IP addon finder mac address format tweak

bundles/org.openhab.core.config.discovery.addon.ip/src/main/java/org/openhab/core/config/discovery/addon/ip/IpAddonFinder.java

@@ -79,7 +79,7 @@
 /**
  * This is a {@link IpAddonFinder} for finding suggested add-ons by sending IP packets to the
  * network and collecting responses.
- * 
+ *
  * This finder is intended to detect devices on the network which do not announce via UPnP
  * or mDNS. Some devices respond to queries to defined multicast addresses and ports and thus
  * can be detected by sending a single frame on the IP network.
@@ -363,10 +363,9 @@ private void scan() {
                     }
                 }
                 String macFormat = parameters.getOrDefault(PARAMETER_MAC_FORMAT, "%02X:");
-                try {
-                    String.format(macFormat, 123);
-                } catch (IllegalFormatException e) {
+                if (!macFormatValid(macFormat)) {
                     logger.warn("{}: discovery-parameter '{}' invalid format specifier", candidate.getUID(), macFormat);
+                    continue;
                 }
 
                 // handle known types
@@ -599,7 +598,7 @@ private boolean isAddonInstalled(String addonId) {
 
     /**
      * Get mac address bytes associated with the given Internet socket address
-     * 
+     *
      * @param inetSocketAddress the Internet address
      * @return the mac address as an array of bytes
      * @throws SocketException if address is not on this PC, or no mac address is associated
@@ -614,18 +613,44 @@ private byte[] macBytesFrom(InetSocketAddress inetSocketAddress) throws SocketEx
 
     /**
      * Use the given format specifier to format an array of mac address bytes
-     * 
+     *
      * @param format a standard format specifier; optionally ends with a delimiter e.g. "%02x:" or "%02X"
      * @param bytes the mac address as an array of bytes
-     * 
+     *
      * @return e.g. '01:02:03:04:A5:B6:C7:D8', '01-02-03-04:a5:b6:c7:d8', or '01020304A5B6C7D8'
      */
     private String macFormat(String format, byte[] bytes) {
         StringBuilder result = new StringBuilder();
         for (byte byt : bytes) {
             result.append(String.format(format, byt));
         }
-        boolean isDelimited = Set.of(':', '-', '.').contains(format.charAt(format.length() - 1));
+        boolean isDelimited = !Character.isLetterOrDigit(format.charAt(format.length() - 1));
         return (isDelimited ? result.substring(0, result.length() - 1) : result).toString();
     }
+
+    /**
+     * Check if the given mac format specifier string is valid
+     */
+    private boolean macFormatValid(String format) {
+        try {
+            String.format(format, (byte) 123);
+        } catch (IllegalFormatException e) {
+            return false;
+        }
+        int last = format.length() - 1;
+        int index = 0;
+        while (index <= last) {
+            if (Character.isLetter(format.charAt(index))) {
+                break;
+            }
+            index++;
+        }
+        switch (last - index) {
+            case 0:
+                return true;
+            case 1:
+                return !Character.isLetterOrDigit(format.charAt(last));
+        }
+        return false;
+    }
 }