From b7eaab4c5d1b2beed13389ed79a07161329ea686 Mon Sep 17 00:00:00 2001
From: Rossen Stoyanchev <rstoyanchev@pivotal.io>
Date: Thu, 12 Sep 2019 14:14:11 +0100
Subject: [PATCH] Handle very early completion notification

On a Servlet container a completion notification may come at any time
even in the UNSUBSCRIBED state, i.e. before the write Publisher has
called onSubscribe.

See: gh-23553
---
 .../reactive/AbstractListenerWriteFlushProcessor.java | 11 +++++++++++
 .../reactive/AbstractListenerWriteProcessor.java      |  6 ++++++
 2 files changed, 17 insertions(+)

diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteFlushProcessor.java b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteFlushProcessor.java
index 329cd3dbcac..81c8098d32a 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteFlushProcessor.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteFlushProcessor.java
@@ -246,6 +246,17 @@ public abstract class AbstractListenerWriteFlushProcessor<T> implements Processo
 					super.onSubscribe(processor, subscription);
 				}
 			}
+
+			@Override
+			public <T> void onComplete(AbstractListenerWriteFlushProcessor<T> processor) {
+				// This can happen on (very early) completion notification from container..
+				if (processor.changeState(this, COMPLETED)) {
+					processor.resultPublisher.publishComplete();
+				}
+				else {
+					processor.state.get().onComplete(processor);
+				}
+			}
 		},
 
 		REQUESTED {
diff --git a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
index 509076d02b8..4f05d5e1e09 100644
--- a/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
+++ b/spring-web/src/main/java/org/springframework/http/server/reactive/AbstractListenerWriteProcessor.java
@@ -322,6 +322,12 @@ public abstract class AbstractListenerWriteProcessor<T> implements Processor<T,
 					super.onSubscribe(processor, subscription);
 				}
 			}
+
+			@Override
+			public <T> void onComplete(AbstractListenerWriteProcessor<T> processor) {
+				// This can happen on (very early) completion notification from container..
+				processor.changeStateToComplete(this);
+			}
 		},
 
 		REQUESTED {