Centralize Server Sent Event utility methods

Prior to this commit, many classes would support writing Server Sent Events in some way to the response output stream. This has lead to some code duplication. This commit refactors the duplicated code in a shared `SseUtils` class. Closes gh-37065
2026-09-20 20:59:07 +00:00 · 2026-08-14 09:19:58 +02:00
parent 999f428987
commit 5abe6d3e5f
9 changed files with 230 additions and 146 deletions
@@ -0,0 +1,81 @@
+/*
+ * Copyright 2002-present the original author or authors.
+ *
+ * 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 org.springframework.web.util;
+
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link SseUtils}.
+ * @author Brian Clozel
+ */
+class SseUtilsTests {
+
+	@Test
+	void appendFieldValueWithoutLineSeparatorAppendsAsIs() {
+		StringBuilder sb = new StringBuilder();
+		sb.append("data:");
+		SseUtils.appendFieldValue("data", "no newlines here", sb);
+		assertThat(sb).hasToString("data:no newlines here");
+	}
+
+	@ParameterizedTest(name = "{1}")
+	@MethodSource("newLineCharacters")
+	void appendFieldValueReplacesLineSeparatorWithFieldPrefix(String newLine, String description) {
+		StringBuilder sb = new StringBuilder();
+		sb.append("data:");
+		SseUtils.appendFieldValue("data", "first" + newLine + "second", sb);
+		assertThat(sb).hasToString("data:first\ndata:second");
+	}
+
+	@ParameterizedTest(name = "{1}")
+	@MethodSource("newLineCharacters")
+	void appendFieldValueUsesEmptyFieldForComments(String newLine, String description) {
+		StringBuilder sb = new StringBuilder();
+		sb.append(":");
+		SseUtils.appendFieldValue("", "first" + newLine + "second", sb);
+		assertThat(sb).hasToString(":first\n:second");
+	}
+
+	@Test
+	void assertNoLineSeparatorAcceptsPlainContent() {
+		SseUtils.assertNoLineSeparator("no newlines here");
+	}
+
+	@ParameterizedTest(name = "{1}")
+	@MethodSource("newLineCharacters")
+	void assertNoLineSeparatorRejectsLineSeparator(String newLine, String description) {
+		assertThatIllegalArgumentException().isThrownBy(() ->
+				SseUtils.assertNoLineSeparator("first" + newLine + "second"));
+	}
+
+	static Stream<Arguments> newLineCharacters() {
+		return Stream.of(
+				Arguments.of("\n", "LF"),
+				Arguments.of("\r", "CR"),
+				Arguments.of("\r\n", "CRLF")
+		);
+	}
+
+}