Configurable valid characters for usernames

Author: BillyGalbreath

patches/server/0221-Configurable-valid-characters-for-usernames.patch

@@ -0,0 +1,10 @@
+--- a/net/minecraft/util/StringUtil.java
++++ b/net/minecraft/util/StringUtil.java
+@@ -87,6 +_,7 @@
+ 
+     // Paper start - Username validation
+     public static boolean isReasonablePlayerName(final String name) {
++        if (true) return org.purpurmc.purpur.PurpurConfig.usernameValidCharactersPattern.matcher(name).matches(); // Purpur - Configurable valid characters for usernames
+         if (name.isEmpty() || name.length() > 16) {
+             return false;
+         }

purpur-server/minecraft-patches/sources/net/minecraft/util/StringUtil.java.patch

@@ -5,6 +5,7 @@
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.regex.Pattern;
 import net.kyori.adventure.bossbar.BossBar;
 import net.kyori.adventure.text.minimessage.MiniMessage;
 import net.minecraft.core.Registry;
@@ -447,4 +448,11 @@ private static void tpsCatchup() {
     private static void networkSettings() {
         useUPnP = getBoolean("settings.network.upnp-port-forwarding", useUPnP);
     }
+
+    public static Pattern usernameValidCharactersPattern;
+    private static void usernameValidationSettings() {
+        String defaultPattern = "^[a-zA-Z0-9_.]*$";
+        String setPattern = getString("settings.username-valid-characters", defaultPattern);
+        usernameValidCharactersPattern = Pattern.compile(setPattern == null || setPattern.isBlank() ? defaultPattern : setPattern);
+    }
 }