Issue #5977 do not force Cache-Control header if already set

jetty-server/src/main/java/org/eclipse/jetty/server/ResourceService.java

@@ -832,7 +832,7 @@ protected void putHeaders(HttpServletResponse response, HttpContent content, lon
             if (_acceptRanges)
                 f.put(ACCEPT_RANGES);
 
-            if (_cacheControl != null)
+            if (_cacheControl != null && !response.containsHeader(HttpHeader.CACHE_CONTROL.asString()))
                 f.put(_cacheControl);
         }
         else
@@ -841,7 +841,7 @@ protected void putHeaders(HttpServletResponse response, HttpContent content, lon
             if (_acceptRanges)
                 response.setHeader(ACCEPT_RANGES.getName(), ACCEPT_RANGES.getValue());
 
-            if (_cacheControl != null)
+            if (_cacheControl != null && !response.containsHeader(HttpHeader.CACHE_CONTROL.name()))
                 response.setHeader(_cacheControl.getName(), _cacheControl.getValue());
         }
     }

jetty-servlet/src/main/java/org/eclipse/jetty/servlet/DefaultServlet.java

@@ -283,7 +283,7 @@ public void init()
         _resourceService.setContentFactory(contentFactory);
         _resourceService.setWelcomeFactory(this);
 
-        List<String> gzipEquivalentFileExtensions = new ArrayList<String>();
+        List<String> gzipEquivalentFileExtensions = new ArrayList<>();
         String otherGzipExtensions = getInitParameter("otherGzipFileExtensions");
         if (otherGzipExtensions != null)
         {

jetty-servlet/src/test/java/org/eclipse/jetty/servlet/CacheControlHeaderTest.java

@@ -0,0 +1,157 @@
+//
+//  ========================================================================
+//  Copyright (c) 1995-2021 Mort Bay Consulting Pty Ltd and others.
+//  ------------------------------------------------------------------------
+//  All rights reserved. This program and the accompanying materials
+//  are made available under the terms of the Eclipse Public License v1.0
+//  and Apache License v2.0 which accompanies this distribution.
+//
+//      The Eclipse Public License is available at
+//      http://www.eclipse.org/legal/epl-v10.html
+//
+//      The Apache License v2.0 is available at
+//      http://www.opensource.org/licenses/apache2.0.php
+//
+//  You may elect to redistribute this code under either of these licenses.
+//  ========================================================================
+//
+
+package org.eclipse.jetty.servlet;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.EnumSet;
+import javax.servlet.DispatcherType;
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletResponse;
+
+import org.eclipse.jetty.http.HttpHeader;
+import org.eclipse.jetty.server.HttpConfiguration;
+import org.eclipse.jetty.server.HttpConnectionFactory;
+import org.eclipse.jetty.server.LocalConnector;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.toolchain.test.MavenTestingUtils;
+import org.junit.jupiter.api.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+
+public class CacheControlHeaderTest
+{
+    private Server server;
+    private LocalConnector connector;
+
+    public static class ForceCacheControlFilter implements Filter
+    {
+        @Override
+        public void init(FilterConfig filterConfig) throws ServletException
+        {
+        }
+
+        @Override
+        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
+        {
+            HttpServletResponse httpResponse = (HttpServletResponse)response;
+            httpResponse.setHeader(HttpHeader.CACHE_CONTROL.asString(), "max-age=0,private");
+            chain.doFilter(request, response);
+        }
+
+        @Override
+        public void destroy()
+        {
+        }
+    }
+
+    public void startServer(boolean forceFilter) throws Exception
+    {
+        server = new Server();
+
+        HttpConnectionFactory httpConnectionFactory = new HttpConnectionFactory(new HttpConfiguration());
+        connector = new LocalConnector(server, null, null, null, -1, httpConnectionFactory);
+
+        ServletContextHandler context = new ServletContextHandler();
+
+        ServletHolder servletHolder = new ServletHolder();
+        servletHolder.setServlet(new DefaultServlet());
+        servletHolder.setInitParameter("cacheControl", "max-age=3600,public");
+        Path resBase = MavenTestingUtils.getTestResourcePathDir("contextResources");
+        servletHolder.setInitParameter("resourceBase", resBase.toFile().toURI().toASCIIString());
+        context.addServlet(servletHolder, "/*");
+        if (forceFilter)
+        {
+            context.addFilter(ForceCacheControlFilter.class, "/*", EnumSet.of(DispatcherType.REQUEST));
+        }
+        server.setHandler(context);
+        server.addConnector(connector);
+
+        server.start();
+    }
+
+    public void stopServer() throws Exception
+    {
+        if (server != null && server.isRunning())
+        {
+            server.stop();
+        }
+    }
+
+    @Test
+    public void testCacheControlFilterOverride() throws Exception
+    {
+        try
+        {
+            startServer(true);
+            StringBuffer req1 = new StringBuffer();
+            req1.append("GET /content.txt HTTP/1.1\r\n");
+            req1.append("Host: local\r\n");
+            req1.append("Accept: */*\r\n");
+            req1.append("Connection: close\r\n");
+            req1.append("\r\n");
+
+            String response = connector.getResponse(req1.toString());
+            assertThat("Response status",
+                       response,
+                       containsString("HTTP/1.1 200 OK"));
+            assertThat("Response headers",
+                        response,
+                        containsString(HttpHeader.CACHE_CONTROL.asString() + ": max-age=0,private"));
+        } 
+        finally
+        {
+            stopServer();
+        }
+    }
+
+    @Test
+    public void testCacheControlDefaultServlet() throws Exception
+    {
+        try
+        {
+            startServer(false);
+            StringBuffer req1 = new StringBuffer();
+            req1.append("GET /content.txt HTTP/1.1\r\n");
+            req1.append("Host: local\r\n");
+            req1.append("Accept: */*\r\n");
+            req1.append("Connection: close\r\n");
+            req1.append("\r\n");
+
+            String response = connector.getResponse(req1.toString());
+            assertThat("Response status",
+                       response,
+                       containsString("HTTP/1.1 200 OK"));
+            assertThat("Response headers",
+                       response,
+                       containsString(HttpHeader.CACHE_CONTROL.asString() + ": max-age=3600,public"));
+        } 
+        finally
+        {
+            stopServer();
+        }
+    }
+
+}