From 3be2b32e21ad91b94346a1b9f8cf58fb3ea48ced Mon Sep 17 00:00:00 2001
From: Arjen Poutsma <apoutsma@pivotal.io>
Date: Tue, 28 Sep 2021 14:56:39 +0200
Subject: [PATCH] Remove only leading space for SSE data

Prior to this commit, all white space was trimmed from Server Sent Event
data. After this commit, only a leading space is removed (if present).

Closes gh-27473
---
 .../codec/ServerSentEventHttpMessageReader.java    |  8 +++++++-
 .../ServerSentEventHttpMessageReaderTests.java     | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

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 035d8b4c73e..d21ec4fe619 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
@@ -147,7 +147,13 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 		for (String line : lines) {
 			if (line.startsWith("data:")) {
 				data = (data != null ? data : new StringBuilder());
-				data.append(line.substring(5).trim()).append('\n');
+				if (line.charAt(5) != ' ') {
+					data.append(line, 5, line.length());
+				}
+				else {
+					data.append(line, 6, line.length());
+				}
+				data.append('\n');
 			}
 			if (shouldWrap) {
 				if (line.startsWith("id:")) {
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 22b77fd693d..82602a526eb 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
@@ -138,6 +138,20 @@ public class ServerSentEventHttpMessageReaderTests extends AbstractLeakCheckingT
 				.verify();
 	}
 
+	@Test
+	public void trimWhitespace() {
+		MockServerHttpRequest request = MockServerHttpRequest.post("/")
+				.body(Mono.just(stringBuffer("data: \tfoo \ndata:bar\t\n\n")));
+
+		Flux<String> data = reader.read(ResolvableType.forClass(String.class),
+				request, Collections.emptyMap()).cast(String.class);
+
+		StepVerifier.create(data)
+				.expectNext("\tfoo \nbar\t")
+				.expectComplete()
+				.verify();
+	}
+
 	@Test
 	public void readPojo() {
 		MockServerHttpRequest request = MockServerHttpRequest.post("/")