Reject Windows reserved filenames in /setwarp (#6487)

Fixes #5430

stop gap for before we do #5267

Author: JRoy

Essentials/src/main/java/com/earth2me/essentials/commands/Commandsetwarp.java

@@ -25,6 +25,10 @@ public void run(final Server server, final User user, final String commandLabel,
             throw new TranslatableException("invalidWarpName");
         }
 
+        if (StringUtil.isReservedFileName(args[0])) {
+            throw new TranslatableException("invalidWarpName");
+        }
+
         final IWarps warps = ess.getWarps();
         Location warpLoc = null;
 

Essentials/src/main/java/com/earth2me/essentials/utils/StringUtil.java

@@ -18,11 +18,21 @@ public final class StringUtil {
     private StringUtil() {
     }
 
+    private static final Pattern WINDOWS_RESERVED = Pattern.compile("^(con|prn|aux|nul|com[0-9]|lpt[0-9])$");
+
     //Used to clean file names before saving to disk
     public static String sanitizeFileName(final String name) {
         return INVALIDFILECHARS.matcher(name.toLowerCase(Locale.ENGLISH)).replaceAll("_");
     }
 
+    /**
+     * Returns true if the given name is a Windows reserved filename (e.g. CON, NUL, AUX).
+     * Using these as file names on Windows will hang or crash the server.
+     */
+    public static boolean isReservedFileName(final String name) {
+        return WINDOWS_RESERVED.matcher(name.toLowerCase(Locale.ENGLISH)).matches();
+    }
+
     //Used to clean strings/names before saving as filenames/permissions
     public static String safeString(final String string) {
         if (string == null) {