/*
* 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 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 ResponseBodyWriteResultPublisher publisherDelegate =
new ResponseBodyWriteResultPublisher();
private final AtomicReference<State> state =
new AtomicReference<>(State.UNSUBSCRIBED);
private volatile DataBuffer currentBuffer;
private volatile boolean subscriberCompleted;
private Subscription subscription;
// Subscriber
@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);
}
// Publisher
@Override
public final void subscribe(Subscriber<? super Void> subscriber) {
this.publisherDelegate.subscribe(subscriber);
}
// 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.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;
}
/**
* 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;
}
/**
* Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)}
* or when only partial data from the {@link DataBuffer} was written.
*/
private void writeIfPossible() {
if (isWritePossible()) {
onWritePossible();
}
}
/**
* Called via a listener interface to determine whether writing is possible.
*/
protected boolean isWritePossible() {
return false;
}
/**
* 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;
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(AbstractResponseBodyProcessor processor,
Subscription subscription) {
Objects.requireNonNull(subscription, "Subscription cannot be null");
if (processor.changeState(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.changeState(this, RECEIVED)) {
processor.receiveBuffer(dataBuffer);
processor.writeIfPossible();
}
}
@Override
void onComplete(AbstractResponseBodyProcessor processor) {
if (processor.changeState(this, COMPLETED)) {
processor.subscriberCompleted = true;
processor.publisherDelegate.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.changeState(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.changeState(WRITING, REQUESTED);
processor.subscription.request(1);
}
else {
processor.changeState(WRITING, COMPLETED);
processor.publisherDelegate.publishComplete();
}
}
else {
processor.changeState(WRITING, RECEIVED);
processor.writeIfPossible();
}
}
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.changeState(this, COMPLETED)) {
processor.publisherDelegate.publishError(t);
}
}
void onComplete(AbstractResponseBodyProcessor processor) {
throw new IllegalStateException(toString());
}
void onWritePossible(AbstractResponseBodyProcessor processor) {
// ignore
}
}
}