Merge branch 'dev/1.1.0' into decode-multiple

api/src/main/java/com/velocitypowered/api/event/player/PlayerChooseInitialServerEvent.java

@@ -0,0 +1,51 @@
+package com.velocitypowered.api.event.player;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.server.RegisteredServer;
+import java.util.Optional;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * Fired when a player has finished connecting to the proxy and we need to choose the first server
+ * to connect to.
+ */
+public class PlayerChooseInitialServerEvent {
+
+  private final Player player;
+  private @Nullable RegisteredServer initialServer;
+
+  /**
+   * Constructs a PlayerChooseInitialServerEvent.
+   * @param player the player that was connected
+   * @param initialServer the initial server selected, may be {@code null}
+   */
+  public PlayerChooseInitialServerEvent(Player player, @Nullable RegisteredServer initialServer) {
+    this.player = Preconditions.checkNotNull(player, "player");
+    this.initialServer = initialServer;
+  }
+
+  public Player getPlayer() {
+    return player;
+  }
+
+  public Optional<RegisteredServer> getInitialServer() {
+    return Optional.ofNullable(initialServer);
+  }
+
+  /**
+   * Sets the new initial server.
+   * @param server the initial server the player should connect to
+   */
+  public void setInitialServer(RegisteredServer server) {
+    this.initialServer = server;
+  }
+
+  @Override
+  public String toString() {
+    return "PlayerChooseInitialServerEvent{"
+        + "player=" + player
+        + ", initialServer=" + initialServer
+        + '}';
+  }
+}

api/src/main/java/com/velocitypowered/api/network/ProtocolVersion.java

@@ -33,7 +33,8 @@ public enum ProtocolVersion {
   MINECRAFT_1_14_1(480, "1.14.1"),
   MINECRAFT_1_14_2(485, "1.14.2"),
   MINECRAFT_1_14_3(490, "1.14.3"),
-  MINECRAFT_1_14_4(498, "1.14.4");
+  MINECRAFT_1_14_4(498, "1.14.4"),
+  MINECRAFT_1_15(566, "1.15-pre2");
 
   private final int protocol;
   private final String name;

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommand.java

@@ -72,7 +72,10 @@ public class VelocityCommand implements Command {
   @Override
   public List<String> suggest(CommandSource source, String @NonNull [] currentArgs) {
     if (currentArgs.length == 0) {
-      return ImmutableList.copyOf(subcommands.keySet());
+      return subcommands.entrySet().stream()
+              .filter(e -> e.getValue().hasPermission(source, new String[0]))
+              .map(Map.Entry::getKey)
+              .collect(ImmutableList.toImmutableList());
     }
 
     if (currentArgs.length == 1) {
@@ -81,7 +84,7 @@ public class VelocityCommand implements Command {
               currentArgs[0].length()))
           .filter(e -> e.getValue().hasPermission(source, new String[0]))
           .map(Map.Entry::getKey)
-          .collect(Collectors.toList());
+          .collect(ImmutableList.toImmutableList());
     }
 
     Command command = subcommands.get(currentArgs[0].toLowerCase(Locale.US));

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

@@ -100,7 +100,7 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
       "              configuration is used if no servers could be contacted."
   })
   @ConfigKey("ping-passthrough")
-  private PingPassthroughMode pingPassthrough;
+  private PingPassthroughMode pingPassthrough = PingPassthroughMode.DISABLED;
 
   @Table("[servers]")
   private final Servers servers;
@@ -192,44 +192,38 @@ public class VelocityConfiguration extends AnnotatedConfig implements ProxyConfi
     }
 
     if (servers.getServers().isEmpty()) {
-      logger.error("You have no servers configured. :(");
-      valid = false;
-    } else {
-      if (servers.getAttemptConnectionOrder().isEmpty()) {
-        logger.error("No fallback servers are configured!");
+      logger.warn("You don't have any servers configured.");
+    }
+
+    for (Map.Entry<String, String> entry : servers.getServers().entrySet()) {
+      try {
+        AddressUtil.parseAddress(entry.getValue());
+      } catch (IllegalArgumentException e) {
+        logger.error("Server {} does not have a valid IP address.", entry.getKey(), e);
         valid = false;
       }
+    }
 
-      for (Map.Entry<String, String> entry : servers.getServers().entrySet()) {
-        try {
-          AddressUtil.parseAddress(entry.getValue());
-        } catch (IllegalArgumentException e) {
-          logger.error("Server {} does not have a valid IP address.", entry.getKey(), e);
-          valid = false;
-        }
+    for (String s : servers.getAttemptConnectionOrder()) {
+      if (!servers.getServers().containsKey(s)) {
+        logger.error("Fallback server " + s + " is not registered in your configuration!");
+        valid = false;
+      }
+    }
+
+    for (Map.Entry<String, List<String>> entry : forcedHosts.getForcedHosts().entrySet()) {
+      if (entry.getValue().isEmpty()) {
+        logger.error("Forced host '{}' does not contain any servers", entry.getKey());
+        valid = false;
+        continue;
       }
 
-      for (String s : servers.getAttemptConnectionOrder()) {
-        if (!servers.getServers().containsKey(s)) {
-          logger.error("Fallback server " + s + " is not registered in your configuration!");
+      for (String server : entry.getValue()) {
+        if (!servers.getServers().containsKey(server)) {
+          logger.error("Server '{}' for forced host '{}' does not exist", server, entry.getKey());
           valid = false;
         }
       }
-
-      for (Map.Entry<String, List<String>> entry : forcedHosts.getForcedHosts().entrySet()) {
-        if (entry.getValue().isEmpty()) {
-          logger.error("Forced host '{}' does not contain any servers", entry.getKey());
-          valid = false;
-          continue;
-        }
-
-        for (String server : entry.getValue()) {
-          if (!servers.getServers().containsKey(server)) {
-            logger.error("Server '{}' for forced host '{}' does not exist", server, entry.getKey());
-            valid = false;
-          }
-        }
-      }
     }
 
     try {

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

@@ -1,5 +1,8 @@
 package com.velocitypowered.proxy.connection.backend;
 
