WW-5256 Add configurable FreeMarker whitespace stripping and compress tag

core/src/main/java/org/apache/struts2/StrutsConstants.java

@@ -326,6 +326,37 @@ public final class StrutsConstants {
 
     public static final String STRUTS_FREEMARKER_WRAPPER_ALT_MAP = "struts.freemarker.wrapper.altMap";
 
+    /**
+     * Controls FreeMarker whitespace stripping during template compilation.
+     * When enabled (default), removes indentation and trailing whitespace from lines containing only FTL tags.
+     * Automatically disabled when devMode is enabled.
+     *
+     * @since 7.2.0
+     */
+    public static final String STRUTS_FREEMARKER_WHITESPACE_STRIPPING = "struts.freemarker.whitespaceStripping";
+
+    /**
+     * Controls whether the compress tag is enabled globally.
+     * When disabled, the compress tag will not compress output regardless of other settings.
+     *
+     * @since 7.2.0
+     */
+    public static final String STRUTS_COMPRESS_ENABLED = "struts.compress.enabled";
+
+    /**
+     * Maximum size (in bytes) of body content that can be compressed. Content exceeding this limit will be skipped without compression.
+     *
+     * @since 7.2.0
+     */
+    public static final String STRUTS_COMPRESS_MAX_SIZE = "struts.compress.maxSize";
+
+    /**
+     * Maximum length of body content to include in log messages. Content longer than this will be truncated with length indicator.
+     *
+     * @since 7.2.0
+     */
+    public static final String STRUTS_COMPRESS_LOG_MAX_LENGTH = "struts.compress.log.maxLength";
+
     /**
      * Extension point for the Struts CompoundRootAccessor
      */
@@ -676,6 +707,7 @@ public final class StrutsConstants {
 
     /**
      * See {@link org.apache.struts2.interceptor.csp.CspNonceReader}
+     *
      * @since 6.8.0
      */
     public static final String STRUTS_CSP_NONCE_READER = "struts.csp.nonce.reader";

