Merge pull request #4063 from ryanjbaxter/handle-null-body-in-RewriteFunction

Author: ryanjbaxter

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/filter/factory/RemoveJsonAttributesResponseBodyGatewayFilterFactory.java

@@ -72,6 +72,9 @@ public GatewayFilter apply(FieldListConfiguration config) {
 		modifyResponseBodyConfig.setOutClass(String.class);
 
 		RewriteFunction<String, String> rewriteFunction = (exchange, body) -> {
+			if (body == null) {
+				return Mono.just("");
+			}
 			if (MediaType.APPLICATION_JSON.isCompatibleWith(exchange.getResponse().getHeaders().getContentType())) {
 				try {
 					JsonNode jsonNode = mapper.readValue(body, JsonNode.class);

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/filter/factory/rewrite/ModifyRequestBodyGatewayFilterFactory.java

@@ -45,6 +45,10 @@
 
 /**
  * GatewayFilter that modifies the request body.
+ * <p>
+ * When the request has no body, the {@link RewriteFunction} is invoked with {@code null}
+ * for the body parameter. Implementations (including Kotlin with a nullable parameter)
+ * must handle this case.
  */
 public class ModifyRequestBodyGatewayFilterFactory
 		extends AbstractGatewayFilterFactory<ModifyRequestBodyGatewayFilterFactory.Config> {

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/filter/factory/rewrite/ModifyResponseBodyGatewayFilterFactory.java

@@ -54,6 +54,10 @@
 
 /**
  * GatewayFilter that modifies the response body.
+ * <p>
+ * When the response has no body, the {@link RewriteFunction} is invoked with {@code null}
+ * for the body parameter. Implementations (including Kotlin with a nullable parameter)
+ * must handle this case.
  */
 public class ModifyResponseBodyGatewayFilterFactory
 		extends AbstractGatewayFilterFactory<ModifyResponseBodyGatewayFilterFactory.Config> {

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/filter/factory/rewrite/RewriteFunction.java

@@ -18,16 +18,20 @@
 
 import java.util.function.BiFunction;
 
+import org.jspecify.annotations.Nullable;
 import org.reactivestreams.Publisher;
 
 import org.springframework.web.server.ServerWebExchange;
 
 /**
  * This interface is BETA and may be subject to change in a future release.
  *
- * @param <T> the type of the first argument to the function
+ * @param <T> the type of the request/response body (may be null when there is no body)
  * @param <R> the type of element signaled by the {@link Publisher}
  */
 public interface RewriteFunction<T, R> extends BiFunction<ServerWebExchange, T, Publisher<R>> {
 
+	@Override
+	Publisher<R> apply(ServerWebExchange exchange, @Nullable T body);
+
 }

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/route/builder/GatewayFilterSpec.java

@@ -307,6 +307,9 @@ public GatewayFilterSpec mapRequestHeader(String fromHeader, String toHeader) {
 
 	/**
 	 * A filter that can be used to modify the request body.
+	 * <p>
+	 * The rewrite function may receive {@code null} for the body when the request has no
+	 * body; implementations must handle this (e.g. use a nullable type in Kotlin).
 	 * @param inClass the class to convert the incoming request body to
 	 * @param outClass the class the Gateway will add to the request before it is routed
 	 * @param rewriteFunction the {@link RewriteFunction} that transforms the request body

spring-cloud-gateway-server-webflux/src/test/java/org/springframework/cloud/gateway/route/builder/GatewayFilterSpecTests.java

@@ -25,6 +25,7 @@
 import org.springframework.cloud.gateway.filter.GatewayFilterChain;
 import org.springframework.cloud.gateway.filter.NettyWriteResponseFilter;
 import org.springframework.cloud.gateway.filter.OrderedGatewayFilter;
+import org.springframework.cloud.gateway.filter.factory.rewrite.ModifyRequestBodyGatewayFilterFactory;
 import org.springframework.cloud.gateway.filter.factory.rewrite.ModifyResponseBodyGatewayFilterFactory;
 import org.springframework.cloud.gateway.route.Route;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -104,6 +105,22 @@ public void testFilters() {
 		assertFilter(route.getFilters().get(1), MyOrderedFilter.class, 1000);
 	}
 
+	@Test
+	public void shouldSetModifyBodyRequestFilterWithRewriteFunctionAndEmptyBodySupplier() {
+		ConfigurableApplicationContext context = mock(ConfigurableApplicationContext.class);
+		Route.AsyncBuilder routeBuilder = Route.async().id("123").uri("abc:123").predicate(exchange -> true);
+
+		when(context.getBean(ModifyRequestBodyGatewayFilterFactory.class))
+			.thenReturn(new ModifyRequestBodyGatewayFilterFactory());
+
+		RouteLocatorBuilder.Builder routes = new RouteLocatorBuilder(context).routes();
+		GatewayFilterSpec spec = new GatewayFilterSpec(routeBuilder, routes);
+		spec.modifyRequestBody(String.class, String.class, (exchange, s) -> Mono.just(s == null ? "emptybody" : s));
+
+		Route route = routeBuilder.build();
+		assertThat(route.getFilters()).hasSize(1);
+	}
+
 	@Test
 	public void shouldSetModifyBodyResponseFilterWithRewriteFunction() {
 		ConfigurableApplicationContext context = mock(ConfigurableApplicationContext.class);