feat(rendering): minify rendered HTML behind FEATURE_FLAG_MINIFY_HTML

dotCMS/src/main/java/com/dotcms/featureflag/FeatureFlagName.java

@@ -83,6 +83,14 @@ public interface FeatureFlagName {
      */
     String FEATURE_FLAG_EDIT_CONTENT_SIDE_PANEL = "FEATURE_FLAG_EDIT_CONTENT_SIDE_PANEL";
 
+    /**
+     * Minifies rendered page HTML (collapses insignificant whitespace and strips comments) before
+     * it is written to the response. Off by default.
+     *
+     * @see com.dotcms.rendering.util.HtmlMinifier
+     */
+    String FEATURE_FLAG_MINIFY_HTML = "FEATURE_FLAG_MINIFY_HTML";
+
     /**
      * libvips image-engine toggle (off by default; the legacy Java2D engine is used
      * otherwise). The new image editor reads this through the configuration endpoint

dotCMS/src/main/java/com/dotcms/rendering/velocity/servlet/VelocityLiveMode.java

@@ -4,6 +4,7 @@
 
 import com.dotcms.api.web.HttpServletRequestThreadLocal;
 import com.dotcms.api.web.HttpServletResponseThreadLocal;
+import com.dotcms.rendering.util.HtmlMinifier;
 import com.dotcms.rendering.velocity.services.VelocityResourceKey;
 import com.dotcms.rendering.velocity.util.VelocityUtil;
 import com.dotcms.security.ContentSecurityPolicyUtil;
@@ -51,11 +52,18 @@
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.validation.constraints.NotNull;
+import org.apache.commons.io.output.StringBuilderWriter;
 import org.apache.commons.io.output.TeeOutputStream;
 import org.apache.velocity.context.Context;
 
 public class VelocityLiveMode extends VelocityModeHandler {
 
+    /**
+     * Initial size of the in-memory buffer used when minification is on. Big enough that a typical
+     * page never triggers a grow-and-copy, and small enough to be irrelevant if a page is tiny.
+     */
+    private static final int MERGE_BUFFER_INITIAL_CAPACITY = 32 * 1024;
+
     final static ThreadLocal<ByteArrayOutputStream> byteArrayLocal = ThreadLocal.withInitial(
             ByteArrayOutputStream::new);
     final static long PAGE_CACHE_TIMEOUT_MILLIS = Config.getIntProperty("PAGE_CACHE_TIMEOUT_MILLIS", 2000);
@@ -267,7 +275,25 @@ PageCacheParameters buildCacheParameters(final long langId, final IHTMLPage html
      */
     private void writePage(final Writer out, final IHTMLPage htmlPage) {
         final Context context = VelocityUtil.getInstance().getContext(request, response);
-        this.getTemplate(htmlPage, mode).merge(context, out);
+
+        if (!HtmlMinifier.isEnabled()) {
+            this.getTemplate(htmlPage, mode).merge(context, out);
+            return;
+        }
+
+        // Merge into memory first so the markup can be minified as a whole. What is written here is
+        // also what gets stored in the page cache, so minification happens once per cache fill
+        // rather than on every cache hit.
+        //
+        // StringBuilderWriter rather than StringWriter: the latter is backed by a synchronized
+        // StringBuffer, and Velocity emits a page as many hundreds of small writes, so the lock is
+        // taken on every one of them. Sizing the buffer up front avoids the repeated grow-and-copy.
+        // minifyBestEffort, not minifyIfEnabled, because the flag was already read above and reading
+        // it twice per render buys nothing.
+        final StringBuilderWriter merged = new StringBuilderWriter(MERGE_BUFFER_INITIAL_CAPACITY);
+        this.getTemplate(htmlPage, mode).merge(context, merged);
+        Try.run(() -> out.write(HtmlMinifier.minifyBestEffort(merged.toString())))
+                .getOrElseThrow(DotRuntimeException::new);
     }
 
 

dotCMS/src/main/java/com/dotcms/rendering/velocity/servlet/VelocityModeHandler.java

@@ -1,5 +1,6 @@
 package com.dotcms.rendering.velocity.servlet;
 
+import com.dotcms.rendering.util.HtmlMinifier;
 import com.dotcms.rendering.velocity.services.VelocityResourceKey;
 import com.dotcms.rendering.velocity.services.VelocityType;
 import com.dotcms.rendering.velocity.util.VelocityUtil;
@@ -105,12 +106,11 @@ public final String eval() {
         try(ByteArrayOutputStream out = new ByteArrayOutputStream(4096)) {
             serve(out);
 
-            if (ContentSecurityPolicyUtil.isConfig()) {
-                final String htmlCode = new String(out.toByteArray(), StandardCharsets.UTF_8);
-                return ContentSecurityPolicyUtil.apply(htmlCode);
-            } else {
-                return new String(out.toByteArray(), StandardCharsets.UTF_8);
-            }
+            final String htmlCode = new String(out.toByteArray(), StandardCharsets.UTF_8);
+
+            return ContentSecurityPolicyUtil.isConfig()
+                    ? HtmlMinifier.minifyIfEnabled(ContentSecurityPolicyUtil.apply(htmlCode))
+                    : HtmlMinifier.minifyIfEnabled(htmlCode);
         } catch (DotDataException | IOException | DotSecurityException e) {
             Logger.debug(VelocityModeHandler.class, e.getMessage(), e);
             throw new DotRuntimeException(e);

dotCMS/src/main/resources/dotmarketing-config.properties

@@ -883,6 +883,11 @@ FEATURE_FLAG_LOCALE_SELECTOR_V2=true
 ## of navigating full-screen (Content Drive) or a centered dialog (UVE).
 FEATURE_FLAG_EDIT_CONTENT_SIDE_PANEL=true
 
+## Native HTML minification of rendered pages. Off by default (rollback safety: pages are
+## served exactly as the templates render them). Collapses insignificant whitespace and strips
+## HTML comments; see com.dotcms.rendering.util.HtmlMinifier.
+FEATURE_FLAG_MINIFY_HTML=false
+
 ## libvips image engine toggle. On by default; the engine still requires the native
 ## libvips library to be present, otherwise it falls back to the legacy Java2D engine
 ## at runtime. Set to false to force the legacy engine. The new image editor reads this