Implement a proper login state machine for logins

Fixes #688 and probably a host of other potential problems.

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

@@ -34,9 +34,8 @@ import com.velocitypowered.natives.encryption.VelocityCipherFactory;
 import com.velocitypowered.natives.util.Natives;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.client.HandshakeSessionHandler;
-import com.velocitypowered.proxy.connection.client.LoginSessionHandler;
+import com.velocitypowered.proxy.connection.client.InitialLoginSessionHandler;
 import com.velocitypowered.proxy.connection.client.StatusSessionHandler;
-import com.velocitypowered.proxy.network.Connections;
 import com.velocitypowered.proxy.protocol.MinecraftPacket;
 import com.velocitypowered.proxy.protocol.StateRegistry;
 import com.velocitypowered.proxy.protocol.VelocityConnectionEvent;
@@ -178,7 +177,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
         if (cause instanceof ReadTimeoutException) {
           logger.error("{}: read timed out", association);
         } else {
-          boolean frontlineHandler = sessionHandler instanceof LoginSessionHandler
+          boolean frontlineHandler = sessionHandler instanceof InitialLoginSessionHandler
               || sessionHandler instanceof HandshakeSessionHandler
               || sessionHandler instanceof StatusSessionHandler;
           boolean isQuietDecoderException = cause instanceof QuietDecoderException;

