Add chat event

api/src/main/java/com/velocitypowered/api/event/ResultedEvent.java

@@ -111,4 +111,45 @@ public interface ResultedEvent<R extends ResultedEvent.Result> {
             return new ComponentResult(false, reason);
         }
     }
+
+    class ChatResult implements Result {
+        private static final ChatResult ALLOWED = new ChatResult(true, null);
+        private static final ChatResult DENIED = new ChatResult(false, null);
+
+        // The server can not accept formatted text from clients!
+        private @Nullable String message;
+        private final boolean allowed;
+
+        protected ChatResult(boolean allowed, @Nullable String message) {
+            this.allowed = allowed;
+            this.message = message;
+        }
+
+        @Override
+        public boolean isAllowed() {
+            return allowed;
+        }
+
+        @Override
+        public String toString() {
+            return allowed ? "allowed" : "denied";
+        }
+
+        public static ChatResult allowed() {
+            return ALLOWED;
+        }
+
+        public static ChatResult denied() {
+            return DENIED;
+        }
+
+        public Optional<String> getMessage() {
+            return Optional.ofNullable(message);
+        }
+
+        public static ChatResult message(@NonNull String message) {
+            Preconditions.checkNotNull(message, "message");
+            return new ChatResult(true, message);
+        }
+    }
 }

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

@@ -0,0 +1,50 @@
+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 org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * This event is fired once the player has been authenticated but before they connect to a server on the proxy.
+ */
+public class PlayerChatEvent implements ResultedEvent<ResultedEvent.ChatResult> {
+    private final Player player;
+    private final String message;
+    private ChatResult result;
+
+    public PlayerChatEvent(Player player, String message) {
+        this.player = Preconditions.checkNotNull(player, "player");
+        this.message = Preconditions.checkNotNull(message, "message");
+        this.result = (ChatResult) ChatResult.allowed();
+    }
+
+    public Player getPlayer() {
+        return player;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    @Override
+    public ChatResult getResult() {
+        return result;
+    }
+
+    @Override
+    public void setResult(@NonNull ChatResult result) {
+        this.result = Preconditions.checkNotNull(result, "result");
+    }
+
+    @Override
+    public String toString() {
+        return "PlayerChatEvent{" +
+                "player=" + player +
+                ", message=" + message +
+                ", result=" + result +
+                '}';
+    }
+
+
+}

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

@@ -1,7 +1,9 @@
 package com.velocitypowered.proxy.connection.client;
 
+import com.velocitypowered.api.event.ResultedEvent;
 import com.velocitypowered.api.event.connection.DisconnectEvent;
 import com.velocitypowered.api.event.connection.PluginMessageEvent;
+import com.velocitypowered.api.event.player.PlayerChatEvent;
 import com.velocitypowered.api.proxy.messages.ChannelIdentifier;
 import com.velocitypowered.proxy.VelocityServer;
 import com.velocitypowered.proxy.connection.MinecraftSessionHandler;
@@ -13,8 +15,10 @@ import com.velocitypowered.proxy.protocol.packet.*;
 import com.velocitypowered.proxy.protocol.util.PluginMessageUtil;
 import com.velocitypowered.proxy.util.ThrowableUtils;
 import io.netty.buffer.ByteBuf;
+import net.kyori.text.Component;
 import net.kyori.text.TextComponent;
 import net.kyori.text.format.TextColor;
+import net.kyori.text.serializer.ComponentSerializers;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
@@ -93,7 +97,18 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                     return;
                 }
             } else {
+                PlayerChatEvent event = new PlayerChatEvent(player, msg);
+                server.getEventManager().fire(event)
+                        .thenAcceptAsync(pme -> {
+                            if (pme.getResult().equals(ResultedEvent.ChatResult.allowed())){
                                 player.getConnectedServer().getMinecraftConnection().write(chat);
+                            } else if (pme.getResult().isAllowed() && pme.getResult().getMessage().isPresent()){
+                                Chat modifiedChat = new Chat();
+                                modifiedChat.setType(Chat.CHAT);
+                                modifiedChat.setMessage(pme.getResult().getMessage().get());
+                                player.getConnectedServer().getMinecraftConnection().write(modifiedChat);
+                            }
+                        }, player.getConnectedServer().getMinecraftConnection().getChannel().eventLoop());
             }
             return;
         }