PR #12441 - Allow HttpFields.asMap to modify the underlying HttpFields

Signed-off-by: Lachlan Roberts <lachlan.p.roberts@gmail.com>

jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java

@@ -928,6 +928,10 @@ public interface HttpFields extends Iterable<HttpField>, Supplier<HttpFields>
         return size;
     }
 
+    /**
+     * @param fields the {@link HttpFields} to convert to a {@link Map}.
+     * @return an unmodifiable {@link Map} representing the contents of the {@link HttpFields}.
+     */
     static Map<String, List<String>> asMap(HttpFields fields)
     {
         Map<String, List<String>> headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
@@ -936,10 +940,20 @@ public interface HttpFields extends Iterable<HttpField>, Supplier<HttpFields>
             if (!headers.containsKey(f.getName()))
             {
                 HttpHeader header = f.getHeader();
-                headers.put(f.getName(), header == null ? fields.getValuesList(f.getName()) : fields.getValuesList(header));
+                List<String> values = header == null ? fields.getValuesList(f.getName()) : fields.getValuesList(header);
+                headers.put(f.getName(), Collections.unmodifiableList(values));
             }
         }
-        return headers;
+        return Collections.unmodifiableMap(headers);
+    }
+
+    /**
+     * @param fields the {@link HttpFields} to convert to a {@link Map}.
+     * @return a {@link Map} where changes to the contents will be reflected in the supplied {@link HttpFields}.
+     */
+    static Map<String, List<String>> asMap(HttpFields.Mutable fields)
+    {
+        return new HttpFieldsMap(fields);
     }
 
     /**

jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFieldsMap.java

@@ -0,0 +1,151 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.http;
+
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+import org.eclipse.jetty.util.StringUtil;
+
+class HttpFieldsMap extends AbstractMap<String, List<String>>
+{
+    private final HttpFields.Mutable httpFields;
+
+    public HttpFieldsMap(HttpFields.Mutable httpFields)
+    {
+        this.httpFields = httpFields;
+    }
+
+    @Override
+    public List<String> get(Object key)
+    {
+        if (key instanceof String s)
+            return httpFields.getValuesList(s);
+        return null;
+    }
+
+    @Override
+    public List<String> put(String key, List<String> value)
+    {
+        List<String> oldValue = get(key);
+        httpFields.put(key, value);
+        return oldValue;
+    }
+
+    @Override
+    public List<String> remove(Object key)
+    {
+        if (key instanceof String s)
+        {
+            List<String> oldValue = get(s);
+            httpFields.remove(s);
+            return oldValue;
+        }
+        return null;
+    }
+
+    @Override
+    public Set<Entry<String, List<String>>> entrySet()
+    {
+        return new AbstractSet<>()
+        {
+            @Override
+            public Iterator<Entry<String, List<String>>> iterator()
+            {
+                return new Iterator<>()
+                {
+                    private final Iterator<String> iterator = httpFields.getFieldNamesCollection().iterator();
+                    private String name = null;
+
+                    @Override
+                    public boolean hasNext()
+                    {
+                        return iterator.hasNext();
+                    }
+
+                    @Override
+                    public Entry<String, List<String>> next()
+                    {
+                        name = iterator.next();
+                        return new HttpFieldsEntry(name);
+                    }
+
+                    @Override
+                    public void remove()
+                    {
+                        if (name != null)
+                        {
+                            HttpFieldsMap.this.remove(name);
+                            name = null;
+                        }
+                    }
+                };
+            }
+
+            @Override
+            public int size()
+            {
+                return httpFields.getFieldNamesCollection().size();
+            }
+        };
+    }
+
+    private class HttpFieldsEntry implements Entry<String, List<String>>
+    {
+        private final String _name;
+
+        public HttpFieldsEntry(String name)
+        {
+            _name = name;
+        }
+
+        @Override
+        public String getKey()
+        {
+            return _name;
+        }
+
+        @Override
+        public List<String> getValue()
+        {
+            return HttpFieldsMap.this.get(_name);
+        }
+
+        @Override
+        public List<String> setValue(List<String> value)
+        {
+            return HttpFieldsMap.this.put(_name, value);
+        }
+
+        @Override
+        public boolean equals(Object o)
+        {
+            if (this == o)
+                return true;
+            if (o instanceof HttpFieldsEntry other)
+                return StringUtil.asciiEqualsIgnoreCase(_name, other.getKey());
+            return false;
+        }
+
+        @Override
+        public int hashCode()
+        {
+            return Objects.hash(StringUtil.asciiToLowerCase(_name));
+        }
+    }
+}

jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeRequest.java

@@ -79,7 +79,7 @@ public class DelegatedJettyClientUpgradeRequest implements UpgradeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeResponse.java

@@ -65,7 +65,7 @@ public class DelegatedJettyClientUpgradeResponse implements UpgradeResponse
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeRequestDelegate.java

@@ -16,7 +16,6 @@ package org.eclipse.jetty.websocket.server.internal;
 import java.net.HttpCookie;
 import java.net.URI;
 import java.security.Principal;
-import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -73,7 +72,7 @@ class UpgradeRequestDelegate implements UpgradeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(request.getHeaders()));
+        return HttpFields.asMap(request.getHeaders());
     }
 
     @Override

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/client/internal/JsrUpgradeListener.java

@@ -13,7 +13,6 @@
 
 package org.eclipse.jetty.ee10.websocket.jakarta.client.internal;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -39,16 +38,11 @@ public class JsrUpgradeListener implements UpgradeListener
         if (configurator == null)
             return;
 
-        // Give headers to configurator
-        HttpFields fields = request.getHeaders();
-        Map<String, List<String>> originalHeaders = HttpFields.asMap(fields);
-        configurator.beforeRequest(originalHeaders);
-
-        // Reset headers on HttpRequest per configurator
         request.headers(headers ->
         {
-            headers.clear();
-            originalHeaders.forEach(headers::put);
+            // Give headers to configurator
+            Map<String, List<String>> headersMap = HttpFields.asMap(headers);
+            configurator.beforeRequest(headersMap);
         });
     }
 
@@ -58,7 +52,7 @@ public class JsrUpgradeListener implements UpgradeListener
         if (configurator == null)
             return;
 
-        HandshakeResponse handshakeResponse = () -> Collections.unmodifiableMap(HttpFields.asMap(response.getHeaders()));
+        HandshakeResponse handshakeResponse = () -> HttpFields.asMap(response.getHeaders());
         configurator.afterResponse(handshakeResponse);
     }
 }

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JakartaWebSocketCreator.java

@@ -156,8 +156,6 @@ public class JakartaWebSocketCreator implements WebSocketCreator
 
         // [JSR] Step 5: Call modifyHandshake
         configurator.modifyHandshake(config, jsrHandshakeRequest, jsrHandshakeResponse);
-        // Set modified headers Map back into response properly
-        jsrHandshakeResponse.setHeaders(jsrHandshakeResponse.getHeaders());
 
         try
         {

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeRequest.java

@@ -15,7 +15,6 @@ package org.eclipse.jetty.ee10.websocket.jakarta.server.internal;
 
 import java.net.URI;
 import java.security.Principal;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -46,7 +45,7 @@ public class JsrHandshakeRequest implements HandshakeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeResponse.java

@@ -22,13 +22,11 @@ import org.eclipse.jetty.websocket.core.server.ServerUpgradeResponse;
 
 public class JsrHandshakeResponse implements HandshakeResponse
 {
-    private final ServerUpgradeResponse delegate;
     private final Map<String, List<String>> headers;
 
     public JsrHandshakeResponse(ServerUpgradeResponse resp)
     {
-        this.delegate = resp;
-        this.headers = HttpFields.asMap(delegate.getHeaders());
+        this.headers = HttpFields.asMap(resp.getHeaders());
     }
 
