Refactor ResponseBodySubscriber to Processor

This commit changes the AbstractResponseBodySubscriber into a
AbstractResponseBodyProcessor<DataBuffer, Void>, so that the processor
can be used as a return value for writeWith.

Additional, this commit no longer closes the response after an eror
occurred.

This fixes #59.

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/AbstractRequestBodyPublisher.java

@@ -52,6 +52,8 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 
 	private Subscriber<? super DataBuffer> subscriber;
 
+	private volatile boolean dataAvailable;
+
 	@Override
 	public void subscribe(Subscriber<? super DataBuffer> subscriber) {
 		if (this.logger.isTraceEnabled()) {
@@ -199,7 +201,9 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 			void subscribe(AbstractRequestBodyPublisher publisher,
 					Subscriber<? super DataBuffer> subscriber) {
 				Objects.requireNonNull(subscriber);
-				if (publisher.changeState(this, DATA_UNAVAILABLE)) {
+				State newState =
+						publisher.dataAvailable ? DATA_AVAILABLE : DATA_UNAVAILABLE;
+				if (publisher.changeState(this, newState)) {
 					Subscription subscription = new RequestBodySubscription(
 									publisher);
 					publisher.subscriber = subscriber;
@@ -209,6 +213,11 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 					throw new IllegalStateException(toString());
 				}
 			}
+
+			@Override
+			void onDataAvailable(AbstractRequestBodyPublisher publisher) {
+				publisher.dataAvailable = true;
+			}
 		},
 		/**
 		 * State that gets entered when there is no data to be read. Responds to {@link
@@ -252,20 +261,11 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 				}
 			}
 
-			@Override
-			void onDataAvailable(AbstractRequestBodyPublisher publisher) {
-				// ignore
-			}
 		},
 		/**
 		 * The terminal completed state. Does not respond to any events.
 		 */
 		COMPLETED {
-			@Override
-			void subscribe(AbstractRequestBodyPublisher publisher,
-					Subscriber<? super DataBuffer> subscriber) {
-				// ignore
-			}
 
 			@Override
 			void request(AbstractRequestBodyPublisher publisher, long n) {
@@ -277,11 +277,6 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 				// ignore
 			}
 
-			@Override
-			void onDataAvailable(AbstractRequestBodyPublisher publisher) {
-				// ignore
-			}
-
 			@Override
 			void onAllDataRead(AbstractRequestBodyPublisher publisher) {
 				// ignore
@@ -309,7 +304,7 @@ abstract class AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
 		}
 
 		void onDataAvailable(AbstractRequestBodyPublisher publisher) {
-			throw new IllegalStateException(toString());
+			// ignore
 		}
 
 		void onAllDataRead(AbstractRequestBodyPublisher publisher) {

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/AbstractResponseBodyProcessor.java