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

@@ -0,0 +1,205 @@
+/*
+ * Copyright (C) 2018 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.connection.client;
+
+import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_8;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.event.connection.DisconnectEvent;
+import com.velocitypowered.api.event.connection.LoginEvent;
+import com.velocitypowered.api.event.connection.PostLoginEvent;
+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.permission.PermissionFunction;
+import com.velocitypowered.api.proxy.server.RegisteredServer;
+import com.velocitypowered.api.util.GameProfile;
+import com.velocitypowered.api.util.UuidUtils;
+import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.config.PlayerInfoForwarding;
+import com.velocitypowered.proxy.config.VelocityConfiguration;
+import com.velocitypowered.proxy.connection.MinecraftConnection;
+import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
+import com.velocitypowered.proxy.protocol.StateRegistry;
+import com.velocitypowered.proxy.protocol.packet.ServerLoginSuccess;
+import com.velocitypowered.proxy.protocol.packet.SetCompression;
+import io.netty.buffer.ByteBuf;
+import java.util.Optional;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import net.kyori.adventure.text.Component;
+import net.kyori.adventure.text.format.NamedTextColor;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+
+public class AuthSessionHandler implements MinecraftSessionHandler {
+
+  private static final Logger logger = LogManager.getLogger(AuthSessionHandler.class);
+
+  private final VelocityServer server;
+  private final MinecraftConnection mcConnection;
+  private final LoginInboundConnection inbound;
+  private GameProfile profile;
+  private @MonotonicNonNull ConnectedPlayer connectedPlayer;
+  private final boolean onlineMode;
+
+  AuthSessionHandler(VelocityServer server, LoginInboundConnection inbound,
+                     GameProfile profile, boolean onlineMode) {
+    this.server = Preconditions.checkNotNull(server, "server");
+    this.inbound = Preconditions.checkNotNull(inbound, "inbound");
+    this.profile = Preconditions.checkNotNull(profile, "profile");
+    this.onlineMode = onlineMode;
+    this.mcConnection = inbound.delegatedConnection();
+  }
+
+  @Override
+  public void activated() {
+    // Some connection types may need to alter the game profile.
+    profile = mcConnection.getType().addGameProfileTokensIfRequired(profile,
+        server.getConfiguration().getPlayerInfoForwardingMode());
+    GameProfileRequestEvent profileRequestEvent = new GameProfileRequestEvent(inbound, profile,
+        onlineMode);
+    final GameProfile finalProfile = profile;
+
+    server.getEventManager().fire(profileRequestEvent).thenComposeAsync(profileEvent -> {
+      if (mcConnection.isClosed()) {
+        // The player disconnected after we authenticated them.
+        return CompletableFuture.completedFuture(null);
+      }
+
+      // Initiate a regular connection and move over to it.
+      ConnectedPlayer player = new ConnectedPlayer(server, profileEvent.getGameProfile(),
+          mcConnection, inbound.getVirtualHost().orElse(null), onlineMode);
+      this.connectedPlayer = player;
+      if (!server.canRegisterConnection(player)) {
+        player.disconnect0(Component.translatable("velocity.error.already-connected-proxy",
+            NamedTextColor.RED), true);
+        return CompletableFuture.completedFuture(null);
+      }
+
+      logger.info("{} has connected", player);
+
+      return server.getEventManager()
+          .fire(new PermissionsSetupEvent(player, ConnectedPlayer.DEFAULT_PERMISSIONS))
+          .thenAcceptAsync(event -> {
+            if (!mcConnection.isClosed()) {
+              // wait for permissions to load, then set the players permission function
+              final PermissionFunction function = event.createFunction(player);
+              if (function == null) {
+                logger.error(
+                    "A plugin permission provider {} provided an invalid permission function"
+                        + " for player {}. This is a bug in the plugin, not in Velocity. Falling"
+                        + " back to the default permission function.",
+                    event.getProvider().getClass().getName(),
+                    player.getUsername());
+              } else {
+                player.setPermissionFunction(function);
+              }
+              completeLoginProtocolPhaseAndInitialize(player);
+            }
+          }, mcConnection.eventLoop());
+    }, mcConnection.eventLoop()).exceptionally((ex) -> {
+      logger.error("Exception during connection of {}", finalProfile, ex);
+      return null;
+    });
+  }
+
+  private void completeLoginProtocolPhaseAndInitialize(ConnectedPlayer player) {
+    int threshold = server.getConfiguration().getCompressionThreshold();
+    if (threshold >= 0 && mcConnection.getProtocolVersion().compareTo(MINECRAFT_1_8) >= 0) {
+      mcConnection.write(new SetCompression(threshold));
+      mcConnection.setCompressionThreshold(threshold);
+    }
+    VelocityConfiguration configuration = server.getConfiguration();
+    UUID playerUniqueId = player.getUniqueId();
+    if (configuration.getPlayerInfoForwardingMode() == PlayerInfoForwarding.NONE) {
+      playerUniqueId = UuidUtils.generateOfflinePlayerUuid(player.getUsername());
+    }
+    ServerLoginSuccess success = new ServerLoginSuccess();
+    success.setUsername(player.getUsername());
+    success.setUuid(playerUniqueId);
+    mcConnection.write(success);
+
+    mcConnection.setAssociation(player);
+    mcConnection.setState(StateRegistry.PLAY);
+
+    server.getEventManager().fire(new LoginEvent(player))
+        .thenAcceptAsync(event -> {
+          if (mcConnection.isClosed()) {
+            // The player was disconnected
+            server.getEventManager().fireAndForget(new DisconnectEvent(player,
+                DisconnectEvent.LoginStatus.CANCELLED_BY_USER_BEFORE_COMPLETE));
+            return;
+          }
+
+          Optional<Component> reason = event.getResult().getReasonComponent();
+          if (reason.isPresent()) {
+            player.disconnect0(reason.get(), true);
+          } else {
+            if (!server.registerConnection(player)) {
+              player.disconnect0(Component.translatable("velocity.error.already-connected-proxy"),
+                  true);
+              return;
+            }
+
+            mcConnection.setSessionHandler(new InitialConnectSessionHandler(player));
+            server.getEventManager().fire(new PostLoginEvent(player))
+                .thenCompose((ignored) -> connectToInitialServer(player))
+                .exceptionally((ex) -> {
+                  logger.error("Exception while connecting {} to initial server", player, ex);
+                  return null;
+                });
+          }
+        }, mcConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while completing login initialisation phase for {}", player, ex);
+          return null;
+        });
+  }
+
+  private CompletableFuture<Void> connectToInitialServer(ConnectedPlayer player) {
+    Optional<RegisteredServer> initialFromConfig = player.getNextServerToTry();
+    PlayerChooseInitialServerEvent event = new PlayerChooseInitialServerEvent(player,
+        initialFromConfig.orElse(null));
+
+    return server.getEventManager().fire(event)
+        .thenRunAsync(() -> {
+          Optional<RegisteredServer> toTry = event.getInitialServer();
+          if (!toTry.isPresent()) {
+            player.disconnect0(Component.translatable("velocity.error.no-available-servers",
+                NamedTextColor.RED), true);
+            return;
+          }
+          player.createConnectionRequest(toTry.get()).fireAndForget();
+        }, mcConnection.eventLoop());
+  }
+
+  @Override
+  public void handleUnknown(ByteBuf buf) {
+    mcConnection.close(true);
+  }
+
+  @Override
+  public void disconnected() {
+    if (connectedPlayer != null) {
+      connectedPlayer.teardown();
+    }
+    this.inbound.cleanup();
+  }
+}

