Improve ProxyExchangeHandlerFunction to preserve original encoding of query parameters during proxy request

ref. https://github.com/spring-cloud/spring-cloud-gateway/issues/3759

Signed-off-by: raccoonback <kosb15@naver.com>

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2023 the original author or authors.
+ * Copyright 2013-2025 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.
@@ -36,7 +36,11 @@ import org.springframework.web.servlet.function.HandlerFunction;
 import org.springframework.web.servlet.function.ServerRequest;
 import org.springframework.web.servlet.function.ServerResponse;
 import org.springframework.web.util.UriComponentsBuilder;
+import org.springframework.web.util.UriUtils;
 
+/**
+ * @author raccoonback
+ */
 public class ProxyExchangeHandlerFunction
 		implements HandlerFunction<ServerResponse>, ApplicationListener<ContextRefreshedEvent> {
 
@@ -84,14 +88,14 @@ public class ProxyExchangeHandlerFunction
 	@Override
 	public ServerResponse handle(ServerRequest serverRequest) {
 		URI uri = uriResolver.apply(serverRequest);
-		boolean encoded = containsEncodedQuery(serverRequest.uri(), serverRequest.params());
+		MultiValueMap<String, String> params = ensureEncodedQueryParameters(serverRequest);
 		// @formatter:off
 		URI url = UriComponentsBuilder.fromUri(serverRequest.uri())
 				.scheme(uri.getScheme())
 				.host(uri.getHost())
 				.port(uri.getPort())
-				.replaceQueryParams(serverRequest.params())
-				.build(encoded)
+				.replaceQueryParams(params)
+				.build(true)
 				.toUri();
 		// @formatter:on
 
@@ -131,6 +135,15 @@ public class ProxyExchangeHandlerFunction
 		return filtered;
 	}
 
+	private static MultiValueMap<String, String> ensureEncodedQueryParameters(ServerRequest serverRequest) {
+		boolean encoded = containsEncodedQuery(serverRequest.uri(), serverRequest.params());
+		MultiValueMap<String, String> params = serverRequest.params();
+		if (!encoded) {
+			params = UriUtils.encodeQueryParams(serverRequest.params());
+		}
+		return params;
+	}
+
 	private static boolean containsEncodedQuery(URI uri, MultiValueMap<String, String> params) {
 		String rawQuery = uri.getRawQuery();
 		boolean encoded = (rawQuery != null && rawQuery.contains("%"))

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

@@ -0,0 +1,98 @@
+/*
+ * Copyright 2025-2025 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.cloud.gateway.server.mvc.handler;
+
+import java.net.URI;
+import java.util.Collections;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.cloud.gateway.server.mvc.common.AbstractProxyExchange;
+import org.springframework.cloud.gateway.server.mvc.common.MvcUtils;
+import org.springframework.cloud.gateway.server.mvc.config.GatewayMvcProperties;
+import org.springframework.cloud.gateway.server.mvc.filter.HttpHeadersFilter.RequestHttpHeadersFilter;
+import org.springframework.cloud.gateway.server.mvc.filter.HttpHeadersFilter.ResponseHttpHeadersFilter;
+import org.springframework.http.HttpHeaders;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
+import org.springframework.web.servlet.function.ServerRequest;
+import org.springframework.web.servlet.function.ServerResponse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author raccoonback
+ */
+class ProxyExchangeHandlerFunctionTest {
+
+	@Test
+	void keepOriginalEncodingOfQueryParameter() {
+		TestProxyExchange proxyExchange = new TestProxyExchange();
+		ProxyExchangeHandlerFunction function = new ProxyExchangeHandlerFunction(proxyExchange, new ObjectProvider<>() {
+			@Override
+			public Stream<RequestHttpHeadersFilter> stream() {
+				return Stream.of((httpHeaders, serverRequest) -> new HttpHeaders());
+			}
+		}, new ObjectProvider<>() {
+			@Override
+			public Stream<ResponseHttpHeadersFilter> stream() {
+				return Stream.of((httpHeaders, serverRequest) -> new HttpHeaders());
+			}
+		});
+
+		function.onApplicationEvent(null);
+
+		MockHttpServletRequest servletRequest = MockMvcRequestBuilders
+			.get("http://localhost/é?foo=value1 value2&bar=value3=")
+			.buildRequest(null);
+		servletRequest.setAttribute(MvcUtils.GATEWAY_REQUEST_URL_ATTR, URI.create("http://localhost:8080"));
+		ServerRequest request = ServerRequest.create(servletRequest, Collections.emptyList());
+
+		function.handle(request);
+
+		URI uri = proxyExchange.getRequest().getUri();
+
+		assertThat(uri).hasToString("http://localhost:8080/%C3%A9?foo=value1%20value2&bar=value3%3D")
+			.hasPath("/é")
+			.hasParameter("foo", "value1 value2")
+			.hasParameter("bar", "value3=");
+	}
+
+	private class TestProxyExchange extends AbstractProxyExchange {
+
+		private Request request;
+
+		protected TestProxyExchange() {
+			super(new GatewayMvcProperties());
+		}
+
+		@Override
+		public ServerResponse exchange(Request request) {
+			this.request = request;
+
+			return ServerResponse.ok().build();
+		}
+
+		public Request getRequest() {
+			return request;
+		}
+
+	}
+
+}