Fix SSL certificate reload: port conflict, redundant reload(), and watcher polling

common/coap-server/src/main/java/org/thingsboard/server/coapserver/DefaultCoapServerService.java

@@ -195,14 +195,31 @@ public class DefaultCoapServerService implements CoapServerService, SmartInitial
         DTLSConnector newConnector = createDtlsConnector(dtlsConnectorConfig);
         CoapEndpoint newEndpoint = buildDtlsEndpoint(networkConfig, newConnector);
 
+        // Stop old endpoint first to release the port before starting the new one
+        if (oldDtlsEndpoint != null) {
+            log.info("Stopping old DTLS endpoint to release the port...");
+            server.getEndpoints().remove(oldDtlsEndpoint);
+            oldDtlsEndpoint.stop();
+        }
+
         server.addEndpoint(newEndpoint);
         try {
             newEndpoint.start();
         } catch (IOException e) {
-            log.error("Failed to start new DTLS endpoint, cleaning up", e);
+            log.error("Failed to start new DTLS endpoint, restoring old endpoint", e);
             server.getEndpoints().remove(newEndpoint);
             newEndpoint.destroy();
             newConnector.destroy();
+            // Attempt to restore the old endpoint
+            if (oldDtlsEndpoint != null) {
+                try {
+                    server.addEndpoint(oldDtlsEndpoint);
+                    oldDtlsEndpoint.start();
+                    log.info("Old DTLS endpoint restored successfully.");
+                } catch (IOException restoreEx) {
+                    log.error("Failed to restore old DTLS endpoint", restoreEx);
+                }
+            }
             throw e;
         }
         log.info("New DTLS endpoint started successfully.");
@@ -212,15 +229,13 @@ public class DefaultCoapServerService implements CoapServerService, SmartInitial
         dtlsCoapEndpoint = newEndpoint;
         tbDtlsCertificateVerifier = (TbCoapDtlsCertificateVerifier) dtlsConnectorConfig.getAdvancedCertificateVerifier();
 
+        // Destroy old resources after successful swap
         if (oldDtlsEndpoint != null) {
-            log.info("Stopping old DTLS endpoint...");
-            server.getEndpoints().remove(oldDtlsEndpoint);
-            oldDtlsEndpoint.stop();
             if (oldDtlsConnector != null) {
                 oldDtlsConnector.destroy();
             }
             oldDtlsEndpoint.destroy();
-            log.info("Old DTLS endpoint stopped and destroyed.");
+            log.info("Old DTLS endpoint destroyed.");
         }
     }
 

common/coap-server/src/test/java/org/thingsboard/server/coapserver/CoapDtlsCertificateReloadTest.java

@@ -189,7 +189,7 @@ public class CoapDtlsCertificateReloadTest {
     }
 
     @Test
-    public void givenReloadCallback_whenStartFails_thenNewResourcesCleaned() throws Exception {
+    public void givenReloadCallback_whenStartFails_thenNewResourcesCleanedAndOldRestored() throws Exception {
         // GIVEN
         when(mockCoapServerContext.getDtlsSettings()).thenReturn(mockDtlsSettings);
 
@@ -210,6 +210,7 @@ public class CoapDtlsCertificateReloadTest {
         doReturn(mockNewEndpoint).when(spyService).buildDtlsEndpoint(any(Configuration.class), any(DTLSConnector.class));
 
         List<Endpoint> endpointsList = new CopyOnWriteArrayList<>();
+        endpointsList.add(mockDtlsEndpoint);
         when(mockCoapServer.getEndpoints()).thenReturn(endpointsList);
 
         // WHEN - the callback catches the IOException internally
@@ -224,12 +225,12 @@ public class CoapDtlsCertificateReloadTest {
         verify(mockNewEndpoint).destroy();
         verify(mockNewConnector).destroy();
         assertThat(endpointsList).doesNotContain(mockNewEndpoint);
+        // Old endpoint was stopped to release port, then restored after new one failed
+        verify(mockDtlsEndpoint).stop();
+        verify(mockDtlsEndpoint).start();
         // Old fields preserved
         assertThat(ReflectionTestUtils.getField(spyService, "dtlsCoapEndpoint")).isSameAs(mockDtlsEndpoint);
         assertThat(ReflectionTestUtils.getField(spyService, "dtlsConnector")).isSameAs(mockDtlsConnector);
-        // Old endpoint not touched
-        verify(mockDtlsEndpoint, never()).stop();
-        verify(mockDtlsEndpoint, never()).destroy();
     }
 
 }

common/transport/transport-api/src/main/java/org/thingsboard/server/common/transport/config/ssl/AbstractSslCredentials.java

@@ -60,8 +60,7 @@ public abstract class AbstractSslCredentials implements SslCredentials {
 
     @Override
     public void reload(boolean trustsOnly) throws IOException, GeneralSecurityException {
-        SslState newState = buildState(trustsOnly);
-        state.set(newState);
+        init(trustsOnly);
     }
 
     private SslState buildState(boolean trustsOnly) throws IOException, GeneralSecurityException {

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

@@ -228,6 +228,10 @@ public class CertificateReloadManager implements SmartInitializingSingleton, Dis
             }
 
             if (consecutiveFailures >= MAX_CONSECUTIVE_FAILURES) {
+                // Update modification times to avoid re-checking mtime and re-computing checksums every poll cycle
+                for (Path path : paths) {
+                    lastModifiedMap.put(path, getLastModifiedTime(path));
+                }
                 return;
             }