Polishing external contribution

- Removed duplicate Client in types names.
- Removed buffering in favor of OutputStream to
  Flow.Publisher<ByteBuffer> bridge.
- Made request and types package private.
- Various other small improvements.

Closes gh-30478

spring-web/src/main/java/org/springframework/http/client/JdkClientClientHttpRequest.java

@@ -1,92 +0,0 @@
-/*
- * Copyright 2023-2023 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.http.client;
-
-import java.io.IOException;
-import java.io.InputStream;
-import java.net.URI;
-import java.net.http.HttpClient;
-import java.net.http.HttpRequest;
-import java.net.http.HttpResponse;
-import java.util.List;
-
-import org.springframework.http.HttpHeaders;
-import org.springframework.http.HttpMethod;
-
-/**
- * {@link ClientHttpRequest} implementation based on the Java {@code HttpClient}.
- *
- * @author Marten Deinum
- * @since 6.1
- */
-public class JdkClientClientHttpRequest extends AbstractBufferingClientHttpRequest {
-
-	/*
-	 * The JDK HttpRequest doesn't allow all headers to be set. The named headers are taken from the default
-	 * implementation for HttpRequest.
-	 */
-	private static final List<String> DISALLOWED_HEADERS =
-			List.of("connection", "content-length", "expect", "host", "upgrade");
-
-	private final HttpClient client;
-	private final URI uri;
-	private final HttpMethod method;
-	public JdkClientClientHttpRequest(HttpClient client, URI uri, HttpMethod method) {
-		this.client = client;
-		this.uri = uri;
-		this.method = method;
-	}
-
-	@Override
-	public HttpMethod getMethod() {
-		return this.method;
-	}
-
-	@Override
-	public URI getURI() {
-		return this.uri;
-	}
-
-	@Override
-	protected ClientHttpResponse executeInternal(HttpHeaders headers, byte[] content) throws IOException {
-
-		HttpRequest.Builder builder = HttpRequest.newBuilder(this.uri)
-				.method(getMethod().name(), HttpRequest.BodyPublishers.ofByteArray(content));
-
-		addHeaders(headers, builder);
-		HttpRequest request = builder.build();
-		HttpResponse<InputStream> response;
-		try {
-			response = this.client.send(request, HttpResponse.BodyHandlers.ofInputStream());
-		} catch (InterruptedException ex)
-		{
-			Thread.currentThread().interrupt();
-			throw new IllegalStateException("Request interupted.", ex);
-		}
-		return new JdkClientClientHttpResponse(response);
-	}
-
-	private static void addHeaders(HttpHeaders headers, HttpRequest.Builder builder) {
-		headers.forEach((headerName, headerValues) -> {
-			if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase())) {
-				for (String headerValue : headerValues) {
-					builder.header(headerName, headerValue);
-				}
-			}
-		});
-	}
-}

spring-web/src/main/java/org/springframework/http/client/JdkClientClientHttpRequestFactory.java

@@ -1,55 +0,0 @@
-/*
- * Copyright 2023-2023 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.http.client;
-
-import java.io.IOException;
-import java.net.URI;
-import java.net.http.HttpClient;
-
-import org.springframework.http.HttpMethod;
-
-
-/**
- * {@link ClientHttpRequestFactory} implementation that uses a
- * <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.net.http/java/net/http/HttpClient.html">HttpClient</a> to create requests.
- *
- * @author Marten Deinum
- * @since 6.1
- */
-public class JdkClientClientHttpRequestFactory implements ClientHttpRequestFactory {
-
-	private HttpClient client;
-
-	private final boolean defaultClient;
-
-
-	public JdkClientClientHttpRequestFactory() {
-		this.client = HttpClient.newHttpClient();
-		this.defaultClient = true;
-	}
-
-	public JdkClientClientHttpRequestFactory(HttpClient client) {
-		this.client = client;
-		this.defaultClient = false;
-	}
-
-	@Override
-	public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
-		return new JdkClientClientHttpRequest(this.client, uri, httpMethod);
-	}
-
-}

