org.eclipse.jetty.io.content.ContentSourcePublisher Maven / Gradle / Ivy
//
// ========================================================================
// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//
package org.eclipse.jetty.io.content;
import java.util.Objects;
import java.util.concurrent.Flow;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import org.eclipse.jetty.io.Content;
import org.eclipse.jetty.util.IteratingCallback;
import org.eclipse.jetty.util.MathUtils;
import org.eclipse.jetty.util.StaticException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Wraps a {@link Content.Source} as a {@link Flow.Publisher}.
* When content is requested via {@link Flow.Subscription#request(long)}, it is
* read from the passed {@link Content.Source} and passed to {@link Flow.Subscriber#onNext(Object)}.
* If no content is available, then the {@link Content.Source#demand(Runnable)} method is used to
* ultimately call {@link Flow.Subscriber#onNext(Object)} once content is available.
* {@link Content.Source} can be consumed only once and does not support multicast subscription.
* {@link Content.Source} will be consumed fully, otherwise will be failed in case of any errors
* to prevent resource leaks.
*/
public class ContentSourcePublisher implements Flow.Publisher
{
private static final Logger LOG = LoggerFactory.getLogger(ContentSourcePublisher.class);
private final AtomicReference content;
public ContentSourcePublisher(Content.Source content)
{
Objects.requireNonNull(content, "Content.Source must not be null");
this.content = new AtomicReference<>(content);
}
@Override
public void subscribe(Flow.Subscriber subscriber)
{
// As per rule 1.11, we have decided to support SINGLE subscriber
// in a UNICAST configuration for this implementation. It means
// that Content.Source can be consumed only once.
Content.Source content = this.content.getAndSet(null);
if (content != null)
onSubscribe(subscriber, content);
else
onMultiSubscribe(subscriber);
}
private void onSubscribe(Flow.Subscriber subscriber, Content.Source content)
{
// As per rule 1.9, we need to throw a `java.lang.NullPointerException`
// if the `Subscriber` is `null`
if (subscriber == null)
{
NullPointerException error = new NullPointerException("Flow.Subscriber must not be null");
content.fail(error);
throw error;
}
ActiveSubscription subscription = new ActiveSubscription(content, subscriber);
// As per rule 1.9, this method must return normally (i.e. not throw).
try
{
subscriber.onSubscribe(subscription);
}
catch (Throwable err)
{
// As per rule 2.13, we MUST consider subscription cancelled and
// MUST raise this error condition in a fashion that is adequate for the runtime environment.
subscription.cancel(new SuppressedException(err));
if (LOG.isTraceEnabled())
LOG.trace("Flow.Subscriber " + subscriber + " violated rule 2.13", err);
}
}
private void onMultiSubscribe(Flow.Subscriber subscriber)
{
// As per rule 1.9, we need to throw a `java.lang.NullPointerException`
// if the `Subscriber` is `null`
if (subscriber == null)
throw new NullPointerException("Flow.Subscriber must not be null");
ExhaustedSubscription subscription = new ExhaustedSubscription();
// As per 1.9, this method must return normally (i.e. not throw).
try
{
// As per rule 1.9, the only legal way to signal about Subscriber rejection
// is by calling onError (after calling onSubscribe).
subscriber.onSubscribe(subscription);
subscriber.onError(new IllegalStateException("Content.Source was exhausted."));
}
catch (Throwable err)
{
// As per rule 2.13, we MUST consider subscription cancelled and
// MUST raise this error condition in a fashion that is adequate for the runtime environment.
if (LOG.isTraceEnabled())
LOG.trace("Flow.Subscriber " + subscriber + " violated rule 2.13", err);
}
}
private static final class ExhaustedSubscription implements Flow.Subscription
{
@Override
public void request(long n)
{
// As per rules 3.6 and 3.7, after the Subscription is cancelled all operations MUST be NOPs.
}
@Override
public void cancel()
{
// As per rules 3.6 and 3.7, after the Subscription is cancelled all operations MUST be NOPs.
}
}
private static final class ActiveSubscription extends IteratingCallback implements Flow.Subscription
{
private static final long NO_MORE_DEMAND = -1;
private static final Throwable COMPLETED = new StaticException("Source.Content read fully");
private final AtomicReference cancelled;
private final AtomicLong demand;
private Content.Source content;
private Flow.Subscriber subscriber;
public ActiveSubscription(Content.Source content, Flow.Subscriber subscriber)
{
this.cancelled = new AtomicReference<>(null);
this.demand = new AtomicLong(0);
this.content = content;
this.subscriber = subscriber;
}
// As per rule 3.3, Subscription MUST place an upper bound on possible synchronous
// recursion between Publisher and Subscriber
//
// As per rule 1.3, onSubscribe, onNext, onError and onComplete signaled to a
// Subscriber MUST be signaled serially.