@@ -0,0 +1,486 @@
+/*
+ * Copyright 2002-2016 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
+ *
+ *      http://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.server.reactive;
+
+import java.io.IOException;
+import java.nio.channels.Channel;
+import java.util.Objects;
+import java.util.concurrent.atomic.AtomicReference;
+import javax.servlet.WriteListener;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.reactivestreams.Processor;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+import reactor.core.util.BackpressureUtils;
+
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.FlushingDataBuffer;
+import org.springframework.core.io.buffer.support.DataBufferUtils;
+import org.springframework.util.Assert;
+
+/**
+ * Abstract base class for {@code Subscriber} implementations that bridge between
+ * event-listener APIs and Reactive Streams. Specifically, base class for the Servlet 3.1
+ * and Undertow support.
+ * @author Arjen Poutsma
+ * @see ServletServerHttpRequest
+ * @see UndertowHttpHandlerAdapter
+ */
+abstract class AbstractResponseBodyProcessor implements Processor<DataBuffer, Void> {
+
+	protected final Log logger = LogFactory.getLog(getClass());
+
+	private final AtomicReference<SubscriberState> subscriberState =
+			new AtomicReference<>(SubscriberState.UNSUBSCRIBED);
+
+	private final AtomicReference<PublisherState> publisherState =
+			new AtomicReference<>(PublisherState.UNSUBSCRIBED);
+
+	private volatile DataBuffer currentBuffer;
+
+	private volatile boolean subscriberCompleted;
+
+	private volatile boolean publisherCompleted;
+
+	private volatile Throwable publisherError;
+
+	private Subscription subscription;
+
+	private Subscriber<? super Void> subscriber;
+
+	// Subscriber
+
+	@Override
+	public final void onSubscribe(Subscription subscription) {
+		if (logger.isTraceEnabled()) {
+			logger.trace("SUB " + this.subscriberState + " onSubscribe: " + subscription);
+		}
+		this.subscriberState.get().onSubscribe(this, subscription);
+	}
+
+	@Override
+	public final void onNext(DataBuffer dataBuffer) {
+		if (logger.isTraceEnabled()) {
+			logger.trace("SUB " + this.subscriberState + " onNext: " + dataBuffer);
+		}
+		this.subscriberState.get().onNext(this, dataBuffer);
+	}
+
+	@Override
+	public final void onError(Throwable t) {
+		if (logger.isErrorEnabled()) {
+			logger.error("SUB " + this.subscriberState + " publishError: " + t, t);
+		}
+		this.subscriberState.get().onError(this, t);
+	}
+
+	@Override
+	public final void onComplete() {
+		if (logger.isTraceEnabled()) {
+			logger.trace("SUB " + this.subscriberState + " onComplete");
+		}
+		this.subscriberState.get().onComplete(this);
+	}
+
+	// Publisher
+
+	@Override
+	public final void subscribe(Subscriber<? super Void> subscriber) {
+		if (logger.isTraceEnabled()) {
+			logger.trace("PUB " + this.publisherState + " subscribe: " + subscriber);
+		}
+		this.publisherState.get().subscribe(this, subscriber);
+	}
+
+	private void publishComplete() {
+		if (logger.isTraceEnabled()) {
+			logger.trace("PUB " + this.publisherState + " publishComplete");
+		}
+		this.publisherState.get().publishComplete(this);
+	}
+
+	private void publishError(Throwable t) {
+		if (logger.isTraceEnabled()) {
+			logger.trace("PUB " + this.publisherState + " publishError: " + t);
+		}
+		this.publisherState.get().publishError(this, t);
+	}
+
+	// listener methods
+
+	/**
+	 * Called via a listener interface to indicate that writing is possible.
+	 * @see WriteListener#onWritePossible()
+	 * @see org.xnio.ChannelListener#handleEvent(Channel)
+	 */
+	protected final void onWritePossible() {
+		this.subscriberState.get().onWritePossible(this);
+	}
+
+	/**
+	 * Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)}
+	 * @param dataBuffer the buffer that was received.
+	 */
+	protected void receiveBuffer(DataBuffer dataBuffer) {
+		Assert.state(this.currentBuffer == null);
+		this.currentBuffer = dataBuffer;
+
+		checkOnWritePossible();
+	}
+
+	/**
+	 * Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)}
+	 * or when only partial data from the {@link DataBuffer} was written.
+	 */
+	protected void checkOnWritePossible() {
+		// no-op
+	}
+
+	/**
+	 * Called when the current buffer should be
+	 * {@linkplain DataBufferUtils#release(DataBuffer) released}.
+	 */
+	protected void releaseBuffer() {
+		if (logger.isTraceEnabled()) {
+			logger.trace("releaseBuffer: " + this.currentBuffer);
+		}
+		DataBufferUtils.release(this.currentBuffer);
+		this.currentBuffer = null;
+	}
+
+	/**
+	 * Writes the given data buffer to the output, indicating if the entire buffer was
+	 * written.
+	 * @param dataBuffer the data buffer to write
+	 * @return {@code true} if {@code dataBuffer} was fully written and a new buffer
+	 * can be requested; {@code false} otherwise
+	 */
+	protected abstract boolean write(DataBuffer dataBuffer) throws IOException;
+
+	/**
+	 * Flushes the output.
+	 */
+	protected abstract void flush() throws IOException;
+
+	/**
+	 * Closes the output.
+	 */
+	protected abstract void close();
+
+	private boolean changeSubscriberState(SubscriberState oldState,
+			SubscriberState newState) {
+		return this.subscriberState.compareAndSet(oldState, newState);
+	}
+
+	private boolean changePublisherState(PublisherState oldState,
+			PublisherState newState) {
+		return this.publisherState.compareAndSet(oldState, newState);
+	}
+
+	private static final class ResponseBodySubscription implements Subscription {
+
+		private final AbstractResponseBodyProcessor processor;
+
+		public ResponseBodySubscription(AbstractResponseBodyProcessor processor) {
+			this.processor = processor;
+		}
+
+		@Override
+		public final void request(long n) {
+			if (this.processor.logger.isTraceEnabled()) {
+				this.processor.logger.trace("PUB " + state() + " request: " + n);
+			}
+			state().request(this.processor, n);
+		}
+
+		@Override
+		public final void cancel() {
+			if (this.processor.logger.isTraceEnabled()) {
+				this.processor.logger.trace("PUB " + state() + " cancel");
+			}
+			state().cancel(this.processor);
+		}
+
+		private PublisherState state() {
+			return this.processor.publisherState.get();
+		}
+
+	}
+
+	/**
+	 * Represents a state for the {@link Subscriber} to be in. The following figure
+	 * indicate the four different states that exist, and the relationships between them.
+	 *
+	 * <pre>
+	 *       UNSUBSCRIBED
+	 *        |
+	 *        v
+	 * REQUESTED -------------------> RECEIVED
+	 *         ^                      ^
+	 *         |                      |
+	 *         --------- WRITING <-----
+	 *                      |
+	 *                      v
+	 *                  COMPLETED
+	 * </pre>
+	 * Refer to the individual states for more information.
+	 */
+	private enum SubscriberState {
+
+		/**
+		 * The initial unsubscribed state. Will respond to {@code onSubscribe} by