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java

@@ -0,0 +1,134 @@
+/*
+ * Copyright 2023-2023 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.http.client;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UncheckedIOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.ByteBuffer;
+import java.util.List;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Flow;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.lang.Nullable;
+import org.springframework.util.StreamUtils;
+
+/**
+ * {@link ClientHttpRequest} implementation based the Java {@link HttpClient}.
+ * Created via the {@link JdkClientHttpRequestFactory}.
+ *
+ * @author Marten Deinum
+ * @author Arjen Poutsma
+ * @since 6.1
+ */
+class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
+
+	/*
+	 * The JDK HttpRequest doesn't allow all headers to be set. The named headers are taken from the default
+	 * implementation for HttpRequest.
+	 */
+	private static final List<String> DISALLOWED_HEADERS =
+			List.of("connection", "content-length", "expect", "host", "upgrade");
+
+	private final HttpClient httpClient;
+
+	private final HttpMethod method;
+
+	private final URI uri;
+
+	private final Executor executor;
+
+
+	public JdkClientHttpRequest(HttpClient httpClient, URI uri, HttpMethod method, Executor executor) {
+		this.httpClient = httpClient;
+		this.uri = uri;
+		this.method = method;
+		this.executor = executor;
+	}
+
+	@Override
+	public HttpMethod getMethod() {
+		return this.method;
+	}
+
+	@Override
+	public URI getURI() {
+		return this.uri;
+	}
+
+
+	@Override
+	protected ClientHttpResponse executeInternal(HttpHeaders headers, @Nullable Body body) throws IOException {
+		try {
+			HttpRequest request = buildRequest(headers, body);
+			HttpResponse<InputStream> response = this.httpClient.send(request, HttpResponse.BodyHandlers.ofInputStream());
+			return new JdkClientHttpResponse(response);
+		}
+		catch (UncheckedIOException ex) {
+			throw ex.getCause();
+		}
+		catch (InterruptedException ex) {
+			Thread.currentThread().interrupt();
+			throw new IOException("Could not send request: " + ex.getMessage(), ex);
+		}
+	}
+
+
+	private HttpRequest buildRequest(HttpHeaders headers, @Nullable Body body) {
+		HttpRequest.Builder builder = HttpRequest.newBuilder()
+				.uri(this.uri);
+
+		headers.forEach((headerName, headerValues) -> {
+			if (!headerName.equalsIgnoreCase(HttpHeaders.CONTENT_LENGTH)) {
+				if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase())) {
+					for (String headerValue : headerValues) {
+						builder.header(headerName, headerValue);
+					}
+				}
+			}
+		});
+
+		builder.method(this.method.name(), bodyPublisher(headers, body));
+		return builder.build();
+	}
+
+	private HttpRequest.BodyPublisher bodyPublisher(HttpHeaders headers, @Nullable Body body) {
+		if (body != null) {
+			Flow.Publisher<ByteBuffer> outputStreamPublisher = OutputStreamPublisher.create(
+					outputStream -> body.writeTo(StreamUtils.nonClosing(outputStream)),
+					this.executor);
+
+			long contentLength = headers.getContentLength();
+			if (contentLength != -1) {
+				return HttpRequest.BodyPublishers.fromPublisher(outputStreamPublisher, contentLength);
+			}
+			else {
+				return HttpRequest.BodyPublishers.fromPublisher(outputStreamPublisher);
+			}
+		}
+		else {
+			return HttpRequest.BodyPublishers.noBody();
+		}
+	}
+
+}

