adding expansion variable resolution for server.env props

src/main/java/io/openliberty/tools/common/plugins/config/ServerConfigDocument.java

@@ -1,5 +1,5 @@
 /**
- * (C) Copyright IBM Corporation 2017, 2025.
+ * (C) Copyright IBM Corporation 2017, 2026.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,8 @@
 import java.util.Set;
 import java.util.Map;
 import java.util.Properties;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import javax.xml.XMLConstants;
 import javax.xml.parsers.DocumentBuilder;
@@ -46,13 +48,12 @@
 import javax.xml.xpath.XPathFactory;
 
 import io.openliberty.tools.common.plugins.util.LibertyPropFilesUtility;
+import io.openliberty.tools.common.plugins.util.OSUtil;
 import io.openliberty.tools.common.plugins.util.PluginExecutionException;
 import org.apache.commons.io.comparator.NameFileComparator;
 import org.w3c.dom.Document;
 import org.w3c.dom.Element;
 import org.w3c.dom.NodeList;
-import org.w3c.dom.Node;
-import org.w3c.dom.NamedNodeMap;
 import org.xml.sax.SAXException;
 
 import io.openliberty.tools.common.CommonLoggerI;
@@ -88,6 +89,11 @@ public class ServerConfigDocument {
     private static final XPathExpression XPATH_SERVER_INCLUDE;
     public static final XPathExpression XPATH_SERVER_VARIABLE;
     private static final XPathExpression XPATH_ALL_SERVER_APPLICATIONS;
+    // Windows style: !VAR!
+    private static final Pattern WINDOWS_EXPANSION_VAR_PATTERN;
+    // Linux style: ${VAR}
+    private static final Pattern LINUX_EXPANSION_VAR_PATTERN;
+    private static final int MAX_SUBSTITUTION_DEPTH = 5;
 
 
     static {
@@ -106,6 +112,8 @@ public class ServerConfigDocument {
             // correct
             throw new RuntimeException(ex);
         }
+        WINDOWS_EXPANSION_VAR_PATTERN = Pattern.compile("!(\\w+)!");
+        LINUX_EXPANSION_VAR_PATTERN = Pattern.compile("\\$\\{(\\w+)\\}");
     }
 
     public Set<String> getLocations() {
@@ -321,6 +329,76 @@ public void processServerEnv() throws Exception, FileNotFoundException {
         parsePropertiesFromFile(new File(libertyDirectoryPropertyToFile.get(ServerFeatureUtil.WLP_USER_DIR),
                 "shared" + File.separator + serverEnvString));
         parsePropertiesFromFile(getFileFromConfigDirectory(serverEnvString));
+        Map<String, String> resolvedMap = new HashMap<>();
+
+        props.forEach((k, v) -> {
+            String key = (String) k;
+            String value = (String) v;
+            Set<String> resolveInProgressProps = new HashSet<>();
+            resolveInProgressProps.add(key);
+            resolvedMap.put(key, resolveExpansionProperties(props, value,key, resolveInProgressProps, MAX_SUBSTITUTION_DEPTH));
+        });
+
+        // After all resolutions are calculated, update the original props
+        props.putAll(resolvedMap);
+    }
+
+    /**
+     * Resolves property placeholders recursively with safety guards.
+     * Uses appendReplacement to ensure a single-pass scan and strict depth control.
+     *
+     * @param props                  The properties source.
+     * @param value                  The string currently being processed.
+     * @param resolveInProgressProps The set of variables in the current stack to detect loops.
+     * @param remainingDepth         Remaining levels of recursion allowed.
+     * @return The resolved string or raw text if depth/circularity limits are hit.
+     */
+    private String resolveExpansionProperties(Properties props, String value, String key, Set<String> resolveInProgressProps, int remainingDepth) {
+        if (value == null) return null;
+
+        // 1. Initial Depth Check
+        if (remainingDepth <= 0) {
+            log.warn("Max substitution depth reached for key: " + key + ". Returning raw value: " + value);
+            return value;
+        }
+        Pattern pattern = OSUtil.isWindows() ? WINDOWS_EXPANSION_VAR_PATTERN : LINUX_EXPANSION_VAR_PATTERN;
+        Matcher matcher = pattern.matcher(value);
+        StringBuffer sb = new StringBuffer();
+
+        while (matcher.find()) {
+            String finalReplacement;
+            String varName = matcher.group(1);
+
+            // 2. Circular Reference Guard
+            if (resolveInProgressProps.contains(varName)) {
+                log.warn("Circular reference detected: " + varName + " depends on itself in key " + key + ". Skipping expansion.");
+                continue;
+            }
+            String replacement = props.getProperty(varName);
+            if (replacement != null) {
+                // 3. Recursive Logic with Depth Guard
+                if (remainingDepth <= 1) {
+                    log.warn("Depth limit hit at '" + varName + "'. Appending raw value without further expansion.");
+                    finalReplacement = replacement;
+                } else {
+                    resolveInProgressProps.add(varName);
+                    try {
+                        String resolved = resolveExpansionProperties(props, replacement, key, resolveInProgressProps, remainingDepth - 1);
+                        finalReplacement = resolved;
+                    } finally {
+                        resolveInProgressProps.remove(varName);
+                    }
+                }
+            } else {
+                // Variable not found in Properties; leave the original ${VAR} or !VAR!
+                finalReplacement = matcher.group(0); // Keep original
+            }
+            matcher.appendReplacement(sb, Matcher.quoteReplacement(finalReplacement));
+            log.debug(String.format("Resolving Property %s for %s. Resolved value is %s", varName , value , sb));
+        }
+        // 4. Finalize the string
+        matcher.appendTail(sb);
+        return sb.toString();
     }
 