     @Override
@@ -36,9 +34,4 @@ public class JsrHandshakeResponse implements HandshakeResponse
     {
         return headers;
     }
-
-    public void setHeaders(Map<String, List<String>> headers)
-    {
-        headers.forEach((key, values) -> delegate.getHeaders().put(key, values));
-    }
 }

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeRequest.java

@@ -121,7 +121,7 @@ public class DelegatedServerUpgradeRequest implements JettyServerUpgradeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(upgradeRequest.getHeaders()));
+        return HttpFields.asMap(upgradeRequest.getHeaders());
     }
 
     @Override

jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee10/websocket/tests/UpgradeHeadersTest.java

@@ -0,0 +1,124 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee10.websocket.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jetty.client.Request;
+import org.eclipse.jetty.client.Response;
+import org.eclipse.jetty.ee10.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee10.websocket.server.JettyWebSocketCreator;
+import org.eclipse.jetty.ee10.websocket.server.config.JettyWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.eclipse.jetty.websocket.client.ClientUpgradeRequest;
+import org.eclipse.jetty.websocket.client.JettyUpgradeListener;
+import org.eclipse.jetty.websocket.client.WebSocketClient;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private WebSocketClient _client;
+    private ServerConnector _connector;
+
+    public void start(JettyWebSocketCreator creator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        JettyWebSocketServletContainerInitializer.configure(contextHandler, (servletContext, container) ->
+            container.addMapping("/", creator));
+        _server.setHandler(contextHandler);
+
+        _server.start();
+        _client = new WebSocketClient();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        start((request, response) ->
+        {
+            // Verify that existing headers can be accessed in a case-insensitive way.
+            if (request.getHeaders().get("cOnnEcTiOn") == null)
+                throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            if (response.getHeaders().get("sErVeR") == null)
+                throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+            // Verify custom header sent from client.
+            if (request.getHeaders().get("SeNtHeadEr") == null)
+                throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+            // Add custom response header.
+            response.getHeaders().put("myHeader", List.of("foobar"));
+            if (response.getHeaders().get("MyHeAdEr") == null)
+                throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+            return new EchoSocket();
+        });
+
+        EventSocket clientEndpoint = new EventSocket();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        ClientUpgradeRequest clientUpgradeRequest = new ClientUpgradeRequest();
+        clientUpgradeRequest.getHeaders().put("sentHeader", List.of("value123"));
+        if (clientUpgradeRequest.getHeaders().get("SenTHeaDer") == null)
+            throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+
+        JettyUpgradeListener upgradeListener = new JettyUpgradeListener()
+        {
+            @Override
+            public void onHandshakeRequest(Request request)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                if (request.getHeaders().get("SenTHeaDer") == null)
+                    throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+            }
+
+            @Override
+            public void onHandshakeResponse(Request request, Response response)
+            {
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (response.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        assertNotNull(_client.connect(clientEndpoint, uri, clientUpgradeRequest, upgradeListener).get(5, TimeUnit.SECONDS));
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        clientEndpoint.session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/client/internal/JsrUpgradeListener.java

@@ -13,7 +13,6 @@
 
 package org.eclipse.jetty.ee9.websocket.jakarta.client.internal;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 
@@ -39,16 +38,11 @@ public class JsrUpgradeListener implements UpgradeListener
         if (configurator == null)
             return;
 
-        // Give headers to configurator
-        HttpFields fields = request.getHeaders();
-        Map<String, List<String>> originalHeaders = HttpFields.asMap(fields);
-        configurator.beforeRequest(originalHeaders);
-
-        // Reset headers on HttpRequest per configurator
         request.headers(headers ->
         {
-            headers.clear();
-            originalHeaders.forEach(headers::put);
+            // Give headers to configurator
+            Map<String, List<String>> headersMap = HttpFields.asMap(headers);
+            configurator.beforeRequest(headersMap);
         });
     }
 