+		 * requesting 1 buffer from the subscription, and change state to {@link
+		 * #REQUESTED}.
+		 */
+		UNSUBSCRIBED {
+			@Override
+			void onSubscribe(AbstractResponseBodyProcessor processor,
+					Subscription subscription) {
+				Objects.requireNonNull(subscription, "Subscription cannot be null");
+				if (processor.changeSubscriberState(this, REQUESTED)) {
+					processor.subscription = subscription;
+					subscription.request(1);
+				}
+				else {
+					super.onSubscribe(processor, subscription);
+				}
+			}
+		},
+		/**
+		 * State that gets entered after a buffer has been
+		 * {@linkplain Subscription#request(long) requested}. Responds to {@code onNext}
+		 * by changing state to {@link #RECEIVED}, and responds to {@code onComplete} by
+		 * changing state to {@link #COMPLETED}.
+		 */
+		REQUESTED {
+			@Override
+			void onNext(AbstractResponseBodyProcessor processor, DataBuffer dataBuffer) {
+				if (processor.changeSubscriberState(this, RECEIVED)) {
+					processor.receiveBuffer(dataBuffer);
+				}
+			}
+
+			@Override
+			void onComplete(AbstractResponseBodyProcessor processor) {
+				if (processor.changeSubscriberState(this, COMPLETED)) {
+					processor.subscriberCompleted = true;
+					processor.close();
+					processor.publishComplete();
+				}
+			}
+		},
+		/**
+		 * State that gets entered after a buffer has been
+		 * {@linkplain Subscriber#onNext(Object) received}. Responds to
+		 * {@code onWritePossible} by writing the current buffer and changes
+		 * the state to {@link #WRITING}. If it can be written completely,
+		 * changes the state to either {@link #REQUESTED} if the subscription
+		 * has not been completed; or {@link #COMPLETED} if it has. If it cannot
+		 * be written completely the state will be changed to {@link #RECEIVED}.
+		 */
+		RECEIVED {
+			@Override
+			void onWritePossible(AbstractResponseBodyProcessor processor) {
+				if (processor.changeSubscriberState(this, WRITING)) {
+					DataBuffer dataBuffer = processor.currentBuffer;
+					try {
+						boolean writeCompleted = processor.write(dataBuffer);
+						if (writeCompleted) {
+							if (dataBuffer instanceof FlushingDataBuffer) {
+								processor.flush();
+							}
+							processor.releaseBuffer();
+							if (!processor.subscriberCompleted) {
+								processor.changeSubscriberState(WRITING, REQUESTED);
+								processor.subscription.request(1);
+							}
+							else {
+								processor.changeSubscriberState(WRITING, COMPLETED);
+								processor.close();
+								processor.publishComplete();
+							}
+						}
+						else {
+							processor.changeSubscriberState(WRITING, RECEIVED);
+							processor.checkOnWritePossible();
+						}
+					}
+					catch (IOException ex) {
+						processor.onError(ex);
+					}
+				}
+			}
+
+			@Override
+			void onComplete(AbstractResponseBodyProcessor processor) {
+				processor.subscriberCompleted = true;
+			}
+		},
+		/**
+		 * State that gets entered after a writing of the current buffer has been
+		 * {@code onWritePossible started}.
+		 */
+		WRITING {
+			@Override
+			void onComplete(AbstractResponseBodyProcessor processor) {
+				processor.subscriberCompleted = true;
+			}
+		},
+		/**
+		 * The terminal completed state. Does not respond to any events.
+		 */
+		COMPLETED {
+			@Override
+			void onNext(AbstractResponseBodyProcessor processor, DataBuffer dataBuffer) {
+				// ignore
+			}
+
+			@Override
+			void onError(AbstractResponseBodyProcessor processor, Throwable t) {
+				// ignore
+			}
+
+			@Override
+			void onComplete(AbstractResponseBodyProcessor processor) {
+				// ignore
+			}
+		};
+
+		void onSubscribe(AbstractResponseBodyProcessor processor, Subscription s) {
+			s.cancel();
+		}
+
+		void onNext(AbstractResponseBodyProcessor processor, DataBuffer dataBuffer) {
+			throw new IllegalStateException(toString());
+		}
+
+		void onError(AbstractResponseBodyProcessor processor, Throwable t) {
+			if (processor.changeSubscriberState(this, COMPLETED)) {
+				processor.publishError(t);
+			}
+		}
+
+		void onComplete(AbstractResponseBodyProcessor processor) {
+			throw new IllegalStateException(toString());
+		}
+
+		void onWritePossible(AbstractResponseBodyProcessor processor) {
+			// ignore
+		}
+	}
+
+	private enum PublisherState {
+		UNSUBSCRIBED {
+			@Override
+			void subscribe(AbstractResponseBodyProcessor processor,
+					Subscriber<? super Void> subscriber) {
+				Objects.requireNonNull(subscriber);
+				if (processor.changePublisherState(this, SUBSCRIBED)) {
+					Subscription subscription = new ResponseBodySubscription(processor);
+					processor.subscriber = subscriber;
+					subscriber.onSubscribe(subscription);
+					if (processor.publisherCompleted) {
+						processor.publishComplete();
+					}
+					else if (processor.publisherError != null) {
+						processor.publishError(processor.publisherError);
+					}
+				}
+				else {
+					throw new IllegalStateException(toString());
+				}
+			}
+
+			@Override
+			void publishComplete(AbstractResponseBodyProcessor processor) {
+				processor.publisherCompleted = true;
+			}
+
+			@Override
+			void publishError(AbstractResponseBodyProcessor processor, Throwable t) {
+				processor.publisherError = t;
+			}
+		},
+		SUBSCRIBED {
+			@Override
+			void request(AbstractResponseBodyProcessor processor, long n) {
+				BackpressureUtils.checkRequest(n, processor.subscriber);
+			}
+
+			@Override
+			void publishComplete(AbstractResponseBodyProcessor processor) {
+				if (processor.changePublisherState(this, COMPLETED)) {
+					processor.subscriber.onComplete();
+				}
+			}
+
+			@Override
+			void publishError(AbstractResponseBodyProcessor processor, Throwable t) {
+				if (processor.changePublisherState(this, COMPLETED)) {
+					processor.subscriber.onError(t);
+				}
+			}
+
+		},
+		COMPLETED {
+			@Override
+			void request(AbstractResponseBodyProcessor processor, long n) {
+				// ignore
+			}
+
+			@Override
+			void cancel(AbstractResponseBodyProcessor processor) {
+				// ignore
+			}
+
+			@Override
+			void publishComplete(AbstractResponseBodyProcessor processor) {
+				// ignore
+			}
+
+			@Override
+			void publishError(AbstractResponseBodyProcessor processor, Throwable t) {
+				// ignore
+			}
+		};
+
+		void subscribe(AbstractResponseBodyProcessor processor,
+				Subscriber<? super Void> subscriber) {
+			throw new IllegalStateException(toString());
+		}
+
+		void request(AbstractResponseBodyProcessor processor, long n) {
+			throw new IllegalStateException(toString());
+		}
+
+		void cancel(AbstractResponseBodyProcessor processor) {
+			processor.changePublisherState(this, COMPLETED);
+		}
+
+		void publishComplete(AbstractResponseBodyProcessor processor) {
+			throw new IllegalStateException(toString());
+		}
+
+		void publishError(AbstractResponseBodyProcessor processor, Throwable t) {
+			throw new IllegalStateException(toString());
+		}
+
+	}
+
+}