     /**

src/test/java/io/openliberty/tools/common/plugins/util/ServerConfigDocumentTest.java

@@ -1,5 +1,5 @@
 /**
- * (C) Copyright IBM Corporation 2023, 2024.
+ * (C) Copyright IBM Corporation 2023, 2026.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,7 @@
  */
 package io.openliberty.tools.common.plugins.util;
 
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
@@ -91,7 +92,19 @@ public void testAppLocationUsesLibertyProperty() throws Exception {
 		assertTrue("App location four not found.", locFourFound);
 		assertTrue("App location five not found.", locFiveFound);
 		assertTrue("App location six not found.", locSixFound);
-
+		if (OSUtil.isWindows()) {
+			assertEquals("Variable Expanded for !VAR!", "DEFINED_VAL", scd.getProperties().getProperty("this2_value"));
+			assertEquals("Variable Expanded for ${VAR}", "DEFINED\\old_value\\dir", scd.getProperties().getProperty("this5_value"));
+			assertEquals("Variable Expanded for recursive this8_value=!this5_value!\\!overriden_value!\\dir", "DEFINED\\old_value\\dir\\old_value\\dir", scd.getProperties().getProperty("this8_value"));
+		} else {
+			assertEquals("Variable Expanded for ${VAR}", "DEFINED_VAL", scd.getProperties().getProperty("this3_value"));
+			assertEquals("Variable Expanded for ${VAR}", "DEFINED/old_value/dir", scd.getProperties().getProperty("this4_value"));
+			assertEquals("Variable Expanded for recursive this7_value=${this3_value}/${overriden_value}/dir", "DEFINED_VAL/old_value/dir", scd.getProperties().getProperty("this7_value"));
+			assertEquals("circular or self reference value is not resolved", "DEFINED_VAL/${self_ref_value}", scd.getProperties().getProperty("self_ref_value"));
+			assertEquals("recursive reference stopped with more than max", "v7_v6_v5_v4_v3_${depth_v2}", scd.getProperties().getProperty("depth_max"));
+			assertEquals("recursive reference stopped with more than max", "v7_v6_v5_v4_v3_v2_${depth_v1}", scd.getProperties().getProperty("depth_v7"));
+		}
+		assertEquals("Variable not Expanded for !this_val", "!this_val", scd.getProperties().getProperty("this6_value"));
 	}
 
 	/**

src/test/resources/serverConfig/liberty/wlp/usr/servers/defaultServer/server.env

@@ -1,5 +1,34 @@
 keystore_password=C7ANPlAi0MQD154BJ5ZOURn
 http.port=1111
+# --- Base Definitions ---
 overriden_value=old_value
 this_value=DEFINED
-bootstrap.properties.override=false
+bootstrap.properties.override=false
+
+# Combines multiple recursive lookups with forward property substitution linux
+this7_value=${this3_value}/${overriden_value}/dir
+# Combines multiple recursive lookups linux
+this4_value=${this_value}/${overriden_value}/dir
+this3_value=${this_value}_VAL
+# self reference -> will throw warning but no infinite loop
+self_ref_value=${this3_value}/${self_ref_value}
+# circular reference -> will throw warning but no infinite loop
+circ_v1=var_${circ_v2}
+circ_v2=var_${circ_v1}
+
+# Combines multiple recursive lookups with forward property substitution windows
+this8_value=!this5_value!\\!overriden_value!\\dir
+this2_value=!this_value!_VAL
+# Combines multiple recursive lookups windows
+this5_value=!this_value!\\!overriden_value!\\dir
+this6_value=!this_val
+
+# testing max recursion level, here since max level is 5, depth_max, depth_v7 will not be resolved
+depth_max=${depth_v7}
+depth_v7=v7_${depth_v6}
+depth_v6=v6_${depth_v5}
+depth_v5=v5_${depth_v4}
+depth_v4=v4_${depth_v3}
+depth_v3=v3_${depth_v2}
+depth_v2=v2_${depth_v1}
+depth_v1=1