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

@@ -40,8 +40,6 @@ import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.util.Optional;
 import net.kyori.adventure.text.Component;
-import net.kyori.adventure.text.TextComponent;
-import net.kyori.adventure.text.TranslatableComponent;
 import net.kyori.adventure.text.format.NamedTextColor;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -144,7 +142,7 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
 
     LoginInboundConnection lic = new LoginInboundConnection(ic);
     server.getEventManager().fireAndForget(new ConnectionHandshakeEvent(lic));
-    connection.setSessionHandler(new LoginSessionHandler(server, connection, lic));
+    connection.setSessionHandler(new InitialLoginSessionHandler(server, connection, lic));
   }
 
   private ConnectionType getHandshakeConnectionType(Handshake handshake) {

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

@@ -18,38 +18,23 @@
 package com.velocitypowered.proxy.connection.client;
 
 import static com.google.common.net.UrlEscapers.urlFormParameterEscaper;
-import static com.velocitypowered.api.network.ProtocolVersion.MINECRAFT_1_8;
 import static com.velocitypowered.proxy.VelocityServer.GENERAL_GSON;
 import static com.velocitypowered.proxy.connection.VelocityConstants.EMPTY_BYTE_ARRAY;
 import static com.velocitypowered.proxy.util.EncryptionUtils.decryptRsa;
 import static com.velocitypowered.proxy.util.EncryptionUtils.generateServerId;
 
 import com.google.common.base.Preconditions;
-import com.velocitypowered.api.event.connection.DisconnectEvent;
-import com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus;
-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.permission.PermissionFunction;
-import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.util.GameProfile;
-import com.velocitypowered.api.util.UuidUtils;
 import com.velocitypowered.proxy.VelocityServer;
-import com.velocitypowered.proxy.config.PlayerInfoForwarding;
-import com.velocitypowered.proxy.config.VelocityConfiguration;
 import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
-import com.velocitypowered.proxy.protocol.StateRegistry;
+import com.velocitypowered.proxy.protocol.netty.MinecraftDecoder;
 import com.velocitypowered.proxy.protocol.packet.EncryptionRequest;
 import com.velocitypowered.proxy.protocol.packet.EncryptionResponse;
 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 io.netty.buffer.ByteBuf;
 import java.net.InetSocketAddress;
 import java.security.GeneralSecurityException;
@@ -57,8 +42,6 @@ import java.security.KeyPair;
 import java.security.MessageDigest;
 import java.util.Arrays;
 import java.util.Optional;
-import java.util.UUID;
-import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ThreadLocalRandom;
 import net.kyori.adventure.text.Component;
@@ -69,9 +52,9 @@ import org.asynchttpclient.ListenableFuture;
 import org.asynchttpclient.Response;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
-public class LoginSessionHandler implements MinecraftSessionHandler {
+public class InitialLoginSessionHandler implements MinecraftSessionHandler {
 
-  private static final Logger logger = LogManager.getLogger(LoginSessionHandler.class);
+  private static final Logger logger = LogManager.getLogger(InitialLoginSessionHandler.class);
   private static final String MOJANG_HASJOINED_URL =
       System.getProperty("mojang.sessionserver", "https://sessionserver.mojang.com/session/minecraft/hasJoined")
           .concat("?username=%s&serverId=%s");
@@ -81,10 +64,10 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
   private final LoginInboundConnection inbound;
   private @MonotonicNonNull ServerLogin login;
   private byte[] verify = EMPTY_BYTE_ARRAY;
-  private @MonotonicNonNull ConnectedPlayer connectedPlayer;
+  private LoginState currentState = LoginState.LOGIN_PACKET_EXPECTED;
 