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequestFactory.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2023-2023 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.http.client;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.util.concurrent.Executor;
+
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
+import org.springframework.http.HttpMethod;
+import org.springframework.util.Assert;
+
+
+/**
+ * {@link ClientHttpRequestFactory} implementation based on the Java
+ * {@link HttpClient}.
+ *
+ * @author Marten Deinum
+ * @author Arjen Poutsma
+ * @since 6.1
+ */
+public class JdkClientHttpRequestFactory implements ClientHttpRequestFactory {
+
+	private final HttpClient httpClient;
+
+	private final Executor executor;
+
+
+	/**
+	 * Create a new instance of the {@code JdkClientHttpRequestFactory}
+	 * with a default {@link HttpClient}.
+	 */
+	public JdkClientHttpRequestFactory() {
+		this(HttpClient.newHttpClient());
+	}
+
+	/**
+	 * Create a new instance of the {@code JdkClientHttpRequestFactory} based on
+	 * the given {@link HttpClient}.
+	 * @param httpClient the client to base on
+	 */
+	public JdkClientHttpRequestFactory(HttpClient httpClient) {
+		Assert.notNull(httpClient, "HttpClient is required");
+		this.httpClient = httpClient;
+		this.executor = httpClient.executor().orElseGet(SimpleAsyncTaskExecutor::new);
+	}
+
+	/**
+	 * Create a new instance of the {@code JdkClientHttpRequestFactory} based on
+	 * the given {@link HttpClient} and {@link Executor}.
+	 * @param httpClient the client to base on
+	 * @param executor the executor to use for blocking write operations
+	 */
+	public JdkClientHttpRequestFactory(HttpClient httpClient, Executor executor) {
+		Assert.notNull(httpClient, "HttpClient is required");
+		Assert.notNull(executor, "Executor must not be null");
+		this.httpClient = httpClient;
+		this.executor = executor;
+	}
+
+
+	@Override
+	public ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod) throws IOException {
+		return new JdkClientHttpRequest(this.httpClient, uri, httpMethod, this.executor);
+	}
+
+}

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpResponse.java

@@ -18,81 +18,89 @@ package org.springframework.http.client;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.http.HttpClient;
 import java.net.http.HttpResponse;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
 
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.HttpStatusCode;
-import org.springframework.lang.Nullable;
+import org.springframework.util.CollectionUtils;
+import org.springframework.util.LinkedCaseInsensitiveMap;
+import org.springframework.util.MultiValueMap;
 import org.springframework.util.StreamUtils;
 
 /**
- * {@link ClientHttpResponse} implementation based on the Java {@code HttpClient}.
+ * {@link ClientHttpResponse} implementation based on the Java {@link HttpClient}.
  *
  * @author Marten Deinum
+ * @author Arjen Poutsma
  * @since 6.1
  */
-public class JdkClientClientHttpResponse implements ClientHttpResponse {
+class JdkClientHttpResponse implements ClientHttpResponse {
 
 	private final HttpResponse<InputStream> response;
-	@Nullable
-	private volatile HttpHeaders headers;
 
-	public JdkClientClientHttpResponse(HttpResponse<InputStream> response) {
+	private final HttpHeaders headers;
+
+	private final InputStream body;
+
+
+	public JdkClientHttpResponse(HttpResponse<InputStream> response) {
 		this.response = response;
+		this.headers = adaptHeaders(response);
+		InputStream inputStream = response.body();
+		this.body = (inputStream != null) ? inputStream : InputStream.nullInputStream();
 	}
 
-	@Override
+	private static HttpHeaders adaptHeaders(HttpResponse<?> response) {
-	public HttpStatusCode getStatusCode() throws IOException {
+		Map<String, List<String>> rawHeaders = response.headers().map();
-		return HttpStatusCode.valueOf(this.response.statusCode());
+		Map<String, List<String>> map = new LinkedCaseInsensitiveMap<>(rawHeaders.size(), Locale.ENGLISH);
+		MultiValueMap<String, String> multiValueMap = CollectionUtils.toMultiValueMap(map);
+		multiValueMap.putAll(rawHeaders);
+		return HttpHeaders.readOnlyHttpHeaders(multiValueMap);
 	}
 
+
 	@Override
-	@Deprecated
+	public HttpStatusCode getStatusCode() {
-	public int getRawStatusCode() {
+		return HttpStatusCode.valueOf(this.response.statusCode());
-		return this.response.statusCode();
 	}
 
 	@Override
 	public String getStatusText() {
-		HttpStatus status = HttpStatus.resolve(this.response.statusCode());
+		// HttpResponse does not expose status text
-		return (status != null) ? status.getReasonPhrase() : "";
+		if (getStatusCode() instanceof HttpStatus status) {
+			return status.getReasonPhrase();
+		}
+		else {
+			return "";
+		}
 	}
 
 	@Override
-	public InputStream getBody() throws IOException {
+	public HttpHeaders getHeaders() {
-		InputStream body = this.response.body();
+		return this.headers;
-		return (body != null ? body : InputStream.nullInputStream());
 	}
 