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/AbstractResponseBodySubscriber.java

@@ -1,321 +0,0 @@
-/*
- * Copyright 2002-2016 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
- *
- *      http://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.server.reactive;
-
-import java.io.IOException;
-import java.nio.channels.Channel;
-import java.util.Objects;
-import java.util.concurrent.atomic.AtomicReference;
-import javax.servlet.WriteListener;
-
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
-import org.reactivestreams.Subscriber;
-import org.reactivestreams.Subscription;
-
-import org.springframework.core.io.buffer.DataBuffer;
-import org.springframework.core.io.buffer.FlushingDataBuffer;
-import org.springframework.core.io.buffer.support.DataBufferUtils;
-import org.springframework.util.Assert;
-
-/**
- * Abstract base class for {@code Subscriber} implementations that bridge between
- * event-listener APIs and Reactive Streams. Specifically, base class for the Servlet 3.1
- * and Undertow support.
- * @author Arjen Poutsma
- * @see ServletServerHttpRequest
- * @see UndertowHttpHandlerAdapter
- */
-abstract class AbstractResponseBodySubscriber implements Subscriber<DataBuffer> {
-
-	protected final Log logger = LogFactory.getLog(getClass());
-
-	private final AtomicReference<State> state =
-			new AtomicReference<>(State.UNSUBSCRIBED);
-
-	private volatile DataBuffer currentBuffer;
-
-	private volatile boolean subscriptionCompleted;
-
-	private Subscription subscription;
-
-	@Override
-	public final void onSubscribe(Subscription subscription) {
-		if (logger.isTraceEnabled()) {
-			logger.trace(this.state + " onSubscribe: " + subscription);
-		}
-		this.state.get().onSubscribe(this, subscription);
-	}
-
-	@Override
-	public final void onNext(DataBuffer dataBuffer) {
-		if (logger.isTraceEnabled()) {
-			logger.trace(this.state + " onNext: " + dataBuffer);
-		}
-		this.state.get().onNext(this, dataBuffer);
-	}
-
-	@Override
-	public final void onError(Throwable t) {
-		if (logger.isErrorEnabled()) {
-			logger.error(this.state + " onError: " + t, t);
-		}
-		this.state.get().onError(this, t);
-	}
-
-	@Override
-	public final void onComplete() {
-		if (logger.isTraceEnabled()) {
-			logger.trace(this.state + " onComplete");
-		}
-		this.state.get().onComplete(this);
-	}
-
-	/**
-	 * Called via a listener interface to indicate that writing is possible.
-	 * @see WriteListener#onWritePossible()
-	 * @see org.xnio.ChannelListener#handleEvent(Channel)
-	 */
-	protected final void onWritePossible() {
-		this.state.get().onWritePossible(this);
-	}
-
-	/**
-	 * Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)}
-	 * @param dataBuffer the buffer that was received.
-	 */
-	protected void receiveBuffer(DataBuffer dataBuffer) {
-		Assert.state(this.currentBuffer == null);
-		this.currentBuffer = dataBuffer;
-
-		checkOnWritePossible();
-	}
-
-	/**
-	 * Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)}
-	 * or when only partial data from the {@link DataBuffer} was written.
-	 */
-	protected void checkOnWritePossible() {
-		// no-op
-	}
-
-	/**
-	 * Called when the current buffer should be
-	 * {@linkplain DataBufferUtils#release(DataBuffer) released}.
-	 */
-	protected void releaseBuffer() {
-		if (logger.isTraceEnabled()) {
-			logger.trace("releaseBuffer: " + this.currentBuffer);
-		}
-		DataBufferUtils.release(this.currentBuffer);
-		this.currentBuffer = null;
-	}
-
-	/**
-	 * Writes the given data buffer to the output, indicating if the entire buffer was
-	 * written.
-	 * @param dataBuffer the data buffer to write
-	 * @return {@code true} if {@code dataBuffer} was fully written and a new buffer
-	 * can be requested; {@code false} otherwise
-	 */
-	protected abstract boolean write(DataBuffer dataBuffer) throws IOException;
-
-	/**
-	 * Writes the given exception to the output.
-	 */
-	protected abstract void writeError(Throwable t);
-
-	/**
-	 * Flushes the output.
-	 */
-	protected abstract void flush() throws IOException;
-
-	/**
-	 * Closes the output.
-	 */
-	protected abstract void close();
-
-	private boolean changeState(State oldState, State newState) {
-		return this.state.compareAndSet(oldState, newState);
-	}
-
-	/**
-	 * Represents a state for the {@link Subscriber} to be in. The following figure
-	 * indicate the four different states that exist, and the relationships between them.
-	 *
-	 * <pre>
-	 *       UNSUBSCRIBED
-	 *        |
-	 *        v
-	 * REQUESTED -------------------> RECEIVED
-	 *         ^                      ^
-	 *         |                      |
