add html compression

pom.xml

@@ -77,6 +77,11 @@
             <version>3.14.0</version>
             <scope>compile</scope>
         </dependency>
+        <dependency>
+            <groupId>com.googlecode.htmlcompressor</groupId>
+            <artifactId>htmlcompressor</artifactId>
+            <version>1.5.2</version>
+        </dependency>
 
         <!-- Sentry -->
         <dependency>

src/main/java/cc/fascinated/backend/filter/HtmlCompressionFilter.java

@@ -0,0 +1,98 @@
+package cc.fascinated.backend.filter;
+
+import com.googlecode.htmlcompressor.compressor.HtmlCompressor;
+import jakarta.servlet.*;
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpServletResponse;
+import jakarta.servlet.http.HttpServletResponseWrapper;
+import org.springframework.stereotype.Component;
+
+import java.io.CharArrayWriter;
+import java.io.IOException;
+import java.io.PrintWriter;
+
+/**
+ * Filter to compress HTML responses using HtmlCompressor.
+ * Author: Fascinated (fascinated7)
+ */
+@Component
+public class HtmlCompressionFilter implements Filter {
+    private final HtmlCompressor htmlCompressor = new HtmlCompressor();
+
+    /**
+     * Applies the HTML compression filter.
+     *
+     * @param request the ServletRequest
+     * @param response the ServletResponse
+     * @param chain the FilterChain
+     * @throws ServletException if an error occurs during filtering
+     * @throws IOException if an input or output error occurs
+     */
+    @Override
+    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+            throws ServletException, IOException {
+
+        ServletResponse newResponse = response;
+
+        // Wrap the response to capture the output
+        if (request instanceof HttpServletRequest) {
+            newResponse = new CharResponseWrapper((HttpServletResponse) response);
+        }
+
+        // Pass the request and response along the filter chain
+        chain.doFilter(request, newResponse);
+
+        // Compress the captured response if it was wrapped
+        if (newResponse instanceof CharResponseWrapper) {
+            String responseContent = newResponse.toString();
+            if (responseContent != null) {
+                response.getWriter().write(htmlCompressor.compress(responseContent));
+            }
+        }
+    }
+
+    /**
+     * Wrapper for HttpServletResponse to capture the output for compression.
+     */
+    private static class CharResponseWrapper extends HttpServletResponseWrapper {
+        private final CharArrayWriter charWriter = new CharArrayWriter();
+        private PrintWriter writer;
+        private boolean getOutputStreamCalled;
+        private boolean getWriterCalled;
+
+        /**
+         * Constructor to wrap the response.
+         * @param response the original HttpServletResponse
+         */
+        public CharResponseWrapper(HttpServletResponse response) {
+            super(response);
+        }
+
+        @Override
+        public ServletOutputStream getOutputStream() throws IOException {
+            if (getWriterCalled) {
+                throw new IllegalStateException("getWriter already called");
+            }
+            getOutputStreamCalled = true;
+            return super.getOutputStream();
+        }
+
+        @Override
+        public PrintWriter getWriter() {
+            if (writer != null) {
+                return writer;
+            }
+            if (getOutputStreamCalled) {
+                throw new IllegalStateException("getOutputStream already called");
+            }
+            getWriterCalled = true;
+            writer = new PrintWriter(charWriter);
+            return writer;
+        }
+
+        @Override
+        public String toString() {
+            return (writer != null) ? charWriter.toString() : null;
+        }
+    }
+}