//
// IteratingCallback guarantee that process() method will be executed by one thread only.
// The process() method can be only initiated from request() or cancel() demands methods.
@Override
protected Action process()
{
Throwable cancelled = this.cancelled.get();
if (cancelled != null)
{
// As per rule 3.13, Subscription.cancel() MUST request the Publisher to eventually
// drop any references to the corresponding subscriber.
this.demand.set(NO_MORE_DEMAND);
if (cancelled != COMPLETED)
this.content.fail(cancelled);
this.content = null;
try
{
if (cancelled == COMPLETED)
this.subscriber.onComplete();
else if (!(cancelled instanceof SuppressedException))
this.subscriber.onError(cancelled);
}
catch (Throwable err)
{
if (LOG.isTraceEnabled())
LOG.trace("Flow.Subscriber " + subscriber + " violated rule 2.13", err);
}
this.subscriber = null;
return Action.SUCCEEDED;
}
Content.Chunk chunk = content.read();
if (chunk == null)
{
content.demand(this::succeeded);
return Action.SCHEDULED;
}
if (Content.Chunk.isFailure(chunk))
{
cancel(chunk.getFailure());
chunk.release();
return Action.IDLE;
}
try
{
this.subscriber.onNext(chunk);
}
catch (Throwable err)
{
cancel(new SuppressedException(err));
if (LOG.isTraceEnabled())
LOG.trace("Flow.Subscriber " + subscriber + " violated rule 2.13", err);
}
chunk.release();
if (chunk.isLast())
{
cancel(COMPLETED);
return Action.IDLE;
}
if (demand.decrementAndGet() > 0)
this.iterate();
return Action.IDLE;
}
@Override
public void request(long n)
{
// As per rules 3.6 and 3.7, after the Subscription is cancelled all operations MUST be NOPs.
if (cancelled.get() != null)
return;
// As per rule 3.9, MUST signal onError with a java.lang.IllegalArgumentException if the argument is <= 0.
if (n <= 0L)
{
String errorMsg = "Flow.Subscriber " + subscriber + " violated rule 3.9: non-positive requests are not allowed.";
cancel(new IllegalArgumentException(errorMsg));
return;
}
// As per rule 3.17, when demand overflows `Long.MAX_VALUE`
// we treat the signalled demand as "effectively unbounded"
if (demand.updateAndGet(it -> it == NO_MORE_DEMAND ? it : MathUtils.cappedAdd(it, n)) != NO_MORE_DEMAND)
this.iterate();
}
@Override
public void cancel()
{
cancel(new CancelledException());
}
public void cancel(Throwable cause)
{
// As per rules 3.6 and 3.7, after the Subscription is cancelled all operations MUST be NOPs.
//
// As per rule 3.5, this handles cancellation requests, and is idempotent, thread-safe and not
// synchronously performing heavy computations
if (cancelled.compareAndSet(null, cause))
this.iterate();
}
// Publisher notes
//
// 1.6 If a Publisher signals either onError or onComplete on a Subscriber,
// that Subscriber’s Subscription MUST be considered cancelled.
// 2.4 Subscriber.onComplete() and Subscriber.onError(Throwable t) MUST consider the
// Subscription cancelled after having received the signal.
//
// Publisher failed -> cancel(Throwable)
// 1.4 If a Publisher fails it MUST signal an onError.
//
// Publisher succeeded -> cancel(COMPLETED)
// 1.5 If a Publisher terminates successfully (finite stream) it MUST signal an onComplete.
// Subscriber
// 2.13 In the case that this rule is violated, any associated Subscription to the Subscriber
// MUST be considered as cancelled, and the caller MUST raise this error condition in a
// fashion that is adequate for the runtime environment.
//
// Subscriber.onSubscribe/onNext/onError/onComplete failed -> cancel(new Suppressed(cause))
// Subscription notes
//
// Subscription.cancel -> cancel(new Cancelled())
// It's not clearly specified in the specification, but according to:
// - the issue: https://github.com/reactive-streams/reactive-streams-jvm/issues/458
// - TCK test 'untested_spec108_possiblyCanceledSubscriptionShouldNotReceiveOnErrorOrOnCompleteSignals'
// - 1.8 If a Subscription is cancelled its Subscriber MUST eventually stop being signaled.
//
// Subscription.request with negative argument -> cancel(err)
// 3.9 While the Subscription is not cancelled, Subscription.request(long n) MUST signal onError with a
// java.lang.IllegalArgumentException if the argument is <= 0.
}
private static class SuppressedException extends Exception
{
SuppressedException(String message)
{
super(message);
}
SuppressedException(Throwable cause)
{
super(cause.getMessage(), cause);
}
}
private static class CancelledException extends SuppressedException
{
CancelledException()
{
super("Subscription was cancelled");
}
}
}
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