-	 *         --------- WRITING <-----
-	 *                      |
-	 *                      v
-	 *                  COMPLETED
-	 * </pre>
-	 * Refer to the individual states for more information.
-	 */
-	private enum State {
-
-		/**
-		 * The initial unsubscribed state. Will respond to {@code onSubscribe} by
-		 * requesting 1 buffer from the subscription, and change state to {@link
-		 * #REQUESTED}.
-		 */
-		UNSUBSCRIBED {
-			@Override
-			void onSubscribe(AbstractResponseBodySubscriber subscriber,
-					Subscription subscription) {
-				Objects.requireNonNull(subscription, "Subscription cannot be null");
-				if (subscriber.changeState(this, REQUESTED)) {
-					subscriber.subscription = subscription;
-					subscription.request(1);
-				}
-				else {
-					super.onSubscribe(subscriber, subscription);
-				}
-			}
-		},
-		/**
-		 * State that gets entered after a buffer has been
-		 * {@linkplain Subscription#request(long) requested}. Responds to {@code onNext}
-		 * by changing state to {@link #RECEIVED}, and responds to {@code onComplete} by
-		 * changing state to {@link #COMPLETED}.
-		 */
-		REQUESTED {
-			@Override
-			void onNext(AbstractResponseBodySubscriber subscriber,
-					DataBuffer dataBuffer) {
-				if (subscriber.changeState(this, RECEIVED)) {
-					subscriber.receiveBuffer(dataBuffer);
-				}
-			}
-
-			@Override
-			void onComplete(AbstractResponseBodySubscriber subscriber) {
-				if (subscriber.changeState(this, COMPLETED)) {
-					subscriber.subscriptionCompleted = true;
-					subscriber.close();
-				}
-			}
-		},
-		/**
-		 * State that gets entered after a buffer has been
-		 * {@linkplain Subscriber#onNext(Object) received}. Responds to
-		 * {@code onWritePossible} by writing the current buffer and changes
-		 * the state to {@link #WRITING}. If it can be written completely,
-		 * changes the state to either {@link #REQUESTED} if the subscription
-		 * has not been completed; or {@link #COMPLETED} if it has. If it cannot
-		 * be written completely the state will be changed to {@link #RECEIVED}.
-		 */
-		RECEIVED {
-			@Override
-			void onWritePossible(AbstractResponseBodySubscriber subscriber) {
-				if (subscriber.changeState(this, WRITING)) {
-					DataBuffer dataBuffer = subscriber.currentBuffer;
-					try {
-						boolean writeCompleted = subscriber.write(dataBuffer);
-						if (writeCompleted) {
-							if (dataBuffer instanceof FlushingDataBuffer) {
-								subscriber.flush();
-							}
-							subscriber.releaseBuffer();
-							boolean subscriptionCompleted = subscriber.subscriptionCompleted;
-							if (!subscriptionCompleted) {
-								subscriber.changeState(WRITING, REQUESTED);
-								subscriber.subscription.request(1);
-							}
-							else {
-								subscriber.changeState(WRITING, COMPLETED);
-								subscriber.close();
-							}
-						}
-						else {
-							subscriber.changeState(WRITING, RECEIVED);
-							subscriber.checkOnWritePossible(); 
-						}
-					}
-					catch (IOException ex) {
-						subscriber.onError(ex);
-					}
-				}
-			}
-
-			@Override
-			void onComplete(AbstractResponseBodySubscriber subscriber) {
-				subscriber.subscriptionCompleted = true;
-			}
-		},
-		/**
-		 * State that gets entered after a writing of the current buffer has been
-		 * {@code onWritePossible started}.
-		 */
-		WRITING {
-			@Override
-			void onComplete(AbstractResponseBodySubscriber subscriber) {
-				subscriber.subscriptionCompleted = true;
-			}
-		},
-		/**
-		 * The terminal completed state. Does not respond to any events.
-		 */
-		COMPLETED {
-			@Override
-			void onNext(AbstractResponseBodySubscriber subscriber,
-					DataBuffer dataBuffer) {
-				// ignore
-			}
-
-			@Override
-			void onError(AbstractResponseBodySubscriber subscriber, Throwable t) {
-				// ignore
-			}
-
-			@Override
-			void onComplete(AbstractResponseBodySubscriber subscriber) {
-				// ignore
-			}
-		};
-
-		void onSubscribe(AbstractResponseBodySubscriber subscriber, Subscription s) {
-			s.cancel();
-		}
-
-		void onNext(AbstractResponseBodySubscriber subscriber, DataBuffer dataBuffer) {
-			throw new IllegalStateException(toString());
-		}
-
-		void onError(AbstractResponseBodySubscriber subscriber, Throwable t) {
-			if (subscriber.changeState(this, COMPLETED)) {
-				subscriber.writeError(t);
-				subscriber.close();
-			}
-		}
-
-		void onComplete(AbstractResponseBodySubscriber subscriber) {
-			throw new IllegalStateException(toString());
-		}
-
-		void onWritePossible(AbstractResponseBodySubscriber subscriber) {
-			// ignore
-		}
-
-	}
-
-}

