Issue612

lib/src/messages/connect/mqtt_client_mqtt_connect_message.dart

@@ -102,6 +102,8 @@ class MqttConnectMessage extends MqttMessage {
   }
 
   /// Sets the authentication
+  /// Note that although passed as a string the password can be any binary data up to a length of
+  /// 65535 bytes.
   MqttConnectMessage authenticateAs(String? username, String? password) {
     if (username != null) {
       variableHeader!.connectFlags.usernameFlag = username.isNotEmpty;

lib/src/mqtt_client.dart

@@ -606,28 +606,33 @@ class MqttClient {
   }
 
   /// Check the username and password validity
-  @protected
   void checkCredentials(String? username, String? password) {
     if (username != null) {
       MqttLogger.log(
         "Authenticating with username '{$username}' "
         "and password '{$password}'",
       );
-      if (username.trim().length >
-          MqttClientConstants.recommendedMaxUsernamePasswordLength) {
-        MqttLogger.log(
-          'MqttClient::checkCredentials - Username length (${username.trim().length}) '
-          'exceeds the max recommended in the MQTT spec. ',
-        );
+      if (Protocol.version == MqttClientConstants.mqttV31ProtocolVersion) {
+        if (username.trim().length >
+            MqttClientConstants.recommendedMaxUsernamePasswordLength) {
+          MqttLogger.log(
+            'MqttClient::checkCredentials - Advisory - Username length (${username.trim().length}) '
+            'exceeds the max recommended in the MQTT 3.1 spec. ',
+          );
+        }
       }
     }
-    if (password != null &&
-        password.trim().length >
+
+    if (password != null) {
+      if (Protocol.version == MqttClientConstants.mqttV31ProtocolVersion) {
+        if (password.trim().length >
             MqttClientConstants.recommendedMaxUsernamePasswordLength) {
-      MqttLogger.log(
-        'MqttClient::checkCredentials - Password length (${password.trim().length}) '
-        'exceeds the max recommended in the MQTT spec. ',
-      );
+          MqttLogger.log(
+            'MqttClient::checkCredentials - Advisory - Password length (${password.trim().length}) '
+            'exceeds the max recommended in the MQTT 3.1 spec. ',
+          );
+        }
+      }
     }
   }
 

lib/src/utility/mqtt_client_logger.dart

@@ -18,12 +18,19 @@ class MqttLogger {
   /// Test output
   static String testOutput = '';
 
-  /// Test mode
-  static bool testMode = false;
-
   /// Log publish message payload data
   static bool logPayloads = true;
 
+  static bool _testMode = false;
+
+  /// Test mode
+  static bool get testMode => _testMode;
+
+  static set testMode(bool state) {
+    _testMode = state;
+    testOutput = '';
+  }
+
   /// Log method
   /// If the optimise parameter is supplied it must have a toString method,
   /// this allows large objects such as lots of payload data not to be

test/mqtt_client_base_test.dart

@@ -1066,6 +1066,67 @@ void main() {
       client.connectTimeoutPeriod = 500;
       expect(client.connectTimeoutPeriod, 5000);
     });
+    test('Check Credentials OK for 3.1', () {
+      final client = MqttClient('aaaa', 'bbbb');
+      client.logging(on: true);
+      MqttLogger.testMode = true;
+      client.setProtocolV31();
+      client.checkCredentials('username', 'password');
+      expect(
+        MqttLogger.testOutput.contains(
+          "Authenticating with username '{username}' "
+          "and password '{password}",
+        ),
+        isTrue,
+      );
+      MqttLogger.testMode = false;
+      client.logging(on: false);
+    });
+    test('Check Credentials username bad for 3.1', () {
+      final client = MqttClient('aaaa', 'bbbb');
+      client.logging(on: true);
+      MqttLogger.testMode = true;
+      client.setProtocolV31();
+      client.checkCredentials('usernameffffffffffffff', 'password');
+      expect(
+        MqttLogger.testOutput.contains('Advisory - Username length'),
+        isTrue,
+      );
+      MqttLogger.testMode = false;
+      client.logging(on: false);
+    });
+    test('Check Credentials password bad for 3.1', () {
+      final client = MqttClient('aaaa', 'bbbb');
+      client.logging(on: true);
+      MqttLogger.testMode = true;
+      client.setProtocolV31();
+      client.checkCredentials('username', 'passwordkkkkkkkkkkkkkkkk');
+      expect(
+        MqttLogger.testOutput.contains('Advisory - Password length'),
+        isTrue,
+      );
+      MqttLogger.testMode = false;
+      client.logging(on: false);
+    });
+    test('Check Credentials always OK for 3.1.1', () {
+      final client = MqttClient('aaaa', 'bbbb');
+      client.logging(on: true);
+      MqttLogger.testMode = true;
+      client.setProtocolV311();
+      client.checkCredentials(
+        'usernamedddddddddddddddd',
+        'passwordfffffffffffffff',
+      );
+      expect(
+        MqttLogger.testOutput.contains(
+          "Authenticating with username '{usernamedddddddddddddddd}' "
+          "and password '{passwordfffffffffffffff}",
+        ),
+        isTrue,
+      );
+      MqttLogger.testMode = false;
+      client.logging(on: false);
+    });
   });
 
   group('Logging', () {