8288109: HttpExchangeImpl.setAttribute does not allow null value after JDK-8266897

src/jdk.httpserver/share/classes/sun/net/httpserver/ExchangeImpl.java

@@ -377,7 +377,11 @@ public void setAttribute (String name, Object value) {
         if (attributes == null) {
             attributes = getHttpContext().getAttributes();
         }
-        attributes.put (name, value);
+        if (value != null) {
+            attributes.put (name, value);
+        } else {
+            attributes.remove (name);
+        }
     }
 
     public void setStreams (InputStream i, OutputStream o) {

test/jdk/com/sun/net/httpserver/ExchangeAttributeTest.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8288109
+ * @summary Tests for HttpExchange set/getAttribute
+ * @library /test/lib
+ * @run junit/othervm ExchangeAttributeTest
+ */
+
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import com.sun.net.httpserver.HttpServer;
+import jdk.test.lib.net.URIBuilder;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.logging.ConsoleHandler;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import static java.net.http.HttpClient.Builder.NO_PROXY;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ExchangeAttributeTest {
+
+    static final InetAddress LOOPBACK_ADDR = InetAddress.getLoopbackAddress();
+    static final boolean ENABLE_LOGGING = true;
+    static final Logger logger = Logger.getLogger("com.sun.net.httpserver");
+
+    @BeforeAll
+    public static void setup() {
+        if (ENABLE_LOGGING) {
+            ConsoleHandler ch = new ConsoleHandler();
+            logger.setLevel(Level.ALL);
+            ch.setLevel(Level.ALL);
+            logger.addHandler(ch);
+        }
+    }
+
+    @Test
+    public void testExchangeAttributes() throws Exception {
+        var handler = new AttribHandler();
+        var server = HttpServer.create(new InetSocketAddress(LOOPBACK_ADDR,0), 10);
+        server.createContext("/", handler);
+        server.start();
+        try {
+            var client = HttpClient.newBuilder().proxy(NO_PROXY).build();
+            var request = HttpRequest.newBuilder(uri(server, "")).build();
+            var response = client.send(request, HttpResponse.BodyHandlers.ofString());
+            assertEquals(200, response.statusCode());
+        } finally {
+            server.stop(0);
+        }
+    }
+
+    // --- infra ---
+
+    static URI uri(HttpServer server, String path) throws URISyntaxException {
+        return URIBuilder.newBuilder()
+                .scheme("http")
+                .loopback()
+                .port(server.getAddress().getPort())
+                .path(path)
+                .build();
+    }
+
+    /**
+     * A test handler that discards the request and sends a response
+     */
+    static class AttribHandler implements HttpHandler {
+        @java.lang.Override
+        public void handle(HttpExchange exchange) throws IOException {
+            try {
+                exchange.setAttribute("attr", "val");
+                assertEquals("val", exchange.getAttribute("attr"));
+                exchange.setAttribute("attr", null);
+                assertNull(exchange.getAttribute("attr"));
+                exchange.sendResponseHeaders(200, -1);
+            } catch (Throwable t) {
+                t.printStackTrace();
+                exchange.sendResponseHeaders(500, -1);
+            }
+        }
+    }
+}