@@ -58,7 +52,7 @@ public class JsrUpgradeListener implements UpgradeListener
         if (configurator == null)
             return;
 
-        HandshakeResponse handshakeResponse = () -> Collections.unmodifiableMap(HttpFields.asMap(response.getHeaders()));
+        HandshakeResponse handshakeResponse = () -> HttpFields.asMap(response.getHeaders());
         configurator.afterResponse(handshakeResponse);
     }
 }

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JakartaWebSocketCreator.java

@@ -156,8 +156,6 @@ public class JakartaWebSocketCreator implements WebSocketCreator
 
         // [JSR] Step 5: Call modifyHandshake
         configurator.modifyHandshake(config, jsrHandshakeRequest, jsrHandshakeResponse);
-        // Set modified headers Map back into response properly
-        jsrHandshakeResponse.setHeaders(jsrHandshakeResponse.getHeaders());
 
         try
         {

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeRequest.java

@@ -15,7 +15,6 @@ package org.eclipse.jetty.ee9.websocket.jakarta.server.internal;
 
 import java.net.URI;
 import java.security.Principal;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -46,7 +45,7 @@ public class JsrHandshakeRequest implements HandshakeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeResponse.java

@@ -22,13 +22,11 @@ import org.eclipse.jetty.websocket.core.server.ServerUpgradeResponse;
 
 public class JsrHandshakeResponse implements HandshakeResponse
 {
-    private final ServerUpgradeResponse delegate;
     private final Map<String, List<String>> headers;
 
     public JsrHandshakeResponse(ServerUpgradeResponse resp)
     {
-        this.delegate = resp;
-        this.headers = HttpFields.asMap(delegate.getHeaders());
+        this.headers = HttpFields.asMap(resp.getHeaders());
     }
 
     @Override
@@ -36,9 +34,4 @@ public class JsrHandshakeResponse implements HandshakeResponse
     {
         return headers;
     }
-
-    public void setHeaders(Map<String, List<String>> headers)
-    {
-        headers.forEach((key, values) -> delegate.getHeaders().put(key, values));
-    }
 }

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeRequest.java

@@ -79,7 +79,7 @@ public class DelegatedJettyClientUpgradeRequest implements UpgradeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeResponse.java

@@ -65,7 +65,7 @@ public class DelegatedJettyClientUpgradeResponse implements UpgradeResponse
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(delegate.getHeaders()));
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServlet.java

@@ -314,7 +314,6 @@ public abstract class JettyWebSocketServlet extends HttpServlet
             try
             {
                 Object webSocket = creator.createWebSocket(request, response);
-                response.copyHeaders();
                 if (webSocket == null)
                     callback.succeeded();
                 return webSocket;

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeRequest.java

@@ -114,7 +114,7 @@ public class DelegatedServerUpgradeRequest implements JettyServerUpgradeRequest
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return Collections.unmodifiableMap(HttpFields.asMap(upgradeRequest.getHeaders()));
+        return HttpFields.asMap(upgradeRequest.getHeaders());
     }
 
     @Override

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeResponse.java

@@ -14,7 +14,6 @@
 package org.eclipse.jetty.ee9.websocket.server.internal;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -33,17 +32,10 @@ public class DelegatedServerUpgradeResponse implements JettyServerUpgradeRespons
 {
     private final ServerUpgradeResponse upgradeResponse;
     private final HttpServletResponse httpServletResponse;
-    private final boolean isUpgraded;
 
     public DelegatedServerUpgradeResponse(ServerUpgradeResponse response)
-    {
-        this(response, false);
-    }
-
-    public DelegatedServerUpgradeResponse(ServerUpgradeResponse response, boolean isUpgraded)
     {
         this.upgradeResponse = response;
-        this.isUpgraded = isUpgraded;
         this.httpServletResponse = (HttpServletResponse)response.getRequest()
             .getAttribute(WebSocketConstants.WEBSOCKET_WRAPPED_RESPONSE_ATTRIBUTE);
     }
@@ -56,11 +48,6 @@ public class DelegatedServerUpgradeResponse implements JettyServerUpgradeRespons
         upgradeResponse.getHeaders().add(name, value);
     }
 
