Server adapters release buffers on error/cancel

Review and update Servlet and Undertow adapters to release any data
buffers they be holding on to at the time of error or cancellation.

Also remove onDiscard hooks from Reactor and Undertow request body.
For Reactor we expect it to be handled. For Undertow there isn't
any Reactor Core upstream for the callback to be useful.

Issue: SPR-17410

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

@@ -130,6 +130,14 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 	 */
 	protected abstract void readingPaused();
 
+	/**
+	 * Invoked after an I/O read error from the underlying server or after a
+	 * cancellation signal from the downstream consumer to allow sub-classes
+	 * to discard any current cached data they might have.
+	 * @since 5.1.2
+	 */
+	protected abstract void discardData();
+
 
 	// Private methods for use in State...
 
@@ -382,7 +390,10 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 		}
 
 		<T> void cancel(AbstractListenerReadPublisher<T> publisher) {
-			if (!publisher.changeState(this, COMPLETED)) {
+			if (publisher.changeState(this, COMPLETED)) {
+				publisher.discardData();
+			}
+			else {
 				publisher.state.get().cancel(publisher);
 			}
 		}
@@ -405,6 +416,7 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 
 		<T> void onError(AbstractListenerReadPublisher<T> publisher, Throwable t) {
 			if (publisher.changeState(this, COMPLETED)) {
+				publisher.discardData();
 				Subscriber<? super T> s = publisher.subscriber;
 				if (s != null) {
 					s.onError(t);

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

@@ -118,6 +118,9 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 
 	@Override
 	public final void subscribe(Subscriber<? super Void> subscriber) {
+		// Technically, cancellation from the result subscriber should be propagated
+		// to the upstream subscription. In practice, HttpHandler server adapters
+		// don't have a reason to cancel the result subscription.
 		this.resultPublisher.subscribe(subscriber);
 	}
 
@@ -136,8 +139,14 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 	 * data item for writing once that is possible.
 	 */
 	protected void dataReceived(T data) {
-		if (this.currentData != null) {
-			throw new IllegalStateException("Current data not processed yet: " + this.currentData);
+		T prev = this.currentData;
+		if (prev != null) {
+			// This shouldn't happen:
+			//   1. dataReceived can only be called from REQUESTED state
+			//   2. currentData is cleared before requesting
+			discardData(data);
+			cancel();
+			onError(new IllegalStateException("Received new data while current not processed yet."));
 		}
 		this.currentData = data;
 	}
@@ -186,6 +195,16 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 	protected void writingFailed(Throwable ex) {
 	}
 
+	/**
+	 * Invoked after any error (either from the upstream write Publisher, or
+	 * from I/O operations to the underlying server) and cancellation
+	 * to discard in-flight data that was in
+	 * the process of being written when the error took place.
+	 * @param data the data to be released
+	 * @since 5.1.2
+	 */
+	protected abstract void discardData(T data);
+
 
 	// Private methods for use from State's...
 
@@ -205,6 +224,7 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 
 	private void changeStateToComplete(State oldState) {
 		if (changeState(oldState, State.COMPLETED)) {
+			discardCurrentData();
 			writingComplete();
 			this.resultPublisher.publishComplete();
 		}
@@ -223,6 +243,14 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 		}
 	}
 
+	private void discardCurrentData() {
+		T data = this.currentData;
+		this.currentData = null;
+		if (data != null) {
+			discardData(data);
+		}
+	}
+
 
 	/**
 	 * Represents a state for the {@link Processor} to be in.
@@ -338,11 +366,14 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 		}
 
 		public <T> void onNext(AbstractListenerWriteProcessor<T> processor, T data) {
-			throw new IllegalStateException(toString());
+			processor.discardData(data);
+			processor.cancel();
+			processor.onError(new IllegalStateException("Illegal onNext without demand"));
 		}
 
 		public <T> void onError(AbstractListenerWriteProcessor<T> processor, Throwable ex) {
 			if (processor.changeState(this, COMPLETED)) {
+				processor.discardCurrentData();
 				processor.writingComplete();
 				processor.resultPublisher.publishError(ex);
 			}

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

@@ -290,6 +290,11 @@ class ServletServerHttpRequest extends AbstractServerHttpRequest {
 			// no-op
 		}
 