core/src/main/java/org/apache/struts2/components/Compress.java

@@ -0,0 +1,196 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.struts2.components;
+
+import org.apache.commons.lang3.BooleanUtils;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.apache.struts2.StrutsConstants;
+import org.apache.struts2.inject.Inject;
+import org.apache.struts2.util.ValueStack;
+import org.apache.struts2.views.annotations.StrutsTag;
+import org.apache.struts2.views.annotations.StrutsTagAttribute;
+
+import java.io.Writer;
+
+/**
+ * <p>
+ * Used to compress HTML output. Just wrap a given section with the tag.
+ * </p>
+ *
+ * <p>
+ * <b>Security considerations:</b>
+ * </p>
+ * <ul>
+ *   <li>Body content is truncated in log messages to prevent sensitive data exposure</li>
+ *   <li>Maximum size limit prevents DoS attacks via large inputs (configurable via struts.compress.maxSize)</li>
+ *   <li>Regex operations include safeguards against ReDoS attacks</li>
+ * </ul>
+ *
+ * <p>
+ * Configurable attributes are:
+ * </p>
+ *
+ * <ul>
+ *    <li>force (true/false) - always compress output, this can be useful in DevMode as devMode disables compression</li>
+ * </ul>
+ *
+ * <p><b>Examples</b></p>
+ * <pre>
+ *  <!-- START SNIPPET: example -->
+ *  &lt;s:compress&gt;
+ *    &lt;s:form action="submit"&gt;
+ *    &lt;s:text name="name" /&gt;
+ *    ...
+ *    &lt;/s:form&gt;
+ *  &lt;/s:compress&gt;
+ *  <!-- END SNIPPET: example -->
+ * </pre>
+ *
+ * <p>Uses conditional compression depending on action</p>
+ * <pre>
+ *  <!-- START SNIPPET: example -->
+ *  &lt;s:compress force="shouldCompress"&gt;
+ *    &lt;s:form action="submit"&gt;
+ *    &lt;s:text name="name" /&gt;
+ *    ...
+ *    &lt;/s:form&gt;
+ *  &lt;/s:compress&gt;
+ *  <!-- END SNIPPET: example -->
+ * </pre>
+ * "shouldCompress" is a field with getter define on action used in expression evaluation
+ *
+ * @since 7.2.0
+ */
+@StrutsTag(name = "compress", tldTagClass = "org.apache.struts2.views.jsp.CompressTag",
+        description = "Compress wrapped content\n\n<p><b>Security:</b> The compress tag includes built-in protections against DoS attacks and sensitive data exposure. Large content exceeding the configured maximum size (default 10MB) will be skipped without compression. Log messages are automatically truncated to prevent sensitive data from appearing in logs.</p>")
+public class Compress extends Component {
+
+    private static final Logger LOG = LogManager.getLogger(Compress.class);
+
+    private String force;
+    private boolean compressionEnabled = true;
+    private Long maxSize = null;
+    private int logMaxLength = 200;
+
+    public Compress(ValueStack stack) {
+        super(stack);
+    }
+
+    @Inject(value = StrutsConstants.STRUTS_COMPRESS_ENABLED, required = false)
+    public void setCompressionEnabled(String compressionEnabled) {
+        this.compressionEnabled = BooleanUtils.toBoolean(compressionEnabled);
+    }
+
+    @Inject(value = StrutsConstants.STRUTS_COMPRESS_MAX_SIZE, required = false)
+    public void setMaxSize(String maxSize) {
+        try {
+            this.maxSize = Long.parseLong(maxSize.trim());
+        } catch (NumberFormatException e) {
+            this.maxSize = null;
+        }
+    }
+
+    @Inject(value = StrutsConstants.STRUTS_COMPRESS_LOG_MAX_LENGTH, required = false)
+    public void setLogMaxLength(String logMaxLength) {
+        try {
+            this.logMaxLength = Integer.parseInt(logMaxLength.trim());
+        } catch (NumberFormatException e) {
+            this.logMaxLength = 200;
+        }
+    }
+
+    @Override
+    public boolean end(Writer writer, String body) {
+        // Check size limit before processing
+        if (exceedsMaxSize(body) && compressionEnabled) {
+            LOG.warn("Body size: {} exceeds maximum allowed size: {}, skipping compression", body.length(), maxSize);
+            return super.end(writer, body, true);
+        }
+
+        Object forceValue = findValue(force, Boolean.class);
+
+        boolean forced = forceValue instanceof Boolean forcedValue && forcedValue;
+
+        if (!compressionEnabled && !forced) {
+            if (LOG.isDebugEnabled()) {
+                LOG.debug("Compression disabled globally, skipping: {}", truncateForLogging(body));
+            }
+            return super.end(writer, body, true);
+        }
+        if (devMode && !forced) {
+            if (LOG.isDebugEnabled()) {
+                LOG.debug("Avoids compressing output: {} in DevMode", truncateForLogging(body));
+            }
+            return super.end(writer, body, true);
+        }
+        if (LOG.isTraceEnabled()) {
+            LOG.trace("Compresses: {}", truncateForLogging(body));
+        }
+        String compressedBody = compressWhitespace(body);
+        if (LOG.isTraceEnabled()) {
+            LOG.trace("Compressed: {}", truncateForLogging(compressedBody));
+        }
+        return super.end(writer, compressedBody, true);
+    }
+
+    @Override
+    public boolean usesBody() {
+        return true;
+    }
+
+    @StrutsTagAttribute(description = "Force output compression")
+    public void setForce(String force) {
+        this.force = force;
+    }
+
+    private String truncateForLogging(String content) {
+        if (content == null) {
+            return null;
+        }
+        if (content.length() <= logMaxLength) {
+            return content;
+        }
+        return content.substring(0, logMaxLength) + "... (truncated, length: " + content.length() + ")";
+    }
+
+    private boolean exceedsMaxSize(String body) {
+        if (maxSize == null || body == null) {
+            return false;
+        }
+        return body.length() > maxSize;
+    }
+
+    private String compressWhitespace(String input) {
+        if (input == null || input.isEmpty()) {
+            return input;
+        }
+
+        // Early exit for very large inputs to prevent ReDoS and excessive processing
+        // This is a secondary check; primary size check happens in end() method
+        if (input.length() > 50_000_000) { // 50MB hard limit for regex operations
+            LOG.warn("Input size: {} exceeds safe processing limit (50MB), returning original content",
+                    input.length());
+            return input;
+        }
+
+        // Simple compression: trim and remove whitespace between tags
+        return input.trim().replaceAll(">\\s+<", "><");
+    }
+}