Make DisconnectEvent more sane

This is a step towards fixing #289 and removing some less-than-optimal behavior in plugins I maintain internally.

api/src/main/java/com/velocitypowered/api/event/connection/DisconnectEvent.java

@@ -1,5 +1,8 @@
 package com.velocitypowered.api.event.connection;
 
+import static com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus.CANCELLED_BY_PROXY;
+import static com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus.SUCCESSFUL_LOGIN;
+
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.proxy.Player;
 
@@ -10,31 +13,50 @@ import com.velocitypowered.api.proxy.Player;
 public final class DisconnectEvent {
 
   private final Player player;
-  private final boolean disconnectedDuringLogin;
+  private final LoginStatus loginStatus;
 
+  @Deprecated
   public DisconnectEvent(Player player) {
     this(player, false);
   }
 
+  @Deprecated
   public DisconnectEvent(Player player,
       boolean disconnectedDuringLogin) {
+    this(player, disconnectedDuringLogin ? CANCELLED_BY_PROXY : SUCCESSFUL_LOGIN);
+  }
+
+  public DisconnectEvent(Player player, LoginStatus loginStatus) {
     this.player = Preconditions.checkNotNull(player, "player");
-    this.disconnectedDuringLogin = disconnectedDuringLogin;
+    this.loginStatus = Preconditions.checkNotNull(loginStatus, "loginStatus");
   }
 
   public Player getPlayer() {
     return player;
   }
 
+  @Deprecated
   public boolean disconnectedDuringLogin() {
-    return this.disconnectedDuringLogin;
+    return this.loginStatus == CANCELLED_BY_PROXY;
+  }
+
+  public LoginStatus getLoginStatus() {
+    return loginStatus;
   }
 
   @Override
   public String toString() {
     return "DisconnectEvent{"
         + "player=" + player + ", "
-        + "disconnectedDuringLogin=" + disconnectedDuringLogin
+        + "loginStatus=" + loginStatus
         + '}';
   }
+
+  public enum LoginStatus {
+
+    SUCCESSFUL_LOGIN,
+    CONFLICTING_LOGIN,
+    CANCELLED_BY_USER,
+    CANCELLED_BY_PROXY
+  }
 }

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

@@ -271,6 +271,10 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
     return channel.config().isAutoRead();
   }
 
+  public boolean isKnownDisconnect() {
+    return knownDisconnect;
+  }
+
   /**
    * Determines whether or not the channel should continue reading data automaticaly.
    * @param autoReading whether or not we should read data automatically

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

@@ -6,6 +6,7 @@ import static java.util.concurrent.CompletableFuture.completedFuture;
 import com.google.common.base.Preconditions;
 import com.google.gson.JsonObject;
 import com.velocitypowered.api.event.connection.DisconnectEvent;
+import com.velocitypowered.api.event.connection.DisconnectEvent.LoginStatus;
 import com.velocitypowered.api.event.player.KickedFromServerEvent;
 import com.velocitypowered.api.event.player.KickedFromServerEvent.DisconnectPlayer;
 import com.velocitypowered.api.event.player.KickedFromServerEvent.Notify;
@@ -586,10 +587,21 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
     if (connectedServer != null) {
       connectedServer.disconnect();
     }
-    boolean isConnected = server.getPlayer(this.getUniqueId()).isPresent();
+
+    Optional<Player> connectedPlayer = server.getPlayer(this.getUniqueId());
     server.unregisterConnection(this);
-    server.getEventManager().fire(new DisconnectEvent(this, !isConnected))
-        .thenRun(() -> this.teardownFuture.complete(null));
+
+    DisconnectEvent.LoginStatus status;
+    if (connectedPlayer.isPresent()) {
+      status = connectedPlayer.get() == this ? LoginStatus.SUCCESSFUL_LOGIN
+          : LoginStatus.CONFLICTING_LOGIN;
+    } else {
+      status = connection.isKnownDisconnect() ? LoginStatus.CANCELLED_BY_PROXY :
+          LoginStatus.CANCELLED_BY_USER;
+    }
+
+    DisconnectEvent event = new DisconnectEvent(this, status);
+    server.getEventManager().fire(event).thenRun(() -> this.teardownFuture.complete(null));
   }
 
   public CompletableFuture<Void> getTeardownFuture() {

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

@@ -202,10 +202,14 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
         onlineMode);
 
     server.getEventManager().fire(profileRequestEvent).thenCompose(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);
+          mcConnection, inbound.getVirtualHost().orElse(null), onlineMode);
       this.connectedPlayer = player;
       if (!server.canRegisterConnection(player)) {
         player.disconnect0(VelocityMessages.ALREADY_CONNECTED, true);