/*
* 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.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import javax.servlet.ReadListener;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.util.BackpressureUtils;
import org.springframework.core.io.buffer.DataBuffer;
/**
* Abstract base class for {@code Publisher} 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 AbstractRequestBodyPublisher implements Publisher<DataBuffer> {
protected final Log logger = LogFactory.getLog(getClass());
private final AtomicReference<State> state =
new AtomicReference<>(State.UNSUBSCRIBED);
private final AtomicLong demand = new AtomicLong();
private Subscriber<? super DataBuffer> subscriber;
@Override
public void subscribe(Subscriber<? super DataBuffer> subscriber) {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.state + " subscribe: " + subscriber);
}
this.state.get().subscribe(this, subscriber);
}
/**
* Called via a listener interface to indicate that reading is possible.
* @see ReadListener#onDataAvailable()
* @see org.xnio.ChannelListener#handleEvent(Channel)
*/
protected final void onDataAvailable() {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.state + " onDataAvailable");
}
this.state.get().onDataAvailable(this);
}
/**
* Called via a listener interface to indicate that all data has been read.
* @see ReadListener#onAllDataRead()
* @see org.xnio.ChannelListener#handleEvent(Channel)
*/
protected final void onAllDataRead() {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.state + " onAllDataRead");
}
this.state.get().onAllDataRead(this);
}
/**
* Called by a listener interface to indicate that as error has occured.
* @param t the error
* @see ReadListener#onError(Throwable)
*/
protected final void onError(Throwable t) {
if (this.logger.isErrorEnabled()) {
this.logger.error(this.state + " onError: " + t, t);
}
this.state.get().onError(this, t);
}
/**
* Reads and publishes data buffers from the input. Continues till either there is no
* more demand, or till there is no more data to be read.
* @return {@code true} if there is more demand; {@code false} otherwise
*/
private boolean readAndPublish() throws IOException {
while (hasDemand()) {
DataBuffer dataBuffer = read();
if (dataBuffer != null) {
BackpressureUtils.getAndSub(this.demand, 1L);
this.subscriber.onNext(dataBuffer);
}
else {
return true;
}
}
return false;
}
protected abstract void checkOnDataAvailable();
/**
* Reads a data buffer from the input, if possible. Returns {@code null} if a buffer
* could not be read.
* @return the data buffer that was read; or {@code null}
*/
protected abstract DataBuffer read() throws IOException;
private boolean hasDemand() {
return this.demand.get() > 0;
}
private boolean changeState(AbstractRequestBodyPublisher.State oldState,
AbstractRequestBodyPublisher.State newState) {
return this.state.compareAndSet(oldState, newState);
}
private static final class RequestBodySubscription implements Subscription {
private final AbstractRequestBodyPublisher publisher;
public RequestBodySubscription(AbstractRequestBodyPublisher publisher) {
this.publisher = publisher;
}
@Override
public final void request(long n) {
if (this.publisher.logger.isTraceEnabled()) {
this.publisher.logger.trace(state() + " request: " + n);
}
state().request(this.publisher, n);
}
@Override
public final void cancel() {
if (this.publisher.logger.isTraceEnabled()) {
this.publisher.logger.trace(state() + " cancel");
}
state().cancel(this.publisher);
}
private AbstractRequestBodyPublisher.State state() {
return this.publisher.state.get();
}
}
/**
* Represents a state for the {@link Publisher} to be in. The following figure
* indicate the four different states that exist, and the relationships between them.
*
* <pre>
* UNSUBSCRIBED
* |
* v
* NO_DEMAND -------------------> DEMAND
* | ^ ^ |
* | | | |
* | --------- READING <----- |
* | | |
* | v |
* ------------> COMPLETED <---------
* </pre>
* Refer to the individual states for more information.
*/
private enum State {
/**
* The initial unsubscribed state. Will respond to {@link
* #subscribe(AbstractRequestBodyPublisher, Subscriber)} by
* changing state to {@link #NO_DEMAND}.
*/
UNSUBSCRIBED {
@Override
void subscribe(AbstractRequestBodyPublisher publisher,
Subscriber<? super DataBuffer> subscriber) {
Objects.requireNonNull(subscriber);
if (publisher.changeState(this, NO_DEMAND)) {
Subscription subscription = new RequestBodySubscription(
publisher);
publisher.subscriber = subscriber;
subscriber.onSubscribe(subscription);
}
else {
throw new IllegalStateException(toString());
}
}
},
/**
* State that gets entered when there is no demand. Responds to {@link
* #request(AbstractRequestBodyPublisher, long)} by increasing the demand,
* changing state to {@link #DEMAND} and will check whether there
* is data available for reading.
*/
NO_DEMAND {
@Override
void request(AbstractRequestBodyPublisher publisher, long n) {
if (BackpressureUtils.checkRequest(n, publisher.subscriber)) {
BackpressureUtils.addAndGet(publisher.demand, n);
if (publisher.changeState(this, DEMAND)) {
publisher.checkOnDataAvailable();
}
}
}
},
/**
* State that gets entered when there is demand. Responds to
* {@link #onDataAvailable(AbstractRequestBodyPublisher)} by
* reading the available data. The state will be changed to
* {@link #NO_DEMAND} if there is no demand.
*/
DEMAND {
@Override
void onDataAvailable(AbstractRequestBodyPublisher publisher) {
if (publisher.changeState(this, READING)) {
try {
boolean demandAvailable = publisher.readAndPublish();
if (demandAvailable) {
publisher.changeState(READING, DEMAND);
publisher.checkOnDataAvailable();
} else {
publisher.changeState(READING, NO_DEMAND);
}
} catch (IOException ex) {
publisher.onError(ex);
}
}
}
},
READING {
@Override
void request(AbstractRequestBodyPublisher publisher, long n) {
if (BackpressureUtils.checkRequest(n, publisher.subscriber)) {
BackpressureUtils.addAndGet(publisher.demand, n);
}
}
},
/**
* The terminal completed state. Does not respond to any events.
*/
COMPLETED {
@Override
void request(AbstractRequestBodyPublisher publisher, long n) {
// ignore
}
@Override
void cancel(AbstractRequestBodyPublisher publisher) {
// ignore
}
@Override
void onAllDataRead(AbstractRequestBodyPublisher publisher) {
// ignore
}
@Override
void onError(AbstractRequestBodyPublisher publisher, Throwable t) {
// ignore
}
};
void subscribe(AbstractRequestBodyPublisher publisher,
Subscriber<? super DataBuffer> subscriber) {
throw new IllegalStateException(toString());
}
void request(AbstractRequestBodyPublisher publisher, long n) {
throw new IllegalStateException(toString());
}
void cancel(AbstractRequestBodyPublisher publisher) {
publisher.changeState(this, COMPLETED);
}
void onDataAvailable(AbstractRequestBodyPublisher publisher) {
// ignore
}
void onAllDataRead(AbstractRequestBodyPublisher publisher) {
if (publisher.changeState(this, COMPLETED)) {
if (publisher.subscriber != null) {
publisher.subscriber.onComplete();
}
}
}
void onError(AbstractRequestBodyPublisher publisher, Throwable t) {
if (publisher.changeState(this, COMPLETED)) {
if (publisher.subscriber != null) {
publisher.subscriber.onError(t);
}
}
}
}
}