Ensure onComplete/onError events will be delivered

Issue: SPR-16207

spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerReadPublisher.java

@@ -312,7 +312,9 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 		}
 
 		<T> void cancel(AbstractListenerReadPublisher<T> publisher) {
-			publisher.changeState(this, COMPLETED);
+			if (!publisher.changeState(this, COMPLETED)) {
+				publisher.state.get().cancel(publisher);
+			}
 		}
 
 		<T> void onDataAvailable(AbstractListenerReadPublisher<T> publisher) {
@@ -325,6 +327,9 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 					publisher.subscriber.onComplete();
 				}
 			}
+			else {
+				publisher.state.get().onAllDataRead(publisher);
+			}
 		}
 
 		<T> void onError(AbstractListenerReadPublisher<T> publisher, Throwable t) {
@@ -333,6 +338,9 @@ public abstract class AbstractListenerReadPublisher<T> implements Publisher<T> {
 					publisher.subscriber.onError(t);
 				}
 			}
+			else {
+				publisher.state.get().onError(publisher, t);
+			}
 		}
 	}
 

spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteFlushProcessor.java

@@ -190,6 +190,9 @@ public abstract class AbstractListenerWriteFlushProcessor<T> implements Processo
 				if (processor.changeState(this, COMPLETED)) {
 					processor.resultPublisher.publishComplete();
 				}
+				else {
+					processor.state.get().onComplete(processor);
+				}
 			}
 		},
 
@@ -212,6 +215,9 @@ public abstract class AbstractListenerWriteFlushProcessor<T> implements Processo
 					else if (processor.changeState(this, COMPLETED)) {
 						processor.resultPublisher.publishComplete();
 					}
+					else {
+						processor.state.get().onComplete(processor);
+					}
 				}
 				else {
 					if (processor.changeState(this, REQUESTED)) {
@@ -238,6 +244,9 @@ public abstract class AbstractListenerWriteFlushProcessor<T> implements Processo
 				if (processor.changeState(this, COMPLETED)) {
 					processor.resultPublisher.publishComplete();
 				}
+				else {
+					processor.state.get().onComplete(processor);
+				}
 			}
 			public <T> void onNext(AbstractListenerWriteFlushProcessor<T> processor, Publisher<? extends T> publisher) {
 				// ignore
@@ -275,6 +284,9 @@ public abstract class AbstractListenerWriteFlushProcessor<T> implements Processo
 			if (processor.changeState(this, COMPLETED)) {
 				processor.resultPublisher.publishError(ex);
 			}
+			else {
+				processor.state.get().onError(processor, ex);
+			}
 		}
 
 		public <T> void onComplete(AbstractListenerWriteFlushProcessor<T> processor) {

spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java

@@ -251,6 +251,9 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 					processor.writingComplete();
 					processor.resultPublisher.publishComplete();
 				}
+				else {
+					processor.state.get().onComplete(processor);
+				}
 			}
 		},
 
@@ -274,15 +277,29 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 						if (writeCompleted) {
 							processor.releaseData();
 							if (!processor.subscriberCompleted) {
-								processor.changeState(WRITING, REQUESTED);
-								processor.suspendWriting();
-								Assert.state(processor.subscription != null, "No subscription");
-								processor.subscription.request(1);
+								if (processor.changeState(WRITING, REQUESTED)) {
+									if (processor.subscriberCompleted) {
+										if (processor.changeState(REQUESTED, COMPLETED)) {
+											processor.writingComplete();
+											processor.resultPublisher.publishComplete();
+										} else {
+											processor.state.get().onComplete(processor);
+										}
+									}
+									else {
+										processor.suspendWriting();
+										Assert.state(processor.subscription != null, "No subscription");
+										processor.subscription.request(1);
+									}
+								}
 							}
 							else {
-								processor.changeState(WRITING, COMPLETED);
-								processor.writingComplete();
-								processor.resultPublisher.publishComplete();
+								if (processor.changeState(WRITING, COMPLETED)) {
+									processor.writingComplete();
+									processor.resultPublisher.publishComplete();
+								} else {
+									processor.state.get().onComplete(processor);
+								}
 							}
 						}
 						else {
@@ -343,6 +360,9 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 				processor.writingComplete();
 				processor.resultPublisher.publishError(ex);
 			}
+			else {
+				processor.state.get().onError(processor, ex);
+			}
 		}
 
 		public <T> void onComplete(AbstractListenerWriteProcessor<T> processor) {

spring-web/src/main/java/org/springframework/http/server/reactive/WriteResultPublisher.java

@@ -158,6 +158,9 @@ class WriteResultPublisher implements Publisher<Void> {
 					Assert.state(publisher.subscriber != null, "No subscriber");
 					publisher.subscriber.onComplete();
 				}
+				else {
+					publisher.state.get().publishComplete(publisher);
+				}
 			}
 			@Override
 			void publishError(WriteResultPublisher publisher, Throwable t) {
@@ -165,6 +168,9 @@ class WriteResultPublisher implements Publisher<Void> {
 					Assert.state(publisher.subscriber != null, "No subscriber");
 					publisher.subscriber.onError(t);
 				}
+				else {
+					publisher.state.get().publishError(publisher, t);
+				}
 			}
 		},
 
@@ -196,7 +202,9 @@ class WriteResultPublisher implements Publisher<Void> {
 		}
 
 		void cancel(WriteResultPublisher publisher) {
-			publisher.changeState(this, COMPLETED);
+			if (!publisher.changeState(this, COMPLETED)) {
+				publisher.state.get().cancel(publisher);
+			}
 		}
 
 		void publishComplete(WriteResultPublisher publisher) {