {
+                    player.disconnect(Component.translatable("velocity.kick.command-rate-limit"));
+                }
+
+                if (velocityServer.getConfiguration().isForwardCommandsIfRateLimited()) {
+                    return false; // Send the packet to the server
+                }
+            } else {
+                failedAttempts = 0;
+            }
+
+            handlePlayerCommandInternal(packetClass().cast(packet));
+            return true;
+        }
+
+        return false;
+    }
+}

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/keyed/KeyedCommandHandler.java

@@ -21,17 +21,18 @@ import com.velocitypowered.api.event.command.CommandExecuteEvent;
 import com.velocitypowered.api.proxy.crypto.IdentifiedKey;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
-import com.velocitypowered.proxy.protocol.packet.chat.CommandHandler;
+import com.velocitypowered.proxy.protocol.packet.chat.RateLimitedCommandHandler;
 import com.velocitypowered.proxy.protocol.packet.chat.builder.ChatBuilderV2;
 import java.util.concurrent.CompletableFuture;
 import net.kyori.adventure.text.Component;
 
-public class KeyedCommandHandler implements CommandHandler<KeyedPlayerCommandPacket> {
+public class KeyedCommandHandler extends RateLimitedCommandHandler<KeyedPlayerCommandPacket> {
 
   private final ConnectedPlayer player;
   private final VelocityServer server;
 
   public KeyedCommandHandler(ConnectedPlayer player, VelocityServer server) {
+    super(player, server);
     this.player = player;
     this.server = server;
   }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/legacy/LegacyCommandHandler.java

@@ -20,16 +20,18 @@ package com.velocitypowered.proxy.protocol.packet.chat.legacy;
 import com.velocitypowered.api.event.command.CommandExecuteEvent;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
-import com.velocitypowered.proxy.protocol.packet.chat.CommandHandler;
+import com.velocitypowered.proxy.protocol.packet.chat.RateLimitedCommandHandler;
+
 import java.time.Instant;
 import java.util.concurrent.CompletableFuture;
 
-public class LegacyCommandHandler implements CommandHandler<LegacyChatPacket> {
+public class LegacyCommandHandler extends RateLimitedCommandHandler<LegacyChatPacket> {
 
   private final ConnectedPlayer player;
   private final VelocityServer server;
 
   public LegacyCommandHandler(ConnectedPlayer player, VelocityServer server) {
+    super(player, server);
     this.player = player;
     this.server = server;
   }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/session/SessionCommandHandler.java

@@ -22,17 +22,19 @@ import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.packet.chat.ChatAcknowledgementPacket;
-import com.velocitypowered.proxy.protocol.packet.chat.CommandHandler;
 import java.util.concurrent.CompletableFuture;
+
+import com.velocitypowered.proxy.protocol.packet.chat.RateLimitedCommandHandler;
 import net.kyori.adventure.text.Component;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
-public class SessionCommandHandler implements CommandHandler<SessionPlayerCommandPacket> {
+public class SessionCommandHandler extends RateLimitedCommandHandler<SessionPlayerCommandPacket> {
 
   private final ConnectedPlayer player;
   private final VelocityServer server;
 
   public SessionCommandHandler(ConnectedPlayer player, VelocityServer server) {
+    super(player, server);
     this.player = player;
     this.server = server;
   }

proxy/src/main/java/com/velocitypowered/proxy/protocol/util/PluginMessageUtil.java

@@ -22,13 +22,20 @@ import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.collect.ImmutableList;
 import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
+import com.velocitypowered.api.proxy.messages.LegacyChannelIdentifier;
+import com.velocitypowered.api.proxy.messages.MinecraftChannelIdentifier;
 import com.velocitypowered.api.util.ProxyVersion;
+import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
 import com.velocitypowered.proxy.protocol.ProtocolUtils;
+import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
 import com.velocitypowered.proxy.protocol.packet.PluginMessagePacket;
+import com.velocitypowered.proxy.util.except.QuietDecoderException;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import java.nio.charset.StandardCharsets;
 import java.util.Collection;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 import java.util.regex.Pattern;
@@ -85,13 +92,18 @@ public final class PluginMessageUtil {
         .equals(UNREGISTER_CHANNEL);
   }
 
