Browse Source
Reactored Servlet 3.1 and Undertow response support into an AbstractResponseBodySubscriber that uses an internal state machine, making thread-safity a lot easier.pull/1111/head
Arjen Poutsma
10 years ago
committed by
Sebastien Deleuze
4 changed files with 442 additions and 242 deletions
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/* |
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* Copyright 2002-2016 the original author or authors. |
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* |
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* Licensed under the Apache License, Version 2.0 (the "License"); |
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* you may not use this file except in compliance with the License. |
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* You may obtain a copy of the License at |
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* |
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* http://www.apache.org/licenses/LICENSE-2.0
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* |
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* Unless required by applicable law or agreed to in writing, software |
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* distributed under the License is distributed on an "AS IS" BASIS, |
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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* See the License for the specific language governing permissions and |
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* limitations under the License. |
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*/ |
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package org.springframework.http.server.reactive; |
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import java.io.IOException; |
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import java.nio.channels.Channel; |
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import java.util.concurrent.atomic.AtomicReference; |
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import javax.servlet.WriteListener; |
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import org.apache.commons.logging.Log; |
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import org.apache.commons.logging.LogFactory; |
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import org.reactivestreams.Subscriber; |
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import org.reactivestreams.Subscription; |
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import reactor.core.util.BackpressureUtils; |
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import org.springframework.core.io.buffer.DataBuffer; |
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import org.springframework.core.io.buffer.FlushingDataBuffer; |
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import org.springframework.core.io.buffer.support.DataBufferUtils; |
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import org.springframework.util.Assert; |
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/** |
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* Abstract base class for {@code Subscriber} implementations that bridge between |
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* event-listener APIs and Reactive Streams. Specifically, base class for the Servlet 3.1 |
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* and Undertow support. |
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* @author Arjen Poutsma |
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* @see ServletServerHttpRequest |
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* @see UndertowHttpHandlerAdapter |
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*/ |
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abstract class AbstractResponseBodySubscriber implements Subscriber<DataBuffer> { |
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protected final Log logger = LogFactory.getLog(getClass()); |
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private final AtomicReference<State> state = |
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new AtomicReference<>(State.UNSUBSCRIBED); |
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private volatile DataBuffer currentBuffer; |
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private volatile boolean subscriptionCompleted; |
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private Subscription subscription; |
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@Override |
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public final void onSubscribe(Subscription subscription) { |
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if (logger.isTraceEnabled()) { |
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logger.trace(this.state + " onSubscribe: " + subscription); |
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} |
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this.state.get().onSubscribe(this, subscription); |
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} |
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@Override |
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public final void onNext(DataBuffer dataBuffer) { |
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if (logger.isTraceEnabled()) { |
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logger.trace(this.state + " onNext: " + dataBuffer); |
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} |
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this.state.get().onNext(this, dataBuffer); |
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} |
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@Override |
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public final void onError(Throwable t) { |
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if (logger.isErrorEnabled()) { |
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logger.error(this.state + " onError: " + t, t); |
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} |
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this.state.get().onError(this, t); |
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} |
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@Override |
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public final void onComplete() { |
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if (logger.isTraceEnabled()) { |
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logger.trace(this.state + " onComplete"); |
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} |
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this.state.get().onComplete(this); |
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} |
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/** |
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* Called via a listener interface to indicate that writing is possible. |
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* @see WriteListener#onWritePossible() |
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* @see org.xnio.ChannelListener#handleEvent(Channel) |
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*/ |
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protected final void onWritePossible() { |
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this.state.get().onWritePossible(this); |
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} |
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/** |
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* Called when a {@link DataBuffer} is received via {@link Subscriber#onNext(Object)} |
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* @param dataBuffer the buffer that was received. |
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*/ |
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protected void receiveBuffer(DataBuffer dataBuffer) { |
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Assert.state(this.currentBuffer == null); |
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this.currentBuffer = dataBuffer; |
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} |
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/** |
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* Called when the current buffer should be |
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* {@linkplain DataBufferUtils#release(DataBuffer) released}. |
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*/ |
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protected void releaseBuffer() { |
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if (logger.isTraceEnabled()) { |
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logger.trace("releaseBuffer: " + this.currentBuffer); |
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} |
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DataBufferUtils.release(this.currentBuffer); |
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this.currentBuffer = null; |
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} |
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/** |
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* Writes the given data buffer to the output, indicating if the entire buffer was |
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* written. |
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* @param dataBuffer the data buffer to write |
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* @return {@code true} if {@code dataBuffer} was fully written and a new buffer |
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* can be requested; {@code false} otherwise |
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*/ |
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protected abstract boolean write(DataBuffer dataBuffer) throws IOException; |
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/** |
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* Writes the given exception to the output. |
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*/ |
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protected abstract void writeError(Throwable t); |
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/** |
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* Flushes the output. |
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*/ |
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protected abstract void flush() throws IOException; |
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/** |
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* Closes the output. |
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*/ |
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protected abstract void close(); |
