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/*
* Copyright (c) 2016-2021 VMware Inc. or its affiliates, All Rights Reserved.
*
* 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 reactor.core.publisher;
import java.util.function.Consumer;
import java.util.function.Supplier;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;
import reactor.util.context.ContextView;
/**
* A domain representation of a Reactive Stream signal.
* There are 4 distinct signals and their possible sequence is defined as such:
* onError | (onSubscribe onNext* (onError | onComplete)?)
*
* @param the value type
*
* @author Stephane Maldini
*/
public interface Signal extends Supplier, Consumer> {
/**
* Creates and returns a {@code Signal} of variety {@code Type.COMPLETE}.
*
* Note that this variant associates an empty {@link Context} with the {@link Signal}.
*
* @param the value type
*
* @return an {@code OnCompleted} variety of {@code Signal}
*/
static Signal complete() {
return ImmutableSignal.onComplete();
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.COMPLETE}, associated
* with a specific {@link Context}.
*
* @param the value type
* @param context the {@link Context} associated with the completing source.
*
* @return an {@code OnCompleted} variety of {@code Signal}
*/
static Signal complete(Context context) {
if (context.isEmpty()) {
return ImmutableSignal.onComplete();
}
return new ImmutableSignal<>(context, SignalType.ON_COMPLETE, null, null, null);
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.FAILED}, which holds
* the error.
*
* Note that this variant associates an empty {@link Context} with the {@link Signal}.
*
* @param the value type
* @param e the error associated to the signal
*
* @return an {@code OnError} variety of {@code Signal}
*/
static Signal error(Throwable e) {
return error(e, Context.empty());
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.FAILED}, which holds
* the error and the {@link Context} associated with the erroring source.
*
* @param the value type
* @param e the error associated to the signal
* @param context the {@link Context} associated with the erroring source
*
* @return an {@code OnError} variety of {@code Signal}
*/
static Signal error(Throwable e, Context context) {
return new ImmutableSignal<>(context, SignalType.ON_ERROR, null, e, null);
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.NEXT}, which holds
* the value.
*
* Note that this variant associates an empty {@link Context} with the {@link Signal}.
*
* @param the value type
* @param t the value item associated to the signal
*
* @return an {@code OnNext} variety of {@code Signal}
*/
static Signal next(T t) {
return next(t, Context.empty());
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.NEXT}, which holds
* the value and the {@link Context} associated with the emitting source.
*
* @param the value type
* @param t the value item associated to the signal
* @param context the {@link Context} associated with the emitting source
*
* @return an {@code OnNext} variety of {@code Signal}
*/
static Signal next(T t, Context context) {
return new ImmutableSignal<>(context, SignalType.ON_NEXT, t, null, null);
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.ON_SUBSCRIBE}.
*
* Note that this variant associates an empty {@link Context} with the {@link Signal}.
*
* @param the value type
* @param subscription the subscription
*
* @return an {@code OnSubscribe} variety of {@code Signal}
*/
static Signal subscribe(Subscription subscription) {
return subscribe(subscription, Context.empty());
}
/**
* Creates and returns a {@code Signal} of variety {@code Type.ON_SUBSCRIBE}, that
* holds the {@link Context} associated with the subscribed source.
*
* @param the value type
* @param subscription the subscription
* @param context the {@link Context} associated with the subscribed source
*
* @return an {@code OnSubscribe} variety of {@code Signal}
*/
static Signal subscribe(Subscription subscription, Context context) {
return new ImmutableSignal<>(context, SignalType.ON_SUBSCRIBE, null, null, subscription);
}
/**
* Check if an arbitrary Object represents a COMPLETE {@link Signal}.
*
* @param o the object to check
* @return true if object represents the completion signal
*/
static boolean isComplete(Object o) {
return o == ImmutableSignal.onComplete() ||
(o instanceof Signal && ((Signal) o).getType() == SignalType.ON_COMPLETE);
}
/**
* Check if a arbitrary Object represents an ERROR {@link Signal}.
*
* @param o the object to check
* @return true if object represents the error signal
*/
static boolean isError(Object o) {
return o instanceof Signal && ((Signal) o).getType() == SignalType.ON_ERROR;
}
/**
* Read the error associated with this (onError) signal.
*
* @return the Throwable associated with this (onError) signal, or null if not relevant
*/
@Nullable
Throwable getThrowable();
/**
* Read the subscription associated with this (onSubscribe) signal.
*
* @return the Subscription associated with this (onSubscribe) signal, or null if not
* relevant
*/
@Nullable
Subscription getSubscription();
/**
* Retrieves the item associated with this (onNext) signal.
*
* @return the item associated with this (onNext) signal, or null if not relevant
*/
@Override
@Nullable
T get();
/**
* Has this signal an item associated with it ? (which only happens if it is an
* (onNext) signal)
*
* @return a boolean indicating whether or not this signal has an item associated with
* it
*/
default boolean hasValue() {
return isOnNext() && get() != null;
}
/**
* Read whether this signal is on error and carries the cause.
*
* @return a boolean indicating whether this signal has an error
*/
default boolean hasError() {
return isOnError() && getThrowable() != null;
}
/**
* Read the type of this signal: {@link SignalType#ON_SUBSCRIBE},
* {@link SignalType#ON_NEXT}, {@link SignalType#ON_ERROR}, or
* {@link SignalType#ON_COMPLETE}
*
* @return the type of the signal
*/
SignalType getType();
/**
* Return the readonly {@link Context} that is accessible by the time this {@link Signal} was
* emitted.
*
* @return an immutable {@link Context}, or an empty one if no context is available.
* @deprecated use {@link #getContextView()} instead. To be removed in 3.5.0
*/
@Deprecated
default Context getContext() {
return Context.of(getContextView());
}
/**
* Return the readonly {@link ContextView} that is accessible by the time this {@link Signal} was
* emitted.
*
* @return a readonly {@link ContextView}, or an empty one if no context is available.
*/
ContextView getContextView();
/**
* Indicates whether this signal represents an {@code onError} event.
*
* @return a boolean indicating whether this signal represents an {@code onError}
* event
*/
default boolean isOnError() {
return getType() == SignalType.ON_ERROR;
}
/**
* Indicates whether this signal represents an {@code onComplete} event.
*
* @return a boolean indicating whether this signal represents an {@code onComplete}
* event
*/
default boolean isOnComplete() {
return getType() == SignalType.ON_COMPLETE;
}
/**
* Indicates whether this signal represents an {@code onSubscribe} event.
*
* @return a boolean indicating whether this signal represents an {@code onSubscribe}
* event
*/
default boolean isOnSubscribe() {
return getType() == SignalType.ON_SUBSCRIBE;
}
/**
* Indicates whether this signal represents an {@code onNext} event.
*
* @return a boolean indicating whether this signal represents an {@code onNext} event
*/
default boolean isOnNext() {
return getType() == SignalType.ON_NEXT;
}
/**
* Propagate the signal represented by this {@link Signal} instance to a
* given {@link Subscriber}.
*
* @param observer the {@link Subscriber} to play the {@link Signal} on
*/
@Override
default void accept(Subscriber observer) {
if (isOnNext()) {
observer.onNext(get());
}
else if (isOnComplete()) {
observer.onComplete();
}
else if (isOnError()) {
observer.onError(getThrowable());
}
else if (isOnSubscribe()) {
observer.onSubscribe(getSubscription());
}
}
}