+  private static final QuietDecoderException ILLEGAL_CHANNEL = new QuietDecoderException("Illegal channel");
+
   /**
    * Fetches all the channels in a register or unregister plugin message.
    *
+   * @param existingChannels the number of channels already registered
    * @param message the message to get the channels from
    * @return the channels, as an immutable list
    */
-  public static List<String> getChannels(PluginMessagePacket message) {
+  public static List<ChannelIdentifier> getChannels(int existingChannels,
+                                                    PluginMessagePacket message,
+                                                    ProtocolVersion protocolVersion) {
     checkNotNull(message, "message");
     checkArgument(isRegister(message) || isUnregister(message), "Unknown channel type %s",
         message.getChannel());
@@ -100,8 +112,28 @@ public final class PluginMessageUtil {
       // has caused issues with 1.13+ compatibility. Just return an empty list.
       return ImmutableList.of();
     }
-    String channels = message.content().toString(StandardCharsets.UTF_8);
+    String payload = message.content().toString(StandardCharsets.UTF_8);
-    return ImmutableList.copyOf(channels.split("\0"));
+    checkArgument(payload.length() <= Short.MAX_VALUE, "payload too long: %s", payload.length());
+    String[] channels = payload.split("\0");
+    checkArgument(existingChannels + channels.length <= ConnectedPlayer.MAX_CLIENTSIDE_PLUGIN_CHANNELS,
+        "too many channels: %s + %s > %s", existingChannels, channels.length, ConnectedPlayer.MAX_CLIENTSIDE_PLUGIN_CHANNELS);
+    ImmutableList.Builder<ChannelIdentifier> channelIdentifiers = ImmutableList.builderWithExpectedSize(channels.length);
+    try {
+      for (String channel : channels) {
+        if (protocolVersion.noLessThan(ProtocolVersion.MINECRAFT_1_13)) {
+          channelIdentifiers.add(MinecraftChannelIdentifier.from(channel));
+        } else {
+          channelIdentifiers.add(new LegacyChannelIdentifier(channel));
+        }
+      }
+    } catch (IllegalArgumentException e) {
+      if (MinecraftDecoder.DEBUG) {
+        throw e;
+      } else {
+        throw ILLEGAL_CHANNEL;
+      }
+    }
+    return channelIdentifiers.build();
   }
 
   /**
@@ -112,16 +144,31 @@ public final class PluginMessageUtil {
    * @return the plugin message to send
    */
   public static PluginMessagePacket constructChannelsPacket(ProtocolVersion protocolVersion,
-                                                            Collection<String> channels) {
+                                                            Collection<ChannelIdentifier> channels) {
     checkNotNull(channels, "channels");
     checkArgument(!channels.isEmpty(), "no channels specified");
     String channelName = protocolVersion.noLessThan(ProtocolVersion.MINECRAFT_1_13)
         ? REGISTER_CHANNEL : REGISTER_CHANNEL_LEGACY;
     ByteBuf contents = Unpooled.buffer();
-    contents.writeCharSequence(String.join("\0", channels), StandardCharsets.UTF_8);
+    contents.writeCharSequence(joinChannels(channels), StandardCharsets.UTF_8);
     return new PluginMessagePacket(channelName, contents);
   }
 
+  private static String joinChannels(Collection<ChannelIdentifier> channels) {
+    checkNotNull(channels, "channels");
+    checkArgument(!channels.isEmpty(), "no channels specified");
+    StringBuilder sb = new StringBuilder();
+    Iterator<ChannelIdentifier> iterator = channels.iterator();
+    while (iterator.hasNext()) {
+      ChannelIdentifier channel = iterator.next();
+      sb.append(channel.getId());
+      if (iterator.hasNext()) {
+        sb.append('\0');
+      }
+    }
+    return sb.toString();
+  }
+
   /**
    * Rewrites the brand message to indicate the presence of Velocity.
    *