+		@Override
+		protected void discardData() {
+			// Nothing to discard since we pass data buffers on immediately..
+		}
+
 
 		private class RequestBodyPublisherReadListener implements ReadListener {
 

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

@@ -318,6 +318,7 @@ class ServletServerHttpResponse extends AbstractListenerServerHttpResponse {
 			}
 			int remaining = dataBuffer.readableByteCount();
 			if (ready && remaining > 0) {
+				// In case of IOException, onError handling should call discardData(DataBuffer)..
 				int written = writeToOutputStream(dataBuffer);
 				if (this.logger.isTraceEnabled()) {
 					this.logger.trace("written: " + written + " total: " + remaining);
@@ -337,6 +338,11 @@ class ServletServerHttpResponse extends AbstractListenerServerHttpResponse {
 		protected void writingComplete() {
 			bodyProcessor = null;
 		}
+
+		@Override
+		protected void discardData(DataBuffer dataBuffer) {
+			DataBufferUtils.release(dataBuffer);
+		}
 	}
 
 }

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

@@ -194,6 +194,10 @@ class UndertowServerHttpRequest extends AbstractServerHttpRequest {
 			}
 		}
 
+		@Override
+		protected void discardData() {
+			// Nothing to discard since we pass data buffers on immediately..
+		}
 	}
 
 	private static class UndertowDataBuffer implements PooledDataBuffer {

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

@@ -174,6 +174,7 @@ class UndertowServerHttpResponse extends AbstractListenerServerHttpResponse impl
 			// Track write listener calls from here on..
 			this.writePossible = false;
 
+			// In case of IOException, onError handling should call discardData(DataBuffer)..
 			int total = buffer.remaining();
 			int written = writeByteBuffer(buffer);
 
@@ -228,6 +229,11 @@ class UndertowServerHttpResponse extends AbstractListenerServerHttpResponse impl
 			cancel();
 			onError(ex);
 		}
+
+		@Override
+		protected void discardData(DataBuffer dataBuffer) {
+			DataBufferUtils.release(dataBuffer);
+		}
 	}
 
 

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

@@ -16,54 +16,90 @@
 
 package org.springframework.http.server.reactive;
 
-import java.io.IOException;
-
+import org.junit.Before;
 import org.junit.Test;
-import org.mockito.invocation.InvocationOnMock;
-import org.mockito.stubbing.Answer;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
 
 import org.springframework.core.io.buffer.DataBuffer;
 
-import static org.mockito.Mockito.doAnswer;
-import static org.mockito.Mockito.isA;
-import static org.mockito.Mockito.mock;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
 
 /**
- * Unit tests for {@link AbstractListenerReadPublisher}
+ * Unit tests for {@link AbstractListenerReadPublisher}.
  *
  * @author Violeta Georgieva
- * @since 5.0
+ * @author Rossen Stoyanchev
  */
 public class ListenerReadPublisherTests {
 
+	private final TestListenerReadPublisher publisher = new TestListenerReadPublisher();
+
+	private final TestSubscriber subscriber = new TestSubscriber();
+
+
+	@Before
+	public void setup() {
+		this.publisher.subscribe(this.subscriber);
+	}
+
+
 	@Test
-	@SuppressWarnings("unchecked")
-	public void testReceiveTwoRequestCallsWhenOnSubscribe() {
-		Subscriber<DataBuffer> subscriber = mock(Subscriber.class);
-		doAnswer(new SubscriptionAnswer()).when(subscriber).onSubscribe(isA(Subscription.class));
+	public void twoReads() {
+
+		this.subscriber.getSubscription().request(2);
+		this.publisher.onDataAvailable();
+
+		assertEquals(2, this.publisher.getReadCalls());
+	}
+
+	@Test // SPR-17410
+	public void discardDataOnError() {
 
-		TestListenerReadPublisher publisher = new TestListenerReadPublisher();
-		publisher.subscribe(subscriber);
-		publisher.onDataAvailable();
+		this.subscriber.getSubscription().request(2);
+		this.publisher.onDataAvailable();
+		this.publisher.onError(new IllegalStateException());
 
-		assertTrue(publisher.getReadCalls() == 2);
+		assertEquals(2, this.publisher.getReadCalls());
+		assertEquals(1, this.publisher.getDiscardCalls());
 	}
 