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/ServletHttpHandlerAdapter.java

@@ -38,7 +38,6 @@ import reactor.core.publisher.Mono;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferFactory;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
-import org.springframework.http.HttpStatus;
 import org.springframework.util.Assert;
 
 /**
@@ -91,13 +90,15 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 		ServletServerHttpRequest request =
 				new ServletServerHttpRequest(servletRequest, requestBody);
 
-		ResponseBodySubscriber responseBody =
-				new ResponseBodySubscriber(synchronizer, this.bufferSize);
+		ResponseBodyProcessor responseBody =
+				new ResponseBodyProcessor(synchronizer, this.bufferSize);
 		responseBody.registerListener();
 		ServletServerHttpResponse response =
 				new ServletServerHttpResponse(servletResponse, this.dataBufferFactory,
-						publisher -> Mono
-								.from(subscriber -> publisher.subscribe(responseBody)));
+						publisher -> Mono.from(subscriber -> {
+							publisher.subscribe(responseBody);
+							responseBody.subscribe(subscriber);
+						}));
 
 		HandlerResultSubscriber resultSubscriber =
 				new HandlerResultSubscriber(synchronizer);
@@ -129,7 +130,7 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 			logger.error("Error from request handling. Completing the request.", ex);
 			HttpServletResponse response =
 					(HttpServletResponse) this.synchronizer.getResponse();
-			response.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
+			response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
 			this.synchronizer.complete();
 		}
 
@@ -206,8 +207,7 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 		}
 	}
 
-
-	private static class ResponseBodySubscriber extends AbstractResponseBodySubscriber {
+	private static class ResponseBodyProcessor extends AbstractResponseBodyProcessor {
 
 		private final ResponseBodyWriteListener writeListener =
 				new ResponseBodyWriteListener();
@@ -218,7 +218,7 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 
 		private volatile boolean flushOnNext;
 
-		public ResponseBodySubscriber(ServletAsyncContextSynchronizer synchronizer,
+		public ResponseBodyProcessor(ServletAsyncContextSynchronizer synchronizer,
 				int bufferSize) {
 			this.synchronizer = synchronizer;
 			this.bufferSize = bufferSize;
@@ -272,13 +272,6 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 			}
 		}
 