 	@Override
-	public HttpHeaders getHeaders() {
+	public InputStream getBody() throws IOException {
-		HttpHeaders headers = this.headers;
+		return this.body;
-		if (headers == null) {
-			headers = new HttpHeaders();
-			for (String headerName : this.response.headers().map().keySet()) {
-				for (String headerValue : this.response.headers().allValues(headerName)) {
-					headers.add(headerName, headerValue);
-				}
-			}
-			this.headers = headers;
-		}
-		return headers;
 	}
 
 	@Override
 	public void close() {
-		InputStream body = this.response.body();
 		try {
 			try {
-				StreamUtils.drain(body);
+				StreamUtils.drain(this.body);
 			}
 			finally {
-				body.close();
+				this.body.close();
 			}
 		}
-		catch (IOException ex) {
+		catch (IOException ignored) {
-			// Ignore exception on close...
 		}
 	}
 }

spring-web/src/main/java/org/springframework/http/client/OutputStreamPublisher.java

@@ -0,0 +1,400 @@
+/*
+ * Copyright 2002-2023 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.http.client;
+
+import java.io.BufferedOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.util.Objects;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Flow;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.LockSupport;
+
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Bridges between {@link OutputStream} and
+ * {@link Flow.Publisher Flow.Publisher<ByteBuffer>}.
+ *
+ * @author Oleh Dokuka
+ * @author Arjen Poutsma
+ * @since 6.1
+ * @see #create(OutputStreamHandler, Executor)
+ */
+final class OutputStreamPublisher implements Flow.Publisher<ByteBuffer> {
+
+	private final OutputStreamHandler outputStreamHandler;
+
+	private final Executor executor;
+
+
+	private OutputStreamPublisher(OutputStreamHandler outputStreamHandler, Executor executor) {
+		this.outputStreamHandler = outputStreamHandler;
+		this.executor = executor;
+	}
+
+
+	/**
+	 * Creates a new {@code Publisher<ByteBuffer>} based on bytes written to a
+	 * {@code OutputStream}.
+	 * <ul>
+	 * <li>The parameter {@code outputStreamHandler} is invoked once per
+	 * subscription of the returned {@code Publisher}, when the first
+	 * {@code ByteBuffer} is
+	 * {@linkplain Flow.Subscription#request(long) requested}.</li>
+	 * <li>Each {@link OutputStream#write(byte[], int, int) OutputStream.write()}
+	 * invocation that {@code outputStreamHandler} makes will result in a
+	 * {@linkplain Flow.Subscriber#onNext(Object) published} {@code ByteBuffer}
+	 * if there is {@linkplain Flow.Subscription#request(long) demand}.</li>
+	 * <li>If there is <em>no demand</em>, {@code OutputStream.write()} will block
+	 * until there is.</li>
+	 * <li>If the subscription is {@linkplain Flow.Subscription#cancel() cancelled},
+	 * {@code OutputStream.write()} will throw a {@code IOException}.</li>
+	 * <li>{@linkplain OutputStream#close() Closing} the {@code OutputStream}
+	 * will result in a {@linkplain Flow.Subscriber#onComplete() complete} signal.</li>
+	 * <li>Any {@code IOException}s thrown from {@code outputStreamHandler} will
+	 * be dispatched to the {@linkplain Flow.Subscriber#onError(Throwable) Subscriber}.
+	 * </ul>
+	 * @param outputStreamHandler invoked when the first buffer is requested
+	 * @param executor used to invoke the {@code outputStreamHandler}
+	 * @return a {@code Publisher<ByteBuffer>} based on bytes written by
+	 * {@code outputStreamHandler}
+	 */
+	public static Flow.Publisher<ByteBuffer> create(OutputStreamHandler outputStreamHandler, Executor executor) {
+		Assert.notNull(outputStreamHandler, "OutputStreamHandler must not be null");
+		Assert.notNull(executor, "Executor must not be null");
+
+		return new OutputStreamPublisher(outputStreamHandler, executor);
+	}
+
+
+	@Override
+	public void subscribe(Flow.Subscriber<? super ByteBuffer> subscriber) {
+		Objects.requireNonNull(subscriber, "Subscriber must not be null");
+