+import static com.velocitypowered.proxy.connection.backend.BungeeCordMessageResponder.getBungeeCordChannel;
+
+import com.google.common.collect.ImmutableList;
 import com.mojang.brigadier.arguments.StringArgumentType;
 import com.mojang.brigadier.builder.LiteralArgumentBuilder;
 import com.mojang.brigadier.builder.RequiredArgumentBuilder;
@@ -31,6 +34,7 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
   private final VelocityServerConnection serverConn;
   private final ClientPlaySessionHandler playerSessionHandler;
   private final MinecraftConnection playerConnection;
+  private final BungeeCordMessageResponder bungeecordMessageResponder;
   private boolean exceptionTriggered = false;
 
   BackendPlaySessionHandler(VelocityServer server, VelocityServerConnection serverConn) {
@@ -44,11 +48,18 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
           "Initializing BackendPlaySessionHandler with no backing client play session handler!");
     }
     this.playerSessionHandler = (ClientPlaySessionHandler) psh;
+
+    this.bungeecordMessageResponder = new BungeeCordMessageResponder(server,
+        serverConn.getPlayer());
   }
 
   @Override
   public void activated() {
     serverConn.getServer().addPlayer(serverConn.getPlayer());
+    MinecraftConnection serverMc = serverConn.ensureConnected();
+    serverMc.write(PluginMessageUtil.constructChannelsPacket(serverMc.getProtocolVersion(),
+        ImmutableList.of(getBungeeCordChannel(serverMc.getProtocolVersion()))
+    ));
   }
 
   @Override
@@ -86,6 +97,10 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(PluginMessage packet) {
+    if (bungeecordMessageResponder.process(packet)) {
+      return true;
+    }
+
     if (!serverConn.getPlayer().canForwardPluginMessage(serverConn.ensureConnected()
         .getProtocolVersion(), packet)) {
       return true;