-  LoginSessionHandler(VelocityServer server, MinecraftConnection mcConnection,
-      LoginInboundConnection inbound) {
+  InitialLoginSessionHandler(VelocityServer server, MinecraftConnection mcConnection,
+                             LoginInboundConnection inbound) {
     this.server = Preconditions.checkNotNull(server, "server");
     this.mcConnection = Preconditions.checkNotNull(mcConnection, "mcConnection");
     this.inbound = Preconditions.checkNotNull(inbound, "inbound");
@@ -92,8 +75,53 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(ServerLogin packet) {
+    assertState(LoginState.LOGIN_PACKET_EXPECTED);
+    this.currentState = LoginState.LOGIN_PACKET_RECEIVED;
     this.login = packet;
-    beginPreLogin();
+
+    PreLoginEvent event = new PreLoginEvent(inbound, login.getUsername());
+    server.getEventManager().fire(event)
+        .thenRunAsync(() -> {
+          if (mcConnection.isClosed()) {
+            // The player was disconnected
+            return;
+          }
+
+          PreLoginComponentResult result = event.getResult();
+          Optional<Component> disconnectReason = result.getReasonComponent();
+          if (disconnectReason.isPresent()) {
+            // The component is guaranteed to be provided if the connection was denied.
+            inbound.disconnect(disconnectReason.get());
+            return;
+          }
+
+          inbound.loginEventFired(() -> {
+            if (mcConnection.isClosed()) {
+              // The player was disconnected
+              return;
+            }
+
+            mcConnection.eventLoop().execute(() -> {
+              if (!result.isForceOfflineMode() && (server.getConfiguration().isOnlineMode()
+                  || result.isOnlineModeAllowed())) {
+                // Request encryption.
+                EncryptionRequest request = generateEncryptionRequest();
+                this.verify = Arrays.copyOf(request.getVerifyToken(), 4);
+                mcConnection.write(request);
+                this.currentState = LoginState.ENCRYPTION_REQUEST_SENT;
+              } else {
+                mcConnection.setSessionHandler(new AuthSessionHandler(
+                    server, inbound, GameProfile.forOfflinePlayer(login.getUsername()), false
+                ));
+              }
+            });
+          });
+        }, mcConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception in pre-login stage", ex);
+          return null;
+        });
+
     return true;
   }
 
@@ -105,6 +133,9 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(EncryptionResponse packet) {
+    assertState(LoginState.ENCRYPTION_REQUEST_SENT);
+    this.currentState = LoginState.ENCRYPTION_RESPONSE_RECEIVED;
+
     ServerLogin login = this.login;
     if (login == null) {
       throw new IllegalStateException("No ServerLogin packet received yet.");
@@ -156,8 +187,9 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
           Response profileResponse = hasJoinedResponse.get();
           if (profileResponse.getStatusCode() == 200) {
             // All went well, initialize the session.
-            initializePlayer(GENERAL_GSON.fromJson(profileResponse.getResponseBody(),
-                GameProfile.class), true);
+            mcConnection.setSessionHandler(new AuthSessionHandler(
+                server, inbound, GENERAL_GSON.fromJson(profileResponse.getResponseBody(), GameProfile.class), true
+            ));
           } else if (profileResponse.getStatusCode() == 204) {
             // Apparently an offline-mode user logged onto this online-mode proxy.
             inbound.disconnect(Component.translatable("velocity.error.online-mode-only",
@@ -184,52 +216,6 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
     return true;
   }
 
