Add ExecutingResponseCreator

This commit adds a new `ResponseCreator` implementation that uses a
`ClientHttpRequestFactory` to perform an actual request.

Closes gh-29721

spring-test/src/test/java/org/springframework/test/web/client/MockRestServiceServerTests.java

@@ -17,13 +17,22 @@
 package org.springframework.test.web.client;
 
 import java.net.SocketException;
+import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.client.ClientHttpRequestFactory;
+import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.mock.http.client.MockClientHttpRequest;
+import org.springframework.mock.http.client.MockClientHttpResponse;
 import org.springframework.test.web.client.MockRestServiceServer.MockRestServiceServerBuilder;
+import org.springframework.test.web.client.response.ExecutingResponseCreator;
 import org.springframework.web.client.RestTemplate;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.assertj.core.api.Assertions.fail;
@@ -88,6 +97,43 @@ class MockRestServiceServerTests {
 		server.verify();
 	}
 
+	@Test
+	void executingResponseCreator() {
+		RestTemplate restTemplateWithMockEcho = createEchoRestTemplate();
+
+		final ExecutingResponseCreator withActualCall = new ExecutingResponseCreator(restTemplateWithMockEcho.getRequestFactory());
+		MockRestServiceServer server = MockRestServiceServer.bindTo(restTemplateWithMockEcho).build();
+		server.expect(requestTo("/profile")).andRespond(withSuccess());
+		server.expect(requestTo("/quoteOfTheDay")).andRespond(withActualCall);
+
+		var response1 = restTemplateWithMockEcho.getForEntity("/profile", String.class);
+		var response2 = restTemplateWithMockEcho.getForEntity("/quoteOfTheDay", String.class);
+		server.verify();
+
+		assertThat(response1.getStatusCode().value())
+				.as("response1 status").isEqualTo(200);
+		assertThat(response1.getBody())
+				.as("response1 body").isNullOrEmpty();
+		assertThat(response2.getStatusCode().value())
+				.as("response2 status").isEqualTo(300);
+		assertThat(response2.getBody())
+				.as("response2 body").isEqualTo("echo from /quoteOfTheDay");
+	}
+
+	private static RestTemplate createEchoRestTemplate() {
+		final ClientHttpRequestFactory echoRequestFactory = (uri, httpMethod) -> {
+			final MockClientHttpRequest req = new MockClientHttpRequest(httpMethod, uri);
+			String body = "echo from " + uri.getPath();
+			final ClientHttpResponse resp = new MockClientHttpResponse(body.getBytes(StandardCharsets.UTF_8),
+					// Instead of 200, we use a less-common status code on purpose
+					HttpStatus.MULTIPLE_CHOICES);
+			resp.getHeaders().setContentType(MediaType.TEXT_PLAIN);
+			req.setResponse(resp);
+			return req;
+		};
+		return new RestTemplate(echoRequestFactory);
+	}
+
 	@Test
 	void resetAndReuseServer() {
 		MockRestServiceServer server = MockRestServiceServer.bindTo(this.restTemplate).build();

spring-test/src/test/java/org/springframework/test/web/client/response/ExecutingResponseCreatorTests.java

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2002-2023 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.test.web.client.response;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.URI;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.client.AbstractClientHttpRequest;
+import org.springframework.http.client.ClientHttpRequest;
+import org.springframework.http.client.ClientHttpRequestFactory;
+import org.springframework.http.client.ClientHttpResponse;
+import org.springframework.mock.http.client.MockClientHttpRequest;
+import org.springframework.mock.http.client.MockClientHttpResponse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+
+/**
+ * Tests for the {@link ExecutingResponseCreator} implementation.
+ *
+ * @author Simon Baslé
+ */
+class ExecutingResponseCreatorTests {
+
+	@Test
+	void ensureRequestNotNull() {
+		final ExecutingResponseCreator responseCreator = new ExecutingResponseCreator((uri, method) -> null);
+
+		assertThatIllegalStateException()
+				.isThrownBy(() -> responseCreator.createResponse(null))
+				.withMessage("Request should be an instance of MockClientHttpRequest");
+	}
+
+	@Test
+	void ensureRequestIsMock() {
+		final ExecutingResponseCreator responseCreator = new ExecutingResponseCreator((uri, method) -> null);
+		ClientHttpRequest notAMockRequest = new AbstractClientHttpRequest() {
+			@Override
+			protected OutputStream getBodyInternal(HttpHeaders headers) throws IOException {
+				return null;
+			}
+
+			@Override
+			protected ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException {
+				return null;
+			}
+
+			@Override
+			public HttpMethod getMethod() {
+				return null;
+			}
+
+			@Override
+			public URI getURI() {
+				return null;
+			}
+		};
+
+		assertThatIllegalStateException()
+				.isThrownBy(() -> responseCreator.createResponse(notAMockRequest))
+				.withMessage("Request should be an instance of MockClientHttpRequest");
+	}
+
+	@Test
+	void requestIsCopied() throws IOException {
+		MockClientHttpRequest originalRequest = new MockClientHttpRequest(HttpMethod.POST,
+				"https://example.org");
+		String body = "original body";
+		originalRequest.getHeaders().add("X-example", "original");
+		originalRequest.getBody().write(body.getBytes(StandardCharsets.UTF_8));
+		MockClientHttpResponse originalResponse = new MockClientHttpResponse(new byte[0], 500);
+		List<MockClientHttpRequest> factoryRequests = new ArrayList<>();
+		ClientHttpRequestFactory originalFactory = (uri, httpMethod) -> {
+			MockClientHttpRequest request = new MockClientHttpRequest(httpMethod, uri);
+			request.setResponse(originalResponse);
+			factoryRequests.add(request);
+			return request;
+		};
+
+		final ExecutingResponseCreator responseCreator = new ExecutingResponseCreator(originalFactory);
+		final ClientHttpResponse response = responseCreator.createResponse(originalRequest);
+
+		assertThat(response).as("response").isSameAs(originalResponse);
+		assertThat(originalRequest.isExecuted()).as("originalRequest.isExecuted").isFalse();
+
+		assertThat(factoryRequests)
+				.hasSize(1)
+				.first()
+				.isNotSameAs(originalRequest)
+				.satisfies(copiedRequest -> {
+					assertThat(copiedRequest)
+							.as("copied request")
+							.isNotSameAs(originalRequest);
+					assertThat(copiedRequest.isExecuted())
+							.as("copiedRequest.isExecuted").isTrue();
+					assertThat(copiedRequest.getBody())
+							.as("copiedRequest.body").isNotSameAs(originalRequest.getBody());
+					assertThat(copiedRequest.getHeaders())
+							.as("copiedRequest.headers").isNotSameAs(originalRequest.getHeaders());
+				});
+	}
+}