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

@@ -0,0 +1,329 @@
+package com.velocitypowered.proxy.connection.backend;
+
+import com.velocitypowered.api.network.ProtocolVersion;
+import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.messages.LegacyChannelIdentifier;
+import com.velocitypowered.api.proxy.messages.MinecraftChannelIdentifier;
+import com.velocitypowered.api.proxy.server.RegisteredServer;
+import com.velocitypowered.api.util.UuidUtils;
+import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.connection.MinecraftConnection;
+import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
+import com.velocitypowered.proxy.protocol.packet.PluginMessage;
+import com.velocitypowered.proxy.protocol.util.ByteBufDataInput;
+import com.velocitypowered.proxy.protocol.util.ByteBufDataOutput;
+import com.velocitypowered.proxy.server.VelocityRegisteredServer;
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
+import java.util.StringJoiner;
+import net.kyori.text.serializer.legacy.LegacyComponentSerializer;
+
+class BungeeCordMessageResponder {
+
+  private static final MinecraftChannelIdentifier MODERN_CHANNEL = MinecraftChannelIdentifier
+      .create("bungeecord", "main");
+  private static final LegacyChannelIdentifier LEGACY_CHANNEL =
+      new LegacyChannelIdentifier("BungeeCord");
+
+  private final VelocityServer proxy;
+  private final ConnectedPlayer player;
+
+  BungeeCordMessageResponder(VelocityServer proxy, ConnectedPlayer player) {
+    this.proxy = proxy;
+    this.player = player;
+  }
+
+  private void processConnect(ByteBufDataInput in) {
+    String serverName = in.readUTF();
+    proxy.getServer(serverName).ifPresent(server -> player.createConnectionRequest(server)
+        .fireAndForget());
+  }
+
+  private void processConnectOther(ByteBufDataInput in) {
+    String playerName = in.readUTF();
+    String serverName = in.readUTF();
+
+    proxy.getPlayer(playerName).flatMap(player -> proxy.getServer(serverName))
+        .ifPresent(server -> player.createConnectionRequest(server).fireAndForget());
+  }
+
+  private void processIp(ByteBufDataInput in) {
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+    out.writeUTF("IP");
+    out.writeUTF(player.getRemoteAddress().getHostString());
+    out.writeInt(player.getRemoteAddress().getPort());
+    sendResponseOnConnection(buf);
+  }
+
+  private void processPlayerCount(ByteBufDataInput in) {
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+    String target = in.readUTF();
+    if (target.equals("ALL")) {
+      out.writeUTF("PlayerCount");
+      out.writeUTF("ALL");
+      out.writeInt(proxy.getPlayerCount());
+    } else {
+      proxy.getServer(target).ifPresent(rs -> {
+        int playersOnServer = rs.getPlayersConnected().size();
+        out.writeUTF("PlayerCount");
+        out.writeUTF(rs.getServerInfo().getName());
+        out.writeInt(playersOnServer);
+      });
+    }
+
+    if (buf.isReadable()) {
+      sendResponseOnConnection(buf);
+    } else {
+      buf.release();
+    }
+  }
+
+  private void processPlayerList(ByteBufDataInput in) {
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+    String target = in.readUTF();
+    if (target.equals("ALL")) {
+      out.writeUTF("PlayerList");
+      out.writeUTF("ALL");
+
+      StringJoiner joiner = new StringJoiner(", ");
+      for (Player online : proxy.getAllPlayers()) {
+        joiner.add(online.getUsername());
+      }
+      out.writeUTF(joiner.toString());
+    } else {
+      proxy.getServer(target).ifPresent(info -> {
+        out.writeUTF("PlayerList");
+        out.writeUTF(info.getServerInfo().getName());
+
+        StringJoiner joiner = new StringJoiner(", ");
+        for (Player online : info.getPlayersConnected()) {
+          joiner.add(online.getUsername());
+        }
+        out.writeUTF(joiner.toString());
+      });
+    }
+
+    if (buf.isReadable()) {
+      sendResponseOnConnection(buf);
+    } else {
+      buf.release();
+    }
+  }
+
+  private void processGetServers() {
+    StringJoiner joiner = new StringJoiner(", ");
+    for (RegisteredServer server : proxy.getAllServers()) {
+      joiner.add(server.getServerInfo().getName());
+    }
+
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+    out.writeUTF("GetServers");
+    out.writeUTF(joiner.toString());
+
+    sendResponseOnConnection(buf);
+  }
+
+  private void processMessage(ByteBufDataInput in) {
+    String target = in.readUTF();
+    String message = in.readUTF();
+    if (target.equals("ALL")) {
+      for (Player player : proxy.getAllPlayers()) {
+        player.sendMessage(LegacyComponentSerializer.INSTANCE.deserialize(message));
+      }
+    } else {
+      proxy.getPlayer(target).ifPresent(player -> {
+        player.sendMessage(LegacyComponentSerializer.INSTANCE.deserialize(message));
+      });
+    }
+  }
+
+  private void processGetServer() {
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+    out.writeUTF("GetServer");
+    out.writeUTF(player.ensureAndGetCurrentServer().getServerInfo().getName());
+
+    sendResponseOnConnection(buf);
+  }
+
+  private void processUuid() {
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+    out.writeUTF("UUID");
+    out.writeUTF(UuidUtils.toUndashed(player.getUniqueId()));
+
+    sendResponseOnConnection(buf);
+  }
+
+  private void processUuidOther(ByteBufDataInput in) {
+    proxy.getPlayer(in.readUTF()).ifPresent(player -> {
+      ByteBuf buf = Unpooled.buffer();
+      ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+      out.writeUTF("UUIDOther");
+      out.writeUTF(player.getUsername());
+      out.writeUTF(UuidUtils.toUndashed(player.getUniqueId()));
+
+      sendResponseOnConnection(buf);
+    });
+  }
+
+  private void processServerIp(ByteBufDataInput in) {
+    proxy.getServer(in.readUTF()).ifPresent(info -> {
+      ByteBuf buf = Unpooled.buffer();
+      ByteBufDataOutput out = new ByteBufDataOutput(buf);
+
+      out.writeUTF("ServerIP");
+      out.writeUTF(info.getServerInfo().getName());
+      out.writeUTF(info.getServerInfo().getAddress().getHostString());
+      out.writeShort(info.getServerInfo().getAddress().getPort());
+
+      sendResponseOnConnection(buf);
+    });
+  }
+
+  private void processKick(ByteBufDataInput in) {
+    proxy.getPlayer(in.readUTF()).ifPresent(player -> {
+      String kickReason = in.readUTF();
+      player.disconnect(LegacyComponentSerializer.INSTANCE.deserialize(kickReason));
+    });
+  }
+
+  private ByteBuf prepareForwardMessage(ByteBufDataInput in) {
+    String channel = in.readUTF();
+    short messageLength = in.readShort();
+
+    ByteBuf buf = Unpooled.buffer();
+    ByteBufDataOutput forwarded = new ByteBufDataOutput(buf);
+    forwarded.writeUTF(channel);
+    forwarded.writeShort(messageLength);
+    buf.writeBytes(in.unwrap().readSlice(messageLength));
+    return buf;
+  }
+
+  private void processForwardToPlayer(ByteBufDataInput in) {
+    proxy.getPlayer(in.readUTF())
+        .flatMap(Player::getCurrentServer)
+        .ifPresent(server -> sendServerResponse(player, prepareForwardMessage(in)));
+  }
+
+  private void processForwardToServer(ByteBufDataInput in) {
+    ByteBuf toForward = prepareForwardMessage(in);
+    String target = in.readUTF();
+    if (target.equals("ALL")) {
+      ByteBuf unreleasableForward = Unpooled.unreleasableBuffer(toForward);
+      try {
+        for (RegisteredServer rs : proxy.getAllServers()) {
+          ((VelocityRegisteredServer) rs).sendPluginMessage(LEGACY_CHANNEL, unreleasableForward);
+        }
+      } finally {
+        toForward.release();
+      }
+    } else {
+      proxy.getServer(target).ifPresent(rs -> ((VelocityRegisteredServer) rs)
+          .sendPluginMessage(LEGACY_CHANNEL, toForward));
+    }
+  }
+
+  // Note: this method will always release the buffer!
+  private void sendResponseOnConnection(ByteBuf buf) {
+    sendServerResponse(this.player, buf);
+  }
+
+  static String getBungeeCordChannel(ProtocolVersion version) {
+    return version.compareTo(ProtocolVersion.MINECRAFT_1_13) >= 0 ? MODERN_CHANNEL.getId()
+        : LEGACY_CHANNEL.getId();
+  }
+
+  // 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());
+
+    PluginMessage msg = null;
+    boolean released = false;
+
+    try {
+      VelocityServerConnection vsc = player.getConnectedServer();
+      if (vsc == null) {
+        return;
+      }
+
+      MinecraftConnection serverConn = vsc.ensureConnected();
+      msg = new PluginMessage(chan, buf);
+      serverConn.write(msg);
+      released = true;
+    } finally {
+      if (!released && msg != null) {
+        msg.release();
+      }
+    }
+  }
+
+  boolean process(PluginMessage message) {
+    if (!MODERN_CHANNEL.getId().equals(message.getChannel()) && !LEGACY_CHANNEL.getId()
+        .equals(message.getChannel())) {
+      return false;
+    }
+
+    ByteBufDataInput in = new ByteBufDataInput(message.content());
+    String subChannel = in.readUTF();
+    switch (subChannel) {
+      case "ForwardToPlayer":
+        this.processForwardToPlayer(in);
+        break;
+      case "Forward":
+        this.processForwardToServer(in);
+        break;
+      case "Connect":
+        this.processConnect(in);
+        break;
+      case "ConnectOther":
+        this.processConnectOther(in);
+        break;
+      case "IP":
+        this.processIp(in);
+        break;
+      case "PlayerCount":
+        this.processPlayerCount(in);
+        break;
+      case "PlayerList":
+        this.processPlayerList(in);
+        break;
+      case "GetServers":
+        this.processGetServers();
+        break;
+      case "Message":
+        this.processMessage(in);
+        break;
+      case "GetServer":
+        this.processGetServer();
+        break;
+      case "UUID":
+        this.processUuid();
+        break;
+      case "UUIDOther":
+        this.processUuidOther(in);
+        break;
+      case "ServerIP":
+        this.processServerIp(in);
+        break;
+      case "KickPlayer":
+        this.processKick(in);
+        break;
+      default:
+        // Do nothing, unknown command
+        break;
+    }
+
+    return true;
+  }
+}

