Exposes timeout in GraphQlSseHandler

Closes gh-1079

spring-graphql/src/main/java/org/springframework/graphql/server/webmvc/GraphQlSseHandler.java

@@ -17,6 +17,7 @@
 package org.springframework.graphql.server.webmvc;
 
 import java.io.IOException;
+import java.time.Duration;
 import java.util.Map;
 import java.util.function.Consumer;
 
@@ -31,6 +32,7 @@ import reactor.core.publisher.Mono;
 import org.springframework.graphql.execution.SubscriptionPublisherException;
 import org.springframework.graphql.server.WebGraphQlHandler;
 import org.springframework.graphql.server.WebGraphQlResponse;
+import org.springframework.lang.Nullable;
 import org.springframework.web.context.request.async.AsyncRequestTimeoutException;
 import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
@@ -47,8 +49,29 @@ import org.springframework.web.servlet.function.ServerResponse;
  */
 public class GraphQlSseHandler extends AbstractGraphQlHttpHandler {
 
+	@Nullable
+	private final Duration timeout;
+
+
+	/**
+	 * Constructor with the handler to delegate to, and no timeout,
+	 * i.e. relying on underlying Server async request timeout.
+	 * @param graphQlHandler the handler to delegate to
+	 */
 	public GraphQlSseHandler(WebGraphQlHandler graphQlHandler) {
+		this(graphQlHandler, null);
+	}
+
+	/**
+	 * Variant constructor with a timeout to use for SSE subscriptions.
+	 * @param graphQlHandler the handler to delegate to
+	 * @param timeout the timeout value to set on
+	 * {@link org.springframework.web.context.request.async.AsyncWebRequest#setTimeout(Long)}
+	 * @since 1.3.3
+	 */
+	public GraphQlSseHandler(WebGraphQlHandler graphQlHandler, @Nullable Duration timeout) {
 		super(graphQlHandler, null);
+		this.timeout = timeout;
 	}
 
 
@@ -76,7 +99,9 @@ public class GraphQlSseHandler extends AbstractGraphQlHttpHandler {
 					.toSpecification());
 		});
 
-		return ServerResponse.sse(SseSubscriber.connect(resultFlux));
+		return ((this.timeout != null) ?
+				ServerResponse.sse(SseSubscriber.connect(resultFlux), this.timeout) :
+				ServerResponse.sse(SseSubscriber.connect(resultFlux)));
 	}