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 69498183a7637cd2dbb859c670e661f8722a090f..5df657555439e07d5fb67db8c82246c15676850d 100644
--- a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
@@ -60,6 +60,7 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener,
     private final String serverId;
     @Nullable
     private ServerPlayer delayedAcceptPlayer;
+    public boolean iKnowThisMayNotBeTheBestIdeaButPleaseDisableUsernameValidation = false; // Paper - username validation overriding
 
     public ServerLoginPacketListenerImpl(MinecraftServer server, Connection connection) {
         this.state = ServerLoginPacketListenerImpl.State.HELLO;
@@ -212,10 +213,38 @@ 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 == '_' || 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]);
         Validate.validState(ServerLoginPacketListenerImpl.isValidUsername(packet.name()), "Invalid characters in username", new Object[0]);
+        // Paper start - validate usernames
+        if (io.papermc.paper.configuration.GlobalConfiguration.get().proxies.isProxyOnlineMode() && io.papermc.paper.configuration.GlobalConfiguration.get().unsupportedSettings.performUsernameValidation) {
+            if (!this.iKnowThisMayNotBeTheBestIdeaButPleaseDisableUsernameValidation && !validateUsername(packet.name())) {
+                ServerLoginPacketListenerImpl.this.disconnect("Failed to verify username!");
+                return;
+            }
+        }
+        // Paper end - validate usernames
         GameProfile gameprofile = this.server.getSingleplayerProfile();
 
         if (gameprofile != null && packet.name().equalsIgnoreCase(gameprofile.getName())) {
diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
index 0f380a7045f89bc383e4eb3d93c1be3885def712..32c8218048fe61c58d78175d50f3d48413ddda6f 100644
--- a/src/main/java/net/minecraft/server/players/PlayerList.java
+++ b/src/main/java/net/minecraft/server/players/PlayerList.java
@@ -659,7 +659,7 @@ 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) || (io.papermc.paper.configuration.GlobalConfiguration.get().proxies.isProxyOnlineMode() && entityplayer.getGameProfile().getName().equalsIgnoreCase(gameprofile.getName()))) { // Paper - validate usernames
                 list.add(entityplayer);
             }
         }