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

@@ -17,9 +17,9 @@ import com.velocitypowered.proxy.protocol.packet.LoginPluginMessage;
 import com.velocitypowered.proxy.protocol.packet.LoginPluginResponse;
 import com.velocitypowered.proxy.protocol.packet.ServerLoginSuccess;
 import com.velocitypowered.proxy.protocol.packet.SetCompression;
+import com.velocitypowered.proxy.util.except.QuietException;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
-import java.io.IOException;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
 import java.util.concurrent.CompletableFuture;
@@ -111,8 +111,19 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public void disconnected() {
-    resultFuture
-        .completeExceptionally(new IOException("Unexpectedly disconnected from remote server"));
+    if (server.getConfiguration().getPlayerInfoForwardingMode() == PlayerInfoForwarding.LEGACY) {
+      resultFuture.completeExceptionally(
+          new QuietException("The connection to the remote server was unexpectedly closed.\n"
+              + "This is usually because the remote server does not have BungeeCord IP forwarding "
+              + "correctly enabled.\nSee "
+              + "https://docs.velocitypowered.com/en/latest/users/player-info-forwarding.html "
+              + "for instructions on how to configure player info forwarding correctly.")
+      );
+    } else {
+      resultFuture.completeExceptionally(
+          new QuietException("The connection to the remote server was unexpectedly closed.")
+      );
+    }
   }
 
   private static ByteBuf createForwardingData(byte[] hmacSecret, String address,

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

@@ -34,6 +34,7 @@ import com.velocitypowered.proxy.protocol.packet.Handshake;
 import com.velocitypowered.proxy.protocol.packet.PluginMessage;
 import com.velocitypowered.proxy.protocol.packet.ServerLogin;
 import com.velocitypowered.proxy.server.VelocityRegisteredServer;
+import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFutureListener;
@@ -210,12 +211,22 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
 
   @Override
   public boolean sendPluginMessage(ChannelIdentifier identifier, byte[] data) {
+    return sendPluginMessage(identifier, Unpooled.wrappedBuffer(data));
+  }
+
+  /**
+   * Sends a plugin message to the server through this connection.
+   * @param identifier the channel ID to use
+   * @param data the data
+   * @return whether or not the message was sent
+   */
+  public boolean sendPluginMessage(ChannelIdentifier identifier, ByteBuf data) {
     Preconditions.checkNotNull(identifier, "identifier");
     Preconditions.checkNotNull(data, "data");
 
     MinecraftConnection mc = ensureConnected();
 
-    PluginMessage message = new PluginMessage(identifier.getId(), Unpooled.wrappedBuffer(data));
+    PluginMessage message = new PluginMessage(identifier.getId(), data);
     mc.write(message);
     return true;
   }

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

@@ -322,8 +322,8 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
       joinGame.setDimension(getFakeTemporaryDimensionId(realDim));
       player.getConnection().delayedWrite(joinGame);
       player.getConnection().delayedWrite(
-          new Respawn(realDim, joinGame.getDifficulty(), joinGame.getGamemode(),
-              joinGame.getLevelType()));
+          new Respawn(realDim, joinGame.getPartialHashedSeed(), joinGame.getDifficulty(),
+              joinGame.getGamemode(), joinGame.getLevelType()));
     }
 
     // Remove previous boss bars. These don't get cleared when sending JoinGame, thus the need to
@@ -392,31 +392,19 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
     }
 
     List<Offer> offers = new ArrayList<>();
-    int longestLength = 0;
     for (String suggestion : suggestions) {
       offers.add(new Offer(suggestion));
-      if (suggestion.length() > longestLength) {
-        longestLength = suggestion.length();
-      }
     }
 
-    TabCompleteResponse resp = new TabCompleteResponse();
-    resp.setTransactionId(packet.getTransactionId());
-
     int startPos = packet.getCommand().lastIndexOf(' ') + 1;
-    int length;
-    if (startPos == 0) {
-      startPos = packet.getCommand().length() + 1;
-      length = longestLength;
-    } else {
-      length = packet.getCommand().length() - startPos;
+    if (startPos > 0) {
+      TabCompleteResponse resp = new TabCompleteResponse();
+      resp.setTransactionId(packet.getTransactionId());
+      resp.setStart(startPos);
+      resp.setLength(packet.getCommand().length() - startPos);
+      resp.getOffers().addAll(offers);
+      player.getConnection().write(resp);
     }
-
-    resp.setStart(startPos);
-    resp.setLength(length);
-    resp.getOffers().addAll(offers);
-
-    player.getConnection().write(resp);
     return true;
   }
 

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

@@ -135,6 +135,18 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
     return Optional.ofNullable(connectedServer);
   }
 
+  /**
+   * Makes sure the player is connected to a server and returns the server they are connected to.
+   * @return the server the player is connected to
+   */
+  public VelocityServerConnection ensureAndGetCurrentServer() {
+    VelocityServerConnection con = this.connectedServer;
+    if (con == null) {
+      throw new IllegalStateException("Not connected to server!");
+    }
+    return con;
+  }
+
   @Override
   public GameProfile getGameProfile() {
     return profile;
@@ -417,33 +429,22 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
       return;
     }
 
-    if (connectedServer == null) {
-      Optional<RegisteredServer> nextServer = getNextServerToTry(rs);
-      if (nextServer.isPresent()) {
-        // There can't be any connection in flight now.
-        resetInFlightConnection();
-        createConnectionRequest(nextServer.get()).fireAndForget();
-      } else {
-        disconnect(friendlyReason);
-      }
+    boolean kickedFromCurrent = connectedServer == null || connectedServer.getServer().equals(rs);
+    ServerKickResult result;
+    if (kickedFromCurrent) {
+      Optional<RegisteredServer> next = getNextServerToTry(rs);
+      result = next.<ServerKickResult>map(RedirectPlayer::create)
+          .orElseGet(() -> DisconnectPlayer.create(friendlyReason));
     } else {
-      boolean kickedFromCurrent = connectedServer.getServer().equals(rs);
-      ServerKickResult result;
-      if (kickedFromCurrent) {
-        Optional<RegisteredServer> next = getNextServerToTry(rs);
-        result = next.<ServerKickResult>map(RedirectPlayer::create)
-            .orElseGet(() -> DisconnectPlayer.create(friendlyReason));
-      } else {
-        // If we were kicked by going to another server, the connection should not be in flight
-        if (connectionInFlight != null && connectionInFlight.getServer().equals(rs)) {
-          resetInFlightConnection();
-        }
-        result = Notify.create(friendlyReason);
+      // If we were kicked by going to another server, the connection should not be in flight
+      if (connectionInFlight != null && connectionInFlight.getServer().equals(rs)) {
+        resetInFlightConnection();
       }
-      KickedFromServerEvent originalEvent = new KickedFromServerEvent(this, rs, kickReason,
-          !kickedFromCurrent, result);
-      handleKickEvent(originalEvent, friendlyReason);
+      result = Notify.create(friendlyReason);
     }
+    KickedFromServerEvent originalEvent = new KickedFromServerEvent(this, rs, kickReason,
+        !kickedFromCurrent, result);
+    handleKickEvent(originalEvent, friendlyReason);
   }
 
   private void handleKickEvent(KickedFromServerEvent originalEvent, Component friendlyReason) {