proxy/src/main/java/com/velocitypowered/proxy/util/VelocityChannelRegistrar.java

@@ -79,10 +79,10 @@ public class VelocityChannelRegistrar implements ChannelRegistrar {
    *
    * @return all legacy channel IDs
    */
-  public Collection<String> getLegacyChannelIds() {
+  public Collection<ChannelIdentifier> getLegacyChannelIds() {
-    Collection<String> ids = new HashSet<>();
+    Collection<ChannelIdentifier> ids = new HashSet<>();
     for (ChannelIdentifier value : identifierMap.values()) {
-      ids.add(value.getId());
+      ids.add(new LegacyChannelIdentifier(value.getId()));
     }
     return ids;
   }
@@ -92,13 +92,13 @@ public class VelocityChannelRegistrar implements ChannelRegistrar {
    *
    * @return the channel IDs for Minecraft 1.13 and above
    */
-  public Collection<String> getModernChannelIds() {
+  public Collection<ChannelIdentifier> getModernChannelIds() {
-    Collection<String> ids = new HashSet<>();
+    Collection<ChannelIdentifier> ids = new HashSet<>();
     for (ChannelIdentifier value : identifierMap.values()) {
       if (value instanceof MinecraftChannelIdentifier) {
-        ids.add(value.getId());
+        ids.add(value);
       } else {
-        ids.add(PluginMessageUtil.transformLegacyToModernChannel(value.getId()));
+        ids.add(MinecraftChannelIdentifier.from(PluginMessageUtil.transformLegacyToModernChannel(value.getId())));
       }
     }
     return ids;
@@ -114,7 +114,7 @@ public class VelocityChannelRegistrar implements ChannelRegistrar {
    * @param protocolVersion the protocol version in use
    * @return the list of channels to register
    */
-  public Collection<String> getChannelsForProtocol(ProtocolVersion protocolVersion) {
+  public Collection<ChannelIdentifier> getChannelsForProtocol(ProtocolVersion protocolVersion) {
     if (protocolVersion.noLessThan(ProtocolVersion.MINECRAFT_1_13)) {
       return getModernChannelIds();
     }

proxy/src/main/java/com/velocitypowered/proxy/util/collect/CappedSet.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2019-2023 Velocity Contributors
+ *
+ * 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.util.collect;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ForwardingSet;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * An unsynchronized collection that puts an upper bound on the size of the collection.
+ */
+public final class CappedSet<T> extends ForwardingSet<T> {
+
+  private final Set<T> delegate;
+  private final int upperSize;
+
+  private CappedSet(Set<T> delegate, int upperSize) {
+    this.delegate = delegate;
+    this.upperSize = upperSize;
+  }
+
+  /**
+   * Creates a capped collection backed by a {@link HashSet}.
+   *
+   * @param maxSize the maximum size of the collection
+   * @param <T>     the type of elements in the collection
+   * @return the new collection
+   */
+  public static <T> Set<T> create(int maxSize) {
+    return new CappedSet<>(new HashSet<>(), maxSize);
+  }
+
+  @Override
+  protected Set<T> delegate() {
+    return delegate;
+  }
+
+  @Override
+  public boolean add(T element) {
+    if (this.delegate.size() >= upperSize) {
+      Preconditions.checkState(this.delegate.contains(element),
+          "collection is too large (%s >= %s)",
+          this.delegate.size(), this.upperSize);
+      return false;
+    }
+    return this.delegate.add(element);
+  }
+
+  @Override
+  public boolean addAll(Collection<? extends T> collection) {
+    return this.standardAddAll(collection);
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/util/ratelimit/CaffeineCacheRatelimiter.java

@@ -22,15 +22,15 @@ import com.github.benmanes.caffeine.cache.Caffeine;
 import com.github.benmanes.caffeine.cache.Ticker;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
-import java.net.InetAddress;
 import java.util.concurrent.TimeUnit;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * A simple rate-limiter based on a Caffeine {@link Cache}.
  */
-public class CaffeineCacheRatelimiter implements Ratelimiter {
+public class CaffeineCacheRatelimiter<T> implements Ratelimiter<T> {
 
-  private final Cache<InetAddress, Long> expiringCache;
+  private final Cache<T, Long> expiringCache;
   private final long timeoutNanos;
 
   CaffeineCacheRatelimiter(long time, TimeUnit unit) {
@@ -49,16 +49,15 @@ public class CaffeineCacheRatelimiter implements Ratelimiter {
   }
 
   /**
-   * Attempts to rate-limit the client.
+   * Attempts to rate-limit the object.
    *
-   * @param address the address to rate limit
+   * @param key the object to rate limit
-   * @return true if we should allow the client, false if we should rate-limit
+   * @return true if we should allow the object, false if we should rate-limit
    */
   @Override
-  public boolean attempt(InetAddress address) {
+  public boolean attempt(@NotNull  T key) {
-    Preconditions.checkNotNull(address, "address");
     long expectedNewValue = System.nanoTime() + timeoutNanos;
-    long last = expiringCache.get(address, (address1) -> expectedNewValue);
+    long last = expiringCache.get(key, (key1) -> expectedNewValue);
     return expectedNewValue == last;
   }
 }

proxy/src/main/java/com/velocitypowered/proxy/util/ratelimit/NoopCacheRatelimiter.java

@@ -17,16 +17,16 @@
 
 package com.velocitypowered.proxy.util.ratelimit;
 
-import java.net.InetAddress;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * A {@link Ratelimiter} that does no rate-limiting.
  */
-enum NoopCacheRatelimiter implements Ratelimiter {
+enum NoopCacheRatelimiter implements Ratelimiter<Object> {
   INSTANCE;
 
