Add keep-alive property for GraphQL SSE handlers

This commit adds a new `spring.graphql.http.sse.keep-alive`
configuration property for MVC and WebFlux SSE handlers.

Closes gh-44743

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/graphql/GraphQlProperties.java

@@ -315,11 +315,24 @@ public class GraphQlProperties {
 
 	public static class Sse {
 
+		/**
+		 * How frequently keep-alive messages should be sent.
+		 */
+		private Duration keepAlive;
+
 		/**
 		 * Time required for concurrent handling to complete.
 		 */
 		private Duration timeout;
 
+		public Duration getKeepAlive() {
+			return this.keepAlive;
+		}
+
+		public void setKeepAlive(Duration keepAlive) {
+			this.keepAlive = keepAlive;
+		}
+
 		public Duration getTimeout() {
 			return this.timeout;
 		}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/graphql/reactive/GraphQlWebFluxAutoConfiguration.java

@@ -94,7 +94,8 @@ public class GraphQlWebFluxAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public GraphQlSseHandler graphQlSseHandler(WebGraphQlHandler webGraphQlHandler, GraphQlProperties properties) {
-		return new GraphQlSseHandler(webGraphQlHandler, properties.getHttp().getSse().getTimeout());
+		return new GraphQlSseHandler(webGraphQlHandler, properties.getHttp().getSse().getTimeout(),
+				properties.getHttp().getSse().getKeepAlive());
 	}
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/graphql/servlet/GraphQlWebMvcAutoConfiguration.java

@@ -98,7 +98,8 @@ public class GraphQlWebMvcAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public GraphQlSseHandler graphQlSseHandler(WebGraphQlHandler webGraphQlHandler, GraphQlProperties properties) {
-		return new GraphQlSseHandler(webGraphQlHandler, properties.getHttp().getSse().getTimeout());
+		return new GraphQlSseHandler(webGraphQlHandler, properties.getHttp().getSse().getTimeout(),
+				properties.getHttp().getSse().getKeepAlive());
 	}
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/graphql/reactive/GraphQlWebFluxAutoConfigurationTests.java

@@ -42,6 +42,7 @@ import org.springframework.graphql.execution.RuntimeWiringConfigurer;
 import org.springframework.graphql.server.WebGraphQlHandler;
 import org.springframework.graphql.server.WebGraphQlInterceptor;
 import org.springframework.graphql.server.webflux.GraphQlHttpHandler;
+import org.springframework.graphql.server.webflux.GraphQlSseHandler;
 import org.springframework.graphql.server.webflux.GraphQlWebSocketHandler;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
@@ -271,6 +272,24 @@ class GraphQlWebFluxAutoConfigurationTests {
 			});
 	}
 
+	@Test
+	void shouldConfigureSseTimeout() {
+		this.contextRunner.withPropertyValues("spring.graphql.http.sse.timeout=10s").run((context) -> {
+			assertThat(context).hasSingleBean(GraphQlSseHandler.class);
+			GraphQlSseHandler handler = context.getBean(GraphQlSseHandler.class);
+			assertThat(handler).hasFieldOrPropertyWithValue("timeout", Duration.ofSeconds(10));
+		});
+	}
+
+	@Test
+	void shouldConfigureSseKeepAlive() {
+		this.contextRunner.withPropertyValues("spring.graphql.http.sse.keep-alive=5s").run((context) -> {
+			assertThat(context).hasSingleBean(GraphQlSseHandler.class);
+			GraphQlSseHandler handler = context.getBean(GraphQlSseHandler.class);
+			assertThat(handler).hasFieldOrPropertyWithValue("keepAliveDuration", Duration.ofSeconds(5));
+		});
+	}
+
 	@Test
 	void routerFunctionShouldHaveOrderZero() {
 		this.contextRunner.withUserConfiguration(CustomRouterFunctions.class).run((context) -> {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/graphql/servlet/GraphQlWebMvcAutoConfigurationTests.java

@@ -108,6 +108,15 @@ class GraphQlWebMvcAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void shouldConfigureSseKeepAlive() {
+		this.contextRunner.withPropertyValues("spring.graphql.http.sse.keep-alive=5s").run((context) -> {
+			assertThat(context).hasSingleBean(GraphQlSseHandler.class);
+			GraphQlSseHandler handler = context.getBean(GraphQlSseHandler.class);
+			assertThat(handler).hasFieldOrPropertyWithValue("keepAliveDuration", Duration.ofSeconds(5));
+		});
+	}
+
 	@Test
 	void simpleQueryShouldWork() {
 		withMockMvc((mvc) -> {