-	private static final class TestListenerReadPublisher extends AbstractListenerReadPublisher {
+	@Test // SPR-17410
+	public void discardDataOnCancel() {
+
+		this.subscriber.getSubscription().request(2);
+		this.subscriber.setCancelOnNext(true);
+		this.publisher.onDataAvailable();
+
+		assertEquals(1, this.publisher.getReadCalls());
+		assertEquals(1, this.publisher.getDiscardCalls());
+	}
+
+
+	private static final class TestListenerReadPublisher extends AbstractListenerReadPublisher<DataBuffer> {
 
 		private int readCalls = 0;
 
+		private int discardCalls = 0;
+
+
+		public int getReadCalls() {
+			return this.readCalls;
+		}
+
+		public int getDiscardCalls() {
+			return this.discardCalls;
+		}
+
 		@Override
 		protected void checkOnDataAvailable() {
 			// no-op
 		}
 
 		@Override
-		protected DataBuffer read() throws IOException {
-			readCalls++;
+		protected DataBuffer read() {
+			this.readCalls++;
 			return mock(DataBuffer.class);
 		}
 
@@ -72,22 +108,48 @@ public class ListenerReadPublisherTests {
 			// No-op
 		}
 
-		public int getReadCalls() {
-			return this.readCalls;
+		@Override
+		protected void discardData() {
+			this.discardCalls++;
+		}
+	}
+
+
+	private static final class TestSubscriber implements Subscriber<DataBuffer> {
+
+		private Subscription subscription;
+
+		private boolean cancelOnNext;
+
+
+		public Subscription getSubscription() {
+			return this.subscription;
 		}
 
+		public void setCancelOnNext(boolean cancelOnNext) {
+			this.cancelOnNext = cancelOnNext;
 		}
 
-	private static final class SubscriptionAnswer implements Answer<Subscription> {
 
 		@Override
-		public Subscription answer(InvocationOnMock invocation) throws Throwable {
-			Subscription arg = (Subscription) invocation.getArguments()[0];
-			arg.request(1);
-			arg.request(1);
-			return arg;
+		public void onSubscribe(Subscription subscription) {
+			this.subscription = subscription;
+		}
+
+		@Override
+		public void onNext(DataBuffer dataBuffer) {
+			if (this.cancelOnNext) {
+				this.subscription.cancel();
+			}
 		}
 
+		@Override
+		public void onError(Throwable t) {
+		}
+
+		@Override
+		public void onComplete() {
+		}
 	}
 