   @Override
-  public boolean attempt(InetAddress address) {
+  public boolean attempt(@NotNull Object key) {
     return true;
   }
 }

proxy/src/main/java/com/velocitypowered/proxy/util/ratelimit/Ratelimiter.java

@@ -17,18 +17,18 @@
 
 package com.velocitypowered.proxy.util.ratelimit;
 
-import java.net.InetAddress;
+import org.jetbrains.annotations.NotNull;
 
 /**
- * Allows rate limiting of clients.
+ * Allows rate limiting of objects.
  */
-public interface Ratelimiter {
+public interface Ratelimiter<T> {
 
   /**
-   * Determines whether or not to allow the connection.
+  * Attempts to rate-limit the object.
-   *
+  *
-   * @param address the address to rate limit
+  * @param key the object to rate limit
-   * @return true if allowed, false if not
+  * @return true if we should allow the object, false if we should rate-limit
-   */
+  */
-  boolean attempt(InetAddress address);
+  boolean attempt(@NotNull T key);
 }

proxy/src/main/java/com/velocitypowered/proxy/util/ratelimit/Ratelimiters.java

@@ -28,8 +28,9 @@ public final class Ratelimiters {
     throw new AssertionError();
   }
 
-  public static Ratelimiter createWithMilliseconds(long ms) {
+  @SuppressWarnings("unchecked")
-    return ms <= 0 ? NoopCacheRatelimiter.INSTANCE : new CaffeineCacheRatelimiter(ms,
+  public static <T> Ratelimiter<T> createWithMilliseconds(long ms) {
+    return ms <= 0 ? (Ratelimiter<T>) NoopCacheRatelimiter.INSTANCE : new CaffeineCacheRatelimiter(ms,
         TimeUnit.MILLISECONDS);
   }
 }

proxy/src/main/resources/com/velocitypowered/proxy/l10n/messages.properties

@@ -62,4 +62,6 @@ velocity.command.dump-server-error=An error occurred on the Velocity servers and
 velocity.command.dump-offline=Likely cause: Invalid system DNS settings or no internet connection
 velocity.command.send-usage=/send <player> <server>
 # Kick
-velocity.kick.shutdown=Proxy shutting down.
+velocity.kick.shutdown=Proxy shutting down.
+velocity.kick.command-rate-limit=You are sending too many commands too quickly.
+velocity.kick.tab-complete-rate-limit=You are sending too many tab complete requests too quickly.

proxy/src/main/resources/default-velocity.toml

@@ -66,6 +66,11 @@ kick-existing-players = false
 #                  configuration is used if no servers could be contacted.
 ping-passthrough = "DISABLED"
 
+# If enabled (default is false), then a sample of the online players on the proxy will be visible
+# when hovering over the player count in the server list.
+# This doesn't have any effect when ping passthrough is set to either "description" or "all".
+sample-players-in-ping = false
+
 # If not enabled (default is true) player IP addresses will be replaced by <ip address withheld> in logs
 enable-player-address-logging = true
 
@@ -151,6 +156,27 @@ accepts-transfers = false
 # threads. Disabled by default. Requires Linux or macOS.
 enable-reuse-port = false
 
+# How fast (in milliseconds) are clients allowed to send commands after the last command
+# By default this is 50ms (20 commands per second)
+command-rate-limit = 50
+
+# Should we forward commands to the backend upon being rate limited?
+# This will forward the command to the server instead of processing it on the proxy.
+# Since most server implementations have a rate limit, this will prevent the player
+# from being able to send excessive commands to the server.
+forward-commands-if-rate-limited = true
+
+# How many commands are allowed to be sent after the rate limit is hit before the player is kicked?
+# Setting this to 0 or lower will disable this feature.
+kick-after-rate-limited-commands = 0
+
+# How fast (in milliseconds) are clients allowed to send tab completions after the last tab completion
+tab-complete-rate-limit = 10
+
+# How many tab completions are allowed to be sent after the rate limit is hit before the player is kicked?
+# Setting this to 0 or lower will disable this feature.
+kick-after-rate-limited-tab-completes = 0
+
 [query]
 # Whether to enable responding to GameSpy 4 query responses or not.
 enabled = false

proxy/src/test/java/com/velocitypowered/proxy/util/VelocityChannelRegistrarTest.java

