Implement Eclipse Jetty core HTTP handler adapter

This provides an implementation of an HTTP Handler Adapter that is coded
directly to the Eclipse Jetty core API, bypassing any servlet
implementation.

This includes a Jetty implementation of the spring `WebSocketClient`
interface, `JettyWebSocketClient`, using an explicit dependency to the
jetty-websocket-api.

Closes gh-32097

Co-authored-by: Lachlan Roberts <lachlan@webtide.com>
Co-authored-by: Arjen Poutsma <arjen.poutsma@broadcom.com>

spring-core/src/test/java/org/springframework/core/io/buffer/JettyDataBufferTests.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2002-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.core.io.buffer;
+
+import java.nio.ByteBuffer;
+
+import org.eclipse.jetty.io.Content;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.BDDMockito.then;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+
+/**
+ * @author Arjen Poutsma
+ */
+public class JettyDataBufferTests {
+
+	private final JettyDataBufferFactory dataBufferFactory = new JettyDataBufferFactory();
+
+	@Test
+	void releaseRetainChunk() {
+		ByteBuffer buffer = ByteBuffer.allocate(3);
+		Content.Chunk mockChunk = mock();
+		given(mockChunk.getByteBuffer()).willReturn(buffer);
+		given(mockChunk.release()).willReturn(false, false, true);
+
+
+
+		JettyDataBuffer dataBuffer = this.dataBufferFactory.wrap(mockChunk);
+		dataBuffer.retain();
+		dataBuffer.retain();
+		assertThat(dataBuffer.release()).isFalse();
+		assertThat(dataBuffer.release()).isFalse();
+		assertThat(dataBuffer.release()).isTrue();
+
+		assertThatIllegalStateException().isThrownBy(dataBuffer::release);
+
+		then(mockChunk).should(times(3)).retain();
+		then(mockChunk).should(times(3)).release();
+	}
+}

spring-core/src/test/java/org/springframework/core/io/buffer/PooledDataBufferTests.java

@@ -69,6 +69,15 @@ class PooledDataBufferTests {
 		}
 	}
 
+	@Nested
+	class Jetty implements PooledDataBufferTestingTrait {
+
+		@Override
+		public DataBufferFactory createDataBufferFactory() {
+			return new JettyDataBufferFactory();
+		}
+	}
+
 
 	interface PooledDataBufferTestingTrait {
 
@@ -82,10 +91,14 @@ class PooledDataBufferTests {
 		default void retainAndRelease() {
 			PooledDataBuffer buffer = createDataBuffer(1);
 			buffer.write((byte) 'a');
+			assertThat(buffer.isAllocated()).isTrue();
 
 			buffer.retain();
+			assertThat(buffer.isAllocated()).isTrue();
 			assertThat(buffer.release()).isFalse();
+			assertThat(buffer.isAllocated()).isTrue();
 			assertThat(buffer.release()).isTrue();
+			assertThat(buffer.isAllocated()).isFalse();
 		}
 
 		@Test