Address code review: fix naming, visibility, and lazy address resolution

- Rename TagsKey → tagsKey and make it private (Java naming convention)
- Make isSSL() private in MqttTransportHandler (internal use only)
- Fix double space in if (isSSL) in MqttTransportContext
- Extract getClientAddr() helper and move clientAddr computation inside
  logging guards so address resolution is skipped when logging is disabled

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

common/transport/mqtt/src/main/java/org/thingsboard/server/transport/mqtt/MqttTransportContext.java

@@ -99,7 +99,7 @@ public class MqttTransportContext extends TransportContext {
     }
 
     public void channelRegistered(boolean isSSL) {
-        if  (isSSL) {
+        if (isSSL) {
             connectionsActiveCounterMQTTS.incrementAndGet();
         } else {
             connectionsActiveCounterMQTT.incrementAndGet();
@@ -107,7 +107,7 @@ public class MqttTransportContext extends TransportContext {
     }
 
     public void channelUnregistered(boolean isSSL) {
-        if  (isSSL) {
+        if (isSSL) {
             connectionsActiveCounterMQTTS.decrementAndGet();
         } else {
             connectionsActiveCounterMQTT.decrementAndGet();

common/transport/mqtt/src/main/java/org/thingsboard/server/transport/mqtt/MqttTransportHandler.java

@@ -180,7 +180,7 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
         this.rpcAwaitingAck = new ConcurrentHashMap<>();
     }
 
-    boolean isSSL() {
+    private boolean isSSL() {
         return sslHandler != null;
     }
 
@@ -258,6 +258,17 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
         }
     }
 
+    private String getClientAddr(ChannelHandlerContext ctx) {
+        try {
+            InetSocketAddress remote = getAddress(ctx);
+            if (remote == null) return "unknown";
+            String host = remote.getAddress() != null ? remote.getAddress().getHostAddress() : remote.getHostString();
+            return host + ":" + remote.getPort();
+        } catch (Exception ignored) {
+            return "unknown";
+        }
+    }
+
     InetSocketAddress getAddress(ChannelHandlerContext ctx) {
         var address = ctx.channel().attr(MqttTransportService.ADDRESS).get();
         if (address == null) {
@@ -1152,15 +1163,9 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
 
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
-        String clientAddr = null;
-        try {
-            InetSocketAddress remote = getAddress(ctx);
-            clientAddr = remote != null ? (remote.getAddress() != null ? remote.getAddress().getHostAddress() : remote.getHostString()) + ":" + remote.getPort() : "IPunknown";
-        } catch (Exception ignored) {
-        }
-
         if (cause instanceof IOException) {
             if (log.isDebugEnabled()) {
+                String clientAddr = getClientAddr(ctx);
                 log.debug("[{}][{}][{}][{}] {}: {}", sessionId,
                         Optional.ofNullable(this.deviceSessionCtx.getDeviceInfo()).map(TransportDeviceInfo::getDeviceId).orElse(null),
                         Optional.ofNullable(this.deviceSessionCtx.getDeviceInfo()).map(TransportDeviceInfo::getDeviceName).orElse(""),
@@ -1169,6 +1174,7 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
                         cause.getMessage(),
                         cause);
             } else if (log.isInfoEnabled()) {
+                String clientAddr = getClientAddr(ctx);
                 log.info("[{}][{}][{}][{}] {}: {}", sessionId,
                         Optional.ofNullable(this.deviceSessionCtx.getDeviceInfo()).map(TransportDeviceInfo::getDeviceId).orElse(null),
                         Optional.ofNullable(this.deviceSessionCtx.getDeviceInfo()).map(TransportDeviceInfo::getDeviceName).orElse(""),
@@ -1177,7 +1183,7 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
                         cause.getMessage());
             }
         } else {
-            log.error("[{}][{}] Unexpected Exception", sessionId, clientAddr, cause);
+            log.error("[{}][{}] Unexpected Exception", sessionId, getClientAddr(ctx), cause);
         }
 
         closeCtx(ctx, MqttReasonCodes.Disconnect.SERVER_SHUTTING_DOWN);

common/transport/transport-api/src/main/java/org/thingsboard/server/common/transport/service/DefaultTransportService.java

@@ -1260,10 +1260,10 @@ public class DefaultTransportService extends TransportActivityManager implements
     public void createGaugeStats(String statsName, AtomicInteger number, String... tags) {
         String key = "thingsboard" + "." + StatsType.TRANSPORT.getName() + "." + statsName;
         statsFactory.createGauge(key, number, tags);
-        statsMap.put(statsName + TagsKey(tags), number);
+        statsMap.put(statsName + tagsKey(tags), number);
     }
 
-    String TagsKey(String... tags) {
+    private String tagsKey(String... tags) {
         if (tags == null || tags.length < 2) return "";
         StringBuilder sb = new StringBuilder("[");
         for (int i = 0; i < tags.length; i += 2) {