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private void changeState(State oldState, State newState) { |
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this.state.compareAndSet(oldState, newState); |
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} |
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/** |
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* Represents a state for the {@link Subscriber} to be in. The following figure |
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* indicate the four different states that exist, and the relationships between them. |
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* |
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* <pre> |
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* UNSUBSCRIBED |
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* | |
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* v |
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* REQUESTED <---> RECEIVED |
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* | | |
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* v v |
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* COMPLETED |
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* </pre> |
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* Refer to the individual states for more information. |
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*/ |
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private enum State { |
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/** |
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* The initial unsubscribed state. Will respond to {@code onSubscribe} by |
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* requesting 1 buffer from the subscription, and change state to {@link |
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* #REQUESTED}. |
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*/ |
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UNSUBSCRIBED { |
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@Override |
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void onSubscribe(AbstractResponseBodySubscriber subscriber, |
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Subscription subscription) { |
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if (BackpressureUtils.validate(subscriber.subscription, subscription)) { |
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subscriber.subscription = subscription; |
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subscriber.changeState(this, REQUESTED); |
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subscription.request(1); |
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} |
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} |
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}, |
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/** |
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* State that gets entered after a buffer has been |
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* {@linkplain Subscription#request(long) requested}. Responds to {@code onNext} |
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* by changing state to {@link #RECEIVED}, and responds to {@code onComplete} by |
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* changing state to {@link #COMPLETED}. |
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*/ |
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REQUESTED { |
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@Override |
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void onNext(AbstractResponseBodySubscriber subscriber, |
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DataBuffer dataBuffer) { |
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subscriber.changeState(this, RECEIVED); |
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subscriber.receiveBuffer(dataBuffer); |
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} |
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@Override |
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void onComplete(AbstractResponseBodySubscriber subscriber) { |
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subscriber.subscriptionCompleted = true; |
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subscriber.changeState(this, COMPLETED); |
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subscriber.close(); |
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} |
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}, |
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/** |
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* State that gets entered after a buffer has been |
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* {@linkplain Subscriber#onNext(Object) received}. Responds to |
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* {@code onWritePossible} by writing the current buffer, and if it can be |
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* written completely, changes state to either {@link #REQUESTED} if the |
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* subscription has not been completed; or {@link #COMPLETED} if it has. |
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*/ |
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RECEIVED { |
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@Override |
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void onWritePossible(AbstractResponseBodySubscriber subscriber) { |
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DataBuffer dataBuffer = subscriber.currentBuffer; |
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try { |
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boolean writeCompleted = subscriber.write(dataBuffer); |
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if (writeCompleted) { |
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if (dataBuffer instanceof FlushingDataBuffer) { |
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subscriber.flush(); |
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} |
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subscriber.releaseBuffer(); |
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boolean subscriptionCompleted = subscriber.subscriptionCompleted; |
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if (!subscriptionCompleted) { |
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subscriber.changeState(this, REQUESTED); |
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subscriber.subscription.request(1); |
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} |
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else { |
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subscriber.changeState(this, COMPLETED); |
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subscriber.close(); |
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} |
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} |
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} |
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catch (IOException ex) { |
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subscriber.onError(ex); |
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} |
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} |
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@Override |
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void onComplete(AbstractResponseBodySubscriber subscriber) { |
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subscriber.subscriptionCompleted = true; |
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} |
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}, |
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/** |
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* The terminal completed state. Does not respond to any events. |
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*/ |
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COMPLETED { |
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@Override |
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void onNext(AbstractResponseBodySubscriber subscriber, |
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DataBuffer dataBuffer) { |
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// ignore
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} |
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@Override |
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void onError(AbstractResponseBodySubscriber subscriber, Throwable t) { |
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// ignore
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} |
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@Override |
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void onComplete(AbstractResponseBodySubscriber subscriber) { |
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// ignore
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} |
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}; |
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void onSubscribe(AbstractResponseBodySubscriber subscriber, Subscription s) { |
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throw new IllegalStateException(toString()); |
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} |
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void onNext(AbstractResponseBodySubscriber subscriber, DataBuffer dataBuffer) { |
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throw new IllegalStateException(toString()); |
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} |
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void onError(AbstractResponseBodySubscriber subscriber, Throwable t) { |
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subscriber.changeState(this, COMPLETED); |
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subscriber.writeError(t); |
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subscriber.close(); |
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} |
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void onComplete(AbstractResponseBodySubscriber subscriber) { |
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throw new IllegalStateException(toString()); |
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} |
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void onWritePossible(AbstractResponseBodySubscriber subscriber) { |
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// ignore
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} |
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} |
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} |
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