From 5d8c5b0d9bf1ecb3b902ed55c320a4ea4fae0b38 Mon Sep 17 00:00:00 2001
From: Rossen Stoyanchev <rstoyanchev@pivotal.io>
Date: Mon, 20 Jan 2020 11:26:58 +0000
Subject: [PATCH] Avoid NPE on comment SSE event

Closes gh-24389
---
 .../http/codec/ServerSentEventHttpMessageReader.java  |  9 ++++++---
 .../codec/ServerSentEventHttpMessageReaderTests.java  | 11 +++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/spring-web/src/main/java/org/springframework/http/codec/ServerSentEventHttpMessageReader.java b/spring-web/src/main/java/org/springframework/http/codec/ServerSentEventHttpMessageReader.java
index 7677c48ebf..86ee2988be 100644
--- a/spring-web/src/main/java/org/springframework/http/codec/ServerSentEventHttpMessageReader.java
+++ b/spring-web/src/main/java/org/springframework/http/codec/ServerSentEventHttpMessageReader.java
@@ -135,7 +135,10 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 		return this.lineDecoder.decode(message.getBody(), STRING_TYPE, null, hints)
 				.doOnNext(limitTracker::afterLineParsed)
 				.bufferUntil(String::isEmpty)
-				.map(lines -> buildEvent(lines, valueType, shouldWrap, hints));
+				.concatMap(lines -> {
+					Object event = buildEvent(lines, valueType, shouldWrap, hints);
+					return (event != null ? Mono.just(event) : Mono.empty());
+				});
 	}
 
 	@Nullable
@@ -168,7 +171,7 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 			}
 		}
 
-		Object decodedData = data != null ? decodeData(data.toString(), valueType, hints) : null;
+		Object decodedData = (data != null ? decodeData(data.toString(), valueType, hints) : null);
 
 		if (shouldWrap) {
 			if (comment != null) {
@@ -180,7 +183,7 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 			return sseBuilder.build();
 		}
 		else {
-			return decodedData;
+			return (decodedData);
 		}
 	}
 
diff --git a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
index c5a5983f07..22b77fd693 100644
--- a/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
+++ b/spring-web/src/test/java/org/springframework/http/codec/ServerSentEventHttpMessageReaderTests.java
@@ -161,6 +161,17 @@ public class ServerSentEventHttpMessageReaderTests extends AbstractLeakCheckingT
 				.verify();
 	}
 
+	@Test // gh-24389
+	void readPojoWithCommentOnly() {
+		MockServerHttpRequest request = MockServerHttpRequest.post("/")
+				.body(Flux.just(stringBuffer(":ping\n"), stringBuffer("\n")));
+
+		Flux<Object> data = this.reader.read(
+				ResolvableType.forType(String.class), request, Collections.emptyMap());
+
+		StepVerifier.create(data).expectComplete().verify();
+	}
+
 	@Test  // SPR-15331
 	public void decodeFullContentAsString() {
 		String body = "data:foo\ndata:bar\n\ndata:baz\n\n";