-    public void copyHeaders()
-    {
-        headers.forEach((key, values) -> upgradeResponse.getHeaders().put(key, values));
-    }
-
     @Override
     public void setHeader(String name, String value)
     {
@@ -100,9 +87,6 @@ public class DelegatedServerUpgradeResponse implements JettyServerUpgradeRespons
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        if (isUpgraded)
-            return Collections.unmodifiableMap(HttpFields.asMap(upgradeResponse.getHeaders()));
-        else
         return HttpFields.asMap(upgradeResponse.getHeaders());
     }
 

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/JettyServerFrameHandlerFactory.java

@@ -41,7 +41,7 @@ public class JettyServerFrameHandlerFactory extends JettyWebSocketFrameHandlerFa
     {
         JettyWebSocketFrameHandler frameHandler = super.newJettyFrameHandler(websocketPojo);
         frameHandler.setUpgradeRequest(new DelegatedServerUpgradeRequest(upgradeRequest));
-        frameHandler.setUpgradeResponse(new DelegatedServerUpgradeResponse(upgradeResponse, true));
+        frameHandler.setUpgradeResponse(new DelegatedServerUpgradeResponse(upgradeResponse));
         return frameHandler;
     }
 }

jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee9/websocket/tests/UpgradeHeadersTest.java

@@ -0,0 +1,124 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee9.websocket.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jetty.client.Request;
+import org.eclipse.jetty.client.Response;
+import org.eclipse.jetty.ee9.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee9.websocket.client.ClientUpgradeRequest;
+import org.eclipse.jetty.ee9.websocket.client.JettyUpgradeListener;
+import org.eclipse.jetty.ee9.websocket.client.WebSocketClient;
+import org.eclipse.jetty.ee9.websocket.server.JettyWebSocketCreator;
+import org.eclipse.jetty.ee9.websocket.server.config.JettyWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private WebSocketClient _client;
+    private ServerConnector _connector;
+
+    public void start(JettyWebSocketCreator creator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        JettyWebSocketServletContainerInitializer.configure(contextHandler, (servletContext, container) ->
+            container.addMapping("/", creator));
+        _server.setHandler(contextHandler);
+
+        _server.start();
+        _client = new WebSocketClient();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        start((request, response) ->
+        {
+            // Verify that existing headers can be accessed in a case-insensitive way.
+            if (request.getHeaders().get("cOnnEcTiOn") == null)
+                throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            if (response.getHeaders().get("sErVeR") == null)
+                throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+            // Verify custom header sent from client.
+            if (request.getHeaders().get("SeNtHeadEr") == null)
+                throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+            // Add custom response header.
+            response.getHeaders().put("myHeader", List.of("foobar"));
+            if (response.getHeaders().get("MyHeAdEr") == null)
+                throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+            return new EchoSocket();
+        });
+
+        EventSocket clientEndpoint = new EventSocket();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        ClientUpgradeRequest clientUpgradeRequest = new ClientUpgradeRequest();
+        clientUpgradeRequest.getHeaders().put("sentHeader", List.of("value123"));
+        if (clientUpgradeRequest.getHeaders().get("SenTHeaDer") == null)
+            throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+
+        JettyUpgradeListener upgradeListener = new JettyUpgradeListener()
+        {
+            @Override
+            public void onHandshakeRequest(Request request)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                if (request.getHeaders().get("SenTHeaDer") == null)
+                    throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+            }
+
+            @Override
+            public void onHandshakeResponse(Request request, Response response)
+            {
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (response.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        assertNotNull(_client.connect(clientEndpoint, uri, clientUpgradeRequest, upgradeListener).get(5, TimeUnit.SECONDS));
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        clientEndpoint.session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}