-  private void beginPreLogin() {
-    ServerLogin login = this.login;
-    if (login == null) {
-      throw new IllegalStateException("No ServerLogin packet received yet.");
-    }
-    PreLoginEvent event = new PreLoginEvent(inbound, login.getUsername());
-    server.getEventManager().fire(event)
-        .thenRunAsync(() -> {
-          if (mcConnection.isClosed()) {
-            // The player was disconnected
-            return;
-          }
-
-          PreLoginComponentResult result = event.getResult();
-          Optional<Component> disconnectReason = result.getReasonComponent();
-          if (disconnectReason.isPresent()) {
-            // The component is guaranteed to be provided if the connection was denied.
-            inbound.disconnect(disconnectReason.get());
-            return;
-          }
-
-          inbound.loginEventFired(() -> {
-            if (mcConnection.isClosed()) {
-              // The player was disconnected
-              return;
-            }
-
-            mcConnection.eventLoop().execute(() -> {
-              if (!result.isForceOfflineMode() && (server.getConfiguration().isOnlineMode()
-                  || result.isOnlineModeAllowed())) {
-                // Request encryption.
-                EncryptionRequest request = generateEncryptionRequest();
-                this.verify = Arrays.copyOf(request.getVerifyToken(), 4);
-                mcConnection.write(request);
-              } else {
-                initializePlayer(GameProfile.forOfflinePlayer(login.getUsername()), false);
-              }
-            });
-          });
-        }, mcConnection.eventLoop())
-        .exceptionally((ex) -> {
-          logger.error("Exception in pre-login stage", ex);
-          return null;
-        });
-  }
-
   private EncryptionRequest generateEncryptionRequest() {
     byte[] verify = new byte[4];
     ThreadLocalRandom.current().nextBytes(verify);
@@ -240,127 +226,6 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
     return request;
   }
 