-		@Override
-		protected void writeError(Throwable t) {
-			HttpServletResponse response =
-					(HttpServletResponse) this.synchronizer.getResponse();
-			response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
-		}
-
 		@Override
 		protected void flush() throws IOException {
 			ServletOutputStream output = outputStream();
@@ -324,14 +317,14 @@ public class ServletHttpHandlerAdapter extends HttpServlet {
 
 			@Override
 			public void onWritePossible() throws IOException {
-				ResponseBodySubscriber.this.onWritePossible();
+				ResponseBodyProcessor.this.onWritePossible();
 			}
 
 			@Override
 			public void onError(Throwable ex) {
 				// Error on writing to the HTTP stream, so any further writes will probably
 				// fail. Let's log instead of calling {@link #writeError}.
-				ResponseBodySubscriber.this.logger
+				ResponseBodyProcessor.this.logger
 						.error("ResponseBodyWriteListener error", ex);
 			}
 		}

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/UndertowHttpHandlerAdapter.java

@@ -70,11 +70,8 @@ public class UndertowHttpHandlerAdapter implements io.undertow.server.HttpHandle
 
 			@Override
 			public void onError(Throwable ex) {
-				if (exchange.isResponseStarted() || exchange.getStatusCode() > 500) {
-					logger.error("Error from request handling. Completing the request.",
-							ex);
-				}
-				else {
+				logger.error("Error from request handling. Completing the request.", ex);
+				if (!exchange.isResponseStarted() && exchange.getStatusCode() <= 500) {
 					exchange.setStatusCode(500);
 				}
 				exchange.endExchange();

spring-web-reactive/src/main/java/org/springframework/http/server/reactive/UndertowServerHttpResponse.java

@@ -79,13 +79,14 @@ public class UndertowServerHttpResponse extends AbstractServerHttpResponse
 
 	@Override
 	protected Mono<Void> writeWithInternal(Publisher<DataBuffer> publisher) {
-		return Mono.from(s -> {
-			// lazily create Subscriber, since calling
-			// {@link HttpServerExchange#getResponseChannel} as done in the
-			// ResponseBodySubscriber constructor commits the response status and headers
-			ResponseBodySubscriber subscriber = new ResponseBodySubscriber(this.exchange);
-			subscriber.registerListener();
-			publisher.subscribe(subscriber);
+		// lazily create Subscriber, since calling
+		// {@link HttpServerExchange#getResponseChannel} as done in the
+		// ResponseBodyProcessor constructor commits the response status and headers
+		return Mono.from(subscriber -> {
+			ResponseBodyProcessor processor = new ResponseBodyProcessor(this.exchange);
+			processor.registerListener();
+			publisher.subscribe(processor);
+			processor.subscribe(subscriber);
 		});
 	}
 
@@ -137,7 +138,7 @@ public class UndertowServerHttpResponse extends AbstractServerHttpResponse
 		}
 	}
 
-	private static class ResponseBodySubscriber extends AbstractResponseBodySubscriber {
+	private static class ResponseBodyProcessor extends AbstractResponseBodyProcessor {
 
 		private final ChannelListener<StreamSinkChannel> listener = new WriteListener();
 
@@ -147,7 +148,7 @@ public class UndertowServerHttpResponse extends AbstractServerHttpResponse
 
 		private volatile ByteBuffer byteBuffer;
 
-		public ResponseBodySubscriber(HttpServerExchange exchange) {
+		public ResponseBodyProcessor(HttpServerExchange exchange) {
 			this.exchange = exchange;
 			this.responseChannel = exchange.getResponseChannel();
 		}
@@ -157,14 +158,6 @@ public class UndertowServerHttpResponse extends AbstractServerHttpResponse
 			this.responseChannel.resumeWrites();
 		}
 
-		@Override
-		protected void writeError(Throwable t) {
-			if (!this.exchange.isResponseStarted() &&
-					this.exchange.getStatusCode() < 500) {
-				this.exchange.setStatusCode(500);
-			}
-		}
-
 		@Override
 		protected void flush() throws IOException {
 			if (logger.isTraceEnabled()) {