+		OutputStreamSubscription subscription = new OutputStreamSubscription(subscriber, this.outputStreamHandler);
+		subscriber.onSubscribe(subscription);
+		this.executor.execute(subscription::invokeHandler);
+	}
+
+
+	/**
+	 * Defines the contract for handling the {@code OutputStream} provided by
+	 * the {@code OutputStreamPublisher}.
+	 */
+	@FunctionalInterface
+	public interface OutputStreamHandler {
+
+		/**
+		 * Use the given stream for writing.
+		 * <ul>
+		 * <li>If the linked subscription has
+		 * {@linkplain Flow.Subscription#request(long) demand}, any
+		 * {@linkplain OutputStream#write(byte[], int, int) written} bytes
+		 * will be {@linkplain Flow.Subscriber#onNext(Object) published} to the
+		 * {@link Flow.Subscriber Subscriber}.</li>
+		 * <li>If there is no demand, any
+		 * {@link OutputStream#write(byte[], int, int) write()} invocations will
+		 * block until there is demand.</li>
+		 * <li>If the linked subscription is
+		 * {@linkplain Flow.Subscription#cancel() cancelled},
+		 * {@link OutputStream#write(byte[], int, int) write()} invocations will
+		 * result in a {@code IOException}.</li>
+		 * </ul>
+		 * @param outputStream the stream to write to
+		 * @throws IOException any thrown I/O errors will be dispatched to the
+		 * {@linkplain Flow.Subscriber#onError(Throwable) Subscriber}
+		 */
+		void handle(OutputStream outputStream) throws IOException;
+
+	}
+
+
+	private static final class OutputStreamSubscription extends OutputStream implements Flow.Subscription {
+
+		static final Object READY = new Object();
+
+		private final Flow.Subscriber<? super ByteBuffer> actual;
+
+		private final OutputStreamHandler outputStreamHandler;
+
+		private final AtomicLong requested = new AtomicLong();
+
+		private final AtomicReference<Object> parkedThreadAtomic = new AtomicReference<>();
+
+		@Nullable
+		private volatile Throwable error;
+
+		private long produced;
+
+
+		public OutputStreamSubscription(Flow.Subscriber<? super ByteBuffer> actual,
+										OutputStreamHandler outputStreamHandler) {
+			this.actual = actual;
+			this.outputStreamHandler = outputStreamHandler;
+		}
+
+		@Override
+		public void write(int b) throws IOException {
+			checkDemandAndAwaitIfNeeded();
+
+			ByteBuffer byteBuffer = ByteBuffer.allocate(1);
+			byteBuffer.put((byte) b);
+			byteBuffer.flip();
+
+			this.actual.onNext(byteBuffer);
+
+			this.produced++;
+		}
+
+		@Override
+		public void write(byte[] b) throws IOException {
+			write(b, 0, b.length);
+		}
+
+		@Override
+		public void write(byte[] b, int off, int len) throws IOException {
+			checkDemandAndAwaitIfNeeded();
+
+			ByteBuffer byteBuffer = ByteBuffer.allocate(len);
+			byteBuffer.put(b, off, len);
+			byteBuffer.flip();
+
+			this.actual.onNext(byteBuffer);
+
+			this.produced++;
+		}
+
+		private void checkDemandAndAwaitIfNeeded() throws IOException {
+			long r = this.requested.get();
+
+			if (isTerminated(r) || isCancelled(r)) {
+				throw new IOException("Subscription has been terminated");
+			}
+
+			long p = this.produced;
+			if (p == r) {
+				if (p > 0) {
+					r = tryProduce(p);
+					this.produced = 0;
+				}
+
+				while (true) {
+					if (isTerminated(r) || isCancelled(r)) {
+						throw new IOException("Subscription has been terminated");
+					}
+
+					if (r != 0) {
+						return;
+					}
+
+					await();
+
+					r = this.requested.get();
+				}
+			}
+		}
+
+		private void invokeHandler() {
+			// assume sync write within try-with-resource block
+
+			// use BufferedOutputStream, so that written bytes are buffered
+			// before publishing as byte buffer
+			try (OutputStream outputStream = new BufferedOutputStream(this)) {
+				this.outputStreamHandler.handle(outputStream);
+			}
+			catch (IOException ex) {
+				long previousState = tryTerminate();
+				if (isCancelled(previousState)) {
+					return;
+				}
+
+				if (isTerminated(previousState)) {