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

@@ -1,24 +1,21 @@
 package com.velocitypowered.proxy.connection.client;
 
 import static com.google.common.net.UrlEscapers.urlFormParameterEscaper;
-import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_13;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_8;
 import static com.velocitypowered.proxy.VelocityServer.GSON;
 import static com.velocitypowered.proxy.connection.VelocityConstants.EMPTY_BYTE_ARRAY;
-import static com.velocitypowered.proxy.connection.VelocityConstants.VELOCITY_IP_FORWARDING_CHANNEL;
 import static com.velocitypowered.proxy.util.EncryptionUtils.decryptRsa;
 import static com.velocitypowered.proxy.util.EncryptionUtils.generateServerId;
 import static org.asynchttpclient.Dsl.asyncHttpClient;
-import static org.asynchttpclient.Dsl.config;
 
 import com.google.common.base.Preconditions;
-import com.google.common.net.UrlEscapers;
 import com.velocitypowered.api.event.connection.LoginEvent;
 import com.velocitypowered.api.event.connection.PostLoginEvent;
 import com.velocitypowered.api.event.connection.PreLoginEvent;
 import com.velocitypowered.api.event.connection.PreLoginEvent.PreLoginComponentResult;
 import com.velocitypowered.api.event.permission.PermissionsSetupEvent;
 import com.velocitypowered.api.event.player.GameProfileRequestEvent;
+import com.velocitypowered.api.event.player.PlayerChooseInitialServerEvent;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.util.GameProfile;
 import com.velocitypowered.proxy.VelocityServer;
@@ -29,17 +26,12 @@ import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.packet.Disconnect;
 import com.velocitypowered.proxy.protocol.packet.EncryptionRequest;
 import com.velocitypowered.proxy.protocol.packet.EncryptionResponse;
-import com.velocitypowered.proxy.protocol.packet.LoginPluginMessage;
-import com.velocitypowered.proxy.protocol.packet.LoginPluginResponse;
 import com.velocitypowered.proxy.protocol.packet.ServerLogin;
 import com.velocitypowered.proxy.protocol.packet.ServerLoginSuccess;
 import com.velocitypowered.proxy.protocol.packet.SetCompression;
 import com.velocitypowered.proxy.util.VelocityMessages;
 import io.netty.buffer.ByteBuf;
-import io.netty.buffer.Unpooled;
 import java.net.InetSocketAddress;
-import java.net.MalformedURLException;
-import java.net.URL;
 import java.security.GeneralSecurityException;
 import java.security.KeyPair;
 import java.util.Arrays;
@@ -50,7 +42,6 @@ import java.util.concurrent.ThreadLocalRandom;
 import net.kyori.text.Component;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.asynchttpclient.Dsl;
 import org.asynchttpclient.ListenableFuture;
 import org.asynchttpclient.Response;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
@@ -66,7 +57,6 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
   private final InitialInboundConnection inbound;
   private @MonotonicNonNull ServerLogin login;
   private byte[] verify = EMPTY_BYTE_ARRAY;
-  private int playerInfoId;
   private @MonotonicNonNull ConnectedPlayer connectedPlayer;
 
   LoginSessionHandler(VelocityServer server, MinecraftConnection mcConnection,
@@ -79,29 +69,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
   @Override
   public boolean handle(ServerLogin packet) {
     this.login = packet;
-    if (mcConnection.getProtocolVersion().compareTo(MINECRAFT_1_13) >= 0) {
-      // To make sure the connecting client isn't Velocity, send a plugin message that Velocity will
-      // recognize and respond to.
-      playerInfoId = ThreadLocalRandom.current().nextInt();
-      mcConnection.write(new LoginPluginMessage(playerInfoId, VELOCITY_IP_FORWARDING_CHANNEL,
-          Unpooled.EMPTY_BUFFER));
-    } else {
-      beginPreLogin();
-    }
-    return true;
-  }
-
-  @Override
-  public boolean handle(LoginPluginResponse packet) {
-    if (packet.getId() == playerInfoId) {
-      if (packet.isSuccess()) {
-        // Uh oh, someone's trying to run Velocity behind Velocity. We don't want that happening.
-        inbound.disconnect(VelocityMessages.NO_PROXY_BEHIND_PROXY);
-      } else {
-        // Proceed with the regular login process.
-        beginPreLogin();
-      }
-    }
+    beginPreLogin();
     return true;
   }
 
@@ -254,12 +222,6 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
   }
 
   private void finishLogin(ConnectedPlayer player) {
-    Optional<RegisteredServer> toTry = player.getNextServerToTry();
-    if (!toTry.isPresent()) {
-      player.disconnect(VelocityMessages.NO_AVAILABLE_SERVERS);
-      return;
-    }
-
     int threshold = server.getConfiguration().getCompressionThreshold();
     if (threshold >= 0 && mcConnection.getProtocolVersion().compareTo(MINECRAFT_1_8) >= 0) {
       mcConnection.write(new SetCompression(threshold));
@@ -292,11 +254,27 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
             mcConnection.setSessionHandler(new InitialConnectSessionHandler(player));
             server.getEventManager().fire(new PostLoginEvent(player))
-                .thenRun(() -> player.createConnectionRequest(toTry.get()).fireAndForget());
+                .thenRun(() -> connectToInitialServer(player));
           }
         }, mcConnection.eventLoop());
   }
 
