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 1e4b288f20153ce0c91fabf164c5c8320c90ba7d..cb5dd77892283a1aaec45434fb99bb7f08ee5394 100644
--- a/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerLoginPacketListenerImpl.java
@@ -90,6 +90,7 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener,
     private final String serverId;
     private final boolean transferred;
     private ServerPlayer player; // CraftBukkit
+    public boolean iKnowThisMayNotBeTheBestIdeaButPleaseDisableUsernameValidation = false; // Paper - username validation overriding
 
     public ServerLoginPacketListenerImpl(MinecraftServer server, Connection connection, boolean transferred) {
         this.state = ServerLoginPacketListenerImpl.State.HELLO;
@@ -171,7 +172,13 @@ public class ServerLoginPacketListenerImpl implements ServerLoginPacketListener,
     @Override
     public void handleHello(ServerboundHelloPacket packet) {
         Validate.validState(this.state == ServerLoginPacketListenerImpl.State.HELLO, "Unexpected hello packet", new Object[0]);
-        Validate.validState(StringUtil.isValidPlayerName(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
+            && !this.iKnowThisMayNotBeTheBestIdeaButPleaseDisableUsernameValidation) {
+            Validate.validState(StringUtil.isReasonablePlayerName(packet.name()), "Invalid characters in username", new Object[0]);
+        }
+        // Paper end - Validate usernames
         this.requestedUsername = packet.name();
         GameProfile gameprofile = this.server.getSingleplayerProfile();
 
diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
index a62858d3cd83358f2356c15fc102b99c41969a74..bb301d1ce9c1792ead2681c9f3d38bb2079b0112 100644
--- a/src/main/java/net/minecraft/server/players/PlayerList.java
+++ b/src/main/java/net/minecraft/server/players/PlayerList.java
@@ -627,7 +627,7 @@ 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);
             }
         }
diff --git a/src/main/java/net/minecraft/util/StringUtil.java b/src/main/java/net/minecraft/util/StringUtil.java
index e588bd7ef0616dc88ce4c0feeeabadc29dcaa550..6c33002dc8bbb3759c3156302ab7d1f26ce5e8ee 100644
--- a/src/main/java/net/minecraft/util/StringUtil.java
+++ b/src/main/java/net/minecraft/util/StringUtil.java
@@ -67,6 +67,25 @@ public class StringUtil {
         return name.length() <= 16 && name.chars().filter(c -> c <= 32 || c >= 127).findAny().isEmpty();
     }
 
+    // Paper start - Username validation
+    public static boolean isReasonablePlayerName(final String name) {
+        if (name.isEmpty() || name.length() > 16) {
+            return false;
+        }
+
+        for (int i = 0, len = name.length(); i < len; ++i) {
+            final char c = name.charAt(i);
+            if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || (c == '_' || c == '.')) {
+                continue;
+            }
+
+            return false;
+        }
+
+        return true;
+    }
+    // Paper end - Username validation
+
     public static String filterText(String string) {
         return filterText(string, false);
     }