From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 1 Jan 2022 05:19:37 -0800
Subject: [PATCH] Validate usernames


diff --git a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
index 33a29890435d6065a2cc4f8e8bf8209c01d5d114..0df723378b49aecacc15400db4b5f56c87a965b3 100644
--- a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
@@ -230,10 +230,38 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener
         // Paper end
     }
 
+    // Paper start - validate usernames
+    public static boolean validateUsername(String in) {
+        if (in == null || in.isEmpty() || in.length() > 16) {
+            return false;
+        }
+
+        for (int i = 0, len = in.length(); i < len; ++i) {
+            char c = in.charAt(i);
+
+            if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || (c == '_')) {
+                continue;
+            }
+
+            return false;
+        }
+
+        return true;
+    }
+    // Paper end - validate usernames
+
     @Override
     public void handleHello(ServerboundHelloPacket packet) {
         Validate.validState(this.state == ServerLoginPacketListenerImpl.State.HELLO, "Unexpected hello packet", new Object[0]);
         this.gameProfile = packet.getGameProfile();
+        // Paper start - validate usernames
+        if (com.destroystokyo.paper.PaperConfig.isProxyOnlineMode()) {
+            if (!validateUsername(this.gameProfile.getName())) {
+                ServerLoginPacketListenerImpl.this.disconnect("Failed to verify username!");
+                return;
+            }
+        }
+        // Paper end - validate usernames
         if (this.server.usesAuthentication() && !this.connection.isMemoryConnection()) {
             this.state = ServerLoginPacketListenerImpl.State.KEY;
             this.connection.send(new ClientboundHelloPacket("", this.server.getKeyPair().getPublic().getEncoded(), this.nonce));
diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
index 042be2cf60a9d01698808d84f2e537a5eb952079..f55f8c0b2c748a5442199c0a7f772b02ed533753 100644
--- a/src/main/java/net/minecraft/server/players/PlayerList.java
+++ b/src/main/java/net/minecraft/server/players/PlayerList.java
@@ -703,7 +703,7 @@ public abstract class PlayerList {
 
         for (int i = 0; i < this.players.size(); ++i) {
             entityplayer = (ServerPlayer) this.players.get(i);
-            if (entityplayer.getUUID().equals(uuid)) {
+            if (entityplayer.getUUID().equals(uuid) || (com.destroystokyo.paper.PaperConfig.isProxyOnlineMode() && entityplayer.getGameProfile().getName().equalsIgnoreCase(gameprofile.getName()))) { // Paper - validate usernames
                 list.add(entityplayer);
             }
         }