+  private void connectToInitialServer(ConnectedPlayer player) {
+    Optional<RegisteredServer> initialFromConfig = player.getNextServerToTry();
+    PlayerChooseInitialServerEvent event = new PlayerChooseInitialServerEvent(player,
+        initialFromConfig.orElse(null));
+
+    server.getEventManager().fire(event)
+        .thenRunAsync(() -> {
+          Optional<RegisteredServer> toTry = event.getInitialServer();
+          if (!toTry.isPresent()) {
+            player.disconnect(VelocityMessages.NO_AVAILABLE_SERVERS);
+            return;
+          }
+          player.createConnectionRequest(toTry.get()).fireAndForget();
+        }, mcConnection.eventLoop());
+  }
+
   @Override
   public void handleUnknown(ByteBuf buf) {
     mcConnection.close();

proxy/src/main/java/com/velocitypowered/proxy/protocol/StateRegistry.java

@@ -5,6 +5,7 @@ import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_12;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_12_1;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_13;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_14;
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_15;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_7_2;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_8;
 import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_9;
@@ -120,51 +121,61 @@ public enum StateRegistry {
           map(0x1F, MINECRAFT_1_14, false));
 
       clientbound.register(BossBar.class, BossBar::new,
-          map(0x0C, MINECRAFT_1_9, false));
+          map(0x0C, MINECRAFT_1_9, false),
+          map(0x0D, MINECRAFT_1_15, false));
       clientbound.register(Chat.class, Chat::new,
           map(0x02, MINECRAFT_1_7_2, true),
           map(0x0F, MINECRAFT_1_9, true),
-          map(0x0E, MINECRAFT_1_13, true));
+          map(0x0E, MINECRAFT_1_13, true),
+          map(0x0F, MINECRAFT_1_15, true));
       clientbound.register(TabCompleteResponse.class, TabCompleteResponse::new,
           map(0x3A, MINECRAFT_1_7_2, false),
           map(0x0E, MINECRAFT_1_9, false),
-          map(0x10, MINECRAFT_1_13, false));
+          map(0x10, MINECRAFT_1_13, false),
+          map(0x11, MINECRAFT_1_15, false));
       clientbound.register(AvailableCommands.class, AvailableCommands::new,
-          map(0x11, MINECRAFT_1_13, false));
+          map(0x11, MINECRAFT_1_13, false),
+          map(0x12, MINECRAFT_1_15, false));
       clientbound.register(PluginMessage.class, PluginMessage::new,
           map(0x3F, MINECRAFT_1_7_2, false),
           map(0x18, MINECRAFT_1_9, false),
           map(0x19, MINECRAFT_1_13, false),
-          map(0x18, MINECRAFT_1_14, false));
+          map(0x18, MINECRAFT_1_14, false),
+          map(0x19, MINECRAFT_1_15, false));
       clientbound.register(Disconnect.class, Disconnect::new,
           map(0x40, MINECRAFT_1_7_2, false),
           map(0x1A, MINECRAFT_1_9, false),
           map(0x1B, MINECRAFT_1_13, false),
-          map(0x1A, MINECRAFT_1_14, false));
+          map(0x1A, MINECRAFT_1_14, false),
+          map(0x1B, MINECRAFT_1_15, false));
       clientbound.register(KeepAlive.class, KeepAlive::new,
           map(0x00, MINECRAFT_1_7_2, false),
           map(0x1F, MINECRAFT_1_9, false),
           map(0x21, MINECRAFT_1_13, false),
-          map(0x20, MINECRAFT_1_14, false));
+          map(0x20, MINECRAFT_1_14, false),
+          map(0x21, MINECRAFT_1_15, false));
       clientbound.register(JoinGame.class, JoinGame::new,
           map(0x01, MINECRAFT_1_7_2, false),
           map(0x23, MINECRAFT_1_9, false),
           map(0x25, MINECRAFT_1_13, false),
-          map(0x25, MINECRAFT_1_14, false));
+          map(0x25, MINECRAFT_1_14, false),
+          map(0x26, MINECRAFT_1_15, false));
       clientbound.register(Respawn.class, Respawn::new,
           map(0x07, MINECRAFT_1_7_2, true),
           map(0x33, MINECRAFT_1_9, true),
           map(0x34, MINECRAFT_1_12, true),
           map(0x35, MINECRAFT_1_12_1, true),
           map(0x38, MINECRAFT_1_13, true),
-          map(0x3A, MINECRAFT_1_14, true));
+          map(0x3A, MINECRAFT_1_14, true),
+          map(0x3B, MINECRAFT_1_15, true));
       clientbound.register(ResourcePackRequest.class, ResourcePackRequest::new,
           map(0x48, MINECRAFT_1_8, true),
           map(0x32, MINECRAFT_1_9, true),
           map(0x33, MINECRAFT_1_12, true),
           map(0x34, MINECRAFT_1_12_1, true),
           map(0x37, MINECRAFT_1_13, true),
-          map(0x39, MINECRAFT_1_14, true));
+          map(0x39, MINECRAFT_1_14, true),
+          map(0x3A, MINECRAFT_1_15, true));
       clientbound.register(HeaderAndFooter.class, HeaderAndFooter::new,
           map(0x47, MINECRAFT_1_8, true),
           map(0x48, MINECRAFT_1_9, true),
@@ -172,20 +183,23 @@ public enum StateRegistry {
           map(0x49, MINECRAFT_1_12, true),
           map(0x4A, MINECRAFT_1_12_1, true),
           map(0x4E, MINECRAFT_1_13, true),
-          map(0x53, MINECRAFT_1_14, true));
+          map(0x53, MINECRAFT_1_14, true),
+          map(0x54, MINECRAFT_1_15, true));
       clientbound.register(TitlePacket.class, TitlePacket::new,
           map(0x45, MINECRAFT_1_8, true),
           map(0x45, MINECRAFT_1_9, true),
           map(0x47, MINECRAFT_1_12, true),
           map(0x48, MINECRAFT_1_12_1, true),
           map(0x4B, MINECRAFT_1_13, true),
-          map(0x4F, MINECRAFT_1_14, true));
+          map(0x4F, MINECRAFT_1_14, true),
+          map(0x50, MINECRAFT_1_15, true));
       clientbound.register(PlayerListItem.class, PlayerListItem::new,
           map(0x38, MINECRAFT_1_7_2, false),
           map(0x2D, MINECRAFT_1_9, false),
           map(0x2E, MINECRAFT_1_12_1, false),
           map(0x30, MINECRAFT_1_13, false),
-          map(0x33, MINECRAFT_1_14, false));
+          map(0x33, MINECRAFT_1_14, false),
+          map(0x34, MINECRAFT_1_15, false));
     }
   },
   LOGIN {