@@ -20,8 +20,10 @@ package com.velocitypowered.proxy.util;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.common.collect.ImmutableSet;
+import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.api.proxy.messages.LegacyChannelIdentifier;
 import com.velocitypowered.api.proxy.messages.MinecraftChannelIdentifier;
+import java.util.stream.Collectors;
 import org.junit.jupiter.api.Test;
 
 class VelocityChannelRegistrarTest {
@@ -46,9 +48,9 @@ class VelocityChannelRegistrarTest {
     // Two channels cover the modern channel (velocity:test) and the legacy-mapped channel
     // (legacy:velocitytest). Make sure they're what we expect.
     assertEquals(ImmutableSet.of(MODERN.getId(), SIMPLE_LEGACY_REMAPPED), registrar
-        .getModernChannelIds());
+        .getModernChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));
     assertEquals(ImmutableSet.of(SIMPLE_LEGACY.getId(), MODERN.getId()), registrar
-        .getLegacyChannelIds());
+        .getLegacyChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));
   }
 
   @Test
@@ -57,9 +59,10 @@ class VelocityChannelRegistrarTest {
     registrar.register(SPECIAL_REMAP_LEGACY, MODERN_SPECIAL_REMAP);
 
     // This one, just one channel for the modern case.
-    assertEquals(ImmutableSet.of(MODERN_SPECIAL_REMAP.getId()), registrar.getModernChannelIds());
+    assertEquals(ImmutableSet.of(MODERN_SPECIAL_REMAP.getId()),
+        registrar.getModernChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));
     assertEquals(ImmutableSet.of(MODERN_SPECIAL_REMAP.getId(), SPECIAL_REMAP_LEGACY.getId()),
-        registrar.getLegacyChannelIds());
+        registrar.getLegacyChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));
   }
 
   @Test
@@ -68,7 +71,9 @@ class VelocityChannelRegistrarTest {
     registrar.register(MODERN, SIMPLE_LEGACY);
     registrar.unregister(SIMPLE_LEGACY);
 
-    assertEquals(ImmutableSet.of(MODERN.getId()), registrar.getModernChannelIds());
+    assertEquals(ImmutableSet.of(MODERN.getId()),
-    assertEquals(ImmutableSet.of(MODERN.getId()), registrar.getLegacyChannelIds());
+        registrar.getModernChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));;
+    assertEquals(ImmutableSet.of(MODERN.getId()),
+        registrar.getLegacyChannelIds().stream().map(ChannelIdentifier::getId).collect(Collectors.toSet()));
   }
 }

proxy/src/test/java/com/velocitypowered/proxy/util/collect/CappedSetTest.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2019-2021 Velocity Contributors
+ *
+ * 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, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.velocitypowered.proxy.util.collect;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.common.collect.ImmutableSet;
+import java.util.Collection;
+import java.util.Set;
+import org.junit.jupiter.api.Test;
+
+class CappedSetTest {
+
+  @Test
+  void basicVerification() {
+    Collection<String> coll = CappedSet.create(1);
+    assertTrue(coll.add("coffee"), "did not add single item");
+    assertThrows(IllegalStateException.class, () -> coll.add("tea"),
+        "item was added to collection although it is too full");
+    assertEquals(1, coll.size(), "collection grew in size unexpectedly");
+  }
+
+  @Test
+  void testAddAll() {
+    Set<String> doesFill1 = ImmutableSet.of("coffee", "tea");
+    Set<String> doesFill2 = ImmutableSet.of("chocolate");
+    Set<String> overfill = ImmutableSet.of("Coke", "Pepsi");
+
+    Collection<String> coll = CappedSet.create(3);
+    assertTrue(coll.addAll(doesFill1), "did not add items");
+    assertTrue(coll.addAll(doesFill2), "did not add items");
+    assertThrows(IllegalStateException.class, () -> coll.addAll(overfill),
+        "items added to collection although it is too full");
+    assertEquals(3, coll.size(), "collection grew in size unexpectedly");
+  }
+
+  @Test
+  void handlesSetBehaviorCorrectly() {
+    Set<String> doesFill1 = ImmutableSet.of("coffee", "tea");
+    Set<String> doesFill2 = ImmutableSet.of("coffee", "chocolate");
+    Set<String> overfill = ImmutableSet.of("coffee", "Coke", "Pepsi");
+
+    Collection<String> coll = CappedSet.create(3);
+    assertTrue(coll.addAll(doesFill1), "did not add items");
+    assertTrue(coll.addAll(doesFill2), "did not add items");
+    assertThrows(IllegalStateException.class, () -> coll.addAll(overfill),
+        "items added to collection although it is too full");
+
+    assertFalse(coll.addAll(doesFill1), "added items?!?");
+
+    assertEquals(3, coll.size(), "collection grew in size unexpectedly");
+  }
+}