-  private void initializePlayer(GameProfile profile, boolean onlineMode) {
-    // Some connection types may need to alter the game profile.
-    profile = mcConnection.getType().addGameProfileTokensIfRequired(profile,
-        server.getConfiguration().getPlayerInfoForwardingMode());
-    GameProfileRequestEvent profileRequestEvent = new GameProfileRequestEvent(inbound, profile,
-        onlineMode);
-    final GameProfile finalProfile = profile;
-
-    server.getEventManager().fire(profileRequestEvent).thenComposeAsync(profileEvent -> {
-      if (mcConnection.isClosed()) {
-        // The player disconnected after we authenticated them.
-        return CompletableFuture.completedFuture(null);
-      }
-
-      // Initiate a regular connection and move over to it.
-      ConnectedPlayer player = new ConnectedPlayer(server, profileEvent.getGameProfile(),
-          mcConnection, inbound.getVirtualHost().orElse(null), onlineMode);
-      this.connectedPlayer = player;
-      if (!server.canRegisterConnection(player)) {
-        player.disconnect0(Component.translatable("velocity.error.already-connected-proxy",
-            NamedTextColor.RED), true);
-        return CompletableFuture.completedFuture(null);
-      }
-
-      logger.info("{} has connected", player);
-
-      return server.getEventManager()
-          .fire(new PermissionsSetupEvent(player, ConnectedPlayer.DEFAULT_PERMISSIONS))
-          .thenAcceptAsync(event -> {
-            if (!mcConnection.isClosed()) {
-              // wait for permissions to load, then set the players permission function
-              final PermissionFunction function = event.createFunction(player);
-              if (function == null) {
-                logger.error(
-                    "A plugin permission provider {} provided an invalid permission function"
-                        + " for player {}. This is a bug in the plugin, not in Velocity. Falling"
-                        + " back to the default permission function.",
-                    event.getProvider().getClass().getName(),
-                    player.getUsername());
-              } else {
-                player.setPermissionFunction(function);
-              }
-              completeLoginProtocolPhaseAndInitialize(player);
-            }
-          }, mcConnection.eventLoop());
-    }, mcConnection.eventLoop()).exceptionally((ex) -> {
-      logger.error("Exception during connection of {}", finalProfile, ex);
-      return null;
-    });  
-  }
-
-  private void completeLoginProtocolPhaseAndInitialize(ConnectedPlayer player) {
-    int threshold = server.getConfiguration().getCompressionThreshold();
-    if (threshold >= 0 && mcConnection.getProtocolVersion().compareTo(MINECRAFT_1_8) >= 0) {
-      mcConnection.write(new SetCompression(threshold));
-      mcConnection.setCompressionThreshold(threshold);
-    }
-    VelocityConfiguration configuration = server.getConfiguration();
-    UUID playerUniqueId = player.getUniqueId();
-    if (configuration.getPlayerInfoForwardingMode() == PlayerInfoForwarding.NONE) {
-      playerUniqueId = UuidUtils.generateOfflinePlayerUuid(player.getUsername());
-    }
-    ServerLoginSuccess success = new ServerLoginSuccess();
-    success.setUsername(player.getUsername());
-    success.setUuid(playerUniqueId);
-    mcConnection.write(success);
-
-    mcConnection.setAssociation(player);
-    mcConnection.setState(StateRegistry.PLAY);
-
-    server.getEventManager().fire(new LoginEvent(player))
-        .thenAcceptAsync(event -> {
-          if (mcConnection.isClosed()) {
-            // The player was disconnected
-            server.getEventManager().fireAndForget(new DisconnectEvent(player,
-                LoginStatus.CANCELLED_BY_USER_BEFORE_COMPLETE));
-            return;
-          }
-
-          Optional<Component> reason = event.getResult().getReasonComponent();
-          if (reason.isPresent()) {
-            player.disconnect0(reason.get(), true);
-          } else {
-            if (!server.registerConnection(player)) {
-              player.disconnect0(Component.translatable("velocity.error.already-connected-proxy"),
-                  true);
-              return;
-            }
-
-            mcConnection.setSessionHandler(new InitialConnectSessionHandler(player));
-            server.getEventManager().fire(new PostLoginEvent(player))
-                .thenCompose((ignored) -> connectToInitialServer(player))
-                .exceptionally((ex) -> {
-                  logger.error("Exception while connecting {} to initial server", player, ex);
-                  return null;
-                });
-          }
-        }, mcConnection.eventLoop())
-        .exceptionally((ex) -> {
-          logger.error("Exception while completing login initialisation phase for {}", player, ex);
-          return null;
-        });
-  }
-
-  private CompletableFuture<Void> connectToInitialServer(ConnectedPlayer player) {
-    Optional<RegisteredServer> initialFromConfig = player.getNextServerToTry();
-    PlayerChooseInitialServerEvent event = new PlayerChooseInitialServerEvent(player,
-        initialFromConfig.orElse(null));
-
-    return server.getEventManager().fire(event)
-        .thenRunAsync(() -> {
-          Optional<RegisteredServer> toTry = event.getInitialServer();
-          if (!toTry.isPresent()) {
-            player.disconnect0(Component.translatable("velocity.error.no-available-servers",
-                NamedTextColor.RED), true);
-            return;
-          }
-          player.createConnectionRequest(toTry.get()).fireAndForget();
-        }, mcConnection.eventLoop());
-  }
-
   @Override
   public void handleUnknown(ByteBuf buf) {
     mcConnection.close(true);
@@ -368,9 +233,23 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public void disconnected() {
-    if (connectedPlayer != null) {
-      connectedPlayer.teardown();
-    }
     this.inbound.cleanup();
   }
+
+  private void assertState(LoginState expectedState) {
+    if (this.currentState != expectedState) {
+      if (MinecraftDecoder.DEBUG) {
+        logger.error("{} Received an unexpected packet requiring state {}, but we are in {}", inbound,
+            expectedState, this.currentState);
+      }
+      mcConnection.close(true);
+    }
+  }
+
+  private enum LoginState {
+    LOGIN_PACKET_EXPECTED,
+    LOGIN_PACKET_RECEIVED,
+    ENCRYPTION_REQUEST_SENT,
+    ENCRYPTION_RESPONSE_RECEIVED
+  }
 }

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

@@ -20,6 +20,7 @@ package com.velocitypowered.proxy.connection.client;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.proxy.LoginPhaseConnection;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
+import com.velocitypowered.proxy.connection.MinecraftConnection;
 import com.velocitypowered.proxy.protocol.packet.LoginPluginMessage;
 import com.velocitypowered.proxy.protocol.packet.LoginPluginResponse;
 import io.netty.buffer.ByteBufUtil;
@@ -144,4 +145,8 @@ public class LoginInboundConnection implements LoginPhaseConnection {
       onAllMessagesHandled.run();
     }
   }
+
+  MinecraftConnection delegatedConnection() {
+    return delegate.getConnection();
+  }
 }