spring-web-reactive/src/test/java/org/springframework/http/server/reactive/ErrorHandlerIntegrationTests.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2002-2016 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
+ *
+ *      http://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.server.reactive;
+
+import java.io.IOException;
+import java.net.URI;
+
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.http.server.reactive.boot.ReactorHttpServer;
+import org.springframework.web.client.ResponseErrorHandler;
+import org.springframework.web.client.RestTemplate;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assume.assumeFalse;
+
+/**
+ * @author Arjen Poutsma
+ */
+public class ErrorHandlerIntegrationTests extends AbstractHttpHandlerIntegrationTests {
+
+	private ErrorHandler handler = new ErrorHandler();
+
+	@Override
+	protected HttpHandler createHttpHandler() {
+		return handler;
+	}
+
+	@Test
+	public void response() throws Exception {
+		// TODO: fix Reactor
+		assumeFalse(server instanceof ReactorHttpServer);
+
+		RestTemplate restTemplate = new RestTemplate();
+		restTemplate.setErrorHandler(NO_OP_ERROR_HANDLER);
+
+		ResponseEntity<String> response = restTemplate
+				.getForEntity(new URI("http://localhost:" + port + "/response"),
+						String.class);
+
+		assertEquals(HttpStatus.INTERNAL_SERVER_ERROR, response.getStatusCode());
+	}
+
+	@Test
+	public void returnValue() throws Exception {
+		// TODO: fix Reactor
+		assumeFalse(server instanceof ReactorHttpServer);
+
+		RestTemplate restTemplate = new RestTemplate();
+		restTemplate.setErrorHandler(NO_OP_ERROR_HANDLER);
+
+		ResponseEntity<String> response = restTemplate
+				.getForEntity(new URI("http://localhost:" + port + "/returnValue"),
+						String.class);
+
+		assertEquals(HttpStatus.INTERNAL_SERVER_ERROR, response.getStatusCode());
+	}
+
+	private static class ErrorHandler implements HttpHandler {
+
+		@Override
+		public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
+			Exception error = new UnsupportedOperationException();
+			String path = request.getURI().getPath();
+			if (path.endsWith("response")) {
+				return response.writeWith(Mono.error(error));
+			}
+			else if (path.endsWith("returnValue")) {
+				return Mono.error(error);
+			}
+			else {
+				return Mono.empty();
+			}
+		}
+	}
+
+	private static final ResponseErrorHandler NO_OP_ERROR_HANDLER =
+			new ResponseErrorHandler() {
+
+				@Override
+				public boolean hasError(ClientHttpResponse response) throws IOException {
+					return false;
+				}
+
+				@Override
+				public void handleError(ClientHttpResponse response) throws IOException {
+				}
+			};
+
+}

spring-web-reactive/src/test/java/org/springframework/http/server/reactive/RandomHandlerIntegrationTests.java

@@ -21,8 +21,6 @@ import java.util.Random;
 
 import org.junit.Test;
 import org.reactivestreams.Publisher;
-import org.reactivestreams.Subscriber;
-import org.reactivestreams.Subscription;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -31,12 +29,9 @@ import org.springframework.core.io.buffer.DataBufferFactory;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
-import org.springframework.http.server.reactive.boot.ReactorHttpServer;
 import org.springframework.web.client.RestTemplate;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assume.assumeFalse;
+import static org.junit.Assert.*;
 
 public class RandomHandlerIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 
@@ -60,7 +55,6 @@ public class RandomHandlerIntegrationTests extends AbstractHttpHandlerIntegratio
 	@Test
 	public void random() throws Throwable {
 		// TODO: fix Reactor support
-		assumeFalse(server instanceof ReactorHttpServer);
 
 		RestTemplate restTemplate = new RestTemplate();
 
@@ -72,14 +66,6 @@ public class RandomHandlerIntegrationTests extends AbstractHttpHandlerIntegratio
 		assertEquals(RESPONSE_SIZE,
 				response.getHeaders().getContentLength());
 		assertEquals(RESPONSE_SIZE, response.getBody().length);
-
-		while (!handler.requestComplete) {
-			Thread.sleep(100);
-		}
-		if (handler.requestError != null) {
-			throw handler.requestError;
-		}
-		assertEquals(REQUEST_SIZE, handler.requestSize);
 	}
 
 
@@ -93,45 +79,21 @@ public class RandomHandlerIntegrationTests extends AbstractHttpHandlerIntegratio
 
 		public static final int CHUNKS = 16;
 
-		private volatile boolean requestComplete;
-
-		private int requestSize;
-
-		private Throwable requestError;
-
 		@Override
 		public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
-			requestError = null;
+			Mono<Integer> requestSizeMono = request.getBody().
+					reduce(0, (integer, dataBuffer) -> integer +
+							dataBuffer.readableByteCount()).
+					doAfterTerminate((size, throwable) -> {
+						assertNull(throwable);
+						assertEquals(REQUEST_SIZE, (long) size);
+					});
 
-			request.getBody().subscribe(new Subscriber<DataBuffer>() {
 
-				@Override
-				public void onSubscribe(Subscription s) {
-					requestComplete = false;
-					requestSize = 0;
-					requestError = null;
-					s.request(Long.MAX_VALUE);
-				}
-
-				@Override
-				public void onNext(DataBuffer bytes) {
-					requestSize += bytes.readableByteCount();
-				}
-
-				@Override
-				public void onError(Throwable t) {
-					requestComplete = true;
-					requestError = t;
-				}
-
-				@Override
-				public void onComplete() {
-					requestComplete = true;
-				}
-			});
 
 			response.getHeaders().setContentLength(RESPONSE_SIZE);
-			return response.writeWith(multipleChunks());
+
+			return requestSizeMono.then(response.writeWith(multipleChunks()));
 		}
 
 		private Publisher<DataBuffer> singleChunk() {