+					// failure due to illegal requestN
+					this.actual.onError(this.error);
+					return;
+				}
+
+				this.actual.onError(ex);
+				return;
+			}
+
+			long previousState = tryTerminate();
+			if (isCancelled(previousState)) {
+				return;
+			}
+
+			if (isTerminated(previousState)) {
+				// failure due to illegal requestN
+				this.actual.onError(this.error);
+				return;
+			}
+
+			this.actual.onComplete();
+		}
+
+
+		@Override
+		public void request(long n) {
+			if (n <= 0) {
+				this.error = new IllegalArgumentException("request should be a positive number");
+				long previousState = tryTerminate();
+
+				if (isTerminated(previousState) || isCancelled(previousState)) {
+					return;
+				}
+
+				if (previousState > 0) {
+					// error should eventually be observed and propagated
+					return;
+				}
+
+				// resume parked thread, so it can observe error and propagate it
+				resume();
+				return;
+			}
+
+			if (addCap(n) == 0) {
+				// resume parked thread so it can continue the work
+				resume();
+			}
+		}
+
+		@Override
+		public void cancel() {
+			long previousState = tryCancel();
+			if (isCancelled(previousState) || previousState > 0) {
+				return;
+			}
+
+			// resume parked thread, so it can be unblocked and close all the resources
+			resume();
+		}
+
+		private void await() {
+			Thread toUnpark = Thread.currentThread();
+
+			while (true) {
+				Object current = this.parkedThreadAtomic.get();
+				if (current == READY) {
+					break;
+				}
+
+				if (current != null && current != toUnpark) {
+					throw new IllegalStateException("Only one (Virtual)Thread can await!");
+				}
+
+				if (this.parkedThreadAtomic.compareAndSet(null, toUnpark)) {
+					LockSupport.park();
+					// we don't just break here because park() can wake up spuriously
+					// if we got a proper resume, get() == READY and the loop will quit above
+				}
+			}
+			// clear the resume indicator so that the next await call will park without a resume()
+			this.parkedThreadAtomic.lazySet(null);
+		}
+
+		private void resume() {
+			if (this.parkedThreadAtomic.get() != READY) {
+				Object old = this.parkedThreadAtomic.getAndSet(READY);
+				if (old != READY) {
+					LockSupport.unpark((Thread)old);
+				}
+			}
+		}
+
+		private long tryCancel() {
+			while (true) {
+				long r = this.requested.get();
+
+				if (isCancelled(r)) {
+					return r;
+				}
+
+				if (this.requested.compareAndSet(r, Long.MIN_VALUE)) {
+					return r;
+				}
+			}
+		}
+
+		private long tryTerminate() {
+			while (true) {
+				long r = this.requested.get();
+
+				if (isCancelled(r) || isTerminated(r)) {
+					return r;
+				}
+
+				if (this.requested.compareAndSet(r, Long.MIN_VALUE | Long.MAX_VALUE)) {
+					return r;
+				}
+			}
+		}
+
+		private long tryProduce(long n) {
+			while (true) {
+				long current = this.requested.get();
+				if (isTerminated(current) || isCancelled(current)) {
+					return current;
+				}
+				if (current == Long.MAX_VALUE) {
+					return Long.MAX_VALUE;
+				}
+				long update = current - n;
+				if (update < 0L) {
+					update = 0L;
+				}
+				if (this.requested.compareAndSet(current, update)) {
+					return update;
+				}
+			}
+		}
+
+		private long addCap(long n) {
+			while (true) {
+				long r = this.requested.get();
+				if (isTerminated(r) || isCancelled(r) || r == Long.MAX_VALUE) {
+					return r;
+				}
+				long u = addCap(r, n);
+				if (this.requested.compareAndSet(r, u)) {
+					return r;
+				}
+			}
+		}
+
+		private static boolean isTerminated(long state) {
+			return state == (Long.MIN_VALUE | Long.MAX_VALUE);
+		}
+
+		private static boolean isCancelled(long state) {
+			return state == Long.MIN_VALUE;
+		}
+
+		private static long addCap(long a, long b) {
+			long res = a + b;
+			if (res < 0L) {
+				return Long.MAX_VALUE;
+			}
+			return res;
+		}
+	}
+}

