util: Fix AdvancedTlsX509KeyManager reloading credentials on every refresh

util/src/main/java/io/grpc/util/AdvancedTlsX509KeyManager.java

@@ -332,15 +332,15 @@ private UpdateResult readAndUpdate(File certFile, File keyFile, long oldKeyTime,
         try {
           X509Certificate[] certs = CertificateUtils.getX509Certificates(certInputStream);
           updateIdentityCredentials(certs, key);
-          return new UpdateResult(true, newKeyTime, newCertTime);
+          return new UpdateResult(true, newCertTime, newKeyTime);
         } finally {
           certInputStream.close();
         }
       } finally {
         keyInputStream.close();
       }
     }
-    return new UpdateResult(false, oldKeyTime, oldCertTime);
+    return new UpdateResult(false, oldCertTime, oldKeyTime);
   }
 
   /**

util/src/test/java/io/grpc/util/AdvancedTlsX509KeyManagerTest.java

@@ -109,6 +109,29 @@ public void updateTrustCredentials_replacesIssuers() throws Exception {
     assertArrayEquals(serverCert0, serverKeyManager.getCertificateChain(alias4));
   }
 
+  @Test
+  public void scheduledReload_doesNotReloadWhenFilesAreUnchanged() throws Exception {
+    FakeClock fakeClock = new FakeClock();
+    AdvancedTlsX509KeyManager serverKeyManager = new AdvancedTlsX509KeyManager();
+
+    // Give the cert and key files distinct modification times, which is the normal case for two
+    // files written at different instants.
+    serverCert0File.setLastModified(TimeUnit.SECONDS.toMillis(1000));
+    serverKey0File.setLastModified(TimeUnit.SECONDS.toMillis(2000));
+
+    serverKeyManager.updateIdentityCredentials(serverCert0File, serverKey0File, 1, TimeUnit.MINUTES,
+        fakeClock.getScheduledExecutorService());
+
+    // Let one refresh cycle run; the scheduled reloader starts from a zero baseline, so it reloads
+    // once and rotates the alias.
+    fakeClock.forwardTime(1, TimeUnit.MINUTES);
+    String aliasAfterFirstCycle = serverKeyManager.chooseEngineServerAlias(null, null, null);
+
+    // Subsequent cycles with the files untouched must not reload, so the alias must stay the same.
+    fakeClock.forwardTime(5, TimeUnit.MINUTES);
+    assertEquals(aliasAfterFirstCycle, serverKeyManager.chooseEngineServerAlias(null, null, null));
+  }
+
   @Test
   public void allAliasMethods_returnNullBeforeCredentialsLoaded() {
     AdvancedTlsX509KeyManager keyManager = new AdvancedTlsX509KeyManager();