org.springframework.http.server.reactive.AbstractListenerWriteFlushProcessor Maven / Gradle / Ivy
/*
* Copyright 2002-2021 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.server.reactive;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.commons.logging.Log;
import org.reactivestreams.Processor;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import org.springframework.core.log.LogDelegateFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
/**
* An alternative to {@link AbstractListenerWriteProcessor} but instead writing
* a {@code Publisher>} with flush boundaries enforces after
* the completion of each nested Publisher.
*
* @author Arjen Poutsma
* @author Violeta Georgieva
* @author Rossen Stoyanchev
* @since 5.0
* @param the type of element signaled to the {@link Subscriber}
*/
public abstract class AbstractListenerWriteFlushProcessor implements Processor, Void> {
/**
* Special logger for debugging Reactive Streams signals.
* @see LogDelegateFactory#getHiddenLog(Class)
* @see AbstractListenerReadPublisher#rsReadLogger
* @see AbstractListenerWriteProcessor#rsWriteLogger
* @see WriteResultPublisher#rsWriteResultLogger
*/
protected static final Log rsWriteFlushLogger =
LogDelegateFactory.getHiddenLog(AbstractListenerWriteFlushProcessor.class);
private final AtomicReference state = new AtomicReference<>(State.UNSUBSCRIBED);
@Nullable
private Subscription subscription;
private volatile boolean sourceCompleted;
@Nullable
private volatile AbstractListenerWriteProcessor currentWriteProcessor;
private final WriteResultPublisher resultPublisher;
private final String logPrefix;
public AbstractListenerWriteFlushProcessor() {
this("");
}
/**
* Create an instance with the given log prefix.
* @since 5.1
*/
public AbstractListenerWriteFlushProcessor(String logPrefix) {
this.logPrefix = logPrefix;
this.resultPublisher = new WriteResultPublisher(logPrefix + "[WFP] ",
() -> {
cancel();
// Complete immediately
State oldState = this.state.getAndSet(State.COMPLETED);
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + oldState + " -> " + this.state);
}
// Propagate to current "write" Processor
AbstractListenerWriteProcessor writeProcessor = this.currentWriteProcessor;
if (writeProcessor != null) {
writeProcessor.cancelAndSetCompleted();
}
this.currentWriteProcessor = null;
});
}
/**
* Create an instance with the given log prefix.
* @since 5.1
*/
public String getLogPrefix() {
return this.logPrefix;
}
// Subscriber methods and async I/O notification methods...
@Override
public final void onSubscribe(Subscription subscription) {
this.state.get().onSubscribe(this, subscription);
}
@Override
public final void onNext(Publisher publisher) {
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + "onNext: \"write\" Publisher");
}
this.state.get().onNext(this, publisher);
}
/**
* Error signal from the upstream, write Publisher. This is also used by
* subclasses to delegate error notifications from the container.
*/
@Override
public final void onError(Throwable ex) {
State state = this.state.get();
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + "onError: " + ex + " [" + state + "]");
}
state.onError(this, ex);
}
/**
* Completion signal from the upstream, write Publisher. This is also used
* by subclasses to delegate completion notifications from the container.
*/
@Override
public final void onComplete() {
State state = this.state.get();
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + "onComplete [" + state + "]");
}
state.onComplete(this);
}
/**
* Invoked when flushing is possible, either in the same thread after a check
* via {@link #isWritePossible()}, or as a callback from the underlying
* container.
*/
protected final void onFlushPossible() {
this.state.get().onFlushPossible(this);
}
/**
* Cancel the upstream chain of "write" Publishers only, for example due to
* Servlet container error/completion notifications. This should usually
* be followed up with a call to either {@link #onError(Throwable)} or
* {@link #onComplete()} to notify the downstream chain, that is unless
* cancellation came from downstream.
*/
protected void cancel() {
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + "cancel [" + this.state + "]");
}
if (this.subscription != null) {
this.subscription.cancel();
}
}
// Publisher implementation for result notifications...
@Override
public final void subscribe(Subscriber subscriber) {
this.resultPublisher.subscribe(subscriber);
}
// Write API methods to be implemented or template methods to override...
/**
* Create a new processor for the current flush boundary.
*/
protected abstract Processor createWriteProcessor();
/**
* Whether writing/flushing is possible.
*/
protected abstract boolean isWritePossible();
/**
* Flush the output if ready, or otherwise {@link #isFlushPending()} should
* return true after.
* This is primarily for the Servlet non-blocking I/O API where flush
* cannot be called without a readyToWrite check.
*/
protected abstract void flush() throws IOException;
/**
* Whether flushing is pending.
*
This is primarily for the Servlet non-blocking I/O API where flush
* cannot be called without a readyToWrite check.
*/
protected abstract boolean isFlushPending();
/**
* Invoked when an error happens while flushing.
*
The default implementation cancels the upstream write publisher and
* sends an onError downstream as the result of request handling.
*/
protected void flushingFailed(Throwable t) {
cancel();
onError(t);
}
// Private methods for use in State...
private boolean changeState(State oldState, State newState) {
boolean result = this.state.compareAndSet(oldState, newState);
if (result && rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + oldState + " -> " + newState);
}
return result;
}
private void flushIfPossible() {
boolean result = isWritePossible();
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(getLogPrefix() + "isWritePossible[" + result + "]");
}
if (result) {
onFlushPossible();
}
}
/**
* Represents a state for the {@link Processor} to be in.