spring-web/src/test/java/org/springframework/http/client/JdkClientHttpRequestFactoryTests.java

@@ -23,11 +23,11 @@ import org.springframework.http.HttpMethod;
 /**
  * @author Marten Deinum
  */
-public class JdkClientClientHttpRequestFactoryTests extends AbstractHttpRequestFactoryTests {
+public class JdkClientHttpRequestFactoryTests extends AbstractHttpRequestFactoryTests {
 
 	@Override
 	protected ClientHttpRequestFactory createRequestFactory() {
-		return new JdkClientClientHttpRequestFactory();
+		return new JdkClientHttpRequestFactory();
 	}
 
 	@Override

spring-web/src/test/java/org/springframework/http/client/OutputStreamPublisherTests.java

@@ -0,0 +1,182 @@
+/*
+ * Copyright 2002-2023 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.http.client;
+
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Flow;
+
+import org.junit.jupiter.api.Test;
+import org.reactivestreams.FlowAdapters;
+import reactor.core.publisher.Flux;
+import reactor.test.StepVerifier;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIOException;
+
+/**
+ * @author Arjen Poutsma
+ * @author Oleh Dokuka
+ */
+class OutputStreamPublisherTests {
+
+	private final Executor executor = Executors.newSingleThreadExecutor();
+
+	@Test
+	void basic() {
+		Flow.Publisher<ByteBuffer> flowPublisher = OutputStreamPublisher.create(outputStream -> {
+			try (Writer writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8)) {
+				writer.write("foo");
+				writer.write("bar");
+				writer.write("baz");
+			}
+		}, this.executor);
+		Flux<String> flux = toString(flowPublisher);
+
+		StepVerifier.create(flux)
+				.assertNext(s -> assertThat(s).isEqualTo("foobarbaz"))
+				.verifyComplete();
+	}
+
+	@Test
+	void flush() {
+		Flow.Publisher<ByteBuffer> flowPublisher = OutputStreamPublisher.create(outputStream -> {
+			try (Writer writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8)) {
+				writer.write("foo");
+				writer.flush();
+				writer.write("bar");
+				writer.flush();
+				writer.write("baz");
+				writer.flush();
+			}
+		}, this.executor);
+		Flux<String> flux = toString(flowPublisher);
+
+		StepVerifier.create(flux)
+				.assertNext(s -> assertThat(s).isEqualTo("foo"))
+				.assertNext(s -> assertThat(s).isEqualTo("bar"))
+				.assertNext(s -> assertThat(s).isEqualTo("baz"))
+				.verifyComplete();
+	}
+
+	@Test
+	void cancel() throws InterruptedException {
+		CountDownLatch latch = new CountDownLatch(1);
+
+		Flow.Publisher<ByteBuffer> flowPublisher = OutputStreamPublisher.create(outputStream -> {
+			try (Writer writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8)) {
+				assertThatIOException()
+						.isThrownBy(() -> {
+							writer.write("foo");
+							writer.flush();
+							writer.write("bar");
+							writer.flush();
+						})
+						.withMessage("Subscription has been terminated");
+				latch.countDown();
+			}
+		}, this.executor);
+		Flux<String> flux = toString(flowPublisher);
+
+		StepVerifier.create(flux, 1)
+				.assertNext(s -> assertThat(s).isEqualTo("foo"))
+				.thenCancel()
+				.verify();
+
+		latch.await();
+	}
+
+	@Test
+	void closed() throws InterruptedException {
+		CountDownLatch latch = new CountDownLatch(1);
+
+		Flow.Publisher<ByteBuffer> flowPublisher = OutputStreamPublisher.create(outputStream -> {
+			Writer writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8);
+			writer.write("foo");
+			writer.close();
+			assertThatIOException().isThrownBy(() -> writer.write("bar"))
+					.withMessage("Stream closed");
+			latch.countDown();
+		}, this.executor);
+		Flux<String> flux = toString(flowPublisher);
+
+		StepVerifier.create(flux)
+				.assertNext(s -> assertThat(s).isEqualTo("foo"))
+				.verifyComplete();
+
+		latch.await();
+	}
+
+	@Test
+	void negativeRequestN() throws InterruptedException {
+		CountDownLatch latch = new CountDownLatch(1);
+
+		Flow.Publisher<ByteBuffer> flowPublisher = OutputStreamPublisher.create(outputStream -> {
+			try(Writer writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8)) {
+				writer.write("foo");
+				writer.flush();
+				writer.write("foo");
+				writer.flush();
+		}
+			finally {
+				latch.countDown();
+			}
+		}, this.executor);
+		Flow.Subscription[] subscriptions = new Flow.Subscription[1];
+		Flux<String> flux = toString(a-> flowPublisher.subscribe(new Flow.Subscriber<>() {
+			@Override
+			public void onSubscribe(Flow.Subscription subscription) {
+				subscriptions[0] = subscription;
+				a.onSubscribe(subscription);
+			}
+
+			@Override
+			public void onNext(ByteBuffer item) {
+				a.onNext(item);
+			}
+
+			@Override
+			public void onError(Throwable throwable) {
+				a.onError(throwable);
+			}
+
+			@Override
+			public void onComplete() {
+				a.onComplete();
+			}
+		}));
+
+		StepVerifier.create(flux, 1)
+				.assertNext(s -> assertThat(s).isEqualTo("foo"))
+				.then(() -> subscriptions[0].request(-1))
+				.expectErrorMessage("request should be a positive number")
+				.verify();
+
+		latch.await();
+	}
+
+	private static Flux<String> toString(Flow.Publisher<ByteBuffer> flowPublisher) {
+		return Flux.from(FlowAdapters.toPublisher(flowPublisher))
+				.map(bb -> StandardCharsets.UTF_8.decode(bb).toString());
+	}
+
+}

