RoutePredicateHandlerMapping doesn't hanle Mono errors properly

spring-cloud-gateway-server-mvc/src/test/java/org/springframework/cloud/gateway/server/mvc/filter/BeforeFilterFunctionsTests.java

@@ -147,6 +147,21 @@ void rewritePlusSignRequestParameter() {
 		assertThat(result.uri().toString()).hasToString("http://localhost/path?baz=qux&foo=replacement%2B");
 	}
 
+	@Test
+	void rewritePlusSignRequestParameter() {
+		MockHttpServletRequest servletRequest = MockMvcRequestBuilders.get("http://localhost/path")
+			.param("foo", "bar")
+			.param("baz", "qux")
+			.buildRequest(null);
+
+		ServerRequest request = ServerRequest.create(servletRequest, Collections.emptyList());
+
+		ServerRequest result = BeforeFilterFunctions.rewriteRequestParameter("foo", "replacement+").apply(request);
+
+		assertThat(result.param("foo")).isPresent().hasValue("replacement+");
+		assertThat(result.uri().toString()).hasToString("http://localhost/path?baz=qux&foo=replacement%2B");
+	}
+
 	@Test
 	void rewriteRequestParameterWithEncodedRemainParameters() {
 		MockHttpServletRequest servletRequest = MockMvcRequestBuilders.get("http://localhost/path")

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/handler/RoutePredicateHandlerMapping.java

@@ -131,24 +131,18 @@ protected Mono<Route> lookupRoute(ServerWebExchange exchange) {
 		return this.routeLocator.getRoutes().filterWhen(route -> {
 			// add the current route we are testing
 			exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, route.getId());
-			try {
-				return route.getPredicate().apply(exchange);
-			}
-			catch (Exception e) {
+
+			return Mono.defer(() -> Mono.from(route.getPredicate().apply(exchange))).onErrorResume(e -> {
 				logger.error("Error applying predicate for route: " + route.getId(), e);
-			}
-			return Mono.just(false);
-		})
-			.next()
-			// TODO: error handling
-			.map(route -> {
-				if (logger.isDebugEnabled()) {
-					logger.debug("Route matched: " + route.getId());
-				}
-				validateRoute(route, exchange);
-				return route;
+				return Mono.just(false);
 			});
-
+		}).next().map(route -> {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Route matched: " + route.getId());
+			}
+			validateRoute(route, exchange);
+			return route;
+		});
 		/*
 		 * TODO: trace logging if (logger.isTraceEnabled()) {
 		 * logger.trace("RouteDefinition did not match: " + routeDefinition.getId()); }

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/handler/RoutePredicateHandlerMappingTests.java

@@ -74,6 +74,11 @@ public void lookupRouteFromAsyncPredicates(CapturedOutput capturedOutput) {
 			.uri("http://localhost")
 			.asyncPredicate(swe -> Mono.just(boom1()))
 			.build();
+		Route routeMonoError = Route.async()
+			.id("routeMonoError")
+			.uri("http://localhost")
+			.asyncPredicate(swe -> Mono.error(new IllegalStateException("boom3")))
+			.build();
 		Route routeFail = Route.async().id("routeFail").uri("http://localhost").asyncPredicate(swe -> {
 			throw new IllegalStateException("boom2");
 		}).build();
@@ -82,7 +87,8 @@ public void lookupRouteFromAsyncPredicates(CapturedOutput capturedOutput) {
 			.uri("http://localhost")
 			.asyncPredicate(swe -> Mono.just(true))
 			.build();
-		RouteLocator routeLocator = () -> Flux.just(routeFalse, routeError, routeFail, routeTrue).hide();
+		RouteLocator routeLocator = () -> Flux.just(routeFalse, routeError, routeMonoError, routeFail, routeTrue)
+			.hide();
 		RoutePredicateHandlerMapping mapping = new RoutePredicateHandlerMapping(null, routeLocator,
 				new GlobalCorsProperties(), new MockEnvironment());
 
@@ -95,6 +101,9 @@ public void lookupRouteFromAsyncPredicates(CapturedOutput capturedOutput) {
 
 		assertThat(capturedOutput.getOut().contains("Error applying predicate for route: routeFail")).isTrue();
 		assertThat(capturedOutput.getOut().contains("java.lang.IllegalStateException: boom2")).isTrue();
+
+		assertThat(capturedOutput.getOut().contains("Error applying predicate for route: routeMonoError")).isTrue();
+		assertThat(capturedOutput.getOut().contains("java.lang.IllegalStateException: boom3")).isTrue();
 	}
 
 	boolean boom1() {