*
*
* UNSUBSCRIBED
* |
* v
* REQUESTED <---> RECEIVED ------+
* | | |
* | v |
* | FLUSHING |
* | | |
* | v |
* +--------> COMPLETED <-----+
*
*/
private enum State {
UNSUBSCRIBED {
@Override
public void onSubscribe(AbstractListenerWriteFlushProcessor processor, Subscription subscription) {
Assert.notNull(subscription, "Subscription must not be null");
if (processor.changeState(this, REQUESTED)) {
processor.subscription = subscription;
subscription.request(1);
}
else {
super.onSubscribe(processor, subscription);
}
}
@Override
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
// This can happen on (very early) completion notification from container..
if (processor.changeState(this, COMPLETED)) {
processor.resultPublisher.publishComplete();
}
else {
processor.state.get().onComplete(processor);
}
}
},
REQUESTED {
@Override
public void onNext(AbstractListenerWriteFlushProcessor processor,
Publisher currentPublisher) {
if (processor.changeState(this, RECEIVED)) {
Processor writeProcessor = processor.createWriteProcessor();
processor.currentWriteProcessor = (AbstractListenerWriteProcessor) writeProcessor;
currentPublisher.subscribe(writeProcessor);
writeProcessor.subscribe(new WriteResultSubscriber(processor));
}
}
@Override
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
if (processor.changeState(this, COMPLETED)) {
processor.resultPublisher.publishComplete();
}
else {
processor.state.get().onComplete(processor);
}
}
},
RECEIVED {
@Override
public void writeComplete(AbstractListenerWriteFlushProcessor processor) {
try {
processor.flush();
}
catch (Throwable ex) {
processor.flushingFailed(ex);
return;
}
if (processor.changeState(this, REQUESTED)) {
if (processor.sourceCompleted) {
handleSourceCompleted(processor);
}
else {
Assert.state(processor.subscription != null, "No subscription");
processor.subscription.request(1);
}
}
}
@Override
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
processor.sourceCompleted = true;
// A competing write might have completed very quickly
if (processor.state.get() == State.REQUESTED) {
handleSourceCompleted(processor);
}
}
private void handleSourceCompleted(AbstractListenerWriteFlushProcessor processor) {
if (processor.isFlushPending()) {
// Ensure the final flush
processor.changeState(State.REQUESTED, State.FLUSHING);
processor.flushIfPossible();
}
else if (processor.changeState(State.REQUESTED, State.COMPLETED)) {
processor.resultPublisher.publishComplete();
}
else {
processor.state.get().onComplete(processor);
}
}
},
FLUSHING {
@Override
public void onFlushPossible(AbstractListenerWriteFlushProcessor processor) {
try {
processor.flush();
}
catch (Throwable ex) {
processor.flushingFailed(ex);
return;
}
if (processor.changeState(this, COMPLETED)) {
processor.resultPublisher.publishComplete();
}
else {
processor.state.get().onComplete(processor);
}
}
@Override
public void onNext(AbstractListenerWriteFlushProcessor proc, Publisher pub) {
// ignore
}
@Override
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
// ignore
}
},
COMPLETED {
@Override
public void onNext(AbstractListenerWriteFlushProcessor proc, Publisher pub) {
// ignore
}
@Override
public void onError(AbstractListenerWriteFlushProcessor processor, Throwable t) {
// ignore
}
@Override
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
// ignore
}
};
public void onSubscribe(AbstractListenerWriteFlushProcessor proc, Subscription subscription) {
subscription.cancel();
}
public void onNext(AbstractListenerWriteFlushProcessor proc, Publisher pub) {
throw new IllegalStateException(toString());
}
public void onError(AbstractListenerWriteFlushProcessor processor, Throwable ex) {
if (processor.changeState(this, COMPLETED)) {
processor.resultPublisher.publishError(ex);
}
else {
processor.state.get().onError(processor, ex);
}
}
public void onComplete(AbstractListenerWriteFlushProcessor processor) {
throw new IllegalStateException(toString());
}
public void writeComplete(AbstractListenerWriteFlushProcessor processor) {
throw new IllegalStateException(toString());
}
public void onFlushPossible(AbstractListenerWriteFlushProcessor processor) {
// ignore
}
/**
* Subscriber to receive and delegate completion notifications for from
* the current Publisher, i.e. for the current flush boundary.
*/
private static class WriteResultSubscriber implements Subscriber {
private final AbstractListenerWriteFlushProcessor processor;
public WriteResultSubscriber(AbstractListenerWriteFlushProcessor processor) {
this.processor = processor;
}
@Override
public void onSubscribe(Subscription subscription) {
subscription.request(Long.MAX_VALUE);
}
@Override
public void onNext(Void aVoid) {
}
@Override
public void onError(Throwable ex) {
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(
this.processor.getLogPrefix() + "current \"write\" Publisher failed: " + ex);
}
this.processor.currentWriteProcessor = null;
this.processor.cancel();
this.processor.onError(ex);
}
@Override
public void onComplete() {
if (rsWriteFlushLogger.isTraceEnabled()) {
rsWriteFlushLogger.trace(
this.processor.getLogPrefix() + "current \"write\" Publisher completed");
}
this.processor.currentWriteProcessor = null;
this.processor.state.get().writeComplete(this.processor);
}
@Override
public String toString() {
return this.processor.getClass().getSimpleName() + "-WriteResultSubscriber";
}
}
}
}