add default implementation for setup Id

Signed-off-by: Eugen Freiter <freiter@gmx.de>

Author: Eugen Freiter

src/main/java/io/github/hapjava/server/HomekitAuthInfo.java

@@ -1,6 +1,7 @@
 package io.github.hapjava.server;
 
 import io.github.hapjava.server.impl.HomekitServer;
+import io.github.hapjava.server.impl.crypto.HAPSetupCodeUtils;
 import java.math.BigInteger;
 
 /**
@@ -27,7 +28,9 @@ public interface HomekitAuthInfo {
    *
    * @return setup id
    */
-  String getSetupId();
+  default String getSetupId() {
+    return HAPSetupCodeUtils.generateSetupId();
+  }
 
   /**
    * A unique MAC address to be advertised with the HomeKit information. This does not have to be

src/main/java/io/github/hapjava/server/impl/crypto/HAPSetupCodeUtils.java

@@ -5,6 +5,26 @@
 import org.bouncycastle.crypto.digests.SHA512Digest;
 
 public class HAPSetupCodeUtils {
+  private static final String ALPHA_NUMERIC_STRING = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+
+  public static String randomAlphaNumeric(int count) {
+    StringBuilder builder = new StringBuilder();
+    while (count-- != 0) {
+      int character = (int) (Math.random() * ALPHA_NUMERIC_STRING.length());
+      builder.append(ALPHA_NUMERIC_STRING.charAt(character));
+    }
+    return builder.toString();
+  }
+
+  public static String generateSetupId() {
+    String setupId =
+        ""
+            + ALPHA_NUMERIC_STRING.charAt((int) (Math.random() * ALPHA_NUMERIC_STRING.length()))
+            + ALPHA_NUMERIC_STRING.charAt((int) (Math.random() * ALPHA_NUMERIC_STRING.length()))
+            + ALPHA_NUMERIC_STRING.charAt((int) (Math.random() * ALPHA_NUMERIC_STRING.length()))
+            + ALPHA_NUMERIC_STRING.charAt((int) (Math.random() * ALPHA_NUMERIC_STRING.length()));
+    return setupId;
+  }
 
   private static byte[] calculateHash(final String input, final Digest digest) {
     byte[] inputAsBytes = input.getBytes();

src/main/java/io/github/hapjava/server/impl/jmdns/JmdnsHomekitAdvertiser.java

@@ -84,6 +84,7 @@ public synchronized void setConfigurationIndex(int revision) throws IOException
 
   private void registerService() throws IOException {
     logger.info("Registering " + SERVICE_TYPE + " on port " + port);
+    logger.trace("MAC:" + mac + " Setup Id:" + setupId);
     Map<String, String> props = new HashMap<>();
     props.put("sf", discoverable ? "1" : "0");
     props.put("id", mac);