Adds KickedFromServerEvent. Fixes #49

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

@@ -0,0 +1,98 @@
+package com.velocitypowered.api.event.player;
+
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.event.ResultedEvent;
+import com.velocitypowered.api.proxy.Player;
+import com.velocitypowered.api.proxy.server.ServerInfo;
+import net.kyori.text.Component;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * Fired when a player is kicked from a server. You may either allow Velocity to kick the player (with an optional reason
+ * override) or redirect the player to a separate server.
+ */
+public class KickedFromServerEvent implements ResultedEvent<KickedFromServerEvent.ServerKickResult> {
+    private final Player player;
+    private final ServerInfo server;
+    private final Component originalReason;
+    private final boolean duringLogin;
+    private ServerKickResult result;
+
+    public KickedFromServerEvent(Player player, ServerInfo server, Component originalReason, boolean duringLogin, Component fancyReason) {
+        this.player = Preconditions.checkNotNull(player, "player");
+        this.server = Preconditions.checkNotNull(server, "server");
+        this.originalReason = Preconditions.checkNotNull(originalReason, "originalReason");
+        this.duringLogin = duringLogin;
+        this.result = new DisconnectPlayer(fancyReason);
+    }
+
+    @Override
+    public ServerKickResult getResult() {
+        return result;
+    }
+
+    @Override
+    public void setResult(@NonNull ServerKickResult result) {
+        this.result = Preconditions.checkNotNull(result, "result");
+    }
+
+    public Player getPlayer() {
+        return player;
+    }
+
+    public ServerInfo getServer() {
+        return server;
+    }
+
+    public Component getOriginalReason() {
+        return originalReason;
+    }
+
+    public boolean kickedDuringLogin() {
+        return duringLogin;
+    }
+
+    public interface ServerKickResult extends ResultedEvent.Result {}
+
+    public static class DisconnectPlayer implements ServerKickResult {
+        private final Component component;
+
+        private DisconnectPlayer(Component component) {
+            this.component = Preconditions.checkNotNull(component, "component");
+        }
+
+        @Override
+        public boolean isAllowed() {
+            return true;
+        }
+
+        public Component getReason() {
+            return component;
+        }
+
+        public static DisconnectPlayer create(Component component) {
+            return new DisconnectPlayer(component);
+        }
+    }
+
+    public static class RedirectPlayer implements ServerKickResult {
+        private final ServerInfo server;
+
+        private RedirectPlayer(ServerInfo server) {
+            this.server = Preconditions.checkNotNull(server, "server");
+        }
+
+        @Override
+        public boolean isAllowed() {
+            return false;
+        }
+
+        public ServerInfo getServer() {
+            return server;
+        }
+
+        public static RedirectPlayer create(ServerInfo info) {
+            return new RedirectPlayer(info);
+        }
+    }
+}

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

@@ -2,6 +2,7 @@ package com.velocitypowered.proxy.connection.client;
 
 import com.google.common.base.Preconditions;
 import com.google.gson.JsonObject;
+import com.velocitypowered.api.event.player.KickedFromServerEvent;
 import com.velocitypowered.api.event.player.PlayerSettingsChangedEvent;
 import com.velocitypowered.api.event.player.ServerPreConnectEvent;
 import com.velocitypowered.api.permission.PermissionFunction;
@@ -36,6 +37,7 @@ import net.kyori.text.serializer.PlainComponentSerializer;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.net.InetSocketAddress;
 import java.util.List;
@@ -190,7 +192,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
             logger.error("{}: unable to connect to server {}", this, info.getName(), throwable);
             userMessage = "Exception connecting to server " + info.getName();
         }
-        handleConnectionException(info, TextComponent.builder()
+        handleConnectionException(info, null, TextComponent.builder()
                 .content(userMessage + ": ")
                 .color(TextColor.RED)
                 .append(TextComponent.of(error, TextColor.WHITE))
@@ -205,14 +207,15 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
         } else {
             logger.error("{}: disconnected while connecting to {}: {}", this, info.getName(), plainTextReason);
         }
-        handleConnectionException(info, TextComponent.builder()
+        handleConnectionException(info, disconnectReason, TextComponent.builder()
                 .content("Unable to connect to " + info.getName() + ": ")
                 .color(TextColor.RED)
                 .append(disconnectReason)
                 .build());
     }
 
-    public void handleConnectionException(ServerInfo info, Component disconnectReason) {
+    private void handleConnectionException(ServerInfo info, @Nullable Component kickReason, Component friendlyReason) {
+        boolean alreadyConnected = connectedServer != null && connectedServer.getServerInfo().equals(info);;
         connectionInFlight = null;
         if (connectedServer == null) {
             // The player isn't yet connected to a server.
@@ -220,14 +223,27 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
             if (nextServer.isPresent()) {
                 createConnectionRequest(nextServer.get()).fireAndForget();
             } else {
-                connection.closeWith(Disconnect.create(disconnectReason));
+                connection.closeWith(Disconnect.create(friendlyReason));
             }
         } else if (connectedServer.getServerInfo().equals(info)) {
             // Already connected to the server being disconnected from.
-            // TODO: ServerKickEvent
-            connection.closeWith(Disconnect.create(disconnectReason));
+            if (kickReason != null) {
+                server.getEventManager().fire(new KickedFromServerEvent(this, info, kickReason, !alreadyConnected, friendlyReason))
+                        .thenAcceptAsync(event -> {
+                            if (event.getResult() instanceof KickedFromServerEvent.DisconnectPlayer) {
+                                KickedFromServerEvent.DisconnectPlayer res = (KickedFromServerEvent.DisconnectPlayer) event.getResult();
+                                connection.closeWith(Disconnect.create(res.getReason()));
+                            } else if (event.getResult() instanceof KickedFromServerEvent.RedirectPlayer) {
+                                KickedFromServerEvent.RedirectPlayer res = (KickedFromServerEvent.RedirectPlayer) event.getResult();
+                                createConnectionRequest(res.getServer()).fireAndForget();
+                            } else {
+                                // In case someone gets creative, assume we want to disconnect the player.
+                                connection.closeWith(Disconnect.create(friendlyReason));
+                            }
+                        }, connection.getChannel().eventLoop());
+            }
         } else {
-            connection.write(Chat.create(disconnectReason));
+            connection.write(Chat.create(friendlyReason));
         }
     }