spring-web/src/test/java/org/springframework/web/client/RestTemplateIntegrationTests.java

@@ -48,6 +48,7 @@ import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
+import org.springframework.http.client.JdkClientHttpRequestFactory;
 import org.springframework.http.client.JettyClientHttpRequestFactory;
 import org.springframework.http.client.OkHttp3ClientHttpRequestFactory;
 import org.springframework.http.client.SimpleClientHttpRequestFactory;
@@ -91,10 +92,11 @@ class RestTemplateIntegrationTests extends AbstractMockWebServerTests {
 
 	static Stream<Named<ClientHttpRequestFactory>> clientHttpRequestFactories() {
 		return Stream.of(
-			named("JDK", new SimpleClientHttpRequestFactory()),
+			named("JDK HttpURLConnection", new SimpleClientHttpRequestFactory()),
 			named("HttpComponents", new HttpComponentsClientHttpRequestFactory()),
 			named("OkHttp", new OkHttp3ClientHttpRequestFactory()),
-			named("Jetty", new JettyClientHttpRequestFactory())
+			named("Jetty", new JettyClientHttpRequestFactory()),
+			named("JDK HttpClient", new JdkClientHttpRequestFactory())
 		);
 	}
 
@@ -225,7 +227,7 @@ class RestTemplateIntegrationTests extends AbstractMockWebServerTests {
 	@ParameterizedRestTemplateTest
 	void patchForObject(ClientHttpRequestFactory clientHttpRequestFactory) throws Exception {
 		assumeFalse(clientHttpRequestFactory instanceof SimpleClientHttpRequestFactory,
-				"JDK client does not support the PATCH method");
+				"HttpURLConnection does not support the PATCH method");
 
 		setUpClient(clientHttpRequestFactory);
 
@@ -254,6 +256,7 @@ class RestTemplateIntegrationTests extends AbstractMockWebServerTests {
 				template.execute(baseUrl + "/status/badrequest", HttpMethod.GET, null, null))
 			.satisfies(ex -> {
 				assertThat(ex.getStatusCode()).isEqualTo(HttpStatus.BAD_REQUEST);
+				assumeFalse(clientHttpRequestFactory instanceof JdkClientHttpRequestFactory, "JDK HttpClient does not expose status text");
 				assertThat(ex.getMessage()).isEqualTo("400 Client Error: [no body]");
 			});
 	}