Fix Alert(null,null) logging in AlertMessage toCompactString()

Previously, AlertMessage.toCompactString() would return "Alert(null,null)"
when the level and description fields were not set. This happened because
the method only checked the config field for description but not for level.

This commit:
- Updates toCompactString() to use config as fallback for both level and description
- Returns "not configured" instead of "null" when no values are available
- Adds comprehensive unit tests to verify the behavior

This provides better logging output before the message is prepared by the
AlertPreparator, resolving issue #212.

Author: TLS-Attacker Developer

TLS-Core/src/main/java/de/rub/nds/tlsattacker/core/protocol/message/AlertMessage.java

@@ -114,30 +114,42 @@ public String toCompactString() {
         StringBuilder sb = new StringBuilder();
         String levelString;
         String descriptionString;
+
+        // Determine level string
         if (level != null && level.getValue() != null) {
             levelString = AlertLevel.getAlertLevel(level.getValue()).name();
+        } else if (config != null && config.length == 2) {
+            // Use config as fallback for level
+            AlertLevel alertLevel = AlertLevel.getAlertLevel((byte) config[0]);
+            if (alertLevel != null) {
+                levelString = alertLevel.name();
+            } else {
+                levelString = "" + config[0];
+            }
         } else {
-            levelString = "null";
+            levelString = "not configured";
         }
+
+        // Determine description string
         if (description != null && description.getValue() != null) {
             AlertDescription desc = AlertDescription.getAlertDescription(description.getValue());
             if (desc != null) {
                 descriptionString = desc.name();
             } else {
                 descriptionString = "" + description.getValue();
             }
-        } else {
-            if (config != null && config.length == 2) {
-                AlertDescription desc = AlertDescription.getAlertDescription((byte) config[1]);
-                if (desc != null) {
-                    descriptionString = desc.name();
-                } else {
-                    descriptionString = "" + config[1];
-                }
+        } else if (config != null && config.length == 2) {
+            // Use config as fallback for description
+            AlertDescription desc = AlertDescription.getAlertDescription((byte) config[1]);
+            if (desc != null) {
+                descriptionString = desc.name();
             } else {
-                descriptionString = "null";
+                descriptionString = "" + config[1];
             }
+        } else {
+            descriptionString = "not configured";
         }
+
         sb.append("Alert(").append(levelString).append(",").append(descriptionString).append(")");
         return sb.toString();
     }

TLS-Core/src/test/java/de/rub/nds/tlsattacker/core/protocol/message/AlertMessageToCompactStringTest.java

@@ -0,0 +1,85 @@
+/*
+ * TLS-Attacker - A Modular Penetration Testing Framework for TLS
+ *
+ * Copyright 2014-2023 Ruhr University Bochum, Paderborn University, Technology Innovation Institute, and Hackmanit GmbH
+ *
+ * Licensed under Apache License, Version 2.0
+ * http://www.apache.org/licenses/LICENSE-2.0.txt
+ */
+package de.rub.nds.tlsattacker.core.protocol.message;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import de.rub.nds.tlsattacker.core.constants.AlertDescription;
+import de.rub.nds.tlsattacker.core.constants.AlertLevel;
+import org.junit.jupiter.api.Test;
+
+public class AlertMessageToCompactStringTest {
+
+    @Test
+    public void testToCompactStringWithNullValues() {
+        AlertMessage message = new AlertMessage();
+        // Both level and description are null, no config set
+        assertEquals("Alert(not configured,not configured)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithConfig() {
+        AlertMessage message = new AlertMessage();
+        // Set config with WARNING level (1) and BAD_RECORD_MAC description (20)
+        message.setConfig(new byte[] {1, 20});
+        assertEquals("Alert(WARNING,BAD_RECORD_MAC)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithExplicitValues() {
+        AlertMessage message = new AlertMessage();
+        message.setLevel(AlertLevel.FATAL.getValue());
+        message.setDescription(AlertDescription.HANDSHAKE_FAILURE.getValue());
+        assertEquals("Alert(FATAL,HANDSHAKE_FAILURE)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithUnknownValues() {
+        AlertMessage message = new AlertMessage();
+        // Use values that don't correspond to known alert types
+        message.setConfig(new byte[] {99, 99});
+        assertEquals("Alert(UNDEFINED,99)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithPartialConfig() {
+        AlertMessage message = new AlertMessage();
+        // Config with only one byte - should fall back to "not configured"
+        message.setConfig(new byte[] {1});
+        assertEquals("Alert(not configured,not configured)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithLevelButNoDescription() {
+        AlertMessage message = new AlertMessage();
+        message.setLevel(AlertLevel.WARNING.getValue());
+        // Description is null, no config
+        assertEquals("Alert(WARNING,not configured)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringWithDescriptionButNoLevel() {
+        AlertMessage message = new AlertMessage();
+        message.setDescription(AlertDescription.CLOSE_NOTIFY.getValue());
+        // Level is null, no config
+        assertEquals("Alert(not configured,CLOSE_NOTIFY)", message.toCompactString());
+    }
+
+    @Test
+    public void testToCompactStringPrefersExplicitValuesOverConfig() {
+        AlertMessage message = new AlertMessage();
+        // Set config
+        message.setConfig(new byte[] {1, 20});
+        // But also set explicit values - these should take precedence
+        message.setLevel(AlertLevel.FATAL.getValue());
+        message.setDescription(AlertDescription.UNEXPECTED_MESSAGE.getValue());
+        assertEquals("Alert(FATAL,UNEXPECTED_MESSAGE)", message.toCompactString());
+    }
+}
+