add support for QR Code for pairing

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;
 
 /**
@@ -21,6 +22,16 @@ public interface HomekitAuthInfo {
    */
   String getPin();
 
+  /**
+   * A setup Id used for pairing the device using QR Code. It can be any alphanumeric combination of
+   * the length of 4.
+   *
+   * @return setup id
+   */
+  default String getSetupId() {
+    return HAPSetupCodeUtils.generateSetupId();
+  }
+
   /**
    * A unique MAC address to be advertised with the HomeKit information. This does not have to be
    * the MAC address of the network interface. You can generate this using {@link

src/main/java/io/github/hapjava/server/impl/HomekitRoot.java

@@ -116,7 +116,8 @@ public void start() {
             port -> {
               try {
                 refreshAuthInfo();
-                advertiser.advertise(label, authInfo.getMac(), port, configurationIndex);
+                advertiser.advertise(
+                    label, authInfo.getMac(), port, configurationIndex, authInfo.getSetupId());
               } catch (Exception e) {
                 throw new RuntimeException(e);
               }

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

@@ -0,0 +1,68 @@
+package io.github.hapjava.server.impl.crypto;
+
+import java.util.Base64;
+import org.bouncycastle.crypto.Digest;
+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() {
+    return randomAlphaNumeric(4);
+  }
+
+  private static byte[] calculateHash(final String input, final Digest digest) {
+    byte[] inputAsBytes = input.getBytes();
+    byte[] retValue = new byte[digest.getDigestSize()];
+    digest.update(inputAsBytes, 0, inputAsBytes.length);
+    digest.doFinal(retValue, 0);
+    return retValue;
+  }
+
+  /**
+   * generate SHA52 Hash for given string. The hash is used for mDNS advertisement.
+   *
+   * @param value value
+   * @return hash
+   */
+  public static String generateSHA512Hash(final String value) {
+    final byte[] hash = calculateHash(value.toUpperCase(), new SHA512Digest());
+    final byte[] hashTuncate = new byte[4];
+    System.arraycopy(hash, 0, hashTuncate, 0, 4);
+    String hashStr = Base64.getEncoder().encodeToString(hashTuncate);
+    return hashStr;
+  }
+
+  /**
+   * generate Setup URI which can be used fo QR Code generation.
+   *
+   * @param pin PIN number without "-"
+   * @param setupId alphanumeric string of the length 4
+   * @param category accessory category
+   * @return setup UID
+   */
+  public static String getSetupURI(final String pin, final String setupId, final int category) {
+    long code =
+        0 << 43 // Version
+            | 0 << 39 // Reserved
+            | ((long) category) << 31 // Category
+            | 0 << 29 // BLE support
+            | 1 << 28 // IP support
+            | 0 << 27 // Paired  / NFC
+            | Integer.valueOf(pin); // PIN
+    String payload = Long.toString(code, 36) + setupId;
+    while (payload.length() < 13) {
+      payload = '0' + payload;
+    }
+    return "X-HM://" + payload.toUpperCase();
+  }
+}

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

@@ -1,5 +1,7 @@
 package io.github.hapjava.server.impl.jmdns;
 
+import static io.github.hapjava.server.impl.crypto.HAPSetupCodeUtils.generateSHA512Hash;
+
 import java.io.IOException;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
@@ -21,21 +23,23 @@ public class JmdnsHomekitAdvertiser {
 
   private String label;
   private String mac;
+  private String setupId;
   private int port;
   private int configurationIndex;
 
   public JmdnsHomekitAdvertiser(InetAddress localAddress) throws UnknownHostException, IOException {
     jmdns = JmDNS.create(localAddress);
   }
 
-  public synchronized void advertise(String label, String mac, int port, int configurationIndex)
-      throws Exception {
+  public synchronized void advertise(
+      String label, String mac, int port, int configurationIndex, String setupId) throws Exception {
     if (isAdvertising) {
       throw new IllegalStateException("HomeKit advertiser is already running");
     }
     this.label = label;
     this.mac = mac;
     this.port = port;
+    this.setupId = setupId;
     this.configurationIndex = configurationIndex;
 
     logger.trace("Advertising accessory " + label);
@@ -80,10 +84,12 @@ 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);
     props.put("md", label);
+    props.put("sh", generateSHA512Hash(setupId + mac));
     props.put("c#", Integer.toString(configurationIndex));
     props.put("s#", "1");
     props.put("ff", "0");

src/test/java/io/github/hapjava/server/impl/HomekitRootTest.java

@@ -26,6 +26,8 @@ public class HomekitRootTest {
   private HomekitAuthInfo authInfo;
 
   private static final int PORT = 12345;
+  private static final String SETUPID = "Gx12";
+
   private static final String LABEL = "Test Label";
 
   @Before
@@ -73,8 +75,10 @@ public void testWebHandlerStops() throws Exception {
   public void testAdvertiserStarts() throws Exception {
     final String mac = "00:00:00:00:00:00";
     when(authInfo.getMac()).thenReturn(mac);
+    when(authInfo.getSetupId()).thenReturn(SETUPID);
+
     root.start();
-    verify(advertiser).advertise(eq(LABEL), eq(mac), eq(PORT), eq(1));
+    verify(advertiser).advertise(eq(LABEL), eq(mac), eq(PORT), eq(1), eq(SETUPID));
   }
 
   @Test