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/GS4QueryHandler.java

@@ -18,6 +18,7 @@ import io.netty.channel.SimpleChannelInboundHandler;
 import io.netty.channel.socket.DatagramPacket;
 import java.net.InetAddress;
 import java.nio.charset.StandardCharsets;
+import java.security.SecureRandom;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
@@ -59,6 +60,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
   private final Cache<InetAddress, Integer> sessions = CacheBuilder.newBuilder()
       .expireAfterWrite(30, TimeUnit.SECONDS)
       .build();
+  private final SecureRandom random;
 
   private volatile @MonotonicNonNull List<QueryResponse.PluginInformation> pluginInformationList
       = null;
@@ -67,6 +69,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
 
   public GS4QueryHandler(VelocityServer server) {
     this.server = server;
+    this.random = new SecureRandom();
   }
 
   private QueryResponse createInitialResponse() {
@@ -111,7 +114,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
       switch (type) {
         case QUERY_TYPE_HANDSHAKE: {
           // Generate new challenge token and put it into the sessions cache
-          int challengeToken = ThreadLocalRandom.current().nextInt();
+          int challengeToken = random.nextInt();
           sessions.put(senderAddress, challengeToken);
 
           // Respond with challenge token

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/JoinGame.java

@@ -12,11 +12,13 @@ public class JoinGame implements MinecraftPacket {
   private int entityId;
   private short gamemode;
   private int dimension;
+  private long partialHashedSeed; // 1.15+
   private short difficulty;
   private short maxPlayers;
   private @Nullable String levelType;
   private int viewDistance; //1.14+
   private boolean reducedDebugInfo;
+  private boolean mystery;
 
   public int getEntityId() {
     return entityId;
@@ -42,6 +44,10 @@ public class JoinGame implements MinecraftPacket {
     this.dimension = dimension;
   }
 
+  public long getPartialHashedSeed() {
+    return partialHashedSeed;
+  }
+
   public short getDifficulty() {
     return difficulty;
   }
@@ -91,6 +97,7 @@ public class JoinGame implements MinecraftPacket {
         + "entityId=" + entityId
         + ", gamemode=" + gamemode
         + ", dimension=" + dimension
+        + ", partialHashedSeed=" + partialHashedSeed
         + ", difficulty=" + difficulty
         + ", maxPlayers=" + maxPlayers
         + ", levelType='" + levelType + '\''
@@ -111,6 +118,9 @@ public class JoinGame implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_13_2) <= 0) {
       this.difficulty = buf.readUnsignedByte();
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      this.partialHashedSeed = buf.readLong();
+    }
     this.maxPlayers = buf.readUnsignedByte();
     this.levelType = ProtocolUtils.readString(buf, 16);
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_14) >= 0) {
@@ -119,6 +129,9 @@ public class JoinGame implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_8) >= 0) {
       this.reducedDebugInfo = buf.readBoolean();
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      this.mystery = buf.readBoolean();
+    }
   }
 
   @Override
@@ -133,6 +146,9 @@ public class JoinGame implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_13_2) <= 0) {
       buf.writeByte(difficulty);
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      buf.writeLong(partialHashedSeed);
+    }
     buf.writeByte(maxPlayers);
     if (levelType == null) {
       throw new IllegalStateException("No level type specified.");
@@ -144,6 +160,9 @@ public class JoinGame implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_8) >= 0) {
       buf.writeBoolean(reducedDebugInfo);
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      buf.writeBoolean(mystery);
+    }
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/Respawn.java

@@ -9,6 +9,7 @@ import io.netty.buffer.ByteBuf;
 public class Respawn implements MinecraftPacket {
 
   private int dimension;
+  private long partialHashedSeed;
   private short difficulty;
   private short gamemode;
   private String levelType = "";
@@ -16,8 +17,10 @@ public class Respawn implements MinecraftPacket {
   public Respawn() {
   }
 
-  public Respawn(int dimension, short difficulty, short gamemode, String levelType) {
+  public Respawn(int dimension, long partialHashedSeed, short difficulty, short gamemode,
+      String levelType) {
     this.dimension = dimension;
+    this.partialHashedSeed = partialHashedSeed;
     this.difficulty = difficulty;
     this.gamemode = gamemode;
     this.levelType = levelType;
@@ -31,6 +34,14 @@ public class Respawn implements MinecraftPacket {
     this.dimension = dimension;
   }
 
+  public long getPartialHashedSeed() {
+    return partialHashedSeed;
+  }
+
+  public void setPartialHashedSeed(long partialHashedSeed) {
+    this.partialHashedSeed = partialHashedSeed;
+  }
+
   public short getDifficulty() {
     return difficulty;
   }
@@ -59,6 +70,7 @@ public class Respawn implements MinecraftPacket {
   public String toString() {
     return "Respawn{"
         + "dimension=" + dimension
+        + ", partialHashedSeed=" + partialHashedSeed
         + ", difficulty=" + difficulty
         + ", gamemode=" + gamemode
         + ", levelType='" + levelType + '\''
@@ -71,6 +83,9 @@ public class Respawn implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_13_2) <= 0) {
       this.difficulty = buf.readUnsignedByte();
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      this.partialHashedSeed = buf.readLong();
+    }
     this.gamemode = buf.readUnsignedByte();
     this.levelType = ProtocolUtils.readString(buf, 16);
   }
@@ -81,6 +96,9 @@ public class Respawn implements MinecraftPacket {
     if (version.compareTo(ProtocolVersion.MINECRAFT_1_13_2) <= 0) {
       buf.writeByte(difficulty);
     }
+    if (version.compareTo(ProtocolVersion.MINECRAFT_1_15) >= 0) {
+      buf.writeLong(partialHashedSeed);
+    }
     buf.writeByte(gamemode);
     ProtocolUtils.writeString(buf, levelType);
   }