 }

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

@@ -0,0 +1,206 @@
+/*
+ * Copyright 2002-2018 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.util.ArrayList;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+
+import org.springframework.core.io.buffer.DataBuffer;
+
+import static junit.framework.TestCase.*;
+import static org.mockito.Mockito.*;
+
+/**
+ * Unit tests for {@link AbstractListenerWriteProcessor}.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class ListenerWriteProcessorTests {
+
+	private final TestListenerWriteProcessor processor = new TestListenerWriteProcessor();
+
+	private final TestResultSubscriber resultSubscriber = new TestResultSubscriber();
+
+	private final TestSubscription subscription = new TestSubscription();
+
+
+	@Before
+	public void setup() {
+		this.processor.subscribe(this.resultSubscriber);
+		this.processor.onSubscribe(this.subscription);
+		assertEquals(1, subscription.getDemand());
+	}
+
+
+	@Test // SPR-17410
+	public void writePublisherError() {
+
+		// Turn off writing so next item will be cached
+		this.processor.setWritePossible(false);
+		DataBuffer buffer = mock(DataBuffer.class);
+		this.processor.onNext(buffer);
+
+		// Send error while item cached
+		this.processor.onError(new IllegalStateException());
+
+		assertNotNull("Error should flow to result publisher", this.resultSubscriber.getError());
+		assertEquals(1, this.processor.getDiscardedBuffers().size());
+		assertSame(buffer, this.processor.getDiscardedBuffers().get(0));
+	}
+
+	@Test // SPR-17410
+	public void ioExceptionDuringWrite() {
+
+		// Fail on next write
+		this.processor.setWritePossible(true);
+		this.processor.setFailOnWrite(true);
+
+		// Write
+		DataBuffer buffer = mock(DataBuffer.class);
+		this.processor.onNext(buffer);
+
+		assertNotNull("Error should flow to result publisher", this.resultSubscriber.getError());
+		assertEquals(1, this.processor.getDiscardedBuffers().size());
+		assertSame(buffer, this.processor.getDiscardedBuffers().get(0));
+	}
+
+	@Test // SPR-17410
+	public void onNextWithoutDemand() {
+
+		// Disable writing: next item will be cached..
+		this.processor.setWritePossible(false);
+		DataBuffer buffer1 = mock(DataBuffer.class);
+		this.processor.onNext(buffer1);
+
+		// Send more data illegally
+		DataBuffer buffer2 = mock(DataBuffer.class);
+		this.processor.onNext(buffer2);
+
+		assertNotNull("Error should flow to result publisher", this.resultSubscriber.getError());
+		assertEquals(2, this.processor.getDiscardedBuffers().size());
+		assertSame(buffer2, this.processor.getDiscardedBuffers().get(0));
+		assertSame(buffer1, this.processor.getDiscardedBuffers().get(1));
+	}
+
+
+	private static final class TestListenerWriteProcessor extends AbstractListenerWriteProcessor<DataBuffer> {
+
+		private final List<DataBuffer> discardedBuffers = new ArrayList<>();
+
+		private boolean writePossible;
+
+		private boolean failOnWrite;
+
+
+		public List<DataBuffer> getDiscardedBuffers() {
+			return this.discardedBuffers;
+		}
+
+		public void setWritePossible(boolean writePossible) {
+			this.writePossible = writePossible;
+		}
+
+		public void setFailOnWrite(boolean failOnWrite) {
+			this.failOnWrite = failOnWrite;
+		}
+
+
+		@Override
+		protected boolean isDataEmpty(DataBuffer dataBuffer) {
+			return false;
+		}
+
+		@Override
+		protected boolean isWritePossible() {
+			return this.writePossible;
+		}
+
+		@Override
+		protected boolean write(DataBuffer dataBuffer) throws IOException {
+			if (this.failOnWrite) {
+				throw new IOException("write failed");
+			}
+			return true;
+		}
+
+		@Override
+		protected void writingFailed(Throwable ex) {
+			cancel();
+			onError(ex);
+		}
+
+		@Override
+		protected void discardData(DataBuffer dataBuffer) {
+			this.discardedBuffers.add(dataBuffer);
+		}
+	}
+
+
+	private static final class TestSubscription implements Subscription {
+
+		private long demand;
+
+
+		public long getDemand() {
+			return this.demand;
+		}
+
+
+		@Override
+		public void request(long n) {
+			this.demand = (n == Long.MAX_VALUE ? n : this.demand + n);
+		}
+
+		@Override
+		public void cancel() {
+		}
+	}
+
+	private static final class TestResultSubscriber implements Subscriber<Void> {
+
+		private Throwable error;
+
+
+		public Throwable getError() {
+			return this.error;
+		}
+
+
+		@Override
+		public void onSubscribe(Subscription subscription) {
+		}
+
+		@Override
+		public void onNext(Void aVoid) {
+		}
+
+		@Override
+		public void onError(Throwable ex) {
+			this.error = ex;
+		}
+
+		@Override
+		public void onComplete() {
+		}
+	}
+
+}

spring-webflux/src/main/java/org/springframework/web/reactive/socket/adapter/AbstractListenerWebSocketSession.java

@@ -250,11 +250,23 @@ public abstract class AbstractListenerWebSocketSession<T> extends AbstractWebSoc
 				logger.trace("Received message: " + message);
 			}
 			if (!this.pendingMessages.offer(message)) {
-				throw new IllegalStateException("Too many messages received. " +
-						"Please ensure WebSocketSession.receive() is subscribed to.");
+				discardData();
+				throw new IllegalStateException(
+						"Too many messages. Please ensure WebSocketSession.receive() is subscribed to.");
 			}
 			onDataAvailable();
 		}
+
+		@Override
+		protected void discardData() {
+			while (true) {
+				WebSocketMessage message = (WebSocketMessage) this.pendingMessages.poll();
+				if (message == null) {
+					return;
+				}
+				message.release();
+			}
+		}
 	}
 
 
@@ -267,6 +279,7 @@ public abstract class AbstractListenerWebSocketSession<T> extends AbstractWebSoc
 			if (logger.isTraceEnabled()) {
 				logger.trace("Sending message " + message);
 			}
+			// In case of IOException, onError handling should call discardData(WebSocketMessage)..
 			return sendMessage(message);
 		}
 
@@ -291,6 +304,11 @@ public abstract class AbstractListenerWebSocketSession<T> extends AbstractWebSoc
 			}
 			this.isReady = ready;
 		}
+
+		@Override
+		protected void discardData(WebSocketMessage message) {
+			message.release();
+		}
 	}
 
 }