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

@@ -0,0 +1,110 @@
+package com.velocitypowered.proxy.protocol.util;
+
+import com.google.common.io.ByteArrayDataInput;
+import io.netty.buffer.ByteBuf;
+import java.io.DataInput;
+import java.io.DataInputStream;
+import java.io.IOException;
+
+/**
+ * A wrapper around {@link io.netty.buffer.ByteBuf} that implements the exception-free
+ * {@link ByteArrayDataInput} interface from Guava.
+ */
+public class ByteBufDataInput implements ByteArrayDataInput, DataInput {
+
+  private final ByteBuf in;
+
+  /**
+   * Creates a new ByteBufDataInput instance. The ByteBufDataInput simply "borrows" the ByteBuf
+   * while it is in use.
+   *
+   * @param buf the buffer to read from
+   */
+  public ByteBufDataInput(ByteBuf buf) {
+    this.in = buf;
+  }
+
+  public ByteBuf unwrap() {
+    return in;
+  }
+
+  @Override
+  public void readFully(byte[] b) {
+    in.readBytes(b);
+  }
+
+  @Override
+  public void readFully(byte[] b, int off, int len) {
+    in.readBytes(b, off, len);
+  }
+
+  @Override
+  public int skipBytes(int n) {
+    in.skipBytes(n);
+    return n;
+  }
+
+  @Override
+  public boolean readBoolean() {
+    return in.readBoolean();
+  }
+
+  @Override
+  public byte readByte() {
+    return in.readByte();
+  }
+
+  @Override
+  public int readUnsignedByte() {
+    return in.readUnsignedByte() & 0xFF;
+  }
+
+  @Override
+  public short readShort() {
+    return in.readShort();
+  }
+
+  @Override
+  public int readUnsignedShort() {
+    return in.readUnsignedShort();
+  }
+
+  @Override
+  public char readChar() {
+    return in.readChar();
+  }
+
+  @Override
+  public int readInt() {
+    return in.readInt();
+  }
+
+  @Override
+  public long readLong() {
+    return in.readLong();
+  }
+
+  @Override
+  public float readFloat() {
+    return in.readFloat();
+  }
+
+  @Override
+  public double readDouble() {
+    return in.readDouble();
+  }
+
+  @Override
+  public String readLine() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public String readUTF() {
+    try {
+      return DataInputStream.readUTF(this);
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+}

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

@@ -0,0 +1,105 @@
+package com.velocitypowered.proxy.protocol.util;
+
+import com.google.common.io.ByteArrayDataOutput;
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufUtil;
+import java.io.DataOutput;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * A {@link DataOutput} equivalent to {@link ByteBufDataInput}.
+ */
+public class ByteBufDataOutput extends OutputStream implements DataOutput, ByteArrayDataOutput {
+
+  private final ByteBuf buf;
+  private final DataOutputStream utf8out;
+
+  public ByteBufDataOutput(ByteBuf buf) {
+    this.buf = buf;
+    this.utf8out = new DataOutputStream(this);
+  }
+
+  @Override
+  public byte[] toByteArray() {
+    return ByteBufUtil.getBytes(buf);
+  }
+
+  @Override
+  public void write(int b) {
+    buf.writeByte(b);
+  }
+
+  @Override
+  public void write(byte[] b) {
+    buf.writeBytes(b);
+  }
+
+  @Override
+  public void write(byte[] b, int off, int len) {
+    buf.writeBytes(b, off, len);
+  }
+
+  @Override
+  public void writeBoolean(boolean v) {
+    buf.writeBoolean(v);
+  }
+
+  @Override
+  public void writeByte(int v) {
+    buf.writeByte(v);
+  }
+
+  @Override
+  public void writeShort(int v) {
+    buf.writeShort(v);
+  }
+
+  @Override
+  public void writeChar(int v) {
+    buf.writeChar(v);
+  }
+
+  @Override
+  public void writeInt(int v) {
+    buf.writeInt(v);
+  }
+
+  @Override
+  public void writeLong(long v) {
+    buf.writeLong(v);
+  }
+
+  @Override
+  public void writeFloat(float v) {
+    buf.writeFloat(v);
+  }
+
+  @Override
+  public void writeDouble(double v) {
+    buf.writeDouble(v);
+  }
+
+  @Override
+  public void writeBytes(String s) {
+    buf.writeCharSequence(s, StandardCharsets.US_ASCII);
+  }
+
+  @Override
+  public void writeChars(String s) {
+    for (char c : s.toCharArray()) {
+      buf.writeChar(c);
+    }
+  }
+
+  @Override
+  public void writeUTF(String s) {
+    try {
+      this.utf8out.writeUTF(s);
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+}

proxy/src/main/java/com/velocitypowered/proxy/server/VelocityRegisteredServer.java

@@ -18,12 +18,16 @@ import com.velocitypowered.api.proxy.server.ServerInfo;
 import com.velocitypowered.api.proxy.server.ServerPing;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
+import com.velocitypowered.proxy.connection.backend.VelocityServerConnection;
 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.netty.MinecraftEncoder;
 import com.velocitypowered.proxy.protocol.netty.MinecraftVarintFrameDecoder;
 import com.velocitypowered.proxy.protocol.netty.MinecraftVarintLengthEncoder;
+import com.velocitypowered.proxy.protocol.packet.PluginMessage;
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
@@ -119,8 +123,18 @@ public class VelocityRegisteredServer implements RegisteredServer {
 
   @Override
   public boolean sendPluginMessage(ChannelIdentifier identifier, byte[] data) {
+    return sendPluginMessage(identifier, Unpooled.wrappedBuffer(data));
+  }
+
+  /**
+   * Sends a plugin message to the server through this connection.
+   * @param identifier the channel ID to use
+   * @param data the data
+   * @return whether or not the message was sent
+   */
+  public boolean sendPluginMessage(ChannelIdentifier identifier, ByteBuf data) {
     for (ConnectedPlayer player : players) {
-      ServerConnection connection = player.getConnectedServer();
+      VelocityServerConnection connection = player.getConnectedServer();
       if (connection != null && connection.getServerInfo().equals(serverInfo)) {
         return connection.sendPluginMessage(identifier, data);
       }

proxy/src/main/java/com/velocitypowered/proxy/util/except/QuietException.java

@@ -0,0 +1,17 @@
+package com.velocitypowered.proxy.util.except;
+
+/**
+ * A special-purpose exception thrown when we want to indicate an error condition but do not want
+ * to see a large stack trace in logs.
+ */
+public class QuietException extends RuntimeException {
+
+  public QuietException(String message) {
+    super(message);
+  }
+
+  @Override
+  public synchronized Throwable fillInStackTrace() {
+    return this;
+  }
+}